Laboratory work: Production of methane and experiments with it. Method for producing absolute ethyl alcohol Alcohols and phenols

ethanol by Winkler, has a number of disadvantages: multiple

distillation, the product is contaminated with ammonia resulting from

hydrolysis of calcium nitride, which is contained as an impurity in calcium metal.

e) Calcium carbide is an effective desiccant, but pollutes

alcohol acetylene and other products. Currently, neither calcium metal nor its carbide is used for ethanol absolutization.

f) Anhydrous copper sulfate is advantageous in that its intensity

blue color can indicate the quality of the original alcohol and the end

process of absolutization. However, at present it is also

practically not used.

g) Azeotropic distillation of an alcohol-benzene mixture used for

for the production of absolute alcohol on a technical scale has also been developed for laboratory conditions. However, practically this

the method is not widely used.

h) Chloride coke was used for dehydration at 95°o

ethanol in the gas phase. This method produced 99.8% ethanol.

Calcium chloride is easily regenerated from the resulting solution.

i) Anhydrous calcium sulfate has also been proposed for ethanol drying. However, it is a relatively weak desiccant and is unsuitable

for complete dehydration of alcohol. In addition, with great content

water, a dihydrate is formed, which is difficult to remove from the flask.

Ethyl alcohol is often used as a solvent in the catalytic hydrogenation of various substances. In this case, the presence of a small amount of water usually does not matter, but it is important to remove substances that poison the catalyst. Pure 95% ethyl alcohol contains very little of these substances, and it is usually sufficient to distill it in a device with ground sections. In this case, the sections are thoroughly cleaned and not lubricated, and the first part of the distillate is discarded. Distilling alcohol over a small amount of Raney nickel is even more effective.

11.3. "-Propyl alcohol

“Propyl alcohol (bp 973) forms an azeotropic mixture with water, boiling at 88° and containing 71% propyl alcohol. Mixes with water in any ratio. Calcium oxide is used to dry it, and calcium hydride is used for final dehydration. When the water content is low, dehydration can be accomplished using sodium propnlate, prepared by dissolving sodium metal in propyl alcohol.

11.4. Isopropyl alcohol

Has t. kip. 82.4°, with water forms an azeotropic mixture with bp. 80° containing 87.4% isopropyl alcohol. Mixes with water in all respects. If the water content is high, isopropyl alcohol is pre-dried with sodium carbonate or potash and finally absolutized with calcium chloride. When the water content is low, calcium oxide is a good desiccant, which reduces the water content to 0.1%; For final dehydration, distillation over anhydrous copper sulfate is recommended. Additionally, all the methods mentioned above for ethyl alcohol can be used to dry isopropyl alcohol.

11.5. Butyl alcohols

“Butyl alcohol (bp. 118°) with water forms an azeotropic mixture with bp. 93°, containing 58% butyl alcohol.

Isobutyl alcohol (bp. 108°) gives an azeotropic mixture with water with bp. 90° containing 67% isobutyl alcohol.

emop-Butyl alcohol (bp. 99.5°) forms an azeotropic mixture with water bp. 87.5°, containing 73% emop-butyl alcohol.

/rzpem-Butyl alcohol (bp 82.5°) forms an azeotropic mixture with water, boiling at 80° and containing 88% mpem-butyl alcohol.

The first three of these alcohols have limited miscibility with water, and in most cases fractional distillation is sufficient to dry them. Chemical desiccants can be calcium oxide, barium oxide, magnesium oxide, or the corresponding sodium alcoholate, obtained by dissolving sodium in this alcohol.

mpem-Butyl alcohol, on the other hand, is miscible with water in all proportions. This is a very valuable solvent, characterized by significant dissolving ability and great resistance to oxidizing agents, halogens, etc. If the water content is high, tert-butyl alcohol is pre-dried with calcium chloride. Small amounts of water are removed using calcium oxide or sodium metal. The high solidification temperature of tert-butyl alcohol (25.7°) allows it to be purified by fractional crystallization.

11.6. Higher aliphatic alcohols

For alcohols of this type, only physical constants are given below. The main method of their purification is distillation, for example with the addition of conventional desiccants (calcium oxide, barium oxide, etc.).

Isoamyl alcohol (bp 132e) forms an azeotropic mixture with water, boiling at 95° and containing 41% alcohol.

Optically active amyl alcohol, bp. 128°.

n-Hexyl alcohol (bp 157.5°) forms an azeotropic mixture with water, boiling at 98° and containing 20% ​​alcohol.

2-Ethylbutanol-1 (bp 146°) image

LABORATORY WORK No. 1

Experience 1. Production of methane and experiments with it

Equipment and reagents: Round bottom test tube, alcohol lamp, tripod, tripod foot, stopper with gas outlet glass and rubber tube, tube with pulled end, two U-shaped tubes, matches, porcelain mortar and pestle, sodium acetate, bromine solution in water, calcium oxide , sodium hydroxide, potassium permanganate solution, activated carbon, electric stove, glass rod.

Work progress: Sodium acetate is dehydrated before the experiment. Salt CH 3 COONa. 3H 2 O is placed in a porcelain cup and heated, stirring with a glass rod. Sodium acetate first dissolves in the water of crystallization, then, after the water evaporates, it is released in solid form. Once the hardened salt has melted again, it is allowed to cool in a desiccator and crushed in a mortar and pestle.

Calcium oxide is calcined before use, cooled in a desiccator and crushed.

Calcium oxide is added to caustic soda, previously crushed in a porcelain mortar, in a ratio of 2:1 by volume of powders. The resulting mixture is called soda lime. Calcium oxide is necessary to eliminate the hygroscopicity of caustic soda.

A round-bottomed reaction tube is filled 3/4 full with a mixture of sodium acetate and soda lime in a powder volume ratio of 1:3 or 1:2. The mixture is thoroughly mixed in a porcelain mortar. Assemble the device according to Fig. 1.

Rice. 1. Production of methane and experiments with it.

The reaction tube is connected to a system of two U-shaped tubes. The right elbow of the second tube is closed with a stopper with a glass tube having an extended end. The tube is filled with activated carbon. A weak solution of potassium permanganate is poured into one U-shaped tube, and bromine water into the other. The reactor tube is heated. Excessive overheating is avoided, which leads to side reactions and the production of undesirable products - acetone, unsaturated hydrocarbons, carbon dioxide, etc. To capture these substances, use a glass tube with activated carbon, which is connected to the gas outlet tube before the gases enter the first U-shaped handset.

Methane obtained during the reaction passes through solutions of KMnO 4 and Br 2, no discoloration of the solutions is observed (the installation is sealed if gas bubbling occurs synchronously in both solutions). At the end of the experiment, bring the flame of a match or splinter to the hole of the tube with the end pulled out. Methane combustion is observed. Write down the equations of chemical reactions.

Safety precautions: Ignite methane after establishing a stable synchronous bubbling of gas in solutions, but not in the first minutes of methane passage. Follow the heating rules and do not hold the alcohol lamp with your hands.

Disposal. Reuse KMnO 4 solution and bromine water. Transfer the reaction product - sodium carbonate with an admixture of sodium acetate and soda lime - completely into a neutralizer container. Wash U-shaped tubes under a hood with a weak alkaline solution of calcium hydroxide.

Experiment 2. Production of ethylene and experiments with it.

Equipment and reagents: Reaction tube, gas outlet tube, two U-shaped tubes, glass tube with activated carbon (with a pulled end), alcohol lamp, stands with legs, boilers, calcium chloride tube, ethyl alcohol, concentrated sulfuric acid, bromine water, permanganate solution potassium, activated carbon.

Procedure: A pre-prepared and cooled mixture (6 ml) of one part alcohol with three parts concentrated sulfuric acid is poured into a dry test tube-reactor (Fig. 2). Several boilers are placed in the test tube to ensure uniform boiling of the reaction mixture. The test tube is fixed in a stand. Connect the reactor tube to the U-shaped tubes using rubber hoses (see installation figure) containing the KMnO 4 solution and bromine water. The right elbow of the second U-shaped tube is closed with a stopper with an inserted glass tube having an extended end. The tube is filled with pre-activated carbon.

Since in the process of heating alcohol and sulfuric acid, in addition to ethylene, other substances are obtained (SO 2, diethyl ether, CO 2, etc.), some of which can also discolor the KMnO 4 solution and bromine water, then on the way of the gas mixture from the test tube-reactor before the first U-shaped tube, you should

Rice. 2. Production of ethylene and experiments with it.

place a calcium chloride tube with activated carbon.

Heat the reactor tube to a uniform boil. Observe the uniform synchronous bubbling of air and then ethylene through the KMnO 4 solution and bromine water. The color of the solutions gradually disappears. After the solutions have completely discolored, bring the flame of a match or a burning splinter to the tube with the end pulled out and ignite the ethylene. Write reaction equations and explain the observed phenomena.

Safety precautions. Ignite ethylene after the KMnO 4 solution and bromine water have completely decolorized. The device must be sealed, which is determined by the synchronous bubbling of gas through solutions of KMnO 4 and bromine water.

Disposal. Due to the oxidation of alcohol, a charred mixture of uncertain composition remains in the reactor tube, which is completely transferred to a neutralizer container. Add a little strong acidified H 2 SO 4 KMnO 4 solution to the solution remaining after bleaching potassium permanganate and boil it. All existing organic compounds are oxidized to carbon dioxide and water:

C x H y O z + KMnO 4 + H 2 SO 4 → MnSO 4 + K 2 SO 4 + CO 2 + H 2 O.

KMnO 4 solution can be used repeatedly. For utilization of the resulting MnSO 4 (after working off the solution), see: Class VIII, topic “Halogens”. Add a small portion of iron powder and a few drops of medium concentration hydrochloric acid to the solution remaining after bleaching bromine water:

Fe + HCI = FeCI 2 + 2H.

After some time, bromine derivatives will be reduced by atomic hydrogen to hydrocarbons and bromide ions, for example, according to the scheme:

The resulting solution is a yellowish-brown color of bromine water, which can be used to determine unsaturated hydrocarbons and demonstrate the oxidizing properties of bromine. Next, the iron powder is separated by filtration, which is washed, dried and used again.

LABORATORY WORK No. 2

Experiment 1. Production of ethylene by dehydration of ethanol over aluminum oxide

The experience described above in producing ethylene by dehydration of ethanol in the presence of H 2 SO 4 (conc) leads to the formation of large amounts of sulfur oxide (IV) and many other toxic compounds hazardous to the environment. Sulfur (IV) oxide very quickly discolors the KMnO 4 solution and bromine water, which makes the described experiment incorrect for educational demonstration purposes: C 2 H 5 OH + 2H 2 SO 4 = 2C + 2SO 2 + 5H 2 O, then:

C + 2H 2 SO 4 = CO 2 + 2SO 2 + 2H 2 O (when heated)

5SO 2 +2KMnO 4 +2H 2 O = K 2 SO 4 +2MnSO 4 +2H 2 SO 4

SO 2 +Br 2 +2H 2 O = H 2 SO 4 +2HBr

A simpler and more environmentally friendly option for producing ethylene is based on passing alcohol vapor over a heated solid aluminum oxide catalyst.

Equipment and reagents: Demonstration round-bottomed test tube, glass and rubber gas outlet tubes, two U-shaped tubes, test tubes, glass tube with an extended end, tripod, tripod foot, alcohol lamp, splinter, ethanol, washed and calcined sand, clay catalyst mixed with aluminum oxide, distilled water.

Work progress: Prepare the catalyst. To do this, the day before class, mix clay with aluminum oxide in a 2:1 ratio, moisten it with water, mix well and roll out peas, which are air-dried.

Dry sand (3-4 cm high) is poured into the demonstration tube (1) and soaked in alcohol. The catalyst is placed on top of the sand almost to the edge of the test tube. The reactor tube is fixed in the leg of the tripod with a slight slope (the bottom is higher than the hole) and connected to two U-shaped tubes (Fig. 3). The catalyst is thoroughly heated, then the sand soaked in alcohol is heated with another alcohol lamp so that there is always alcohol vapor in the container (do not overheat!). Under these conditions, in addition to ethylene, butadiene can also be produced, which casts doubt on the correctness of the experiment. To absorb butadiene, ethanol is poured into the first U-shaped tube (2). The solubility of butadiene in alcohol is 15 ml per 100 ml of solvent. All butadiene remains in alcohol, since the gas mixture leaving the first U-shaped tube does not give a pink color with a solution of a high-quality reagent for butadiene - quinone.

Rice. 3. Production of ethylene by dehydration of ethanol over a solid catalyst.

Another U-shaped tube (3) is filled with alcohol or water to produce an ethylene solution. The solubility of ethylene in water and alcohol is 25.6 and 360 ml per 100 ml of solvent, respectively. Thus, it is possible to obtain a solution of ethylene in water and alcohol, which is used for the determination of unsaturated organic substances.

The extension of the last U-shaped tube is connected to a gas outlet tube, which is placed in a test tube (4) first with bromine water and then with a solution of potassium permanganate. Discoloration of the solutions is observed. Before the end of the experiment, a glass tube with an extended end is attached to the gas outlet tube. Ethylene is set on fire with a splinter flame. Observe the combustion of ethylene with a luminous flame. Write the reaction equations.

Safety precautions. 1. The demonstration reactor tube is heated evenly to prevent cracking and combustion of gaseous substances formed in the test tube. 2. Place a baking sheet with sand under the heated test tube. 3. The installation must be sealed.

Disposal. A solution of butadiene and ethylene in alcohol should be used in alcohol lamps, as well as to demonstrate their unsaturated nature. Dispose of the decolorized KMnO 4 solution and bromine water according to the instructions in the previous experiment.

Experience 2. Preparation of acetylene and experiments with it

Equipment and reagents: Wurtz demonstration tube, glass and rubber gas tubes, two U-shaped tubes, a tube with an extended end filled with activated carbon, stands, tripod arms, syringe, syringe needle, rubber stoppers, tweezers, splinter, matches, calcium carbide , saturated sodium chloride solution, KMnO 4 solution, bromine water.

Procedure: Carefully place several pieces of calcium carbide into the Wurtz tube (4). The opening of the test tube is closed with a stopper (5). Next, connect the reactor tube with U-shaped tubes according to Fig. 4.

The work is carried out on a demonstration table, since the by-products of the reaction of technical calcium carbide with water are completely absorbed by the adsorbent - activated carbon. It is important to ensure the tightness of the installation, which is achieved by tightly fitting the plugs and rubber tubes to the glass test tubes and glass tubes.

Rice. 4. Preparation of acetylene and experiments with it.

The right elbow of the second U-shaped tube is closed with a stopper containing a glass tube filled with activated carbon. A diluted solution of KMnO 4 and bromine water is poured into U-shaped tubes. Using a long syringe needle, pierce the rubber hose connecting the reactor to the first U-shaped tube, and slowly introduce a saturated solution of sodium chloride into the reactor tube with calcium carbide, adjusting the amount of added solution and the intensity of acetylene release.

Discoloration of solutions of KMnO 4 and bromine water is observed. After the solutions have decolorized, bring the flame of a splinter to a tube with activated carbon and observe the smoky flame of burning acetylene. Write equations of chemical processes and explain the observed phenomena.

Safety precautions. Do not pick up pieces of calcium carbide with your hands. Add an aqueous solution of sodium chloride to calcium carbide in small portions. Use up all the calcium carbide. Check the tightness of the installation: there should be synchronous bubbling of gas bubbles through both solutions in the U-shaped tubes.

Disposal. Pour a strong KMnO 4 solution from a syringe into the reactor tube and mix the contents. Acetylene and other hydrolysis products (H 2 S, PH 3, etc.) are oxidized, the air remains clean. After some time, open the test tube and pour the resulting suspension of complex composition into a neutralizer container with an alkaline solution.

Disposal of the bleached KMnO 4 solution and bromine water is carried out according to the instructions in experiment No. 2.

In a chemistry circle, if you have a small electric arc furnace, as well as the required current source, you can get some calcium carbide. In a small graphite crucible or in a recess hollowed out in a thick carbon electrode, place a mixture of equal (by weight) quantities of calcium oxide (quicklime) and pieces of coke the size of a pinhead. Excess coal will burn when exposed to atmospheric oxygen. The experimental scheme is shown in the figure.

We bring the upper electrode into contact with the mixture, creating an electric arc. The mixture conducts current thanks to the pieces of coal. Let the arc burn for 20-30 minutes at the highest possible current. Eyes should be protected from bright light with glasses with very dark lenses (welding glasses).

After cooling, the mixture turns into a melt, which, if the experiment was successful, contains small pieces of carbide. To check this, place the resulting mass in water and collect the resulting gas bubbles in a test tube turned upside down and filled with water.

If there is no electric arc furnace in the laboratory, then gas can easily be obtained from commercially available calcium carbide. Let's fill several test tubes with gas - completely, half, one-third, etc. It is impossible to fill wider vessels, such as glasses, with gas, because water will flow out of them, and the glasses will contain mixtures of gas and air. When they ignite, as a rule, a strong explosion occurs.

Calcium carbide interacts with water according to the equation:

CaC 2 + 2H 2 O = Ca(OH) 2 + C 2 H 2

Along with calcium hydroxide (slaked lime), this reaction leads to the formation of ethyne, an unsaturated hydrocarbon with a triple bond. Thanks to this bond, ethylene exhibits high reactivity.
Ethyn research

Let's prove the presence of an unsaturated bond in ethyne (acetylene) using Bayer's reagent or bromine water. To do this, place the reagent in a test tube and pass ethyne through it. We will get it in another test tube from several pieces of calcium carbide. We close this test tube with a rubber stopper with two holes. We will insert a glass tube with a curved end into one of them in advance - it should be immersed in a test tube with the reagent. Insert a drip funnel into the other hole and first close the tap. M
You can take a simple glass funnel instead, replacing the tap with a clamp, as when producing methane. Pour water into the funnel and, carefully opening the tap, slowly, drop by drop, add it to the carbide. Due to the explosive nature of ethylene, we will conduct the experiment near an open window or in a fume hood. Under no circumstances should there be open flames or turned on heating devices around.

Ethine in its pure state is a gas with a slightly intoxicating odor. Ethine obtained from technical carbide is always contaminated with unpleasant-smelling toxic impurities of hydrogen phosphorous (phosphine) and arsenic hydrogen (arsine). Mixtures of ethylene with air containing from 3 to 70% ethylene are explosive. Ethyne dissolves very easily in acetone. In the form of such a solution, it can be stored and transported in steel cylinders (Pure ethylene has almost no odor. Its mixtures with air explode from a spark in a wider range of ethylene concentrations - from 2.3 to 80.7%. - Note translation).

Ethine can be converted into a wide variety of compounds, which in particular have become important for the production of plastics, synthetic rubber, drugs and solvents. For example, when hydrogen chloride is added to ethyne, vinyl chloride (vinyl chloride) is formed - the starting material for the production of polyvinyl chloride (PVC) and plastics based on it. Ethanal is obtained from ethyne, which we will get to know later, and from it many other products are obtained.

These figures indicate the enormous importance of calcium carbide and related processes.

In 1828, a young German chemist, Professor Friedrich Wöhler, first obtained an organic compound - urea - by synthesis from inorganic starting substances. In the middle of the last century, Swedish chemist Jacob Berzelius synthesized more than 100 different organic compounds. (It is impossible not to mention here other founders of organic synthesis. In 1842, the Russian chemist N. N. Zinin first synthesized aniline, which was previously obtained only from plant materials. In 1845, the German chemist Kolbe synthesized acetic acid, in 1854 the French Bertlogir, in 1861 by A. M. Butlerov - a sugary substance. Interesting information about the life and work of these scientists is contained, in particular, in the book of K. Manolov “Great Chemists T. 1 and 2. Transl. . (M., Publishing house "Mir", 1976), - Note translation)

Since then, thousands of chemists in all countries, through persistent and hard work, have created or isolated many new organic substances from natural sources. They investigated their properties and published the results of their work in scientific journals.

By the beginning of the 20th century. About 50,000 different organic compounds have already been studied, mostly obtained by synthesis. By 1930 the number had risen to 300,000, and at present the number of pure and trace-free organic compounds appears to be well over 800,000. However, the possibilities are far from being exhausted. Every day, more and more new substances are found and studied all over the world.

Most organic compounds have not found practical application. Many of them are known from personal experience only to a very narrow circle of chemists. Despite this, the labor expended was by no means in vain, since some substances turned out to be valuable dyes, medicines or new types of materials. It often happens that a substance that has been known for several decades and has long been described in the scientific literature suddenly acquires great practical importance. For example, the activity of some complex compounds against insect pests has recently been discovered. It is likely that other compounds that are still mentioned only in old, dust-covered scientific journals will soon find use as dyes, medicines, or in some other field. It is even possible that they will acquire exceptional importance in the national economy.

Now we will independently obtain and study several substances that are especially important in industry.

WINE ALCOHOL AND ITS RELATIVES

System first! When entering the world of organic chemistry, you can immediately get lost if you do not first familiarize yourself with the classes of organic compounds and the basics of the language of organic chemistry. In fact, most organic substances can be divided into groups with similar structures and similar properties. Chemists, using Latin and Greek roots, and, in addition, largely invented gobbledygook, created such a well-thought-out system of names that immediately tells a specialist to which class certain substances should be classified. One problem: along with the names according to the uniform rules of international nomenclature, for many compounds their own names are still used, related to the origin of these compounds, their most remarkable properties or other factors. Therefore, many compounds in this book will have multiple names.

We are already familiar with saturated and unsaturated hydrocarbons. Saturated hydrocarbons are called alkanes, unsaturated ones with a double bond are called alkenes, and those with a triple bond are called alkynes. We know that these hydrocarbons, if arranged in order of increasing number of carbon atoms, form homologous series.

Along with hydrocarbons, organic compounds that also contain oxygen are of great importance. Let us first consider three series of oxygen-containing organic compounds:

alkanols(alcohols)

alkanali(aldehydes)

alkanoic acids(formerly known as carboxylic acids)

Methane derivatives are the following compounds:

CH 3 -OH H-CHO H-COOH

methanol methanal methanoic acid

(methyl alcohol) (formaldehyde, (formic acid)

formic aldehyde)

Ethane derivatives are the following representatives of these three classes of compounds:

CH 3 -CH 2 -OH CH 3 - CHO CH 3 - COOH

ethanol ethanal ethanoic acid

(ethyl alcohol) (acetaldehyde, (acetic acid)

acetaldehyde)

Similarly, for all subsequent hydrocarbons, related or oxygen-containing compounds are known. In general, derivatives of any hydrocarbons correspond to the following formulas:

R-OHR-CHO R-COOH

alkanol alkanal alkanoic acid

(alcohol) (aldehyde) (carboxylic acid)

The number of possible compounds of these three classes will increase sharply if we take into account that in higher hydrocarbons each isomer forms different oxygen compounds. Thus, butane and isobutane correspond to different alcohols - butyl and isobutyl:

CH 3 -CH 2 -CH 2 -CH 3 CH 3 -CH 2 -CH 2 -OH

butane butanol-1

(butyl alcohol)

CH 3 -CH(CH 3)-CH 3 CH 3 -CH(CH 3)-CH 2 -OH

2-methylpropane 2-methylpropanol-1

(isobutane) (isobutyl alcohol)

In addition, additional isomers appear due to the fact that characteristic oxygen-containing groups, for example, the alcohol group OH, can be bonded either to the ends of the chain or to one of the intermediate carbon atoms. Examples include propyl and isopropyl alcohols:

CH 3 -CH 2 -CH 3 CH 3 -CH 2 -CH 2 -OH CH 3 -CH(OH)-CH 3,

propane propanol-1 propanol-2

(propyl alcohol) (isopropyl alcohol)

Groups characteristic of classes of compounds are called functional groups. These groups include, for example, the hydroxyl group OH of alkanols and the carboxyl group COOH of carboxylic acids. Later we will look at some examples of functional groups containing elements other than oxygen. Changing functional groups and introducing them into molecules of organic substances, as a rule, is the main task of organic synthesis.

Of course, in one molecule there can be several identical or different groups at the same time. We will learn about several representatives of this series of substances - compounds with several functions.

However, enough theory! Let us finally proceed to the experiments - we will obtain the above-mentioned oxygen-containing derivatives of methane and ethane, carry out their transformations and study their properties. These compounds, whose names have long been known to us, are very important for chemical technology. Let them help us become acquainted with the basics of industrial organic synthesis, although we will not be able to directly reproduce the industrial method of their production. They will also give us insight into the most important properties of compound classes.
Methanol research

By dry distilling wood, we have already obtained a few drops of crude methanol (methyl alcohol). Currently, the vast majority of methanol is obtained by synthesis from water gas:

CO + 2H 2 = CH 3 OH

The constituents of water gas combine to form methanol. In addition, higher alcohols are also formed in small quantities. This process requires a temperature of 400 °C, a pressure of 200 atm and is accelerated in the presence of oxide catalysts.

Methanol serves as a solvent and intermediate in the production of dyes. But its main consumer is the production of plastics, which requires large quantities of methanal (formaldehyde). Methanal is produced by the oxidation of methanol with atmospheric oxygen. In industry, a mixture of methanol vapor and air at 400 °C is passed over a copper or silver catalyst.

To simulate this process, bend a piece of copper wire with a diameter of 0.5-1 mm into a spiral and use tongs to bring it into the non-luminous zone of the Bunsen burner flame. The wire is heated and coated with a layer of copper (II) oxide. Let's place the methanol we obtained earlier (10 drops) in a fairly wide test tube and lower a hot copper spiral into it. As a result of heating, methanol evaporates and, under the influence of a catalyst - copper - combines with oxygen to form methanal (we recognize it by its characteristic pungent odor). In this case, the surface of the copper wire is restored. The reaction occurs with the release of heat. With large amounts of methanol vapor and air, the copper remains heated until the reaction is complete. Please note that methanol is very toxic! Therefore, we will not conduct experiments with large quantities.

Even a small sip of methanol can cause complete loss of vision and sometimes death. Therefore, methanol should always be stored in such a way that no one can drink it by mistake. However, methanol, along with other compounds, is specially added in small quantities to the alcohol used for combustion in order to denature it. Therefore, denatured alcohol is also poisonous!
Experiments with methanal

We will conduct the following experiments with commercial formaldehyde. Formalin is a 35-40% solution of methanal (formaldehyde) in water. Usually it still contains a small amount of unreacted toxic methanol. Methanal itself causes the coagulation of proteins and, therefore, is also a poison.

Let's carry out a series of simple experiments. In a test tube or small flask, evaporate a few milliliters of formaldehyde. The result will be a white, sparingly soluble mass, a sample of which we will then heat in another test tube. At the same time, it will evaporate, and by the smell you can feel that methanal has formed again. In its pure state, methanal is a gas that turns into liquid at normal pressure and –19 °C. Already in the cold and even more so with slight heating or in the presence of acids, methanal begins to polymerize. At the same time, many of its molecules connect with each other and form long chains of paraform:

CH 2 -O-CH 2 -O-CH 2 -O-CH 2 -O...

Strong heating leads to the reverse conversion of paraform to methanal.

Polymerization is characteristic of many alkanals and indicates the presence of an unsaturated bond in them. Polymerization reactions underlie the production of many plastics. Methanal gradually polymerizes in solution with the formation of increasingly longer chain molecules. Such polymerized formaldehyde can be regenerated by heating paraform and absorbing the methanal vapor released by water.

Methanal and other alkanals (aldehydes) give a characteristic color reaction with the so-called Schiff reagent, which can serve for their recognition. Let's prepare the reagent by taking a little fuchsin dye on the tip of a scalpel and dissolving it in a few milliliters of warm distilled water. To this solution, we will add an aqueous solution of sulfurous acid in portions until it becomes discolored. Pour a few milliliters of the reagent obtained in this way into a test tube, add a few drops of methanal solution and mix. A purple color will soon appear. After conducting a series of experiments with increasingly dilute methanal solution, we can verify the sensitivity of this qualitative reaction.

Let's pour a few milliliters of Fehling's reagent into a test tube, which can be prepared by mixing equal amounts of the following stock solutions:

Fehling's stock solution No. 1: 7 g copper (II) sulfate in 100 ml distilled water

Fehling's stock solution No. 2: 37 g of Rochelle salt and 10 g of sodium hydroxide in 100 ml of distilled water

Fehling's reagent itself is very unstable, and the original solutions can be stored. These solutions can sometimes be purchased in finished form in pharmacies.

Now add about 1 ml of methanal solution to the finished Fehling’s reagent and heat it to a boil. In this case, elemental copper is released, which forms a beautiful mirror coating on the walls of the test tube (copper mirror). You just need to first degrease the test tube with a chrome mixture. Other alkanals form a brick-red precipitate of copper(I) oxide.

Instead of Fehling's reagent, an ammonia solution of silver salt can be used. We will gradually add a dilute aqueous solution of ammonia to a dilute (approximately 2%) solution of silver nitrate - exactly until the precipitate that initially formed dissolves again. In a test tube, thoroughly washed with a chrome mixture and rinsed several times with distilled water, pour 2 ml of the prepared silver salt solution and 5-8 ml of methanal solution and carefully heat this mixture, preferably in a water bath. A distinct mirror forms on the walls of the test tube, and the solution, thanks to the tiny particles of silver that fall out, acquires an intense black color.

Alkanals (aldehydes) are very easily oxidized, resulting in the formation, as a rule, of alkanoic (carboxylic) acids. Thus, in relation to oxidizing agents they behave as reducing agents. For example, alkanals reduce cupric salt to copper(I) oxide or even elemental copper. They reduce an ammonia solution of silver salt to release metallic silver. These reactions are common to alkanals and other reducing agents, such as grape sugar, which we will discuss later.

Under the action of other oxidizing agents, alkanals are also oxidized to form alkanoic acids, and sometimes even to carbon dioxide and water. In a test tube, carefully add a 10% solution of hydrogen peroxide (peroxide) to several milliliters of methanal solution. Then heat the mixture and hold moistened blue litmus paper in the vapor over the test tube. Its redness indicates that methane (formic) acid has formed in the test tube.

Methane (formic) acid is the simplest organic acid. In technology, it is obtained by adding carbon monoxide to sodium hydroxide under pressure. According to Eq.

NaOH + CO = HCOONa

in this case, the sodium salt of formic acid is formed - sodium methate, or sodium formate. It serves as an intermediate product in the production of other compounds and is used in textile and leather production. Methane acid has a strong disinfectant and preservative effect, so it is used to protect food products and silage from spoilage. Some preparations used for ensiling are mainly a solution of methanoic acid.

We will conduct the following experiments with methanoic acid purchased at the store. (Caution! Concentrated methane acid is poisonous and corrosive to the skin!)

Pour 5 ml of dilute sulfuric acid into a test tube and add a solution of potassium permanganate - enough so that the liquid is strongly colored. After this, add another 5 ml of approximately 80% methanoic acid. When heated, the mixture becomes discolored due to the reduction of permanganate to manganese (II) sulfate. In this case, methanoic acid is oxidized to carbon dioxide and water.

In subsequent test tube experiments, we will check whether magnesium, zinc, iron and nickel are dissolved in 60% methanoic acid. Active metals react with methane and other organic acids to form salts and release hydrogen. Thus, organic acids behave quite similarly to inorganic ones, but, as a rule, they are weaker.

Concentrated sulfuric acid and some catalysts decompose methane acid into carbon monoxide CO and water. Heat 1 ml of anhydrous methanoic acid with an excess of concentrated sulfuric acid in a test tube closed with a rubber stopper into which a glass tube is inserted. Gas escapes from this tube and, when ignited, burns with a pale blue flame. This is the poisonous carbon monoxide (carbon monoxide) that we are already familiar with. Due to the danger involved, the experiment should be carried out in a fume hood or outdoors.

In conclusion, it should also be noted that methanoic acid and its salts are often found in nature. As can be seen from its second name (formic), this acid is part of the poisonous secretions of ants. In addition, it is found in the secretions of bees, in nettles, etc.
Experiments with ethanol

So, we got acquainted with methanol, methanal and methanoic acid. Compounds like these, containing two carbon atoms, are of greatest importance in technology.

Ethanol (ethyl alcohol), commonly referred to simply as alcohol, is produced by what is known as alcoholic fermentation. Many types of sugars, as well as the saccharification product of starch in the presence of malt, are broken down by microscopically small yeast fungi to form alcohol and carbon dioxide. Anyone who has ever seen fruit juice ferment has observed the intense release of carbon dioxide from the outlet tube. And the fact that the resulting wine actually contains alcohol can be easily seen by the behavior of the person who drinks this wine.

Since alcoholic fermentation can occur spontaneously, diluted alcohol has been known to people since ancient times as an stimulating drink. There is hardly any need to talk about the disastrous consequences of drunkenness. Young people in particular should completely abstain from drinking alcoholic beverages.

The alcohol content during fermentation of sugar solutions and fruit juices varies widely. However, since yeast cannot exist at high alcohol concentrations, no more than 15% alcohol can be obtained through fermentation. Vodka and more concentrated alcohol are obtained from dilute solutions by distillation. Such distillation is legally permitted only at state-owned distilleries. The receipt of even the smallest amount of alcohol by private individuals, even for chemical experiments, is strictly prohibited by law.

Edible alcohol and alcohol for cosmetic purposes are produced only from grain (Potato starch is also used for this purpose. - Note translation). Starch is first converted into sugar, which is then fermented into alcohol. Industrial alcohol is obtained in large quantities as a result of fermentation of sulfite liquor, that is, from pulp and paper production waste. An increasingly large part of industrial alcohol - an indispensable solvent and starting material in organic synthesis - is currently produced synthetically from calcium carbide through ethylene and ethanal (The most advanced method for producing ethanol is its synthesis from ethylene (ethylene) by adding water to it in the presence of a catalyst . Note translation).

Pure alcohol goes on sale under the name rectified alcohol. It contains 4-6% water. Since rectification is expensive, we use it only in a few experiments. In cases where this is not specified, we will be content with much cheaper denatured alcohol, which, as we well know, is used as a fuel. This is also 95% alcohol, but so that it is not suitable for drinking, substances that are poisonous and have an unpleasant taste or odor (methanol, pyridine, phthalic acid ester) are added to it.

Since we still have a wide variety of experiments with alcohol ahead of us, for now we will limit ourselves to only two. Firstly, we can easily prove the presence of water in the rectified product. Heat several crystals of copper sulfate in a crucible until a colorless anhydrous salt is formed. Then add a pinch of the resulting salt to the alcohol sample and shake. The presence of water is detected by the blue color of the solution. Anhydrous alcohol, also called absolute alcohol, can only be obtained by processing with special drying agents.

Denatured alcohol serves as a good fuel for alcohol lamps and tourist stoves. Recently, it has even been used as rocket fuel. True, in campsites it is gradually being replaced by propane, which is delivered in small steel cylinders.

Many attempts are also being made to produce so-called “dry alcohol”. Its various varieties, as a rule, do not contain alcohol at all. We can also convert alcohol into a semi-solid state by dissolving about 5 g of soap shavings in 20 ml of denatured alcohol with stirring. The result is a gelatinous mass that can be cut into pieces. Like liquid alcohol, it burns with a pale blue flame.

Obtaining ethanal

The oxidation of ethanol produces ethanal (acetic aldehyde) and then ethanoic acid (acetic acid). Strong oxidizing agents immediately convert ethanal into acetic acid. Oxidation by air oxygen under the influence of bacteria also leads to the same result. We can easily verify this if we dilute the alcohol a little and leave it in an open cup for a while, and then check the reaction with litmus. To obtain table vinegar, they still mainly use acetic acid fermentation of alcohol or low-grade wines (wine vinegar). To do this, the alcohol solution is slowly passed through sawdust from beech wood under intensive air supply. 5% or 10% table vinegar or the so-called vinegar essence containing 40% acetic acid goes on sale (In the USSR, the concentration of food vinegar essence supplied to the retail chain is 80%, and the concentration of table vinegar is 9%.- Note translation). For most experiments it will suit us. Only in some cases will you need anhydrous (glacial) acetic acid, which is classified as a poison. You can buy it at a pharmacy or chemical store. Already at 16.6 °C it hardens into a crystalline mass similar to ice. Synthetically, acetic acid is obtained from ethyne through ethanal.

The repeatedly mentioned ethanal, or acetaldehyde, is the most important intermediate product in chemical technology based on the use of calcium carbide. It can be converted into acetic acid, alcohol, or butadiene, the starting material for synthetic rubber. Ethanal itself is produced industrially by adding water to ethyne. In the GDR, at the synthetic butadiene rubber plant in Schkopau, this process is carried out in powerful continuous reactors. The essence of the process is that ethine is introduced into heated dilute sulfuric acid, in which catalysts - mercury salts and other substances - are dissolved (This reaction was discovered by the Russian scientist M. G. Kucherov in 1881 - Note translation). Since mercury salts are very poisonous, we will not synthesize ethanal from ethyne ourselves. Let's choose a simpler method - careful oxidation of ethanol.

Pour 2 ml of alcohol (denatured alcohol) into a test tube and add 5 ml of 20% sulfuric acid and 3 g of finely ground potassium dichromate. Then quickly close the test tube with a rubber stopper into which a curved glass tube is inserted. Heat the mixture to a boil over a low flame and pass the resulting vapors through ice water. The resulting ethanal dissolves in water and can be detected with
The essence of the reactions described above for the determination of alkanals. In addition, the solution exhibits an acidic reaction because oxidation easily proceeds further with the formation of acetic acid.

To obtain ethanal in larger quantities and more pure, we will assemble, guided by the drawing, a more complex installation. However, this experiment can only be performed in a circle or if the reader has extensive experience. Ethanal is poisonous and very volatile!

The left side of the installation is designed to pass a current of carbon dioxide (carbon dioxide). The latter is necessary to remove the evolved ethanal from the reaction sphere before it is oxidized further to acetic acid. Let's place pieces of marble in a flask and add dilute hydrochloric acid to them in small portions. To do this, you need a drip funnel with a long outlet tube (at least 25 cm). You can tightly attach such a tube to a regular drip funnel using a rubber hose. This tube must be filled with acid at all times so that carbon dioxide can overcome the excess resistance of the subsequent part of the installation and does not escape in the opposite direction (You can also use a dropping funnel without a long outlet tube. In this case, you need to insert another We insert one short glass tube into the stopper that closes the dropping funnel, and connect both tubes with a rubber hose. It is even more convenient to use the Kipp apparatus. Note translation).

How to ensure equalization of pressure in the gas release device is shown in the figure on page 45.

First, pour 20 ml of denatured alcohol into another vessel that serves as a reactor - a 250 ml round-bottomed flask. Then dissolve 40 g of finely ground potassium or sodium dichromate (Poison!) in 100 ml of diluted sulfuric acid (Add 20 ml of concentrated sulfuric acid to 80 ml of water.) Due to the higher density of sulfuric acid, it is imperative to add it to water, and not vice versa. Sulfuric acid is always added gradually and only while wearing safety glasses. Under no circumstances should you pour water into sulfuric acid!

We immediately place one third of the prepared solution into the reactor, and the rest into a dropping funnel connected to the reactor. Let's insert a tube outlet into the reactor connecting it to a device for releasing carbon dioxide. This tube must be immersed in liquid.

Finally, the cooling system deserves special attention. In a tube that extends upward from the reactor at an angle, vapors of alcohol and acetic acid should condense. It is best to cool this tube using an external lead coil running running water through it. In extreme cases, we can do without refrigeration, but then we will get a dirtier product. To condense ethanal, which already boils at 20.2 °C, we use a direct refrigerator. It is, of course, advisable to take an efficient refrigerator - coil, ball or with internal cooling. In extreme cases, a not too short Liebig refrigerator will do. In any case, the cooling water must be very cold. Tap water is only suitable for this in winter. At other times of the year, you can pass ice water from a large tank installed at a sufficient height. We cool the receivers - two test tubes connected to each other - by immersing them in a cooling mixture of equal (by weight) quantities of crushed ice or snow and table salt. Despite all these precautions, ethanal vapor still partially escapes. Since ethanal has an unpleasant, pungent odor and is toxic, the experiment must be carried out in a fume hood or in the open air.

Only now, when the installation is charged and assembled, will we begin the experiment. First, let's check the operation of the gas release device by adding a small amount of hydrochloric acid to the marble. In this case, the installation is immediately filled with carbon dioxide. If it certainly passes through the reactor and no leaks are detected, we will proceed to the actual production of ethanal. We will stop the gas evolution, turn on the entire cooling system and heat the contents of the reactor to a boil. Since the oxidation of alcohol now releases heat, the burner can be removed. After this, we will again gradually add hydrochloric acid so that a moderate current of carbon dioxide passes through the reaction mixture all the time. At the same time, the remaining dichromate solution should flow slowly from the dropping funnel into the reactor.

At the end of the reaction, each of the two receivers contains several milliliters of almost pure ethanal. We plug the test tubes with cotton wool and store them in the cold for the next experiments. Long-term storage of ethanal is impractical and dangerous, since it evaporates too easily and, when in a bottle with a ground-in stopper, can forcefully knock out the stopper. Ethanal is sold only in sealed thick-walled glass ampoules.

Experiments with ethanal

In addition to the qualitative reactions described above, we can conduct a number of other experiments with small amounts of ethanal,

In a test tube, carefully add 1 drop of concentrated sulfuric acid to 1-2 ml of ethanal (wearing safety glasses and at a distance from you) using a glass rod. A violent reaction begins. As soon as it subsides, dilute the reaction mixture with water and shake the test tube. A liquid is released which, unlike ethanal, does not mix with water and boils only at 124 °C. It is obtained by combining three ethanal molecules to form a ring:

E that ethanal polymer is called paraldehyde. When distilled with dilute acids, it turns back into ethanal. Paraldehyde is used in medicine as a sleeping pill.

In the next experiment, we carefully heat a small amount of ethanal with a concentrated solution of sodium hydroxide. A yellow “aldehyde resin” is released. It also arises due to the addition of ethanal molecules to each other. However, unlike paraldehyde, the molecules of this resin are built from a large number of ethanal molecules.

Another solid polymerization product, metaldehyde, is formed when ethanal is cold treated with hydrogen chloride gas. Previously, it found some use as a solid fuel ("dry alcohol").

Dilute approximately 0.5 ml of ethanal with 2 ml of water. Add 1 ml of a diluted solution of sodium hydroxide or soda and heat for several minutes. We will smell an exceptionally pungent odor of crotonaldehyde. (Conduct the experiment in a fume hood or in the open air!).

From ethanal, as a result of the addition of two of its molecules to each other, an aldol is first formed, which is also an intermediate product in the production of butadiene. It contains both alkanal and alkanol functional groups.

By eliminating water, the aldol turns into crotonaldehyde:

SOLVENTS IN HOUSEHOLD AND TECHNOLOGY

These days, organic solvents can be found in any home. Who hasn't used a stain remover to remove grease or tar stains from clothes? All varnishes and many adhesives, such as rubber, also contain various organic solvents. If you have some experience, you can already tell by smell which substance serves as a solvent in these mixtures.

Organic solvents are required in almost any production. Fats and oils are extracted from plants using solvents. The plastics, textile and paint industries consume huge quantities of solvents. The situation is the same in the production of medicines and cosmetics, and in many other sectors of the economy.

Many people have probably encountered some of the main solvents, such as gasoline and alcohol. Many factors come into play when evaluating a solvent. First of all, of course, it is important which substances dissolve well in it. Thus, many resins, medicines and cosmetics dissolve well in alcohol, while fats and paraffin dissolve very poorly in it. In addition, when comparing solvents, their flammability, boiling point, toxicity and, last but not least, cost play a significant role.

We will carry out the following experiments with several compounds that are especially often used as solvents.
Carbon tetrachloride is a non-flammable solvent

If all four hydrogen atoms in methane are replaced with chlorine, you get carbon tetrachloride (carbon tetrachloride). Carbon tetrachloride is a liquid that boils at 76 °C and has a density of 1.593 g/cm 3 . Thus, it is much heavier than water and almost immiscible with it. Carbon tetrachloride excellently dissolves resins, fats, etc. and has a great advantage over other solvents: it does not burn. Against! Its heavy vapors suppress flames, which is why it is used in fire extinguishers.

Let's pour some gasoline, alcohol or acetone into a cup and carefully set fire to this flammable liquid in the open air. If we now add a few milliliters of carbon tetrachloride, the fire will go out. It should be taken into account that when extinguishing with carbon dioxide, a very poisonous gas, phosgene COCl 2, can be formed. Therefore, this fire extinguishing agent should only be used in enclosed spaces with appropriate precautions. Recently, fire extinguishers charged with carbon tetrachloride are falling out of use. Instead, fire extinguishers now use mixed bromine-chlorine or fluorine-chlorine derivatives of hydrocarbons.

In the next experiment, mix 2 ml of carbon tetrachloride with 1.5 g of zinc dust. The latter is a very fine powder, which is obtained by condensation of zinc vapor. Add more burnt magnesia or zinc oxide to the mixture to form a paste of medium viscosity. Place it on a piece of sheet iron or in an iron crucible and heat it in the open air over bare fire to 200 °C. In this case, a violent reaction begins, leading to an increase in the temperature of the mixture above 1000 °C. At the same time, thick smoke is released. Carbon tetrachloride and zinc react to form zinc chloride:

2Zn + CCl 4 = 2ZnCl 2 + C

Zinc chloride evaporates at high temperatures and forms a fog, attracting water from the air.

Other metals, especially iron, also react slowly with carbon tetrachloride. Therefore, it promotes corrosion and is not suitable as a solvent for metal varnishes and similar purposes.

Carbon tetrachloride is quite poisonous. Inhalation of its vapors in small doses has a narcotic effect, and in large doses or in so-called chronic poisoning leads to severe liver damage. Therefore, caution is required when working with carbon tetrachloride! Reliable ventilation will prevent the accumulation of carbon tetrachloride vapors in the air.

The next important representative of the solvent group is propanone (acetone).

By dry distillation of wood, we obtained the calcium salt of acetic acid - “gray wood vinegar powder.” Anyone who has not carried out this experiment can easily prepare the indicated salt by neutralizing a dilute solution of acetic acid (table vinegar) with calcium carbonate or calcium hydroxide.

To obtain acetone, place a few grams of wood vinegar powder in a test tube made of refractory glass. We close the test tube with a rubber stopper, into the hole of which a curved glass tube is inserted. Let's cool this tube using a lead coil. The receiver can be a test tube immersed in ice water. Due to the flammability of the product, the outlet pipe should not be too short so that the distance between the flame and the receiver is as large as possible. In addition, we take into account that the experiment can only be carried out in a fume hood or in the open air.

Heat the test tube with powder strongly with a Bunsen burner. Vapors are released, and a mobile liquid condenses in the receiver, which, depending on the degree of purity of the original salt, has a color from yellow to brownish. It consists mainly of acetone, used as a fat solvent:

The excellent properties of this solvent can be easily verified by dissolving small amounts of fat, wax, varnish and other organic substances. Many plastics also dissolve in acetone or at least swell in it. Try using it on a piece of celluloid, polystyrene or other plastic. Needless to say, it is an excellent solvent, and, unlike carbon tetrachloride, it does not cause corrosion. But it is very flammable. To make sure of this, pour a little into a cup and set it on fire, carefully bringing the source of fire closer.

In its pure state, acetone (propanone) is a colorless liquid that boils already at 56.2 °C and has a peculiar, not unpleasant odor. Previously, it was obtained mainly by dry distillation of gray wood vinegar powder, and today it is produced by various methods, including from acetic acid by passing its vapor over a catalyst, oxidation of isopropyl alcohol and fermentation of starch under the influence of appropriate bacteria. In recent years, acetone has been produced simultaneously with phenol in a roundabout way - through the stage of cumene formation - from gases from petrochemical production.

In terms of its chemical structure, acetone is the simplest representative of alkanones (ketones), related to alkanals (aldehydes). While alkanals, such as methanal or ethanal, contain a C=O group at the end of the molecule, in alkanones such a group is located at the “internal”, i.e., not at the outermost carbon atom in the chain. Alkanones exhibit less unsaturation than alkanals and are therefore not detected by the qualitative reactions characteristic of alkanals. (Check!)

In conclusion, let's look at ether, which, in addition to its use in medicine for anesthesia, is an excellent solvent for fats and many other substances.

Strictly speaking, there are different ethers, which, like alkanals or alkanones, form a class of compounds with similar properties. Ordinary ether should strictly be called diethyl ether. It is formed from two molecules of ethanol by elimination of water, usually with concentrated sulfuric acid:

We get a small amount of ether. To do this, pour about 2 ml of denatured alcohol and 1.5 ml of concentrated sulfuric acid into a test tube. Let's select a stopper with two holes for the test tube. Into one of them we will insert a small dropping funnel or just a small funnel with an elongated tube, the exit from which will first be closed using a piece of rubber hose and a clamp. Using the second hole in the stopper, we attach a vapor cooling device to the test tube - the same as when producing ethanal. The receiver must be cooled with ice and water, because ether already boils at 34.6 °C! Due to its unusually easy flammability, the refrigerator should be as long as possible (at least 80 cm) so that there is sufficient distance between the source of fire and the receiver. For the same reason, we will conduct the experiment away from flammable objects, in the open air or in a fume hood. Pour about 5 more ml of denatured alcohol into the funnel and carefully heat the test tube on an asbestosed grid with a Bunsen burner to approximately 140 ° C (The temperature should not exceed 145 0 C, since at a higher temperature (about 170 0 C) ethene is formed. Even when working with low the amount of ether should always take into account the risk of fire. Therefore, we recommend replacing the burner with a closed electric stove and installing a protective screen between the heat source and the receiver. When using a dropping funnel, carefully lubricate and check the tap. It is best to take a test tube with a side outlet tightly attached to the refrigerator as a receiver. , onto which you can put a rubber hose to increase the distance between the escaping ether vapor and the heat source. It is better to cool the receiver with a mixture of ice and salt -. Note translation). A very volatile distillate condenses in the receiver, and in case of insufficient cooling we will smell the characteristic smell of ether. Carefully opening the clamp, we will gradually add alcohol in small portions. At the end of the reaction, the sulfuric acid is increasingly diluted with the resulting water, as a result of which the formation of the ether stops and the alcohol is distilled.

If the experiment is carried out carefully, we will obtain about 4 ml of a very mobile, transparent liquid, which consists mainly of ether. If you apply a few drops of it on your finger, you will feel a strong cold. The fact is that the ether quickly evaporates, and the heat of evaporation is taken away from its environment.

At chemical plants and in hospitals, very strong explosions occurred when working with ether. With prolonged contact with atmospheric oxygen and under the influence of sunlight, easily explosive peroxides are formed in the ether. Therefore, under no circumstances will we store more ether. We will not need it in any of the experiments recommended in this book. We will only need ether in a mixture with two parts of alcohol as a solvent for collodion. Therefore, we will immediately dilute the remainder of the ether with double the amount of alcohol and store it only in the form of this safe mixture in a securely closed dark brown glass bottle.

Prolonged inhalation of ether vapor causes loss of consciousness, which was first used in 1846 by Jackson and Morton for anesthesia (For this purpose, ether during a surgical operation was first used by Long (USA) in 1842, but this experiment was not published. - Note translation). Thoroughly purified ether is still used for this purpose. However, one can hope that the readers of this book are trustworthy and, of course, will not conduct dangerous, irresponsible and categorically unacceptable experiments of their own related to anesthesia.

Concluding this section on solvents, it should be emphasized that in the following parts of the book we will also get acquainted with other important solvents, for example, benzene and esters, which are excellent dissolvers of varnishes and plastics.

The carbon skeleton of the organic compounds we have looked at so far has been straight or branched chains. The German chemist August Kekule first discovered that the molecules of many other organic compounds are built like a ring. The most important ring (cyclic carbon compound) - benzene - is contained in an amount of 1-2% in coal tar, from which it is obtained.

Benzene is a colorless liquid that boils at 80.2 °C and solidifies at 5.5 °C. For those who store their reagents in an unheated room, the freezing of benzene is a sign that it is time to find a warmer place for the bottles with aqueous solutions so that they do not break when the water begins to freeze.

Benzene is highly flammable! Place a few drops of it on a watch glass and carefully hold a burning match. Benzene will ignite before the flame comes into contact with the liquid. It burns with a smoky flame, indicating a high carbon content. The gross formula of benzene is C 6 H 6. Thus, it has the same ratio of carbon and hydrogen as ethylene. Indeed, benzene is formed from three molecules of ethyne when the latter is passed through a hot iron or quartz tube. But under no circumstances will we carry out this reaction ourselves because of the danger of an explosion that will occur if air gets into the tube.

Despite the similarity in the composition of benzene and ethylene, their chemical properties are completely different. Using bromine water or Bayer's reagent, we can easily prove that benzene does not undergo reactions typical of unsaturated compounds. Obviously, this is due to its special structure. Kekule proposed a formula for benzene that contains three double bonds in a six-membered ring. However, according to new ideas, the stable structure of benzene is better explained by the fact that the “excess” valence electrons, as shown in the formula given in the middle, belong to the entire ring, forming a single “electron cloud”:

Benzene derivatives, of which several hundred thousand are now known, are formed by introducing functional groups into the ring, as well as as a result of the addition of additional rings or carbon side chains to the benzene ring. In the following experiments we will obtain and study some of the simplest and at the same time most important benzene derivatives in technology.

Nitrobenzene from benzene

Unlike open-chain hydrocarbons, for which this is very difficult, in aromatic hydrocarbons you can easily introduce the nitro group NO 2.

To obtain nitrobenzene, we first need 15 ml of benzene, 20 ml of concentrated sulfuric acid and 15 ml of concentrated nitric acid, and at the end of the experiment - water and diluted sodium hydroxide. Benzene is very poisonous; Under no circumstances should you inhale its vapors.

First of all, let's prepare all the necessary equipment. Let's select an Erlenmeyer flask with a capacity of 125 ml with a rubber stopper, into the hole of which a not too thin glass tube about 50 cm long is inserted. We will also need a separating funnel (capacity 150 ml), a water bath and a thermometer with a scale up to 100 ° C. Let's prepare two more pans - one with ice water, and the other with water heated to 60 °C.

Due to the risk of splashes in the eyes, this experiment - as always when working with concentrated acids - can only be carried out with safety glasses!

First place concentrated sulfuric acid in an Erlenmeyer flask and then very carefully, all the time slightly shaking the flask, add nitric acid in small portions. Cool the heated nitrating mixture by immersing the flask in cold water. Then insert a thermometer into the flask and begin to gradually add benzene, continuously stirring the liquid in the flask with a glass rod. The temperature should not exceed 50-60 °C. If it rises higher, then before adding the next portion of benzene, it is necessary to soak the flask in ice water. When all the benzene has been added, we will keep the flask with a vertically inserted tube for some more time in a bath of warm water, the temperature of which will be maintained from 50 to 60 ° C, adding hotter water if necessary.

After this, transfer the contents of the flask into a separatory funnel. We will find two layers: the top layer contains nitrobenzene, and the bottom contains excess nitrating mixture. Let's salt this mixture of acids, add about 30 ml of water to the separating funnel, shake vigorously and separate the nitrobenzene, which now, due to its high density, forms the lower layer. For further cleaning, it must be washed in the same way with a highly diluted solution of caustic soda and finally again with water.

Nitrobenzene is a pale yellow liquid with a boiling point of 210 °C and a density of 1.203 g/cm 3 at 20 °C. If during the experiment we allow an excessive increase in temperature, the nitrobenzene will be more colored due to the admixture of dinitrobenzene. Nitrobenzene is very poisonous (If nitrobenzene gets on the skin, the affected area should be washed with alcohol and then with warm water and soap. – Note translation). You should also beware of inhaling its harmful fumes, which have a characteristic strong odor of bitter almonds. Although such an aroma is needed in perfumery, the use of nitrobenzene for this is strictly prohibited due to its toxicity. Typically, safe benzaldehyde, which has the same odor, is used for the same purpose.

N itrobenzene for us - just as for the chemical industry - is only an intermediate product. We will also move on and obtain from it by reduction aniline - the ancestor of synthetic dyes (This reaction is called the Zinin reaction. Russian chemist N.N. Zinin in 1842 first carried out the reduction of nitrobenzene into aniline under the action of ammonium sulfide. - Note translation).

To get the amino group NH 2, we must replace oxygen with hydrogen in the nitro group. In industry, nitrobenzene is currently usually reduced in the gas phase by passing its vapor in a mixture with hydrogen over a copper catalyst. We, working with small quantities, will prefer the older method, in which reduction is carried out in the liquid phase with hydrogen at the time of separation - in Latin this is in statu nascendi. To do this, we obtain hydrogen by the action of hydrochloric acid on iron filings or, better, on granulated zinc or tin.

Let's carry out the experiment as follows. In an Erlenmeyer flask - the same as when obtaining nitrobenzene - place 10 g of nitrobenzene and 15 g of iron filings or granulated zinc. First, add 5 ml of concentrated hydrochloric acid and immediately close the flask with a stopper into which a glass tube is inserted vertically. With gentle shaking, a violent reaction will begin. At the same time, the flask heats up, and it must be cooled with moderately cold water - so that the reaction does not stop completely. From time to time we will remove the plug with the tube and add another 5-8 ml of hydrochloric acid. When we add only 50 ml of hydrochloric acid, we wait until the reaction subsides, and in a fume hood or in the open air we heat the flask with the same glass tube in a water bath for 30 minutes to an hour.

Finally, dilute the reaction mixture with water and, to neutralize the acid, add a solution of soda ash or baking soda (sodium bicarbonate) to an alkaline reaction. To do this, transfer the mixture from the flask into a beaker and first add water, and then the specified solution. A brown liquid with a peculiar odor will be released. This is aniline, which can be separated by careful decantation. It is better, although more troublesome, to isolate it by steam distillation.

Attention! Aniline is a very strong poison, which should only be stored closed and labeled “poison”. When working with aniline, you must be careful not to inhale its vapors. It is best - just like diethyl ether - to store aniline only in the form of a diluted alcohol solution.

Aniline served as the starting material for the production of the first synthetic organic dyes. A long time ago, Runge discovered the first aniline dye, which is still used to detect aniline.

Mix a few drops of aniline with 10 ml of water and add a filtered aqueous solution of bleach. The intense violet color is explained by the formation of a dye, the complex structure of which was a difficult puzzle even for chemists of the 20th century. Let us save aniline for the next experiments and note in conclusion that most dyes these days are obtained not from aniline, but from other compounds.

Of the other benzene derivatives, we mention here only phenol, toluene and naphthalene. Phenol was also in first discovered by Runge in coal tar. It is an aromatic compound with a hydroxyl group and is therefore similar to alkanols. However, unlike alkanols, phenol has a weakly acidic reaction and easily reacts with alkalis to form phenolates. Therefore, it can be dissolved in alkalis. We have already obtained related cresols from dry distillation of wood and semi-coking of brown coal. This can be proven by adding a solution of iron(III) chloride to the extract of wood tar or lignite tar and tar water. Phenol and related substances give a color from blue to blue-violet. True, for extracts of resin and tar, this color can be masked by their own brown color.

Pure phenol is a solid that melts at 40.8 °C and boils at 182.2 °C. At 16 °C it dissolves in 12 parts of water, and the resulting solution turns litmus paper red. (Check!) In turn, phenol also dissolves some water in itself and becomes liquid, even when only 5% water is dissolved in it! If we add water to solid phenol, we will first obtain a liquid solution of water in phenol, and with further addition of water, a solution of phenol in water.

Due to the growth of plastics production, phenol has become one of the most important intermediate products in the chemical industry. World production now appears to reach almost 200,000 tons per year. In the GDR, a significant amount of phenol is obtained from the semi-coking of brown coal. In addition, more and more phenol is produced through synthesis.

When two or three OH groups are introduced into the benzene ring, polyhydric phenols are formed. They are strong reducing agents and are therefore used as developers in photography, such as hydroquinone. Triatomic phenol - pyrogallol - easily absorbs even atmospheric oxygen.

Toluene is a benzene derivative in which one hydrogen atom is replaced by a methyl group. This liquid is similar in properties to benzene; it is used as a solvent and also for production in explosives. With the introduction of three nitro groups, toluene is converted into trinitrotoluene, one of the most powerful explosives. Cresols, formed in large quantities during semi-coking, are also toluene derivatives containing an OH group. They thus correspond to phenol.

U Let's remember naphthalene - this is the simplest representative of hydrocarbons with several rings. In it, both benzene rings share two carbon atoms. Such substances are called condensed aromatic compounds.

Coal tar contains almost 64% naphthalene. It forms shiny crystalline plates that melt at 80°C and boil at 218°C. Despite this, naphthalene evaporates quickly even at room temperature. If you leave naphthalene crystals open for several days, they will noticeably shrink and a pungent smell of naphthalene will appear in the room. Naphthalene used to be part of most anti-moth products. Now, for this purpose, it is increasingly being replaced by other substances that have a less intrusive odor.

In industry, large quantities of phthalic acid are produced from naphthalene - the starting material for the production of valuable dyes. Later we will make some dyes ourselves.

IN In conclusion, let's give another example heterocyclic compound. Heterocyclic are substances containing in the ring not only carbon atoms, but also atoms of other elements (one or more oxygen, nitrogen or sulfur atoms). This unusually broad range of compounds includes important natural substances such as indigo and morphine, as well as fragments of certain amino acid molecules.

Let's look at furfural. We see that its molecule contains a five-membered ring of four carbon atoms and one oxygen atom. Judging by the side chain, furfural can be said to be a heterocyclic alkanal.
Let's get furfural from bran

Place 50 g of bran in a conical or round-bottomed flask and mix it with 150 ml of 10-15% sulfuric acid solution. Distill about 100 ml of liquid from the flask. It contains about 1 g of dissolved furfural. Let's extract it from the distillate with ether or carbon tetrachloride and evaporate the organic solvent in a fume hood. Next, we will carry out only two simple qualitative reactions.

In the first experiment, we add a few drops of hydrochloric acid and a little aniline to a sample of the resulting solution. Already in the cold, a bright red color appears.

In the next experiment, we will again add hydrochloric acid and a few grains of phloroglucinol (this is a triatomic phenol) to the solution under study. When boiled, a cherry-red color will appear.

When boiled with dilute acids, certain types of sugars - pentoses - form furfural. Pentoses are found in bran, straw, etc. and can be detected by the above methods.
With these few (out of 800,000!) examples, we will finish our short journey into the world of organic compounds. In the following chapters we will look at some of the most important applications of organic chemistry.
5. Materials for every taste

PLASTICS YESTERDAY, TODAY AND TOMORROW

1. Each of the four substances, three of which are simple substances, and the fourth is an oxide of some element, is capable of interacting with the other three. Suggest possible formulas for such substances and provide equations for the corresponding chemical reactions.
2. Calcium carbide and water can become raw materials for the production of such chemical compounds as: a) ethane, b) acetic acid, c) ethylene and polyethylene, d) vinyl chloride and polyvinyl chloride, e) benzene. Write the reaction equations for the production of these compounds, having at your disposal calcium carbide, water and any other inorganic substances.
3. From what substance, as a result of sequential reactions of oxidation, exchange and substitution, can 3-nitrobenzoic acid be obtained without using other organic substances? Write the reaction equations and indicate the conditions for their occurrence.
4. To decolorize equal volumes of bromine water of equal concentration, different amounts of the two isomers are required. Give examples of two pairs of such isomers, write the equations for the corresponding reactions.
5. A volume of 10 ml of hydrocarbon gas is mixed with 70 ml of oxygen. The resulting mixture was set on fire. At the end of the reaction and after condensation of water vapor, the volume of the gas mixture was 65 ml. When the resulting gas mixture was passed through a sodium hydroxide solution taken in excess, its volume decreased to 45 ml. Determine the molecular formula of a hydrocarbon, assuming that the volumes of gases are measured under standard conditions.
6. Letter from D.I. Mendeleev.
   "Your Majesty! Allow me to give you a reprint of the message, from which it follows that I have discovered a new element……. At first I was of the opinion that this element fills the gap between antimony and bismuth in your remarkably insightfully constructed periodic table and that this element coincides with your ekaantimony, but everything points to the fact that here we are dealing with eka……. I hope to tell you soon more about this interesting substance; today I limit myself only to notifying you of the very likely triumph of your ingenious research and testifying to you my respect and deep respect.
   Devotee………… ………….
   Freiberg, Saxony.
   February 26, 1886."

   Who wrote the letter to D.I. Mendeleev?
   One of the few minerals that forms the one mentioned in D.I.’s letter. A periodic element that also contains sulfur and silver. The mass fractions of sulfur and silver in the mineral are 17.06% and 76.50%, respectively. Establish the formula of the mineral and give its name. Give an equation for the reaction of fusion of a mineral with soda in the presence of potassium nitrate. How can one isolate the simple substance discussed in the letter from the resulting alloy? Where is it used?
   What methods exist for purifying this simple substance?

The most common dehydrating agent for organic liquids containing small amounts of water is calcined calcium chloride.

Alcohols and amines cannot be dried with calcium chloride.

Calcium chloride CaCl2 must be dehydrated before work by calcining it in an iron frying pan. The salt is poured in a layer no thicker than 1-2 cm and heated with a strong burner flame. First, the salt melts, releasing water of crystallization, and then the latter gradually evaporates. Water vapor breaking through the layer of salt causes it to scatter; Therefore, it is not recommended to pour a thick layer of salt. When all the water has evaporated, calcination is continued for some time, then the baked salt is broken into smaller pieces and, while still warm, placed in a completely dry jar prepared in advance. The jar must be closed hermetically so that air, which always contains a certain amount of water vapor, does not penetrate into it.

If the jar is closed with a cork stopper, then the top should be carefully filled with paraffin or wax.

The laboratory should always have a certain supply of calcined CaCl2.

To dehydrate any organic liquid, one or another amount of CaCl2 is taken depending on the water content in it. You should not take too much salt, as this will inevitably lead to loss of the dehydrated substance. Salt in the required amount is poured into a vessel with the liquid to be dried, the vessel is tightly closed with a stopper and shaken several times. The mixture is then left to stand for at least 12 hours. After this, the liquid is poured into a distillation flask and distilled (see above). Calcium chloride can be used repeatedly if it is reheated after each use. Therefore, in laboratories where you often have to deal with CaCl2, there should be jars into which waste salt should be poured; as it accumulates, it is calcined again. Since this also burns the remains of the liquid that was dried with this salt, the calcination of the used CaCl2 should be carried out somewhat differently than the pure one.

First, the salt is carefully heated until liquid vapors are removed and the heating is gradually increased. Otherwise, a fire may occur, especially if the salt contains residues of ether, acetone or other flammable substances. Calcination should be carried out in a fume hood.

Among other salts, calcined sodium sulfate is used for drying organic liquids. It is calcined in the same way as CaCl2. Sodium sulfate Na2SO4 is not as strong a drying agent as CaCI2.

To dry alcohols, use copper sulfate CuSO4 or calcium oxide CaO. Copper sulfate CuSO4 5H2O in the form of blue crystals contains water of crystallization; If you heat the salt, you get an anhydrous yellowish salt. When humidified, one molecule of salt initially attaches only two molecules of water and turns blue. Knowing the water content in alcohol, you can calculate the amount of CuSO4 required to completely dry it.

After adding CuSO4 to the alcohol, the flask is shaken several times and then heated in a water bath under reflux until the salt turns light blue. After this, having separated the salt by filtration, the alcohol is distilled off.

However, it is very difficult to obtain completely anhydrous, so-called absolute, alcohol. After drying it, CuSO4 alcohol must be distilled two or three more times with pure CaO, and the receiver must be tightly connected to the refrigerator and equipped with a calcium chloride tube with dry calcium chloride.

But even after this, up to 0.5% water remains in the alcohol, the removal of which is the most difficult. Sodium and calcium metals are sometimes used to remove this residue.

The best dehydrating agent for alcohol is magnesium ethoxide, which can be easily obtained by reacting magnesium and ethyl alcohol (the alcohol should contain no more than 1% water) in the presence of a small amount of iodine. Dehydration of alcohol using this method is carried out as follows.

5 g of magnesium shavings are poured into a 1.5 liter flask with a reflux condenser, 65-70 ml of alcohol is poured, 0.5 g of iodine (catalyst) is added and heated until the latter dissolves, after which hydrogen is released:

Mg+ 2C2H5OH -> Mg (OC2H5)2 + H2

When the reaction is over, add 800-900 ml of ordinary absolute alcohol to the solution, i.e., one that contains 0.5-0.7% water, boil for half an hour at reflux and then distill off the absolute alcohol.

Other alcohols, such as methyl and n-propyl, can be dehydrated in the same way.

The alcohol can be dried with calcium metal using a reflux flask. 20 g of dry calcium shavings are added to 1 liter of alcohol and heated in a water bath until boiling, which is maintained for several hours, after which the alcohol is distilled in compliance with all the precautions described above.

Water, benzene and ethyl alcohol form an azeotropic mixture. With the content of ethyl alcohol, water and benzene in the ratio of 18.5: 7.4: 74.1, the mixture boils at 65 0C, which makes it possible to use such a mixture to remove traces of water from alcohol.

To do this, dry benzene is added to ethyl alcohol containing at least 99% C2HsOH. For almost 1 hour of water contained in alcohol, you should take 11 - 12 hours of dry benzene. After this, the mixture is subjected to fractional distillation. The first fraction is distilled at 64.85 ° C and consists of alcohol, water and benzene. The second fraction boils at 68.25° C and consists of excess benzene and alcohol. That part of the ethyl alcohol that remains in the distillation vessel is absolute ethyl alcohol.

Dehydrated alcohol should be very carefully protected from air moisture. Therefore, quickly pour it into a well-dried container and carefully close it. This method can be used to dehydrate all alcohols except methyl alcohol.

The completeness of alcohol dehydration can be determined based on the following qualitative samples:

a) anhydrous alcohol dissolves caustic barite, forming a yellow-colored solution;

b) the paraffin solution does not form turbidity in it;

c) in absolute alcohol, anhydrous copper sulfate does not change its color.

Drying agents are used to dehydrate solid organic compounds (of fructose and especially those substances that can soften, melt or decompose at the temperature required to remove water by direct heating). To do this, the solid is filled with absolute ethyl alcohol, and then benzene is added. Heating is carried out on a water bath. When all the liquid has distilled off, the remaining benzene and alcohol are removed from the flask by blowing dry air

Diethyl ether can be dehydrated with a small amount of sodium metal.

Metallic sodium is stored under a layer of kerosene, petroleum jelly or toluene in jars. The need for such storage of metallic sodium is caused by the following: 1) it oxidizes strongly in air, 2) it must be isolated from water, since if a drop of water gets on it, an explosion may occur. Sodium metal must be handled with care. It is necessary to ensure that there is no water near the work site. Working near a sink or near water taps is completely unacceptable.

Kerosene, petroleum jelly and toluene, in which sodium is stored, must be neutral and, naturally, do not contain water.

This piece is quickly pressed with filter paper and a piece of the required size is cut from it with a clean, dry knife. The remaining portion is immediately put back into the jar.

The cut piece of sodium is pressed again with filter paper so that no kerosene or petroleum jelly remains on it. After this, to remove sodium oxide from the surface of the metal, a thin layer (“crust”) is cut off with a clean, dry knife, and the trimmings are placed in a jar with metallic sodium. The purified piece of sodium is cut with a knife into several smaller pieces about 2 mm3 in size and then quickly placed in ether or other liquid that needs to be dried. The flask must be closed with a stopper and a calcium chloride tube.

After the sodium has been in the liquid to be dried for 12-24 hours, the liquid is distilled off over metallic sodium. When the distillation is complete, the remaining meth< талла переносят в банку с керосином или вазелиновым маслом. Лучше иметь отдельную банку, куда следует класть как обрезки («корочки»), так и металл, уже упо-треблявшийся для работы.

It is also recommended to store sodium metal (and potassium) in plastic wrap. The sodium is placed in a bag of polyethylene film having a thickness of 0.5 mm (this thickness can be achieved by putting several layers of ordinary plastic film together), the open end of the bag is sealed. If you need to take a certain amount of sodium, the bag is opened, the substance is pulled out of it, a piece is cut off with a clean knife and the remaining part is pushed back into the bag, the edges of which are first bent so that no air enters it, and then sealed. The sodium trimmings can be placed in the same or another bag and sealed by sealing.

Scraps and spent pieces of sodium metal can be reused if they are melted down. The melting point of sodium metal is 98°C. Sodium cannot be melted in the open air. Therefore, it is melted in a liquid that is not affected by metallic sodium and which boils at a temperature not lower than 150 ° C. Kerosene can serve as such a substance, but even better, i.e. safer, is Vaseline oil. Having placed the trimmings and pieces of sodium in one of these liquids, the latter is heated to approximately 12O0C. The metallic sodium is melted and at the bottom of the porcelain cup in which the heating takes place, a piece of metal with a clean surface is formed. If melting produces separate balls of metal, they are connected by using a thin glass rod. When all the metal has fused, the liquid is allowed to cool, then it is carefully drained (but not all), and the sodium is grabbed with dry tweezers and placed in kerosene.

Organic liquids can also be dried using calcium carbide CaCr. Calcium carbide decomposes with water to form acetylene and calcium hydroxide:

CaC2 + 2H2O = C2H2 + Ca(OH)2

The use of calcium carbide for drying is possible only in cases where the liquid being dried does not react with CaC2, C2H2, or Ca(OH)2. Since when drying with calcium carbide a gas (acetylene) is released, the flask where the drying is carried out must be closed with a stopper with a calcium chloride tube.

Drying is either carried out directly by pouring pure powdered CaC2 into the liquid to be dried (in an amount of up to 10-15% of the mass of the taken liquid, depending on the water content), or the liquid vapor is dried. *

To dry liquid vapors with calcium carbide, install a device consisting of a flask, a reflux condenser and a bath. Pour the dried substance into the flask and strengthen it in the bath. In a ball refrigerator, a fine metal mesh is placed between the second and third or third and fourth balls; CaC2 pieces of such a size are carefully thrown into the refrigerator that they freely pass through its tube. Having filled two or three balls in this way, strengthen the condenser in the neck of the flask and heat it. Vapors of a substance containing water pass through the CaC2 layer and, upon cooling and condensation, the dehydrated substance flows into the flask. Dehydration is carried out for 2-3 hours, and the end can be judged by the fact that the powder or lumps of carbide begin to blur.

The device can be assembled in another way. The liquid to be dehydrated is placed in a Claisen flask. The neck of the flask, which is connected to the refrigerator, is filled with calcium carbide. The liquid is distilled, and its vapors are dehydrated as they pass through the carbide layer. The dehydrated liquid is collected in a receiver, taking care to ensure that the distilled liquid does not reabsorb water vapor from the environment.

Using CaC2, it is possible not only to dehydrate a liquid, but also to quantify the water content in it; To do this, the acetylene formed is captured with acetone and determined in the form of copper acetylene. The amount of copper acetylene is used to judge the water content in the liquid. This drying method is one of the best. Its disadvantage is that acetylene gets into the dehydrated liquid, which can only be removed by heating.

Another thing worth mentioning is dehydration by freezing; thus, for example; benzene can be dehydrated. The latter turns into a solid state at 4°C. By cooling aqueous benzene to 1 or even 0°C, crystalline benzene is obtained, and the separated water is drained.

The so-called gypsum method * for dehydrating alcohol deserves mention. In addition, the use of magnesium perchlorate (a strong water-removing agent, superior even to phosphorus anhydride) is recommended. The latter substance can be used for drying mainly chemically resistant substances.

If a drying agent is added to liquids with high viscosity, drying continues for a long time and, in addition, a significant amount of liquid remains on the surface of the solid. In these cases, it is recommended to add a suitable dry solvent (for example, ether) to the liquid to be dried and then dry it as described above. During subsequent distillation, the solvent can be easily removed.

In many cases, especially when analyzing organic substances, when determining carbon and hydrogen, anhydrous calcium sulfate (CaSO4) is used as a water absorber. Anhydrous calcium sulfate is obtained by heating dihydrate or hemihydrate calcium sulfate at a temperature of 225±5°C. The temperature at which CaSO4 is dried is very important for obtaining a preparation suitable for the rapid absorption of water vapor. Under no circumstances should heating be allowed above the specified temperature. Before drying, CaSO4 2H2O or CaSO4 0.5H2O is crushed and sifted through a sieve with cells of 1-2 mm. The sifted grains (but not the fines that have passed through the sieve!) are placed in calcium chloride tubes, most often U-shaped, which are heated for 2-3 hours at 225 ± 5 ° C with air previously dried over Pr05 drawn through them. The air flow rate is about 50 ml/min. When CaSO4 reacts with water, the hemihydrate CaSO4 0.5H2O is formed. Anhydrous calcium sulfate can absorb 6.6% of water from the total mass. It can be regenerated many times, it is neutral, chemically inert and does not blur when saturated with water.

* Luhder E., Z. Spirilusinduslrie S., 7, 67 (1934).

Choosing the right drying agent for each case is very important, since if you select the wrong dehydrating agent, you can ruin the whole job. Therefore, it is important to know which drying agents can be used for different substances.

Inorganic substances commonly used for drying can be divided into the following groups:

1. Easily oxidizing metals: Na, Ca.

2. Oxides that easily bind water: CaO, P2O5.

3. Hygroscopic hydroxides: NaOH or KOH.

4. Anhydrous salts: a) alkaline (K2CO3), b) neutral (CaCl2, Na2SO4, CuSO4, CH3COONa).

In table 15 provides instructions for choosing a drying agent when dehydrating various organic liquids.

New methods of dehydration include the use of the principle of water adsorption *. Water is removed from organic solvents by passing them through a glass column with a diameter of 15-40 mm filled with activated Al2O3. According to the completeness of dehydration by this method, solvents are arranged in the following row: benzene > chloroform > diethyl ether > ethyl acetate > acetone. Ethyl alcohol can be dehydrated up to 99.5% with this absorbent.

Together with water, A1203 also sorbs many other contaminants. Spent A1203 is not regenerated and replaced with fresh one.

A very effective way of drying organic liquids and gases is drying with zeolites, the residual moisture is equal to ten thousandths of a percent.

NaA zeolite is suitable for deep drying of transformer oil, various oil fractions, refrigerants, alcohols, as well as many petrochemical synthesis products.

CaA zeolite can be used for selective extraction of polar substances (H2O, H2S1CO2, etc.).

* Angew. Chem., 67, Ki 23, 741 (1955); RZHKhim, 1955, Ki 14, 85, ref. 42799; Lab. Sci., 4, no. 4, 111 (1956); RJHnm. 1957, Ki 8, 95, ref. 26289; Chem. Rund., 11, K." 7, 164 (1958); RZhKhim, 1959, Ka 1, 163, ref. 1120.

Products used for drying organic liquids