Chapter VI

Ethers, Esters, and Anhydrides

95. Preparation of Ether from Alcohol (Section 115). - (a) Caution. - Ether is very inflammable and very volatile; as its vapor readily ignites, vessels containing ether should not be brought near a flame or allowed to stay in a warm place. Place 50 cc. of ethyl alcohol in a 500 cc. distilling flask and add slowly, with constant shaking, 50 cc. of concentrated sulphuric acid. Close the neck of the flask with a two-holed stopper bearing a thermometer and a dropping funnel (Fig. 16, page 27), both of which reach to the bottom of the flask[1]. Place the flask on a sand-bath and connect it by means of a tightly fitting stopper with a long condenser, through which a rapid stream of cold water is passing. Use as a receiver a filter-bottle which is connected with the condenser by a tightly fitting stopper. Attach to the side-arm of the filter-bottle a long rubber tube, which extends almost to the floor. This tube serves to conduct the vapor of the ether, which is very heavy, away from any flames present on the desk. Heat the contents of the flask slowly. When the temperature reaches 140°, and ether distils over, add through the funnel 100 cc. of alcohol, allowing the latter to drop at about the same rate as that at which the ether distils (about 2 drops per second). During the entire time the temperature of the mixture in the flask should be maintained at 140°-145°.

Take the receiver away from the immediate vicinity of any flames, and transfer the contents to a separatory funnel. Shake the ether with about one-half its volume of a dilute solution of sodium hydroxide. Draw off the lower aqueous layer, which should still be alkaline, and shake the ether with about one-half its volume of a saturated solution of common salt. Draw off the lower layer, and run the ether into a small distilling flask.

Add anhydrous calcium chloride (about one-fourth the volume of the ether). Close the neck of the flask with a stopper bearing a small drying tube containing calcium chloride, and place over the side-arm a cork which has been bored one-half way through its length, the hole having a diameter equal to that of the sidearm of the flask. Set the flask aside for at least an hour. Replace the drying tube by a thermometer and distil the ether directly from the calcium chloride, using a water-bath. Collect the distillate in a receiver as described above. Record the boiling-point and the weight of the product obtained. Ether boils at 35°. Write equations for the reactions which take place when alcohol is treated with sulphuric acid, and when the product of this reaction is heated with alcohol at about 140°. What would happen if in the experiment the temperature were allowed to rise as high as 180°?

(b) Absolute ether. - The ether prepared as described in (a) above contains traces of alcohol and water. In order to prepare ether free from these substances proceed as follows: Shake 200 cc. of commercial ether with about 20 cc. of a dilute solution of sodium hydroxide. Draw off the aqueous layer and shake the ether three times with a saturated solution of sodium chloride, using about 25 cc. each time. Transfer the ether to a bottle and add about 20 grams of anhydrous calcium chloride. Place a drying tube containing anhydrous calcium chloride in the neck of the bottle, and allow the ether to stand over night. Decant the ether into a dry bottle and add about 5 grams of sodium in the form of a wire or thin shavings. Insert a calcium chloride tube in the neck of the bottle and allow it to stand until the evolution of hydrogen ceases. The sodium is soon covered with a coating of hydroxide and ceases to act. This coating can be removed by pressing upon the shavings of sodium with a stout glass rod, or fresh pieces of the metal may be added from time to time. For most purposes the ether purified in this way can be used without distillation; it can be carefully decanted from the solid substances present. In order to redistil it, the ether is transferred to a clean dry flask containing about 1 gram of sodium shavings and distilled from a water-bath, taking the precautions described in (a) above, and using a carefully dried condenser and receiver. The first few cubic centimeters which distil should be rejected, as they contain the moisture present in the condenser tube and receiver. How could you determine whether the sample of ether purified contained alcohol?

Note. - (a) The ether prepared in this way contains water, alcohol, and sulphur dioxide, which is formed as the result of the reduction of sulphuric acid by the alcohol or carbon which separates. Ether is less soluble in water which is saturated with sodium chloride than in pure water. It is often advisable when extracting an aqueous solution with ether to saturate the solution with salt, in order to avoid loss of ether.

96. Properties of Ether (Sections 115 to 119). - (a) Volatility of ether. - Place a few drops of ether in the palm of your hand and breathe sharply across it. Explain the result.

(b) Inflammability of ether. - Place a few drops of ether on a watch-glass and apply a lighted match.

(c) Explosive mixture of ether and air. - Hold for about 5 seconds the neck of an open bottle containing ether over an empty wide-mouthed 250 cc. bottle, and then drop a lighted match into the latter.

(d) Solubility of ether in water. - Test roughly the solubility of ether in water as follows: Into a 100 cc. flask place 5 cc. of ether and add 40 cc. of water. Close the flask with a stopper and shake vigorously. Add water in portions of 5 cc. and shake each time, until the ether has completely dissolved. State the solubility you find as the result of your experiment.

(e) Solubility of water in ether. - Shake 10 cc. of ether with 10 cc. of water. Decant off the ether through a dry filter-paper into a dry test-tube. Test the filtered ether for water by means of anhydrous copper sulphate. (See experiment 79c, page 55.) Is water soluble in ether?

(f) Solubilities of ether. - Test the solubility of ether in an equal volume of alcohol, benzene, petroleum ether, dilute hydrochloric acid, and a solution of sodium hydroxide.

(g) Solubility of ether in sulphuric acid. - Add very cautiously to 2 cc. of ether about 5 cc. of concentrated sulphuric acid. The tube should. be shaken under water to keep the mixture cold. Is ether soluble in concentrated sulphuric acid? Pour the mixture slowly into a test-tube containing cracked ice. Are two layers formed? Explain. (See Section 117.)

(h) Reaction between ether and sulphuric acid. - Repeat experiment (g), but warm the mixture gently over a free flame before it is poured onto the ice. Are two layers formed? Explain.

(i) Ether and sodium. - Add a shaving of sodium to about 5 cc. of absolute ether. If a gas is evolved, wait until the evolution ceases and add a fresh piece of sodium. Explain the result. If anhydrous ether is not available the experiment can be performed with ordinary ether, but a number of additions of sodium will be necessary before the metal does not react with the liquid. Why?

(j) Decomposition of ether by hydriodic acid. - Mix in a test-tube, kept cold by immersion in water, 1 cc. of ether and 3 cc. of hydriodic acid (sp. gr. 1.7). Fit the tube by means of a cork to a delivery-tube bent at a right angle. (See Fig. 18, page 30.) The end of the tube should extend nearly to the bottom of a test-tube which is placed in cold water. Heat the mixture of acid and ether carefully. When about one-third of the liquid has distilled over, add a little water to the contents of the cold tube and shake. Are there two liquids? Is one heavier than water? (Eq.)

97. Preparation of a Mixed Ether: Isoamyl Ethyl Ether (Section 116). - Place 50 grams of isoamyl alcohol in a 200 cc. round-bottomed flask provided with a reflux condenser. Add slowly through the condenser 6 grams of sodium cut in small pieces. The alcohol maybe heated slightly to hasten the reaction. When all the sodium has dissolved, add cautiously through the condenser, as the reaction is apt to be a violent one, 30 grams of ethyl bromide. Heat to boiling for 1 hour. (Eq.). Distil directly from the flask, using a water condenser, and collect the distillate in the following fractions: 80°-110°, 110°-114°, 114°-120°, 120°-130°. Fractionate twice. (See §21-23, and experiment 64, page 42.) Redistil the portion boiling at 110°-114°, and collect and weigh the part which distils at 111°-113°. Determine the specific gravity of your product (§56, page 37), and determine whether it dissolves in concentrated sulphuric acid. Calculate the percentage yield of ether obtained from the ethyl bromide used. The yield in the experiment should be about 50 per cent.

Isoamyl ethyl ether boils at 112°, and has the specific gravity 0.764 at 18°.

Note. - An excess of alcohol is used in the experiment to facilitate the reaction between it and sodium. Sodium isoamylate is a solid which is soluble in isoamyl alcohol. The sodium and ethyl bromide are used in the proportion of one atomic weight of the former to one molecular weight of the latter.


Acid Anhydrides

98. Preparation and Properties of Acetic Anhydride (Sections 120, 121). - (a) Place 50 grams of freshly fused sodium acetate[2] in a 250 cc. distilling flask. Connect the flask with a condenser and a receiver, using for the latter a distilling flask which is fitted tightly to the condenser by means of a stopper. Protect the inside of the flask from moisture by connecting a drying tube to the side-arm of the receiver. Insert in the neck of the flask a cork bearing a separatory funnel which contains 40 grams of acetyl chloride. Immerse the flask in cold water and add about one-half of the acetyl chloride very slowly. The liquid should not be allowed to get hot enough to boil. Disconnect the flask from the condenser and shake it cautiously, while it is still in the water. Replace the condenser and add the rest of the chloride. If any liquid distils over during the addition of the acetyl chloride, it should be returned to the distilling flask. Replace the separatory funnel by a cork and distil, keeping the flame in motion to avoid local over-heating. Add about 2 grams of fused sodium acetate to the receiver and distil; note the boiling-point of the liquid, and weigh the product obtained. (Eq.) Calculate the theoretical yield, and the percentage of this obtained in the experiment. If the substances from which the anhydride is prepared are not brought together in the proportions represented by the chemical equation, from which substances should the theoretical yield be calculated? In the above experiment which substance is used in excess? Why?

Acetic anhydride boils at 138°. The yield should be from 35 to 40 grams.

(b) Acetic anhydride and water. - Add about 1 cc. of acetic anhydride to 5 cc. of water. Do the two liquids mix? Shake the test-tube vigorously and finally warm gently. (Eq.)

(c) Acetic anhydride and sodium hydroxide. - Shake 2 cc. of the anhydride with 5 cc. of a solution of sodium hydroxide. (Eq.)

(d) Acetic anhydride and alcohol. - Repeat experiment 79h, page 56.

(e) Identification of acetic anhydride. - Add cautiously 2 cc. of acetic anhydride to 2 cc. of aniline, and heat the mixture to boiling. Pour the product while still hot into about 20 cc. of cold water. Shake vigorously, decant off the water and wash twice with cold water. Dissolve the product in boiling water, avoiding an excess of the solvent. Filter hot through a fluted filter-paper, and cool the solution in running water. Filter off the crystals by suction (§12, page 7), dry them on a porous plate, and determine their melting-point. If the compound does not melt sharply, it should be recrystallized from boiling water.

Acetanilide, the product of this reaction, melts at 116°, boils at 304°, and crystallizes from hot water in colorless prisms. (See note below and Section 416.)

Notes. - (a) The first distillate is redistilled from a small amount of sodium acetate in order to convert any unchanged acetyl chloride into anhydride.

(b, c, and d) These reactions apply in general to anhydrides and are useful in their identification. The determination of the physical properties of the acids or esters formed is often made in the identification of anhydrides. Sulphuric acid is a valuable catalytic agent in the reaction which takes place between alcohols and anhydrides.

(e) The chemical reaction in this test is analogous to that which takes place between an anhydride and ammonia:

(CH₃CO)₂O + 2NH₃ = CH₃CO.NH₂ + CH₃COONH₄

Aniline is related to ammonia; its formula is NH₂C₅H₅. The reaction with acetic anhydride takes place according to the following equation:

(CH₃CO)₂O + 2NH₂C₆H₅ = CH₃CO.NHC₆H₅ + CH₃COONH₃C₆H₅

In the case of ammonia, acctamide is formed; the product with aniline is acetanilide. The second substance formed is the aniline salt of acetic acid; this is soluble in water and is readily removed when the product of the reaction is crystallized. The preparation of anilides in this way from acid anhydrides is often effected in the identification of anhydrides. The anilides are solids, which can be readily purified; as a consequence, an identification can be accomplished with a very small amount of a substance.

99. Preparation of Succinic Anhydride (Section 122). - Hood. - Heat to boiling for about one-half hour, in a dry round-bottomed flask provided with a return condenser, mixture of 10 grams of phosphorus oxychloride and 15 grams of succinic acid. It is advisable to use a return condenser like the one illustrated in Fig. 15, page 26.

When the flask is cold, add 50 cc. of acetone and heat on the steam-bath until the solid has dissolved. Filter hot and set aside to crystallize. Filter off the crystals by suction (§12, page 7), and wash them with a few cubic centimeters of cold acetone. Weigh the product and determine its melting-point. Calculate the percentage yield.

Succinic anhydride melts at 120°; it may be recrystallized from hot chloroform, in which it is difficultly soluble, or from acetone.

Note. - Phosphorus oxychloride is used as a dehydrating agent in this preparation. The reaction takes place according to the following equation:

2(CH₂COOH)₂ + POCl₃ = 2(CH₂CO)₂O + HPO₃ + 3HCl


Esters

100. Preparation of Potassium Ethyl Sulphate (Section 127). - (a) Pour into a small flask 20 cc. of ethyl alcohol, and add slowly with constant shaking 10 cc. of concentrated sulphuric acid. Connect the flask with a refiux condenser and heat in a boiling water-bath for one-half hour. Cool the liquid and pour it slowly into 200 cc. of cold water. The solution contains ethyl sulphuric acid, alcohol, and sulphuric acid. The acids are separated by making use of the fact that barium ethyl sulphate is soluble in water and barium sulphate is insoluble. Add to the solution, with constant stirring, small quantities of barium carbonate[3] as long as carbon dioxide is evolved. Filter in a porcelain funnel, and wash the precipitate twice with about 20 cc. of hot water.

The filtered solution contains barium ethyl sulphate. Write equations for all the reactions. Test 5 cc. of the solution for barium in the usual way. (Eq.) Test the solution for a sulphate. Result? Heat about 5 cc. of the solution with about 1 cc. of dilute hydrochloric acid. (Eq.)

(b) Conversion of barium ethyl sulphate into potassium ethyl sulphate. - Heat the rest of the solution of barium ethyl sulphate to boiling and add a solution of potassium carbonate until the solution is slightly alkaline. (Eq.) Filter hot, wash the precipitate twice with a small amount of hot water, and evaporate the filtrate to crystallization (see §9, page 6) on the steam-bath. When cold, filter off the crystals and wash them with a little cold alcohol; dry on a porous tile. The salt can be recrystallized from boiling alcohol.

101. Preparation of Ethyl Acetate from Alcohol and Acetic Acid (Section 128). - Mix in a dry 200 cc. distilling flask 50 grams of alcohol; 60 grams of glacial acetic acid, and 4 cc. of concentrated sulphuric acid. Cover the side-arm of the flask with a cork bored half way through its length. Connect the flask with a reflux condenser, and heat to boiling for 30 minutes. (See Fig. 14, page 25.) At the end of this time, arrange the apparatus for distillation, using a water condenser and having a thermometer to record the temperature of the vapor. Distil into a flask; when the temperature registers 100°, collect separately about 1 cc. of the distillate and add it to about 5 cc. of water. If the mixture does not separate into two layers, stop the distillation. Shake the distillate in the flask with 30 cc. of water, and add solid sodium carbonate until a drop of the ester is neutral to moist litmus paper. Transfer to a separatory funnel, draw off the water, and shake the ester twice with a saturated solution of calcium chloride, using 50 cc. each time. Draw off the ester into a distilling flask, add about one-fourth its volume of anhydrous calcium chloride, close the flask and cover the side-arm with corks, and let stand for at least 1 hour. Distil from a water-bath. Note the boiling-point and the weight of ester obtained, and calculate the percentage yield from the acetic acid used. Why from the acetic acid?

Ethyl acetate boils at 77°, has the specific gravity of 0.9028 18°/4°, and is soluble in 17 parts of water at 17.5°. The yield should be 80 to 85 per cent of the theoretical.

Note. - The sulphuric acid used in the preparation serves as a catalytic agent. The amount of alcohol used is that equivalent to the acid (equal molecular proportions) plus that which combines with the sulphuric acid to form ethyl hydrogen sulphate. The ester obtained in the first distillation contains alcohol and acetic acid. The former is removed by shaking with calcium chloride, and the latter by treatment with sodium carbonate.

102. Formation of Ethyl Acetate from Acetyl Chloride and from Acetic Anhydride. - Consult your notes on experiments 79g and h, page 56. If you have not carried out the experiments, do so now.

103. Properties of Ethyl Acetate (Section 130). - (a) Hydrolysis of ethyl acetate. - Place 25 cc. of ethyl acetate and a solution of 14 grams of sodium hydroxide in 200 cc. of water in a round-bottomed flask connected by a tightly fitting cork to a reflux condenser. Place the flask in boiling water, and heat until liquid ceases to flow back from the condenser (about three-fourths of an hour). Transfer the liquid to a distilling flask, and distil off 50 cc. into a small flask. Reserve for future study the contents of the distilling flask. Add solid potassium carbonate to the distillate in small portions. Close the flask and shake it. Repeat the addition of the salt until a part of it remains undissolved. Pour the two layers into a separatory funnel, run off the lower aqueous solution, and shake again with a small quantity of dry potassium carbonate. Place the alcohol in a small distilling flask, add about one-fourth its volume of anhydrous copper sulphate, and allow the mixture to stand about 15 minutes with occasional shaking. Distil the alcohol on a water-bath directly from the flask, and note its boiling-point. Apply the iodoform test to a few drops of the alcohol (experiment 81b, page 57).

Make the original aqueous solution obtained in the hydrolysis strongly acid with dilute sulphuric acid (Eq.), and distil over 50 cc. What does the distillate contain? Prove your conclusions by a suitable test. Explain how the procedure used in this experiment serves to separate an acid and an alcohol. Is the process one of general applicability?

(b) Ethyl acetate and concentrated sulphuric acid. - Add gradually with constant shaking, and keeping the mixture cool by running water, 2 cc. of ethyl acetate to 4 cc. of concentrated sulphuric acid. Pour the solution very slowly, keeping the tube cold, into 10 cc. of cold water. Will this test distinguish an ester from an ether? From a saturated hydrocarbon?

Repeat the experiment, but heat the mixture for a minute at about 100° before adding the solution to water. (Eq.)

(c) Ethyl acetate and hydriodic acid. - Repeat experiment 96j, using ethyl acetate in place of ether. For what is the test used? Will alcohol give a positive result?

104. Preparation of Isoamyl Acetate from Sodium Acetate. - Place in a 750 cc. round-bottomed flask, provided with a return condenser, 60 grams of finely powdered anhydrous sodium acetate (see experiment 66a), and add through the condenser, very slowly, 70 grams (38 cc.) of concentrated sulphuric acid Add, next, 65 grams of isoamyl alcohol. Heat on a wire gauze for onehalf hour. Connect the flask with a condenser arranged for distillation, and distil as long as liquid passes over. Pour the distillate into a separatory funnel, and wash it twice with an equal volume of water. Separate the ester, and dry it over anhydrous calcium chloride. Pour off the liquid and distil. Collect and weigh the portion which boils at 137°-141°. Calculate the theoretical yield from the sodium acetate used, and the percentage of this obtained. Test the solubility of isoamyl acetate in concentrated sulphuric acid.

Isoamyl acetate boils at 139°. The yield should be about 67 grams.

Note. - It is often advisable to prepare esters from salts rather than from the free acids. The salts can be more readily obtained in an anhydrous condition and, being solids, smaller quantities can be handled conveniently. In the preparation of esters from salts, enough sulphuric acid must be added to liberate the organic acid; equal molecular quantities must be used, since acid sulphates are formed. A small excess of sulphuric acid should be present to act as a catalytic agent. Enough of the alcohol is used to interact with both the organic acid and the excess of sulphuric acid.


Fats and Oils

105. Properties of Fats and Oils (Sections 135-137). - (a) Solubility of fats and oils. - Test the solubility of 1 gram of lard and 1 cc. of olive oil in water, ether, alcohol, chloroform, and petroleum ether.

(b) Extraction of fat. - Partly fill a small evaporating dish with sand; pour 25 cc. of milk into the dish and evaporate on the steambath to dryness. Grind the residue and put it, together with 100 cc. of ether or petroleum ether, into a dry stoppered bottle. At the next exercise filter off the ether into a beaker, and set it aside to evaporate spontaneously. Examine the resulting product. What is it?

(c) Saponification of a fat. - Read your notes on the saponification of lard (experiment 92a, page 64). If you have not performed the experiment, do so now.

(d) Saponification of olive oil. - Warm together on the steambath for 10 minutes 5 cc. of olive oil and 1 gram of sodium hydroxide dissolved in 20 cc. of alcohol. Pour the product into water and add dilute sulphuric acid. (Eq.)

(e) Saponification of butter. - Saponify 15 grams of butter with 5 cc. of a concentrated solution of sodium hydroxide (1:1), carrying out the experiment as described in the similar experiment with lard (experiment 92a, page 64). As soon as the mixture is thick and homogeneous, pour it into 15 cc. of water. Transfer the solution of soap to a distilling flask, acidify with 25 cc. of sulphuric acid (1 part of acid to 4 of water), and distil over about 15 cc. Test the distillate with litmus paper. Are the volatile acids soluble in water? Note the odor of the solution. What causes the odor? Determine whether the oily layer in the distilling flask contains acids. Find out if it is soluble in alkalies. What happens when an acid is added to the alkaline solution so formed?

(f) Test for unsaturated glycerides. - Dissolve 5 cc. of olive oil or cotton-seed oil in 5 cc. of carbon tetrachloride, and add a solution of bromine in carbon tetrachloride, drop by drop.

(g) Oils and concentrated sulphuric acid. - Add to 10 cc. of olive oil or cotton-seed oil contained in a small beaker 5 cc. of concentrated sulphuric acid. Stir with a thermometer and note the rise in temperature. Repeat, using kerosene. Is there a difference? Explain.

(h) Emulsification of oils. - In five test-tubes prepare the following mixtures: (1) 10 cc. of a 0.2 per cent solution of sodium carbonate and 2 drops of neutral olive oil. (2) 10 cc. of a 0.2 per cent solution of sodium carbonate and 2 drops of rancid olive oil. (3) 10 cc. of a warm solution of soap and 2 drops of the neutral oil. (4) 10 cc. of white of egg solution and 2 drops of neutral oil. (5) 10 cc. of water and 2 drops of neutral oil. Shake the tubes very vigorously and let them stand for a few minutes.

Record the results in each case. Under what conditions is the oil most perfectly emulsified?

Examine a drop of milk under a microscope.

Notes. - (b) The fat can be extracted from milk in the usual way in a separatory funnel with ether. In the analysis of foods, however, the product is always dried before extraction. Milk can be dried as directed above, or it can be absorbed on filter-paper which is then dried.

(d) If saponification is complete there should be no separation of oil when the product is diluted with water.

(e) When this reaction is carried out quantitatively and 5 grams of fat or oil are used, the number of cubic centimeters of a tenth normal solution of sodium hydroxide required to neutralize the soluble volatile acids is called the Reichert-Meissl number.

(g) The reaction illustrated in this test is the basis of a method used in the analysis of oils. The number of degrees rise in temperature when 50 grams of an oil are treated with 10 cc. of sulphuric acid, in a vessel constructed in such a way as to avoid loss of heat by radiation, is called the Maumené number of the oil.

(h) Oils which have become rancid contain free fatty acids. The latter can be detected as follows: Dissolve in about 2 cc. of alcohol a drop of phenolphthalein solution and 1 or 2 drops of a very dilute solution of sodium hydroxide. To the resulting solution, which should have a light pink color, add an alcoholic solution of the fat to be tested for free acid. If the latter is present the color will disappear.

If a sample of rancid olive oil is not available for the experiment, mix together the neutral oil and oleic acid in the proportion of 1 cc. of the former to 1 drop of the latter, and shake 2 drops of the mixture with the solution of sodium carbonate.

The factors which lead to the formation of emulsions are not definitely known. The most permanent emulsions are formed when an insoluble oil is shaken with a solution which contains a substance that interacts with one of the constituents of the oil to produce a colloid. This occurs when an oil containing free fatty acids is shaken with an aqueous solution of an alkali. A layer of soap is formed around the particles of the oil, and it is probable that a layer of oil may surround the colloidal particles of soap. When a solution of egg albumin is shaken with olive oil, a layer of the coagulated protein is formed around the drops of the oil and emulsification takes place.



[1] If a dropping funnel is not available or if the tube of the funnel is not long enough, arrange the apparatus as described in §40, page 27.

[2] For the preparation of fused sodium acetate see experiment 66a, page 43.

[3] If barium carbonate is not available, calcium carbonate may be used.