Chapter IV

Alcohols

76. Properties of Methyl Alcohol (Section 49). - (a) Inflammability of methyl alcohol. - Pour about 1 cc. of methyl alcohol into an evaporating dish and apply a burning match. (Eq.) Note the appearance of the flame.

(b) Solubility of methyl alcohol. - Test the solubility of methyl alcohol in water, ether, ethyl alcohol, petroleum ether, and benzene. Use about 1 cc. of the alcohol in each test.

(c) Methyl alcohol as a solvent. - Test the solubility of anhydrous calcium chloride and sodium chloride in methyl alcohol.

(d) Methyl alcohol and sodium. - Add a piece of sodium the size of a small pea to 5 cc. of methyl alcohol. (Eq.)

77. Tests for Methyl Alcohol. - (a) Methyl salicylate. - Mix together in a test-tube about 0.2 gram of salicylic acid, 1 cc. of concentrated sulphuric acid, and 1 cc. of methyl alcohol, and warm gently. Note and describe the odor. The compound formed is the methyl ester of a salicylic acid, HO.C₆H₄.COOCH₃.

(b) Formaldehyde (Section 143). - Dissolve 5 drops of methyl alcohol in 3 cc. of water. Wind a piece of stout copper wire around a lead pencil so that a closely coiled spiral about 2 cm. in length is formed; leave about 20 cm. of the wire to serve as a handle. Heat the spiral in the upper part of a Bunsen flame, and plunge it while red hot into the solution of methyl alcohol. Withdraw the spiral, cool the liquid under running water, and heat again with the hot spiral. In this way the methyl alcohol is oxidized by the hot copper oxide formed on the wire. Note the odor of the liquid while hot. Cool the liquid, add 2 drops of a 0.5 per cent solution of resorcin and pour the resulting mixture, slowly so the two liquids do not mix, down the side of an inclined test-tube containing about 5 cc. of concentrated sulphuric acid.

78. Preparation of Ethyl Alcohol by Fermentation (Section 52). - (a) Dissolve 40 grams of commercial anhydrous glucose in 350 cc. of water in a 500 cc. bottle. Add one-fourth of a yeast cake ground to a smooth paste with 50 cc. of water, and about 0.5 gram of Witte's peptone[1]. Close the bottle with a rubber stopper through which passes one end of a glass tube bent in two right angles to form three sides of a rectangle. The other end of the tube passes to the bottom of a test-tube which is held in place by means of cork along the side of which a groove is cut to allow the escape of gas. The test-tube is one-half filled with a solution of barium hydroxide. By using the apparatus arranged in this way, any gas evolved must pass through the solution of barium hydroxide before it escapes. Mark the bottle with your name by means of a label, and set it in a warm place (about 30°). Examine the contents of the bottle at the next laboratory exercise. Has the amount of yeast increased in quantity? What gas has been evolved?

The product obtained is a dilute solution of ethyl alcohol which contains small quantities of other substances. The alcohol should be separated, and the amount formed in the reaction determined as follows: Decant through a folded filter-paper, taking care not to disturb the sediment of yeast, about 250 cc. of the solution. While waiting for the solution to filter, weigh to centigrams a clean dry 100 cc. flask, around the neck of which has been pasted a narrow strip of paper to serve as a reference mark. Fill the flask up to the nark with distilled water, and weigh again. Place exactly 200 cc. of the filtered solution from the fermentation into a 500 cc. distilling flask, neutralize, using litmus paper, with a dilute (10 per cent) solution of sodium hydroxide, and distil into the weighed flask until the liquid fills it exactly to the mark. (For the arrangement of the distilling flask and condenser see Fig. 2, page 9.) Weigh the flask and contents. Save the distillate for a later experiment. Calculate the specific gravity of the distillate, which contains all the alcohol that was present in 200 cc. of the product of fermentation. By reference to a table of the specific gravity of aqueous solutions of alcohol, calculate the weight of alcohol obtained from the 40 grams of glucose used in the experiment. What was the total volume of the solution fermented? Calculate the theoretical amount of alcohol obtainable from 40 grams of glucose and the percentage of this (the yield) obtained in your experiment.

Write an equation for the reaction by which alcohol is formed from glucose. Why is the solution kept in a warm place during fermentation? Why is the solution neutralized before distillation? How could you determine whether an acid volatile with steam was formed during the fermentation?

(b) Place the dilute alcohol obtained in (a) above in a 200 cc. distilling flask and distil off slowly about 50 cc. Add to this distillate solid anhydrous potassium carbonate as long as the salt dissolves.

(c) Test the product obtained in (a) or (b) by the iodoform test. (Experiment 81b, page 57.)

Notes. - (a) If very accurate results are desired it is necessary to take into account the temperature of the water in standardizing the contents of the flask, and to note the temperature of the dilute alcohol. The specific gravities of aqueous solutions of alcohol vary with the temperature. In the analysis of beverages for alcohol the specific gravity is usually determined by means of a hydrometer or a Westfall balance.

(b) The alcohol obtained in this way still contains water. It may be rendered anhydrous by a second treatment with potassium carbonate and with lime as described in experiment 80 below. The soluble monatomic alcohols can be separated from not too dilute solutions in water by saturating them with potassium carbonate.

79. Properties of Ethyl Alcohol (Sections 53, 57). - (a) Inflammability of alcohol. - Touch a lighted match to a few drops of alcohol on a watch-glass.

(b) Solubility of alcohol. - Test the solubility of alcohol, using about 5 cc. in each experiment, in water, benzene, kerosene, and concentrated sulphuric acid.

(c) Test for water in alcohol. - Add to 5 cc. of commercial 95 per cent alcohol about 1 gram of anhydrous copper sulphate, which can be prepared by cautiously heating the crystalline salt over a free flame in an evaporating dish. Note the change in color. Explain. Repeat the experiment, using absolute alcohol. For what purpose could this reaction be used?

(d) Place a crystal of potassium permanganate in about 5 cc. of 95 per cent alcohol. Repeat, using absolute alcohol.

(e) Alcohol and sodium. - Add to about 5 cc. of absolute alcohol a piece of sodium the size of a pea. Test the evolved gas. (Eq.) Evaporate the solution on a water-bath. Dissolve the resulting product in water and test the solution with litmus paper. (Eq.)

(f) Alcohol and hydrobromic acid. - Place 2 cc. of alcohol and 10 cc. of hydrobromic acid (sp. gr. 1.49) into a test-tube supported in a clamp and provided with a delivery-tube. (See Fig. 18, page 30.) Let the second end of the tube pass to within 1 inch of the bottom of a test-tube which is placed in a beaker containing cold water. Heat the solution of alcohol and acid carefully until about 5 cc. of liquid have distilled over. Examine the distillate. (Eq.)

(g) Alcohol and acetyl chloride. - Hood. - In making the following test take care that the mouth of the test-tube is directed away from you. Add acetyl chloride cautiously, drop by drop, from a pipette to 2 cc. of alcohol in a test-tube, which is kept cool by immersion in water, as long as reaction takes place. Note the gas evolved. (Eq.) Pour the contents of the tube cautiously into 5 cc. of cold water, and shake. Note the odor of the product.

(h) Alcohol and acetic anhydride. - Caution. - The reaction which takes place in this experiment is apt to occur with violence. The experiment should be performed under the hood. In a test-tube add 2 cc. of alcohol to 2 cc. of acetic anhydride. Is there any evidence of action? Support the tube in a vertical position by means of a clamp. Place a glass rod into concentrated sulphuric acid, and then rub it against the neck of the bottle to remove the drop that adheres. Put the rod with the trace of acid into the mixture of alcohol and anhydride. Wait until the mixture boils. (Eq.) Add the product to 5 cc. of cold water. If the ester does not separate, saturate the aqueous solution with sodium chloride. Note the odor of the product formed.

(i) Oxidation of alcohol. - Heat together about 1 cc. of alcohol, 5 cc. of a solution of potassium bichromate, and 5 cc. of dilute sulphuric acid. Note the change in color and the production of a characteristic odor. Write the equations for the reaction, including the change which takes place in the potassium bichromate.

Note. - (h) Sulphuric acid serves as a valuable catalytic agent in bringing about a reaction between alcohols and acid anhydrides.

80. Preparation of Absolute Alcohol (Section 53). - (a) In a 500 cc. flask add quicklime broken into small lumps to 200 cc. of 95 per cent alcohol until the pieces just project above the surface of the liquid. Connect the flask with a reflux condenser (§38, page 25), and heat to boiling on a water-bath for 1 hour. Do not place the flask in the boiling water. Remove the bath, and when the alcohol ceases boiling arrange the condenser for distillation (Fig. 2, page 9). Distil from the water-bath and collect the distillate in a filter-bottle, which is attached to the condenser by means of a cork stopper. In order to protect the alcohol, which is hygroscopic, from the moisture in the air, connect to the side-arm of the bottle by means of a piece of rubber tubing a small drying tube containing calcium chloride. Collect the first 10 cc. in a small dry flask, and then adjust the filter-bottle to receive the rest of the distillate. Keep the absolute alcohol in a stoppered bottle for future use. Why is the first part of the distillate rejected? Give a reason for the fact that absolute alcohol can not be obtained from a mixture with water by fractional distillation. What substance other than quicklime could be used for freeing alcohol from water? Could phosphorus pentoxide, concentrated sulphuric acid, or calcium chloride be used? State a reason for your answer in each case.

(b) Test portions of the first distillate, and of the absolute alcohol obtained for water with anhydrous copper sulphate and with potassium permanganate. (See experiment 79c and d, page 55.)

81. Tests for Ethyl Alcohol (Sections 57, 214). - (a) Ethyl acetate. - Warm gently together in a test-tube about 1 cc. of alcohol, 1 cc. of glacial acetic acid, and 2 cc. of concentrated sulphuric acid. Note the odor. (Eq.)

(b) Iodoform test. - Add 5 drops of alcohol and about 1 cc. of a dilute solution (10 per cent) of sodium hydroxide to 5 cc. of water in a test-tube. Add to the mixture, drop by drop, a solution of iodine in potassium iodide[2] until a faint yellow color persists after the solution is shaken. Heat the test-tube until it feels warm to the hand (about 60°). If a precipitate does not separate at once set the tube aside for a few minutes. Note the odor and color of the precipitate.

Notes. - (a) Tests which are based on the recognition of odors are not reliable for the absolute identification of compounds. Whenever possible the compound to be identified is converted into a solid substance, which possesses a definite melting-point. For a test for ethyl alcohol based on this principle see The Identification of Pure Organic Compounds, by S. P. Mulliken, Vol. I, page 168.

(b) A number of substances yield iodoform when treated with iodine and sodium hydroxide. Isopropyl alcohol and acetone give the test immediately in the cold.

82. Preparation of Allyl Alcohol (Sections 69, 80). - (a) Into a 500 cc. distilling flask, which is connected with a condenser and receiver, place 50 grams of oxalic acid, 200 grams of glycerol and 0.5 gram ammonium chloride. Fit into the neck of the flask by means of a stopper a thermometer so placed that the bulb is near the bottom of the flask. Heat over a wire gauze cautiously. Carbon dioxide is rapidly evolved and the thermometer registers about 130° for some time. As the temperature rises the evolution of gas slackens and finally ceases. When the temperature reaches 195°, the receiver, which contains a dilute aqueous solution of formic acid, is changed. At about 200° carbon dioxide is again evolved and water and allyl alcohol distil over. When the thermometer registers 260°, the distillation is stopped.

The distillate which contains the allyl alcohol is redistilled slowly from a flask fitted in the usual way with a thermometer. When the temperature reaches 103°, test from time to time about 2 cc. of the distillate for allyl alcohol by saturating it with solid anhydrous potassium carbonate. When an oil no longer separates, stop the distillation. Combine the products and saturate the solution with solid anhydrous potassium carbonate. Separate the layer of oil, and redistil. The allyl alcohol obtained in this way boils at 87°-97° and contains water. Weigh the product obtained and note its odor. The alcohol can be used for the experiments described below. In order to obtain the alcohol in dry condition, it should be placed in a flask and treated with barium oxide until the pieces project from the surface of the liquid. The flask should then be connected with a return condenser and allowed to stand over night. It is necessary to use the condenser, as the heat evolved in the union of the water and oxide often heats the alcohol to boiling. The alcohol obtained directly by distillation from the barium oxide boils at 96°-98°. The yield of alcohol is about 40 per cent of the theoretical.

Allyl alcohol boils at 96.6° and has the specific gravity 0.872 at 0°.

83. Properties of Allyl Alcohol (Section 69). - (a) Test the solubility of allyl alcohol in water.

(b) Allyl alcohol and bromine. - Hood. - To 1 cc. of allyl alcohol add bromine, drop by drop, as long as reaction occurs. (Eq.)

(c) Allyl alcohol and acetyl chloride. - Hood. - Add acetyl chloride cautiously (see experiment 79g, page 56) to 2 cc. of allyl alcohol until reaction ceases. (Eq.) Pour the product into 5 cc. of cold water. Shake and note the odor.

(d) Application of the iodoform reaction to allyl alcohol. - Determine whether allyl alcohol gives the iodoform reaction. Carry out the test as in experiment 81b, page 57.

(e) Allyl alcohol and oxidizing agents. - Hood. - Heat a mixture of 1 drop of the alcohol, 5 cc. of a solution of potassium bichromate, and 5 cc. of dilute sulphuric acid. Note the odor of acrolein (Section 153), which is the aldehyde obtained by the oxidation of allyl alcohol. (Eq.) Clean the tube under the hood.

84. Properties of Glycerol (Sections 73, 74, 153). - (a) Solubility of glycerol. - Test the solubility of glycerol in water, alcohol, ether, petroleum ether, and benzene.

(b) Conversion of glycerol into acrolein. - Cover the bottom of a test-tube with powdered acid potassium sulphate and then add about 5 drops of glycerol. Heat strongly and note the odor. (Eq.)

(c) Test for glycerol with borax bead. - Prepare a borax bead in the usual way. Place the bead when cold into an aqueous solution of glycerol, and then insert into a Bunsen flame. Note the color of the flame. Glycerol liberates boric acid from borax.

(d) Test for glycerol with a solution of borax. - Make a dilute solution (about 1 per cent) of borax in a test-tube. Add 2 drops of a phenolphthalein solution. What is the color? Why? Add now a neutral aqueous solution of glycerol slowly until the color is destroyed. Heat the solution to boiling and then cool.

(e) Test for glycerol by the preparation of glyceryl tribenzoate. - To obtain a solid derivative of glycerol the melting-point of which can be determined proceed as follows: Place in a small flask 3 drops of glycerol, 1 cc. of benzoyl chloride, and 10 cc. of a 10 per cent solution of sodium hydroxide. Cork the flask, and shake vigorously for 10 minutes. At the end of this time the compound formed will adhere to the sides of the flask. Decant off the liquid, and wash with cold water. Pour off as much as possible of the latter, and add 10 cc. of alcohol. Heat on the steam-bath, and filter the hot solution into a small flask. Add 2 cc. of water, stopper the flask, and shake it vigorously under running water. Filter off the crystals by suction, and wash them with a mixture of 5 cc. of alcohol and 2 cc. of water. Let the product, which is the tribenzoate of glycerol, (C₆H₅C00)₃C₃H₅, dry in the air, and then determine its melting-point, which is 71°-72°. If the compound does not melt sharply, recrystallize it from alcohol and water as before.

Notes. - (b) If larger quantities of glycerol are used the acid potassium sulphate should be replaced by phosphorus pentoxide; with this reagent frothing is avoided and no sulphur dioxide is formed.

(d) Other polyatomic alcohols behave as glycerol does in this test. Ammonium salts cause the disappearance of the color of the phenolphthalein, but the color is not restored in this case by boiling.

(e) Alcohols in general are converted into esters of benzoic acid when treated with benzoyl chloride as described in the test. (Baumann and Schotten reaction, Section 463.) It should be noted that glycol gives an ester which melts at 71°; it is evident, therefore, that the test is not applicable in the presence of glycol.


[1] Yeast requires for its growth certain salts which are present in Witte's peptone. If the latter is not available it may be replaced by 20 cc. of a solution made by dissolving 10 grams each of potassium phosphate, magnesium chloride, and calcium nitrate in 1 liter of water.

[2] This solution is made by dissolving 1 part of iodine and 5 parts of potassium iodide in 15 parts of water.