Condensation Reactions: A Laboratory Preparation of Ethylidene Glycerol M. MARTIN MAGLIO and CHARLES A. BURGER Advance Solvents and Chemical Corporation, New York, New York
A
CETALS, which are becoming increasingly important commercially, are only too seldom emphasized in the study of elementary organic chemistry. It is true that the lecturer may spend a total of several hours in discussing this topic from time to time as it occurs in the standard text, but practically no stress is applied, in that it is completely overlooked by the authors of our conventional laboratory manuals on organic chemistry. As a result, the industrially inexperienced chemistry graduate often has a vague and confused picture of the entire subject. We hope to remedy this situation somewhat by offering a simple illustration of a typical condensation reaction, i. e., the preparation of a cyclic acetal by the reaction of glycerol and acetaldehyde in the presence of a desiccating catalyst. Ethylidene glycerol was first prepared by Harnitzky and Menschutkine (4) from glycerol and acetaldehyde in a sealed tube a t 180°C. I t was next prepared by Nef (lZ), using a similar procedure. Hibbert (5) also synthesized it using mineral acids such as hydrochluric, sulfuric, and phosphoric acids and iodine as catalysts. Hill, Whelen, and Hibbert (9) also prepared the compound from glycerol and paraldehyde. It has also been obtained (7) in a 63 per cent yield from glycerol and ethylene in the presence of a catalyst consisting of mercuric sulfate and sulfuric acid. Related compounds have been synthesized, employing mineral acids (1, 3) and organic sulfonic acids (13) as catalysts and anhydrous sodium sulfate (3) and calcium carbide (11) as desiccants. Acetaldehyde reacts with glycerol to yield a mixture of two isomers as illustrated in the accompanying equation.
EXPERIMENTAL
Apparatus. The equipment consists of a one-liter, three-necked, round-bottomed, electrically heated flask equipped with a thermometer and dropping funnel in one side-neck, a reflux condenser in the other, and a mercury-sealed mechanical agitator in the center neck. Reactants. The reactants consist of 95 per cent glycerol (97 g.), acetaldehyde (181 g.), solvent naphtha #4 (boiling point 80-85OC.) (200 g.), and p-toluenesulfonic acid monohydrate (3 g.). Procedure. The glycerol, naphtha, and acid catalyst are agitated in the flask thoroughly for ten minutes to disperse the catalyst. The acetaldehyde is then added from the dropping funnel over a period of 20 minutes, an obviously exothermic reaction taking place a t room temperature. After the addition of aldehyde is complete, the heterogeneous mixture is agitated a t reflux (about 5S°C. hatch temperature) for three hours. The cooled mixtute is allowed to stand in a separatory funnel, and the lower layer is drawn off. The upper layer of diluent is discarded, for ethylidene glycerol is insoluble in it. The lower layer is neutralized with 1.5 g. of powdered, freshly fused sodium acetate and 3.0 g. of sodium carbonate, dried over anhydrous sodium sulfate and filtered by gravity. The clear a t r a t e is then fractionally distilled a t atmospheric pressure in the presence of small amount of sodium carbonate through a ten-inch Vigreux column to remove the excess acetaldehyde, the temperature a t the top of the distillation column rising to 60°C. The residue is subsequently distilled under reduced pressure, a 70 per cent yield of colorless liquid boiling at 80 to 8 5 T . a t 21 mm. being obtained. Analysis. The analytical procedure, based on the method of Levenson (lo), consists in the hydrolysis of a sample by means of 42.5 per cent phosphoric acid, distilling the liberated acetaldehyde into a standard solution of alkali containing hydrogen peroxide to oxidize the aldehyde to the corresponding acid, and titrating the excess caustic with standard acid. A blank is run on the reagents, of course. The calculations are based on the followingequation: Net ml. H.SO, X N X M.W. of CHICH< X 100
Both the 1,2- and the 1,3- isomers are possible as indicated by Harnitzky and Menschutkine ( 4 ) , Nef (12), Fischer (Z), and Hill, et al. (8), the partition between the two isomeric forms varying considerably according to the experimental method and conditions. Interestingly enough, acetone results only in the 5-membered ring compound ( 6 ) .
1000 X Sample = Per cent of
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