IX
GLYCEROL a-MONOCHLOROHYDRIN
C3H5(OH)3 + HCl—> CH2ClCHOHCH2OH + H2O
Prepared by J. B. CONANT and O. R. QUAYLE. Checked by O. KAMM and A. O. MATTHEWS.
1. Procedure
FIVE HUNDRED grams of glycerol (90 per cent) and 10 g. of glacial acetic acid are mixed in a weighed 1-l. flask, which is placed in an oil bath heated to 105-110'0. A rapid stream of dry hydrogen chloride is introduced into the mixture. The flask is removed from the bath from time to time and reweighed. At the end of about four hours the flask will have gained 190 g. in weight. The reaction is then complete.
The product is distilled under diminished pressure. Below 114'0/14 mm., 220-250 g. distil; this portion is mostly water. The monochlorohydrin is collected between 114-120'0/14 mm.; it weighs 360 g., which is 66 per cent of the theoretical amount. About 20 g. more may be obtained by neutralizing the first fraction and separating the aqueous layer.
2. Notes
The same apparatus is employed as in the preparation of dichlorohydrin (preparation VIII, p. 29).
The portion boiling 120-130'0/14 mm. only amounts to 15-30 g., showing that very little of the b-compound is formed. This is further shown by the fact that the dichlorohydrin formed by continued action of hydrogen chloride under the same conditions contains very little, if any, a, b dichloride.
Two kilograms of concentrated sulfuric acid and 750 g. of concentrated hydrochloric acid are sufficient to produce the necessary amount of hydrogen chloride.
A light straw-colored final product is obtained in some cases.
An alternative procedure which is slower and gives slightly lower yields, but does not require a hydrogen chloride generator, is as follows:
Three hundred grams of glycerol, 600 cc. of hydrochloric acid (sp. gr. 1.19) and 15 g. of glacial acetic acid are heated under a reflux condenser for ten hours, in a 2-l. flask. The boiling should be very gentle in the early stage of the reaction, as considerable hydrochloric acid vapor is evolved. As the reaction progresses, and the evolution of acid vapors diminishes, the mixture is more strongly heated.
The reaction products are distilled under ordinary pressure until the temperature of the liquid has reached 140'0 (thermometer bulb immersed in the liquid). The residual products are distilled under diminished pressure, and the following fractions obtained. (1) Up to 115'0/11 mm.; (2) 115-117'0/ 11 mm.; (3) 117-170'0/11 mm. (1) is mostly aqueous hydrochloric acid; (2) is the monochlorohydrin; and (3) is glycerol. The second portion is redistilled and the portion boiling at 115-118'0/11 mm. or 133-136'0/20 mm. is collected. The yield is 190-205 g., 53-57 per cent of the theoretical amount.
3. Other Methods of Preparation
The following methods of preparing monochlorohydrin are described in the literature: action on glycerol of gaseous hydrogen chloride;[1] action of gaseous hydrogen chloride on glycerol mixed with an equal volume of acetic acid;[2] action of aqueous hydrochloric acid on glycerol[3] alone or with an organic acid (1-2 per cent), such as acetic, as a catalyst;[4] gaseous hydrogen chloride with an organic acid, as acetic, as a catalyst;[1b] gaseous hydrogen chloride with the ester of an organic or inorganic acid as a catalyst;[2b] the action of sulfur monochloride on glycerol.[3b]
[1] Ann. 88, 311 (1853); Ann. chim. phys. (3) 41, 297 (1834); V. R. P. 254,709; 269,657; Frdl. 11, 31 (1912).
[2] Ann. chim. phys. (3) 60, 18 (1860).
[3] D. R. P. 180,668; Frdl. 8, 27 (1907); J. Am. Chem. Soc. 42, 2096 (1920).
[4] D. R. P. 197,309; Frdl. 9, 34 (1908).
[1b] D. R. P. 197,308; Frdl. 9, 33 (1908).
[2b] D. R. P. Anm. 23,510; 16,579; Frdl. 9, 36 (1908).
[3b] D. R. P. 201,230; Frdl. 9, 35 (1908).