Organic Syntheses Part 5

The product is now cooled, placed in a 4-l. beaker, and treated with solid sodium carbonate until just alkaline to litmus.

Water is added from time to time, to facilitate the reaction with the sodium carbonate and to prevent the separation of salt; about 500 cc. are required. The mixture is transferred to a separatory funnel and the aqueous layer separated.

The crude dichlorohydrin, which weighs 1250 g., is distilled in vacuo.

The first fraction boiling below 68'0/14 mm. weighs 225 g., and consists of water and some dichlorohydrin; the dichlorohydrin is collected between 68-75'0/14 mm., and weighs about 775 g. The water is separated from the first fraction, which is then redistilled and yields 100 g.

of dichlorohydrin. A still further amount of material (40-45 g.) may be obtained by extracting with benzene, the aqueous layer obtained in the neutralization process. This is, however, hardly profitable.

The neutralization and distillation will require about four hours.

The 875 g. of dichlorohydrin thus obtained boils over a 7'0 range; this is 70 per cent of the theoretical amount.

Redistillation yields 700-720 g. boiling 70-73'0/14 mm.

(57 per cent of the theoretical amount).

2. Notes

The most convenient hydrogen chloride generator is that described by Sweeney.[1] Concentrated hydrochloric acid is introduced into concentrated sulfuric acid, by means of a dropping funnel and a _capillary tube leading to the bottom of the sulfuric acid container_. It is convenient to use a 3-l. bottle for this container and a 1-l. funnel to contain the hydrochloric acid.

The gas is dried by pa.s.sing through a wash-bottle containing concentrated sulfuric acid. An empty catch-flask should be connected between the generator and the absorption flask in case any glycerol tends to suck back at the start of the reaction.

About 6 kg. of concentrated hydrochloric acid and 10 kg.

of concentrated sulfuric acid are required in one run.

The generating flask will have to be recharged every six hours; it should be half filled with sulfuric acid. Aside from this, the apparatus needs no attention. The oil bath can be conveniently heated on an electric hot plate.

The dichlorohydrin boiling over a 7'0 range is sufficiently pure for most purposes. It contains very little, if any, isomeric dichlorohydrin, since on oxidation it gives dichloroacetone in good yields.

3. Other Methods of Preparation

The following methods of preparing dichlorohydrin are described in the literature: the action of gaseous hydrogen chloride on glycerol;[1b] the action of gaseous hydrogen chloride on glycerol mixed with an equal volume of acetic acid;[2] the action of hydrogen chloride gas on glycerol containing 1-2 per cent of some organic acid, as acetic, as a catalyst;[3] the action of aqueous solution of hydrochloric acid on glycerol containing acetic acid as a catalyst;[4]

the action of sulfur monochloride on glycerol.[5]

The previous work, described in the literature, indicated that the best yields were obtained by the treatment of glycerol containing 1-2 per cent of acetic acid as a catalyst by gaseous hydrogen chloride.

Therefore this method was employed.

[1a] J. Am. Chem. Soc. 39, 2187 (1917)

[1b] Ann. 88, 311 (1853); Ann. chim. phys. (3) 41, 297 (1854); (6), 22, 437 (1891); Bull. soc. chim. (2), 48, 237 (1887); Z. physik. Chem. 92, 717 (1918); 93, 59 (1919); 94, 691 (1920); D. R P. 263,106; 272,337; Frdl. 11, 33 (1912).

[2] Ann. Spl. 1, 2I8 (1861); Ann. chim. phys. (3) 60, 18 (1860).

[3] D. R. P. 197,308; Frdl. 9, 33 (1908).

[4] D. R. P. 197,309; Frdl. 9, 33 (1903).

[5] Ann. 122, 73 (1862); 168, 43 (1873); Ber. 5, 354 (1872); Ann. chim. phys. (6) 22, 437 (1891).

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).