Organic Syntheses Part 4

Water, ethyl alcohol and carbon tetrachloride form a ternary mixture boiling at about 61'0. This vapor mixture, on condensation, separates into two phases; the heavier liquid consists of carbon tetrachloride and alcohol with only small amounts of water; the lighter liquid consists of approximately 65 per cent alcohol, 25 per cent water and 10 per cent carbon tetrachloride.

By taking advantage of this fact, it is possible to conduct the esterification at a temperature so low that the ethyl hydrogen oxalate first formed does not decompose into ethyl formate and other products, as is the case when the customary methods of esterification are employed.

The reaction may be carried out somewhat more expeditiously if the oxalic acid be dehydrated independently before it is mixed with the alcohol; indeed, it is also possible to remove the bulk of the water from the alcohol itself by a similar method, before mixing it with the oxalic acid. However, since water is formed during the esterification, little is gained by this procedure.

It is not absolutely necessary to remove the last traces of water from the alcohol-carbon tetrachloride layer by means of pota.s.sium carbonate before returning it to the reaction mixture; this process is, however, so simple and requires so little attention that there is no doubt that it is of material aid in cutting down the time of operation.

The advantages of using crystallized oxalic acid and commercial 95 per cent alcohol, instead of the anhydrous reagents, are obvious.

When technical oxalic acid is used, the yields are usually smaller by 5 to 10 per cent.

The apparatus shown in Fig. 1 may be somewhat more simply constructed by using rubber connections in several places, thus eliminating a certain amount of gla.s.s blowing, and making a more flexible piece of apparatus.

The side-arm of the separator may be made with two rubber connections,-- one above and one below the tube leading to the pota.s.sium carbonate tube.

The long return tube to the flask may be constructed with a rubber joint very near the carbonate tube and one near the flask.

3. Other Methods of Preparation

Ethyl oxalate has been prepared in poor yields by the following methods: by distilling a mixture of anhydrous oxalic acid and absolute alcohol;[1] by heating a mixture of anhydrous oxalic acid and 97 per cent alcohol under a reflux condenser and fractionating the resulting mixture;[2] by distilling a mixture of anhydrous oxalic acid and absolute alcohol, the vapor of absolute alcohol being pa.s.sed simultaneously into the mixture;[3] by allowing a saturated solution of oxalic acid in alcohol to stand for a long time at 40-50'0.[4]

A good yield has been obtained by Anschutz[5] by a method involving saturation of a mixture of crystallized oxalic acid and alcohol with hydrogen chloride, removal of the alcohol and water by distillation under reduced pressure, and repet.i.tion of the treatment with the alcohol and hydrogen chloride, the process being carried out several times.

[1] Jahresb. 1861, 598.

[2] J prakt. Chem. (2), 34, 500 (1886).

[3] Monatsh. 17, 614 (1896).

[4] Ann. 65, 350 (1848).

[5] Ber. 16, 2414 (1883),

VII

ETHYL PHENYLACETATE

C6H5CH2CN + C2H5OH + H2SO4 + H2O--> C6H5CH2CO2C2H5 + NH4HSO4

Prepared by ROGER ADAMS and A. F. THAL. Checked by OLIVER KAMM.

1. Procedure

IN a 3-l. round-bottom flask, fitted with an efficient reflux condenser, are mixed 750 g. of 95 per cent alcohol, 750 g.

of concentrated sulfuric acid and 450 g. of benzyl cyanide.

The mixture, which soon separates into two layers, is heated to boiling over a low flame, for six to seven hours, cooled and poured into 2 l. of water, and the upper layer is separated.

This is washed with a little 10 per cent sodium carbonate solution to remove small amounts of phenylacetic acid which may have been formed, and then distilled _in vacuo_. A small amount of water goes over first and then a pure product boiling 132-138'0/32 mm.

(120-125'0/17-18 mm.). The yield varies in general between 525 and 550 g.

(83-87 per cent of the theoretical amount).

2. Notes

The benzyl cyanide can be most conveniently prepared according to the directions in preparation III (p. 9); the product which boils over a 5'0 range should be used.

In was.h.i.+ng the layer of ethyl phenylacetate with sodium carbonate it is sometimes advisable to add a certain amount of sodium chloride so that the ester will separate more readily.

The product obtained is water-clear and practically colorless.

Although the product is collected over a 5'0 range, most of the liquid is found to boil over a 1'0 range, if distilled slowly without superheating.

The boiling point of ethyl phenylacetate is near that of benzyl cyanide.

However, a Kjeldahl a.n.a.lysis of the product shows that only a trace of nitrogen compounds is present.

3. Other Methods of Preparation

Ethyl phenylacetate may be prepared by the treatment of benzyl cyanide with alcohol and hydrochloric acid gas.[1] It is much more convenient in the laboratory, however, to use sulfuric acid in place of hydrochloric acid; in fact, the yields obtained are better than those recorded in the literature. This ester may also be made by the esterification of phenylacetic acid with hydrochloric acid and alcohol;[2] or with alcohol and sulfuric acid;[3]

the following less important methods of preparation may be mentioned; the action of benzyl magnesium chloride upon ethyl chlorocarbonate,[4]

and the action of copper on a mixture of bromobenzene and ethyl chloroacetate at 180'0.[5]

[1] Ber. 20, 592 (1887); Ann. 296, 361 (1897)

[2] Ber. 2, 208 (1869).

[3] Ann. 296, 2, footnote (1897); Compt. rend. 152, 1855 (1911).

[4] Ber. 36, 3088 (1903).

[5] Ber. 2, 738 (1869).

VIII

GLYCEROL a, g-DICHLOROHYDRIN

C3H5(OH)3 + 2HCl--> CH2ClCHOHCH2Cl + 2H2O

Prepared by J. B. CONANT and O. R. QUAYLE. Checked by O. KAMM and A. O. MATTHEWS.

1. Procedure

ONE kilo of 90 per cent glycerol (sp. gr. 1.243) and 20 g.

of acetic acid are placed in a weighed 2-l. flask which is immersed in an oil bath heated to 100-110'0. The flask is fitted with a two-hole stopper, which carries a long tube reaching to the bottom of the flask and a short exit tube. The former is connected to a hydrogen chloride generator, the latter to a catch-bottle and some system for absorbing any excess of hydrogen chloride.

A stream of dry hydrogen chloride is pa.s.sed into the mixture.

The absorption of gas is very rapid at the start, but gradually falls off towards the end of the reaction; the stream of hydrogen chloride should be regulated accordingly. The flask is removed from time to time and weighed; when the absorption of gas practically ceases, the increase in weight will be about 875 g.

(25 per cent more than the theoretical amount).