Sartori The War Gases Chemistry and analysis

HEXACHLOROMETHYL CARBONATE 115

Statistics based on data obtained during the war of 1914-18 show that trichloromethyl chloroformate is a war gas which when used in projectiles produces a large number of deaths.

/OCC13 CO<

\OCC1S

This compound, also known as " Triphosgene," was prepared for the first time by Councler x in 1880, by the chlorination of methyl carbonate.

It is obtained as a by-product in the preparation of trichloromethyl chloroformate when methyl chloroformate which is impure with dimethyl carbonate is employed.

LABORATORY PREPARATION

Hexachloromethyl carbonate is prepared, according to Councler, by passing dry chlorine through dimethyl carbonate exposed to direct sunlight. After some days' chlorination colourless crystals separate. When the whole mass has become solid, a current of dry carbon dioxide is passed through to remove the chlorine and hydrochloric acid present.

The product obtained is dried on filter paper, washed many times with a little absolute ether and dried in vacua over sulphuric acid.

PHYSICAL AND CHEMICAL PROPERTIES

White crystals, melting at 78° to 79° C. It has an odour of phosgene and boils at ordinary pressure at 205° to 206° C. with partial decomposition. S.G. about 2. Soluble in benzene, carbon tetrachloride, ether, etc.

On heating near its boiling point at ordinary pressures, it decomposes to form phosgene and diphosgene, which further

decomposes into phosgene. The reaction of decomposition is thus 2 :

/OCC13

C0( -* 3COC12

XOCC13

The presence of catalysts such as ferric chloride facilitates this decomposition.

Cold water reacts very slowly with hexachloromethyl carbonate,

1COUNCLER, Ber.,1880, 13, 1698.

2HOOD and MURDOCH, /. Phys. Chem., 1919, 23, 509.

(B) THE ETHYL ACETATE GROUP

The halogen derivatives of ethyl acetate are compounds which have been known for some time and are used nowadays for organic syntheses both in the laboratory and in industry. They have a powerful action on the eyes and were used as war gases in the war of 1914-18.

They are commonly prepared by the esterification of ethyl alcohol by the corresponding acids : monochloracetic, bromoacetic, etc., using sulphuric acid as dehydrating agent. This acid first reacts with alcohol to form ethyl hydrogen sulphate :

/OC2H5 C2H5OH + H2S04 = H20 + S02(NOH

which then condenses with the monohalogenated acid forming the ester:

-I- CH2C1-COOH = H2SO4 + CH2C1

COO • C2H5 The compoundsof this type have the halogen atom bound very

unstably to the remainder of the molecule. It is easily split off by the action of water, alkaline solutions and ammonia. This instability considerably reduces the value of these substances as war gases.

COO.•<C2H5.

Ethyl chloroacetate may easily be prepared by the reaction of chloroacetyl chloride with alcohol,1 or by means of the action of ethyl alcohol on monochloroacetic acid in presence of sulphuric acid:

CH2C1

+ H2O

COOH

It is also prepared by the action of phosphorus pentachloride on ethyl glycollate 2 :

CH2OH

1WILLM, Ann., 1857, 102, 109.

2A. HENRY, Ann., 1870, 156, 176.

n8 HALOGENATED ESTERS OF ORGANIC ACIDS

or by the action of water on dichlorovinyl ethyl ether.

C-C10C2H5 COOC2H5

LABORATORY PREPARATION 1

Into a flask of about 200 ml. capacity fitted with a reflux condenser, 75 gm. monochloracetic acid, 45 gm. 95% alcohol and 10 gm. sulphuric acid (S.G. 1-84) are introduced. These are stirred and heated on the water-bath at 100° C.for about 5-6 hours. At the end of the heating the mass is allowed to cool and then poured into a separatory funnel containing about 150 ml. cold water. The ethyl chloroacetate layer is separated, washed once more with water and then fractionally distilled.

PHYSICAL AND CHEMICAL PROPERTIES

Ethyl chloroacetate is a colourless, mobile liquid with an odour of fruit, boiling at 143-5° C. at a pressure of 758 mm. of mercury (Willm) and decomposing by long heating at the boiling point.2 Its specific gravity is 1-1585 at 20° C., and its vapour density has been experimentally found to be 4-46 (Willm), while the calculated value is 4-23.

It is insoluble in water, but easily soluble in the common organic solvents.

It is easily decomposed by alkalies and also by hot water. In this decomposition, besides the saponification of the ester:

the halogen atom of the CH2C1 group is also substituted by a hydroxyl with formation of the corresponding hydroxy-acid :

CH2C1 CH2OH

COOH COOH

It reacts with ammonia to form chloroacetamide :

1CONRAD, Ann., 1877, 188, 218.

2VANDERVELDE, Bull. acad. roy. belg., 1897, [3] 34, 894.

Ethyl bromoacetate is a clear, colourless liquid boiling at ordinary pressure at 168° C.1 On cooling by means of a mixture of carbon dioxide and ether, it solidifies in colourless needles which melt at — 13-8° C. Its specific gravity is 1-53 at 4° C. In the vapour state it has a density of 5-8. It is insoluble in water but soluble in most of the organic solvents. Its volatility at 20° C. is 21,000 mgm. per cu. m. of air.

Chemically it is not a very stable compound, and is partially decomposed even by water and completely by sodium or potassium hydroxide solutions on boiling. The hydrolysis is as follows :

CH2Br—COOC2H5+2NaOH=CH2OH—COONa+C2HBOH+NaBr.

Ethyl bromoacetate on treatment with mercury ethyl at 150° C. decomposes according to the equation 2 :

CH8Br—COOC2H5+Hg(C2H5)2=C2HBHgBr+CH3—COOC2H8+C2H4.

Ethyl bromoacetate, because of its relatively high boiling point and its low volatility can be used in shells without causing a visible cloud on bursting.

It has no corrosive action on iron.

The limit of insupportability for man is 40 mgm. per cu. m. of air (Flury). The minimum concentration capable of provoking

COC)O.C2H5.

Ethyl iodoacetate was used by the Allies in shells, especially in mixtures with chloropicrin (10%).

This substance cannot be prepared, like the two preceding, by esterification of iodoacetic acid with ethyl alcohol. It is necessary to start with ethyl chloroacetate or bromoacetate, both of which react with potassium iodide to form the iodo-compound.

Perkin and Duppa,3 commencingwith ethyl bromoacetate and potassium iodide, prepared ethyl iodoacetate for the first time.

LABORATORY PREPARATION

25 gm. ethyl chloroacetate are dissolved in 150 ml. alcohol in a flask fitted with a reflux condenser, then 35 gm. potassium iodide

HALOGENATED ESTERS: IDENTIFICATION 123

Analysis of the Halogenated Esters

IDENTIFICATION

The various chlorinated methyl chloroformates are identified by the diverse manners in which they react with alkali. The method described dates from Hentschel in 1887 and is still used to-day.1

Identification of Monochloromethyl Chloroformate. Monochloromethyl chloroformate when treated with water or aqueous sodium hydroxide is decomposed even in the cold according to the equation :

Cl—COOCH2C1 + H20 = CH2O + CO2 + zHCl,

producing formaldehyde which may be easily identified by one of the common reagents for an aldehyde, such as the Schiff reagent, a 0-025% aqueous solution of fuchsin decolorised with sulphur dioxide.

As the other chlorinated methyl chloroformates when they react with alkaline solutions form no formaldehyde, this method may be used for the identification of the monochloro derivative even in the presence of diand trimethyl chloroformates.

Identification of Dichloromethyl Chloroformate. On treating dichloromethyl chloroformate with water or an alkaline solution it decomposes according to the following equation :

Cl—COOCHC12 + H20 = CO + C02 + 3HC1,

thus forming carbon monoxide, unlike the other derivatives. By applying one of the usual methods for the identification of this carbon monoxide, evolved when the substance being examined is treated with an alkaline solution, the presence of dichloromethyl chloroformate may be confirmed.

Identification of Trichloromethyl Chloroformate. This substance may be identified by its reaction with an aqueous solution of aniline (3 : 100). Like phosgene and dichloromethyl chloroformate, a white crystalline precipitate of diphenyl urea forms, which may be confirmed by microscopic examination (rhombic prisms) or by a determination of its melting point (236°C.).

Identification of trichloromethyl chloroformate may also be made by using dimethyl amino benzaldehyde and diphenylamine paper, prepared as described on p. 81. In presence of trichloromethyl chloroformate this turns yellow as in the presence of phosgene.

1 HENTSCHEL, /. prakt. Chent., 1887, 36, 99, 305.