Sartori The War Gases Chemistry and analysis

by Helfrich 1 in 1920 by treating dichloroethyl sulphide with sodium iodide in alcoholic solution.

It is produced in the reaction between dichloroethyl sulphide and the Grignard reagent (see p. 248), and also, together with dithiane methiodide, by the action of methyl iodide on dichloroethyl or dibromoethyl sulphide.2 It has also been obtained by the action of hydriodic acid on an aqueous solution of divinyl sulphide.3

PREPARATION

Diiodoethyl sulphide is prepared according to Grignard by treating dichloroethyl sulphide with sodium iodide in acetic acid solution and heating to 60° C. On pouring the product into water, a crystalline product is obtained and this is then purified by recrystallisation.

PHYSICAL AND CHEMICAL PROPERTIES

Diiodoethyl sulphide forms bright yellow prisms melting at 62° C. according to Grignard, 4 and at 68° to 70° C. according to Kretov.5

It decomposes in time, especially if exposed to light, or on heating even to 100° C.

It is insoluble in water and soluble in the common organic solvents. On treatment with alkali it is readily hydrolysed. With oxidising agents it is converted into diiodoethyl sulphoxide (white crystals, melting at 104-5° C.) or into diiodoethyl sulphone (small white needles, m.p. 203° C.) This latter compound has also been prepared by the action of hydriodic acid on thioxane sulphone 8 :

Diiodoethyl sulphide reacts with methyl iodide more readily than the dichlorocompound to form dithiane methiodide 7 :

6KRETOV, /. Rusk. Fis. Khim. Obsc., 1929, 61, 2345.

6FROMM and UNGAR, Ber., 1923, 56, 2287.

7J. ALEXANDER and McCoMBiE, loc. cit.

DICHLOROETHYL SULPHIDE : DETERMINATION 249

On treating an aqueous solution containing 0-1% gold chloride or 0-05% palladium chloride with dichloroethyl sulphide a

This reaction may also be carried out on filter paper. In this case a reddish-brown stain is formed with a 10% gold chloride solution and a yellow stain with a 0-2% palladium chloride solution.

According to Obermiller,1 these reactions are specific for dichloroethyl sulphide and are not influenced by the presence of any other war gas, nor by the hydrolysis products of dichloroethyl sulphide.

The sensitivity with gold chloride is of the order of 10 mgm. dichloroethyl sulphide per cu. m. of air.

An apparatus has been designed for detecting the presence of dichloroethyl sulphide in a sample of air by this reaction.2 The air is drawn by means of a small pump through a glass tube containing silica-gel, to which are added, after a certain number of strokes of the pump, several drops of gold chloride solution. A little more air is drawn through the tube and then a few drops of hydrogen peroxide are added.

In the presence of dichloroethyl sulphide a yellow ring forms.

the reduction to metallic selenium, in the form of an orange-yellow suspension, of selenious acid when it reacts with dichloroethyl sulphide, and on the nephelometric measurement of the suspension formed.

The selenious acid employed in this method of analysis is prepared by dissolving i gm. SeO2 in 100 ml. of an aqueous solution of sulphuric acid (i : i by weight).

In practice the determination is carried out by bubbling the mixture of air and dichloroethyl sulphide through the reagent and then heating to 85° C. for 10 minutes. The solution is then allowed to cool and the quantity of gas present obtained by nephelometric comparison with a standard solution.

1 OBERMILLER, Z. angew. Chem., 1936, 49, 162.

250 SULPHUR COMPOUNDS

By this method quantities of dichloroethyl sulphide may be determined of the order of o-i-o-ooi mgm. with a maximum error of 0-005 mgm.

The Potentiometric Method of Hopkins. Another method of determining small quantities of dichloroethyl sulphide in air has been proposed by Hopkins.1 It consists in hydrolysing the dichloroethyl sulphide with water at 35° C. and determining the hydrogen ion concentration of the solution obtained by a potentiometric method.

In carrying out this determination it is recommended that the gas should be bubbled through two tubes in series containing water at 35° C. In this way the dichloroethyl sulphide is hydrolysed rapidly and by measuring the hydrogen ion concentration of the solution (methyl red indicator) the quantity of dichloroethyl sulphide may be obtained.

Maxim's Method. This is based on the oxidation of the sulphur atom in dichloroethyl sulphide and its determination as barium sulphate.2

It is carried out by passing the gas containing dichloroethyl sulphide first through an ordinary combustion tube (whose length is chosen according to the quantity of gas to be examined),filled with fragments of pumice and heated to redness, and then through a wash-bottle containing a 20% solution of barium chloride and 10-20 ml. hydrogen peroxide. The dichloroethyl sulphide on passing through the combustion tube is converted into sulphur

of this fraction the purity of the product may be estimated approximately.

Two other methods which have been proposed are described

DICHLOROETHYL SULPHIDE : DETERMINATION 251

between dichloroethyl sulphide and cuprous chloride, forming a double salt of definite composition :

fClCH2-CH2\ n

>S • Cu2Cl2 LC1CH2-CH/ J2

Description of the Method : About i gm. of the sample is weighed accurately into a 100 ml. flask with a tight stopper. 10 ml. of a solution of cuprous chloride in absolute alcohol containing hydrochloric acid1 are added and the mixture continually agitated, without heating, for 10 minutes so as to ensure complete solution of the dichloroethyl sulphide. At the end of this time, the mixture is cooled with water and still agitated while 50 ml. of a 5% aqueous solution of sodium chloride are added from a burette. A precipitate of the double salt separates as fine colourless needles. After allowing to stand for a short time, the solution is filtered through glass wool, the filtrate being collected in a dry receiver. The excess cuprous chloride in the filtered liquid is then estimated in the following manner :

30 ml. of the filtrate are measured into a 250 ml. flask by means of a burette and 5 ml. 20 volume hydrogen peroxide are added to oxidise the copper to the divalent condition.

The contents of the flask are then boiled, being taken almost to dryness and taken up with water several times (generally twice) so as to remove the hydrogen peroxide completely. The residue is diluted once more with 50 ml. water and a solution of sodium carbonate added until a slight precipitate is formed, this being then redissolved with a few drops of dilute acetic acid. Excess potassium iodide is added and the liberated iodine is titrated with a decinormal solution of sodium thiosulphate.

At the same time the alcoholic cuprous chloride solution is also titrated with the same thiosulphate solution, after first oxidising the cuprous chloride with 5-10 ml. hydrogen peroxide and following the procedure described.

From the results of this determination, the percentage of dichloroethyl sulphide present in the original sample may be obtained by the following calculation :

1 The solution of cuprous chloride must be prepared freshly immediately before use, and it is therefore advisable to have a 10% solution of hydrochloric acid in absolute alcohol available, and to dissolve 5 gm. of cuprous chloride in 50 ml. of this immediately before use.

added to the acetic acid solution. After heating and subsequently cooling, the contents of the flask (crystals and liquid) are poured into a tared 500 ml. graduated flask containing 100 ml. carbon tetrachloride and 200 ml. water.

The flask is shaken to dissolve the diiodoethyl sulphide, the contents diluted to volume and shaken again to homogenise the solution. After allowing to stand so that the two liquids separate, 50 ml. of the aqueous layer are taken, the iodine liberated with sodium nitrite and titrated as in (i).

% dichloroethyl sulphide = ^ [io^0 + 1-5 — (8^1 + A2)]

There are no indications in the literature of the repeatability or accuracy of the results obtained by this method.

(C) CHLOROANHYDRIDES AND ESTERS OF SULPHURIC ACID

Being dibasic, sulphuric acid can form two chloroanhydrides, chlorosulphonic acid and sulphuryl chloride.

While chlorosulphonic acid may be considered as the acid chloroanhydride of sulphuric acid, sulphuryl chloride is the true chloroanhydride. The chlorine atom in these compounds, as in all the chloroanhydrides, has little stability ; it is readily split off by water. However, while chlorosulphonic acid reacts with water with great readiness, sulphuryl chloride reacts very

slowly.

Chlorosulphonic acid has little toxicity and has been chiefly employed in warfare as a smoke producer. Sulphuryl chloride was used particularly in admixture with other war gases (cyanogen chloride, chloropicrin, etc.).

254 SULPHUR COMPOUNDS

Sulphuric acid forms two types of esters like the two types of chloroanhydrides :

/OH /OR

Of these esters, methyl sulphuric acid and dimethyl sulphate were employed as war gases. They have great toxic power and act on the respiratory passages and on the skin.

These esters are insoluble in water though they are decomposed on contact with water to split off the alkyl group, especially dimethyl sulphate. This same scission also takes place in presence of other substances containing the hydroxyl group. It is for this reason that dimethyl sulphate is widely employed both in the laboratory and in industry as a methylating agent.

Furthermore, beside the chloroanhydrides and the esters already mentioned, sulphuric acid can form compounds of mixed type, of the general formula :

/OR

SO/ NC1

These compounds, which may be considered as chloroanhydrides of alkylsulphuric acids, have little stability. They are readily decomposed by cold water or by the action of the alkali hydroxides with splitting off of the halogen and formation of the alkyl sulphuric acids :

It is interesting to consider the behaviour of these substances to the hydrolysing action of water, mentioned above. While the ethers readily split off the alkyl group, the chloroanhydrides of the alkyl sulphuric acids contain an alkyl which is not easily removed. It seems that in the latter compound the chlorine atom hinders the hydrolytic process.

In the war of 1914-18 methyl chlorosulphonate and ethyl chlorosulphonate were employed as war gases. Owing to the presence of halogen in their molecules, these substances have a powerful lachrymatory action, but their toxicity is less than that of the sulphates.