Sartori The War Gases Chemistry and analysis

both the hydrogen atoms have been substituted by alkyl groups.

These compounds have no toxic action on the human organism, but, like the sulphur derivatives already described, a certain degree of toxicity and in some cases powerful vesicant power are acquired when one or more of the hydrogen atoms in the alkyl radicals are substituted by one or more halogen atoms. Thus from methyl sulphide, chloromethyl sulphide is obtained, this having a toxic power on the respiratory system. From ethyl sulphide, derivatives are obtained which have differing toxic actions according to whether the halogen atom is attached at position a or /?:

/CH2-CH3

S

(XCH2-CH3

The monosubstituted derivatives, ethyl /J chloroethyl sulphide and ethyl /? bromoethyl sulphide,1 are weak in toxicity, as is also the disubstituted compound aa' dichloroethyl sulphide.2 The disubstituted derivative with both the halogen atoms in the /? position, j3£' dichloroethyl sulphide, however, is powerfully toxic and vesicant : it is more commonly known as "Mustard Gas."

Other derivatives analogous to ftp' dichloroethyl sulphide have been prepared, such as /?/?' dibromoethyl sulphide 3 and /?/?' diiodoethyl sulphide,4 which have similar physiopathological properties, as well as homologues of /?/?' dichloroethyl sulphide such as /?/?' dichloropropyl sulphide (I) and j3j8' dichlorobutyl sulphide (II) :

These two substances resemble /?/?' dichloroethyl sulphide in odour, but show some differences in offensive action, for it has been found that only /J/J' dichlorobutyl sulphide possesses vesicant action and that to a much milder degree than the ethyl compound.5

STEINKOPF, Ber., 1920, 53, 1007. BALES, /. Ghent. Soc., 1922, 121, 2137. STEINKOPF, Ber., 1920, 53, ion.

HELFRICH and REID, /. Am. Chem. Soc., 1920, 42, 1219.

POPE, /. Chem. Soc., 1921, 119, 396 ; COFFEY, /. Chem. Soc., 1921, 119, 94-

216 SULPHUR COMPOUNDS

Derivatives have also been prepared with the chlorine atom in the y position, like yy' dichloropropyl sulphide, whose toxic properties are, however, as yet unknown,1 and also derivatives with chlorine atoms in the /J and y positions, such as /J/J'yy' tetrachloropropyl sulphide:

/CH2-CHC1-CH2C1

S

(NCH2-CHC1-CH2C1

whose physiopathological properties are similar to those of /3j8' dichloroethyl sulphide, but not so vigorous.2

Attempts made to prepare substances like 88' dichlorobutyl sulphide with chlorine atoms in the 8 position have not been successful up to the present.

With regard to the relations between the chemical structure of these substances and their vesicant power, the following observations may be made :

(a)Of the halogenated sulphides prepared and studied only those with the halogen atoms at the end of the carbon chain have vesicant properties.

(b)The CH2-group in the a position should remain unsubstituted. It has been shown that on substituting a hydrogen atom in this group with a halogen atom, as in a/?/?' trichloroethyl sulphide (I),

or replacing each pair of hydrogen atoms in the two CH2-groups with oxygen, as in monochloroacetic thioanhydride (II) :

the products are completely or almost completely deprived of vesicant properties.

(c) The introduction of one or more sulphur atoms linked with one or more CH2-groups, between the chloroethyl groups, as in dichloroethyl ethylene dithioglycol 3 :

S-CH.-CH,C1

CH2

GH2

S-CH2-CH2C1

1BENNETT, J. Chem. Soc., 1925, 127, 2671.

2E. BOGGIO-LERA, Chim. e Industria, 1935, 334.

3BENNETT, /. Chem. Soc., 1921, 119, 1860 ; ROSEN, /. Am. Chem. Soc., 1922, 44, 634.

DICHLOROETHYL SULPHIDE: INTRODUCTION 217

diminishes the vesicant power, but confers orticant properties (seep. 147).

Of the analogues of dichloroethyl sulphide, the following have a place in the chemistry of the war gases :

(a) j8/3' dichloroethyl selenide,1 crystals melting at 24-2° C.,2 which have a vesicant action on the skin like that of the corresponding sulphide but to a less degree. This action is

"Iprite " from the locality (Ypres in Flanders) where it was first used, is due to Despretz,4 who obtained it in 1822 by the reaction of ethylene on sulphur chloride.

It is also known as " Sen/gas," " Mustard Gas " (England),

"Yperite " (France) and " Lost " (Germany). This last name is derived by joining the first letters of the names of the two

Germans, Lommel and Steinkopf, who proposed and studied the use of this gas in warfare. In America, it is refered to in the Chemical Warfare Service as " HS."

The application of this substance as a war gas, which commenced in July 1917 by the Germans, marked the beginning of a new period of chemical warfare and constituted a great surprise for the Allied armies. It was identified a few days after it was first used, but its preparation on an industrial scale required several months of study and research by the Allies. By the end of the war, however, the potential production of the Allied plants was greater than that of the German.

PREPARATION

After Despretz, this substance was prepared by Riche5 in 1854, and later by Guthrie 6 in 1860, while studying the condensa-

1 H. BAUSOR and coll., /. Chem. Soc., 1920, 117, 1453 ; C. BOORD, /. Am.

218 SULPHUR COMPOUNDS

tion products of the halogens and of the halogenated sulphur compounds with the defines. Guthrie, to whom many accounts have erroneously attributed the discovery of dichloroethyl sulphide, prepared it like Despretz by bubbling ethylene through sulphur chloride and noticed its peculiar vesicant properties.

At the same time, but independently of Guthrie's work, Niemann,1 in 1860, employing the same method as Despretz, obtained dichloroethyl sulphide, but was not able to determine its chemical constitution.

Later, in 1886, Meyer 2 made a special study of the compound and succeeded in preparing it in the pure state by a completely new process depending on the chlorination of thiodiglycol with phosphorus trichloride, and described its physical, chemical and biological properties.

More recently, in 1912, Clarke3 prepared this compound by a method similar to that of Meyer, that is, by chlorination of thiodiglycol, but used hydrochloric acid instead of phosphorus trichloride.

In 1920, Gibson and Pope* perfected Guthrie's method by. bubbling dry and completely alcohol-free ethylene through sulphur dichloride maintained in agitation at 40° to 45° C. :

By employing sulphur monochloride instead of the dichloride, the reaction passes through the following phases, according to Conant5 :

S2C12 ^ ± 8 4 - SC12

Furthermore, the following secondary reaction takes place :

NIEMANN, Ann., 1860, 113, 288.

V. MEYER, Ber., 1886, 19, 632, 3259.

CLARKE, /. Chem. Soc., 1912, 101, 1583.

GIBSON and POPE, /. them. Soc., 1920, 117, 271.

CONANT and coll., /. Am. Chem. Soc., 1920, 42, 585.

220 SULPHUR COMPOUNDS

sulphuric acid, and serve to dry the ethylene. It is advisable not to connect the wash-bottle /// to the Woulfe's bottle until the evolution of the ethylene has become regular.

25 gm. alum and a mixture of 25 gm. ethyl alcohol and 150 gm. concentrated sulphuric acid (density 1-84) are placed in the flask C, which is then heated cautiously. As soon as the current of ethylene becomes steady, wash-bottle /// is connected with the Woulfe's bottle, in which 20 gm. sulphur chloride have been previously placed. At the same time a mixture of 150 gm. ethyl alcohol and 300 gm. concentrated sulphuric acid is introduced drop by drop into C from the tap-funnel D.

During the passage of the ethylene, a further 30 gm. sulphur chloride are added from the tap-funnel B in three portions and the Woulfe's bottle is immersed in a vessel containing water so that the temperature of the reaction mixture does not exceed 35° C. The passage of the ethylene through the Woulfe's bottle is continued until all the sulphur chloride has been used up. This stage is determined by treating a little of the product with sodium iodide solution.

At the end of the reaction the product is distilled under reduced pressure, the fraction passing over between 106° and 108° C. at 15 mm. pressure being collected.

INDUSTRIAL MANUFACTURE

Dichloroethyl sulphide may be prepared industrially by several processes, all of which are based on one of the two methods described above : Meyer's and Guthrie's.

The various stages of manufacture by Meyer's process, which is referred to as " the German process," as it was largely employed during the war of 1914-18 by Germany, may be schematically expressed as follows :

(a) Preparation of Ethylene :

C2H6OH = H2O + CH2 = CH2.

(b) Preparation of Ethylene Chlorohydrin :

Ca(ClO)2 + H2O + CO2 = CaC03 + aHCIO

CH2 = CH2 + HC10 = C1.CH2.CH2.OH

(c) Preparation of Thiodiglycol :

222 SULPHUR COMPOUNDS

chlorohydrin, is distilled in steam so as to obtain a solution containing 18-20% of the chlorohydrin.1

Preparation of Thiodiglycol. The theoretical quantity of sodium sulphide is added to the chlorohydrin solution, prepared as already described, and the mixture heated to about 90° to 100° C., the product being drawn over into an evaporator and again heated to remove all the water. The thiodiglycol formed is filtered, and distilled in vacua.

NOTE. According to Nenitzescu,2 the preparation of thiodiglycol may be carried out by acting on ethylene oxide with hydrogen sulphide at 40° to 60° C. in presence of a small quantity of thiodiglycol which acts as a solvent for the two gases.

CH2\

thiodiglycol is carried out in cylindrical cast-iron pans, 2-5 m. in height and 2-8 m. in diameter, lead-lined and jacketed so that the reaction mass may be heated and cooled. The hydrochloric acid necessary for the chlorination is first passed through sulphuric acid and then introduced into the thiodiglycol as slowly as possible so as to obtain complete absorption. During the reaction the temperature is held at about 50° C. Two layers form in the pan, a heavy oily one consisting of a solution of dichloroethyl sulphide in thiodiglycol and an upper one consisting of an aqueous solution of hydrochloric acid. At the end of the reaction, the oily layer is drawn over into a lead-lined iron vessel fitted with lead coils for heating and a condenser, also constructed of lead, connected to a vacuum pump. The water is removed by distillation under reduced pressure (60-70 mm.) and the residual liquid then treated in a mixer with suitable solvents.

Guthrie's Method (theAllied Process). This method, comparatively simple for preparing small quantities of dichloroethyl sulphide in the laboratory, presented considerable technical difficulties when first used on the industrial scale. These were later overcome by the efforts of English and American chemists.3

Compared with the Meyer process, the Guthrie method allows

• A.GREEN,/. Soc. Chem. Ind., 1919, 38,363, 469 ; GIBSON and POPE, /. Chem.

Soc., 1920, 117, 271,

the product to be prepared more rapidly and in better yield, but it requires careful control during the course of the reaction.1

Several systems of manufacture were proposed and actually employed during the war for the preparation of dichloroethyl sulphide by this process.2 The most successful procedure in practice was that of Levinstein which was first used in America and then later by the Allies.

The preparation of dichloroethyl sulphide by this method was carried out in a cylindrical vessel of sheet steel or cast-iron, lead-lined and jacketed, of about 100 cm. diameter and 130 cm. in height, fitted with an agitator. This vessel has a lid through which a pipe passes to within a short distance of the bottom in order to introduce the ethylene.

Sufficient sulphur monochloride to cover the end of the tube is first placed in the vessel and then ethylene is bubbled in, so arranging the speed of its introduction and the cooling that the temperature of the reaction mixture remains at 30° to 35°C. Meanwhile more sulphur monochlorideis added in small portions. Employing 430 kgm. of ethylene, which needs 750 kgm. sulphur chloride, the reaction is completed in about 20 hours. At the end of the reaction the product is siphoned into a settling vessel where the sulphur is removed.

PHYSICAL PROPERTIES

In the pure state, dichloroethyl sulphide is an oily, colourless liquid which boils at 760 mm. pressure at 217-5° C.3 and melts at 14-4° C.4 In the crude state, it is brown and has a characteristic odour which is reminiscent of mustard. The melting point of the crude product is lower than that of the pure substance and varies with the impurities present.

The latent heat of fusion is 25 calories, the refractive index nD

Chetn. Rev., 1934, 426).

* For detailed descriptions of the French method (Pascal), see GIUA, Chimica