CHAPTER VII

LACHRYMATORS

Without question the eyes are the most sensitive part of the body so far as chemical warfare is concerned. Lachrymators are substances which affect the eyes, causing involuntary weeping. These substances can produce an intolerable atmosphere in concentrations one thousand times as dilute as that required for the most effective lethal agent. The great military value of these gases has already been mentioned and will be discussed more fully later.

There are a number of compounds which have some value as lachrymators, though a few are very much better than all the others. Practically all of them have no lethal properties in the concentrations in which they are efficient lachrymators, though we must not lose sight of the fact that many of them have a high lethal value if the concentration is of the order of the usual poison gas. The lachrymators are used alone when it is desired to neutralize a given territory or simply to harrass the enemy. At other times they are used with lethal gases to force the immediate or to prolong the wearing of the mask.

A large number of the lachrymators contain bromine. In order to maintain the gas warfare requirements, it was early decided that the bromine supply would have to be considerably increased. The most favorable source of bromine is the subterranean basin found in the vicinity of Midland, Michigan. Because of the extensive experience of the Dow Chemical Co. in all matters pertaining to the production of bromine, they were given charge of the sinking of seventeen government wells, capable of producing 650,000 pounds of bromine per year. While the plant was not operated during the War, it was later operated to complete a contract for 500,000 pounds of bromine salts. They will be held as a future war asset of the United States.

The principal lachrymators used during the War were:

Bromoacetone, Bromomethylethylketone, Benzyl bromide, Ethyl iodoacetate, Bromobenzyl cyanide, Phenyl carbylamine chloride.

Chloropicrin is something of a lachrymator, but it has greater value as a toxic gas.

HALOGENATED KETONES

One of the earliest lachrymators used was bromoacetone. Because of the difficulty of obtaining pure material, the commercial product, containing considerable dibromoacetone and probably higher halogenated bodies, was used. The presence of these higher bromine derivatives considerably decreased its efficiency as a lachrymator. The preparation of bromoacetone involved the loss of considerable bromine in the form of hydrobromic acid. This led the French to study various methods of preparation, and they finally obtained a product containing 80 per cent bromoacetone and 20 per cent chloroacetone, which they called “martonite.” As the war progressed, acetone became scarce, and the Germans substituted methylethylketone, for which there was little use in other war activities. This led to the French “homomartonite.”

Various other halogen derivatives of ketones have been studied in the laboratory, but none have proven of as great value as bromoacetone, either from the standpoint of toxicity or lachrymatory power.

_Bromoacetone_ may be prepared by the action of bromine (liquid or vapor) upon acetone (with or without a solvent). Aqueous solutions of acetone, or potassium bromide solutions of bromine, have also been used.

Pure bromoacetone is a water clear liquid. There are great differences in the properties ascribed to this body by different investigators. This probably is due to the fact that the monobromo derivative is mixed with those containing two or more atoms of bromine. A sample boiling at 126-127° and melting at -54°, had a specific gravity of 1.631 at 0°. It has a vapor pressure of 9 mm. of mercury at 20°.

While bromoacetone is a good lachrymator, it possesses the disadvantage that it is not very stable. Special shell linings are necessary, and even then the material may be decomposed before the shell is fired. The Germans used a lead-lined shell, while considerable work has been carried out in this country with enamel lined shell. Glass lined shell may also be used. It is interesting to note that, while bromoacetone decomposes upon standing in the shell, it is stable upon detonation. No decomposition products are found after the explosion, and even unchanged liquid is found in the shell. It may be considered as having a low persistency, since the odor entirely disappears from the surface of the ground in twenty-four hours.

Bromoacetone was also used by the Germans in glass hand grenades (Hand-a-Stink Kugel) and later in metal grenades. The metal grenades weighed about two pounds and contained about a pound and a half of the liquid.

_Martonite_ was prepared by the French in an attempt more completely to utilize the bromine in the preparation of bromoacetone. They regenerated the bromine by the use of sodium chlorate:

NaClO₃ + 6HBr = NaCl + 3Br₂ + 3H₂O

In practice sulfuric acid is used with the sodium chlorate, so that the final products are sodium acid sulfate and a mixture of 20 per cent chloroacetone and 80 per cent bromoacetone, according to the reaction:

5(CH₃)₂CO + 4Br + H₂SO₄ + NaClO₃ =

4CH₂BrCOCH₃ + CH₂ClCO CH₃ + NaHSO₄ + 3H₂O.

This product is equally as effective as bromoacetone alone and is very much cheaper to manufacture. In general its properties resemble very closely those of bromoacetone.

GERMAN MANUFACTURE OF BROMOACETONE AND BROMOMETHYLETHYL KETONE[17]

These two products were prepared by identical methods. About two-thirds of the product produced by the factory was prepared from methylethyl ketone which was obtained from the product resulting from the distillation of wood. The method employed was to treat an aqueous solution of potassium or sodium chlorate with acetone or methylethyl ketone, and then add slowly the required amount of bromine. The equation for the reaction in the case of acetone is as follows:

CH₃COCH₃ + Br₂ = CH₂BrCOCH₃ + HBr

Ten kg.-mols of acetone or methylethyl ketone were used in a single operation. About 10 per cent excess of chlorate over that required to oxidize the hydrobromic acid formed in the reaction was used. The relation between the water and the ketone was in the proportion of 2 parts by weight of the former to 1 part by weight of the latter. For 1 kg.-mol. wt. of the ketone, 10 per cent excess over 1 kg. atomic-weight of bromine was used.

[Footnote 17: Norris, J. _Ind. Eng. Chem._, 11, 828 (1919).]

The reaction was carried out either in earthenware vessels or in iron kettles lined with earthenware. The kettles were furnished with a stirrer made of wood, and varied in capacity from 4,000 to 5,000 liters. They were set in wooden tanks and cooled by circulating water. The chlorate was first dissolved in the water and then the ketone added. Into this mixture the bromine was allowed to run slowly while the solution was stirred and kept at a temperature of from 30° to 40° C. The time required for the addition of the bromine was about 48 hrs. When the reaction was complete, the oil was drawn off into an iron vessel and stirred with magnesium oxide in the presence of a small amount of water in order to neutralize the free acid. It was then separated and dried with calcium chloride. At this point a sample of the material was taken and tested. The product was distilled to tell how much of it boiled over below 130° when methylethyl ketone had been used. If less than 10 per cent distilled over, the bromination was considered to be satisfactory. If, however, a larger percentage of low boiling material was obtained, the product was submitted to further bromination. The material obtained in this way was found on analysis to contain slightly less than the theoretical amount of monobromoketone.

It was finally transferred by suction or by pressure into tank-wagons. At first lead-lined tanks were used, but later it was found that tanks made of iron could be substituted. In order to take care of the small amount of hydrobromic acid, which is slowly formed, a small amount of magnesium oxide was added to the material. The amount of the oxide used was approximately in the proportion of 1 part to 1000 parts of ketone. When the magnesium oxide was used, it was found that the bromoketone kept without appreciable decomposition for about 2 months. The yield of the product from 580 kg. of acetone (10 kg.-mol. wts.) was 1,100 kg. The yield from 720 kg. of methylethyl ketone (10 kg.-mol. wts.) was 1,250 kg.

HALOGENATED ESTERS

The use of ethyl iodoacetate was advocated at a time when the price of bromine seemed prohibitive. Because of the relative price of bromine and iodine under ordinary conditions, it is not likely that it would be commonly used. However, it is an efficient lachrymator and is more stable than the halogenated ketones, so that on a smaller scale it might be advisable to use it.

It is prepared by the reaction of sodium iodide upon an alcoholic solution of ethyl chloroacetate. It is a colorless oil, boiling at 178-180° C. (69° C. at 12 mm.) and having a density of about 1.8. It is very much less volatile than bromoacetone, having a vapor pressure of 0.54 mm. of mercury at 20° C. Ethyl iodoacetate is about one-third as toxic as bromoacetone, but has about the same lachrymatory value.

AROMATIC HALIDES

“Benzyl bromide” was also used during the early part of the war, usually mixed with bromoacetone. The material was not pure benzyl bromide, but the reaction product of bromine upon xylene, and should perhaps be referred to as “xylyl bromide.”

Pure benzyl bromide is a colorless liquid, boiling at 198-199° C., and having an odor reminiscent of water cress and then of mustard oil. The war gas is probably a mixture of mono- and dibromo derivatives, boiling at 210-220° C., and having a density at 20° C. of 1.3. The mixture of benzyl and xylyl bromides used by the Germans was known as “T-Stoff,” while the mixture of 88 per cent xylyl bromide and 12 per cent bromoacetone was called “Green T-Stoff.”

As in the case of the halogenated acetones, it is necessary to use lead lined shell for these compounds. Enamel and glass lined shell may be used and give good results. While they are difficult of manufacture, satisfactory methods were being developed at the close of the war.

“T-Stoff” may be detected by the nose in concentrations of one part in one hundred million of air, and will cause profuse lachrymation with one part in a million. It is a highly persistent material and may last, under favorable circumstances, for several days. While it is relatively non-toxic, French troops were rendered unconscious by it during certain bombardments in the Argonne in the summer of 1915.

A number of derivatives of the benzyl halides have been tested and some have proven to be very good lachrymators. The difficulty of their preparation on a commercial scale has made it inadvisable to use them, and especially inasmuch as bromobenzyl cyanide has proven to be such a valuable compound.

BROMOBENZYL CYANIDE

Bromobenzyl cyanide is, chemically, α-bromo-α-tolunitrile, or phenyl-bromo-acetonitrile, C₆H₅CHBrCN. It is prepared by the action of bromine upon benzyl cyanide.

Benzyl cyanide is prepared by the action of sodium cyanide upon a mixture of equal parts of 95 per cent alcohol and benzyl chloride. The benzyl chloride in turn is obtained by the chlorination of toluene at 100°. The material must be fairly pure in order that the benzyl cyanide reaction may proceed smoothly. The cyanide is subjected to a fractional distillation and that part boiling within 3 degrees (the pure product boils at 231.7° C.) is treated with bromine vapor mixed with air. It has been found necessary to catalyze the reaction by sunlight, artificial light or the addition of a small amount of bromobenzyl cyanide.

The product obtained from this reaction, if the hydrobromic acid which is formed is carefully removed by a stream of air, is sufficiently pure for use as a lachrymator. It melts from 16 to 22° C., while the pure product melts at 29° C. It cannot be distilled, even in a high vacuum. It has a low vapor pressure and thus is a highly persistent lachrymator.

Bromobenzyl cyanide is about as toxic as chlorine, but is many times as effective a lachrymator as any of the halogenated ketones or aromatic halides studied. It has a pleasant odor and produces a burning sensation on the mucous membrane.

Like the other halogen containing compounds, lead or enamel lined shell are necessary for preserving the material any length of time. In all of this work the United States was at a very marked disadvantage. While the Allies and the Germans could prepare substances of this nature and use them in shell within a month, the United States was sure that shell filled at Edgewood Arsenal probably would not be fired within three months. This means that much greater precautions were necessary, both as to the nature of the shell lining and as to the purity of the “war gas.”

The question of protection against lachrymatory gases was never a serious one. During the first part of the war this was amply supplied by goggles. Later, when the Standard Respirator was introduced, it was found that ample protection was afforded against all the lachrymators. Their principal value is against unprotected troops and in causing men to wear their masks for long periods of time.

The comparative value of the various lachrymators mentioned above is shown in the following table:

Bromobenzyl cyanide 0.0003 Martonite 0.0012 Ethyl iodoacetate 0.0014 Bromoacetone 0.0015 Xylyl bromide 0.0018 Benzyl bromide 0.0040 Bromo ketone 0.011 Choroacetone 0.018 Chloropicrin 0.019

The figures give the concentration (milligram per liter of air) necessary to produce lachrymation. The method used in obtaining these figures is given in Chapter XXI .

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