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.