| Chemical Abstract Number (CAS #) |
505602
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| Synonyms | Mustard gas |
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Ethane, 1,1'-thiobis[2-chloro- | bis(2-Chloroethyl) sulfide | Sulfur mustard | Yperite | HD (chemical warfare agent) |
| Analytical Methods |
EPA Method 8240B |
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EPA Method 8260A |
| Molecular Formula | C4H8Cl2S |
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| Use | VESICANT IN CHEMICAL WARFARE, MODEL CMPD IN BIOLOGICAL STUDIES
ON ALKYLATING AGENTS
ORG SYNTHESIS
Medication: Formerly used topically in the treatment of psoriasis.
MUSTARD GAS WAS USED AS A VESICANT IN CHEM WARFARE DURING WORLD
WAR I & IN ETHIOPIA IN 1936 ALTHOUGH NO FURTHER MILITARY USE WAS
REPORTED, PRODUCTION & STOCKPILING CONTINUED, ESPECIALLY DURING
WORLD WAR II & STOCKS MAY STILL HAVE EXISTED IN USA AS RECENTLY AS
1974
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| Apparent Color | COLORLESS OILY LIQUID ; YELLOW PRISMS ; OILY LIQUID FORMS PRISMS
ON COOLING
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| Odor | WEAK, SWEET, AGREEABLE ODOR
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| Boiling Point | 217 DEG C
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| Melting Point | 13-14 DEG C
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| Molecular Weight | 159.07
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| Density | 1.2741 @ 20 DEG C/4 DEG C LIQ
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| Odor Threshold Concentration | 1.30X10-3 mg/l (gas) (detection in air, chemically pure)
2.30X10-3 ppm (detection in air, purity not specified)
Odor 0.0150 mg/cu m (low) odor 0.0150 mg/cu m (high).
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| Sensitivity Data | SEVERE IRRITANT TO SKIN, EYES & RESPIRATORY TRACT
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| Environmental Impact | Bis(2-chloroethyl) sulfide (HD, mustard gas) may be released to the environment during
its production, storage, transport, and disposal, as well as during its clinical and research use as an
alkylating agent. When released on soil at low concns, bis(2-chloroethyl)sulfide should be lost by
hydrolysis and volatilization. Some leaching should also occur. However, no experimental data
are available on the fate of very low concns of bis(chloroethyl)sulfide in soil. When
bis(2-chloroethyl)sulfide is introduced into water at very low concns so that it is dissolved, it will
rapidly hydrolyze, forming mustard chlorohydrin and thiodiglycol. At 0, 25, and 40 deg C, the
estimated half-lives of bis(2-chloroethyl)sulfide when dissolved in large amounts of water are 1.75
hr, 4 minutes, and 43 seconds, respectively. Volatilization will be slow by comparison. Hydrolysis
in seawater will be a factor of 2.5 slower because of the common-ion effect exerted by the
chloride ion. Despite its high rate of hydrolysis, undissolved bis(2-chloroethyl)sulfide may persist
for longer periods of time because its rate of solution is slow. In the atmosphere,
bis(2-chloroethyl)sulfide vapor will degrade primarily by reaction with photochemically-produced
hydroxyl radicals; the resulting half-life is 1.4 days. Releases in chemical warfare may be by aerial
spraying or from bursting munitions that would shower droplets of the chemical agents over the
terrain. The persistence of HD sprayed on several soils at a variety of weather conditions ranged
from 31 to 51 hr at 25 deg C and 50 to 92 days at 0 deg C. Persistence was lowest for heavy rain
and highest in light rain. Persistence on snow has reported to range from 14-56 days. The
bis(2-chloroethyl)sulfide does not appear to migrate into the snow, but rather stays on the surface.
Disposal by land or sea burial might result in releases of large quantities of neat
bis(2-chloroethyl)sulfide . Bulk quantities of bis(2-chloroethyl)sulfide buried on land may last for
decades. When bulk quantities of bis(2-chloroethyl) sulfide are disposed of at sea, some
bis(chloroethyl)sulfide will form a surface film that will disappear as a result of hydrolysis and
volatilization within several days. Most of the bis(chloroethyl)sulfide will sink to the bottom of the
water because bis(chloroethyl)sulfide is heavier than water. This bis(chloroethyl)sulfide will be
degraded by hydrolysis; however, the hydrolysis will be limited by the rate of dissolution. The rate
of dissolution will depend on the exposed surface, the amount of agitation, and the temperature.
The temperature at the bottom of a body of water may be below 14.4 deg C and
bis(chloroethyl)sulfide will then be a solid. Dissolution under these circumstances may take
several months to years. Dissolved bis(chloroethyl)sulfide in the main body of seawater will be
lost by hydrolysis with its half-life ranging from 15 min at 25 deg C to 175 min at 5 deg C.
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| Environmental Fate | TERRESTRIAL FATE: FOR SOME TIME AFTER JULY 1917, MUCH OF FRENCH
SOIL IN REGION OF BATTLE LINES WAS CONTAMINATED WITH MUSTARD GAS
IN AREA OF FALLING SHELLS IN FRANCE HAVE BEEN ESTIMATED TO BE 3 & 5
PPM, RESPECTIVELY
TERRESTRIAL FATE: When bis(2-chloroethyl) sulfide (HD) is released in soil, losses would
primarily result from volatilization and hydrolysis. Some leaching will also be expected. For some
time after 1917, much of the French soil in the region of the battle lines was contaminated with
mustard gas, suggesting that HD is reasonably persistent in soil . Field reports dating back to
World War I report that after used as a chemical warfare agent, an area is safe after 3 days to 3
weeks . The World Health Organization reports a persistence of 12-48 hr at 10 deg C with rain
and a moderate wind, 2-7 days at 15 deg C with sun and a light breeze, and 2-8 wk at -10 deg C
with sun, no wind, and a snow cover . Experimental measurements of concn of HD in the soil
or in the air above the soil were not reported; HD levels were simply considered low enough for
soldiers to reenter the area. Soldiers have been burned while digging in areas where HD has not
been used for 3 yr and it has lasted for several decades in land dumps. This indicates that HD may
be very persistent in soil, especially when bulk quantities are involved . The case of soldiers
being burned by HD while digging in an area where it had not been used for 3 years, suggests that
the HD had leached into the soil.
TERRESTRIAL FATE: When disseminated over bare or vegetated terrain, water may be quite
limited and may be largely derived from the atmosphere; hydrolysis would therefore depend on
the humidity and the diffusion of water vapor into an agent droplet . When disseminated over
snow and ice, water will be plentiful and taken up according to the agent's solubility; locally
concentrated, unbuffered solutions may result . Even then, HD hydrolysis may be limited by its
low solubility and the fact that it freezes at 14 deg C. The persistence in five soils ranged from 27
to 68 hr, with sand having the longest persistence and gravelly soil the least(2,SRC). Calculated
values for pooled samples at 25 deg C for a variety of weather conditions are (weather condition -
persistence in terms of agent density decline in hours): calm, dry - 41.5; windy, dry - 47.3; light
rain - 51.2; heavy rain - 30.5 . At 0 deg C the respective persistence times were 63.8, 72.6,
92.3, 49.7 days . It is not clear why volatilization losses are lowest under conditions of light rain
or why the half-life should be greater under windy conditions than calm ones.
TERRESTRIAL FATE: The nature of the terrain has an important bearing on the behavior of the
contaminant. Evaporation from grassland will be more rapid than from a permeable surface such
as sand . In a field experiment designed to simulate a chemical attack, a small sample of HD
was placed on top of the snow surface; another sample was immediately covered with 5 cm of
snow in order to simulate a snowfall after an attack . Less than 0.1% of the HD was found after
14 days in both the uncovered and snow-covered samples. Experiments clearly showed that
covering the sample with snow and increasing droplet size increased persistence; this has been
ascribed to reduced volatilization and dissolution. None of the agents studied, including HD,
tended to migrate into the snow. Another investigator reported a persistence of 56 days in snow
at -10 deg C . In view of the fact that snow samples are quite variable, this value is not
necessarily in conflict with the first (14 day) result. It has been suggested that HD may react in
warm, dry soil to form 1,2-bis(2-chloroethylthio)ethane and higher adducts; however, no
experimental evidence of such reactions have been reported.
AQUATIC FATE: When bis(2-chloroethyl) sulfide (HD) is introduced into water at very low
concns so that it is dissolved, it will rapidly hydrolyze, forming mustard chlorohydrin (CH) and
thiodiglycol (TDG). At 0, 25, and 40 deg C, the estimated half-lives of HD when dissolved in
large amounts of water are 1.75 hr 4 minutes, and 43 seconds, respectively. Hydrolysis in
seawater will be a factor of 2.5 slower because of the common-ion effect exerted by the chloride
ion. On the other hand, the half-life resulting from volatilization is expected to be much lower, 1.9
days from a model river and longer in a pond or lake. The situation is radically different at low
temperatures and in heterogeneous mixtures. The rate of dissolution of HD is very slow. HD is a
solid below 14.4 deg C which exacerbates this situation. At higher concn of HD, sulfonium salts
(HD-TDG, HD-2TDG, CH-TDG) may form from the reaction of TDG with HD or CH; an
equilibrium exits between TDG and CH-TDG. High HD concns may exist around HD droplets
and when water dissolves inside an HD droplet.
AQUATIC FATE: When HD is introduced into seawater, three zones with different behavior are
observed . A small amount of HD will remain on the surface in a surface film where it will be
destroyed by hydrolysis and to some extent volatilization; this surface film may last from one to
several days. Bulk HD, or droplets formed by wind action on the surface film, will sink to the
bottom of the water because HD is heavier than water. This HD will be degraded by hydrolysis;
however, the hydrolysis rate will essentially be the rate of dissolution. The rate of dissolution will
depend on the exposed surface, the amount of agitation, and the temperature. The temperature at
the bottom of body of water may be below 14.4 deg C and HD will then be a solid. Dissolution
under these circumstances may take several months at the very least; a one ton solid cylinder of
HD would take about 5 yr to dissolve. In the water column of a body of seawater, dissolved HD
will be lost by hydrolysis with its half-life ranging from 15 min at 25 deg C to 175 min at 5 deg C.
ATMOSPHERIC FATE: When used as a chemical agent, bis(2-chloroethyl) sulfide (HD will be
disseminated using aerial sprays or munitions and will be initially in the form of droplets. These
droplets would be subject to gravitational settling; HD vapor from resulting deposits may reenter
the atmosphere by evaporation. In the atmosphere, HD vapor will degrade by reaction with
photochemically produced hydroxyl radicals; the resulting half life being estimated as 1.4 days.
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