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Chemistry of CS
CS is the
short name for o-chlorobenzylidene
malononitrile, which was developed by Carson and
Staughton in 1928. C and S are surname initials of Carson
and Staughton. CS
is the condensation product of chlorobenzaldehyde with
malononitrile and its molecular weight is 188.6.
CS is a white crystalline product with a melting point of 94
¡ã Celsius and aboiling point of 310 - 315 ¡ã Celsius. CS is
soluble in organic solvents. In methylene chloride (MC) at
room temperature, the solubility of CS is
approximately 39 % by weight; in acetone, the solubility is
approximately 42 % (Edgewood Arsenal Technical Report 4301,
Weimer et al. 1969).The solubility of CS in water, on the
other hand, is very low (2 x 10-4 M). CS is
hydrolyzed in water and the products of this hydrolysis are
ochlorobenzaldehyde and malononitrile. Hydrolysis means the
cleavage of a molecule, in this case
CS, by the addition of
water. Hydrolysis is important in
toxicology and is catalyzed by a large number of different
hydrolytic enzymes. Because of this process, the amount of
CS in
water or water-containing fluids is reduced by 50 % within
14 minutes at pH 7.4 and 25 ¡ã Celsius, or within 0.17
minutes at pH 11.4 and 25 ¡ã Celsius. The time required to
reduce the amount of a substance by 50 % is called the
half-life of this substance. In acid solutions of pH 4 and
below, CS
is quite stable. The watery lining fluid of the respiratory
tract has a pH value of approx. 7, but inside the organelles
of the alveolar
macrophages (cells that take up material deposited on the
surface of the alveoli), the pH is between 4 and 5. The
normal decomposition of CS produces CN, C2H2, HCl, NOx, CO,
COCl2, and N2O. Preparations of CS used to generate
CS-containing
atmospheres are the following: (1)
CS melted and sprayed in
the molten form; (2) spraying of
CS dissolved in methylene
chloride (10 %) or in acetone (5 %); (3) dispersion of CS2
as dry powder [CS2 is a siliconized, micropulverized form of
CS with
improved flow properties and greater weather resistance (95
% micropulverized CS
with silica (Cab-o-sil) treated with hexamethyldisilazone);
this mixture prevents agglomeration, increases flowability
and also markedly increases hydrophobicity]; and (4)
dispersion of CS from thermal grenades by generation
of hot gases. The particle size (mass median diameter) of
the CSaerosol
generated from MC/acetone solution, by spraying melted
CS or
firing thermal grenades is reported to be in the range of
0.5 - 2 ¦Ìm. Particle size can vary depending on the
generated droplet size of the dispersed fluid and in respect
of powders on the micronization process used.
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