Engineering Chemistry S Datta

EXPLOSIVES AND PROPELLANTS 343
by enclosing the material in a waterproof metallic container. Because it is not sensitive
to impact, friction and shock, it is the safest high-velocity agent.
(ii) Chlorate explosive. Sodium or potassium chlorate mixed with oxidisable materials
like sugar, charcoal, sulfur etc., becomes highly inflammable and sensitive to impact.
Recently, a desensitizing material or liquid ingredient is added to this mixture to
overcome the above disadvantage. But though being cheap, they are not popular.
(iii) Liquid oxygen explosives. Carbonaceous absorbent materials like lampblack or
other carbon black are packed in a porous container and this cartridge is dipped into
liquid oxygen to get saturated. These liquid oxygen explosives are of high strength
and velocity but they have several disadvantages. They are highly sensitive to shock.
The strength does not remain constant since the liquid oxygen steadily evaporates
and hence they cannot be stored for long.
Manufacture of Important Explosives
(i) Nitroglycerine: The raw materials are 99% pure glycerine, HNO 3
and H 2
SO 4
.H 2
SO 4
is taken in slight excess of HNO 3
and is absolutely free from water. In a steel nitrating
vessel, which is cooled externally by brine, the mixed acid is taken and nitroglycerine
is added and nitration is done at a very low temperature under stirring. The resulting
nitroglycerine and spent acid, having a composition of 76% H 2
SO 4
, 7% HNO 3
and
17% H 2
O are run to a separator. After about 3/4 of an hour, they form separate
layers, nitroglycerine being on the top. The nitroglycerine is drawn off, washed with
water, the acid is neutralised with a weak solution of Na 2
CO 3
under vigorous stirring.
The yield is around 230, calculated on the basis of glycerine as 100.
In recent years, continuous process has been developed. It is very important that to
avoid any accidental explosion a close control of the temperature is to be done during
nitration. This nitroglycerine is then converted to dynamites by absorbing in different
inert materials.
CH2OH
CH2 − ONO2
⏐
Conc. H SO ⏐
2 4
CHOH + 3 HNO3
⎯⎯⎯⎯→ CH − ONO2
+ 3H 2 O
⏐
⏐
CH2OH
CH2 − ONO2
(ii) Trinitrotoluene (TNT): TNT is prepared by nitration of toluene using 1:1 mixtures of
H 2
SO 4
and HNO 3
in a stirred tank reactor. Either a two or a three-step process is
used, the former separating out the mono-nitro compound first, then preparing bi
and tri compounds in one step.
CH 3
+ 3HNO 3
Conc.
HSO 2 4
CH 3
ON 2
NO 2
+3H 2
O
NO 2
Six isomers are possible for the trinitro compound. The formation of these isomers
and oxidation products leads to the formation of undesirable impurities. The liquid
product containing TNT is taken out, washed with ammoniacal solution of Na 2
SO 3
and finally with cold water. TNT is crystallized and the purified material melts at
80.8°C, which is finally dried and stored.