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459 CHEMISTRY AND TECHNOLOGY OF EXPLOSIVES

For preparing 1,2,4-chlorodinitrobenzene of high purity, p- chloronitrobenzene

should be used as starting material since mixtures of o- and p- chloronitrobenzenes

yield mixtures of two dinitro-isomers, namely, 1,2,6- and 1,2,4,-. The corresponding

reactions are shown in the diagram on p. 465.

The chloronitrobenzene isomers are highly toxic. Due to their high vapour

pressures in summer time or in warm places the atmosphere may contain sufficient

chloronitrobenzene to cause poisoning, which may sometimes be fatal. The maximum

allowable concentration of chloronitrobenzene in the air is 0.001 mg/l., according

to Lazarev [16].

Acute poisoning is characterized by symptoms similar to those appearing in

poisoning by nitrobenzene. Lazarev [16] thought nerve paralysis might occur, as

well as loss of reflex and tonic spasm. Skin irritation also takes place.

DINITRO DERIVATIVES OF CHLOROBENZENE

Among the six chlorodinitrobenzenes known, the 1,2,4- and 1,2,6-isomers are

the most important as they are the principal products of the nitration of chloro-

benzene. 1-Chloro-2,4-dinitrobenzene results from the nitration of o- and p- chloro-

nitrobenzenes and 1-chloro-2,6-dinitrobenzene from the o- isomer. Apart from

these, the 1,3,4-isomer, which forms in the nitration of m- chloronitrobenzene,

is of some importance.

All these compounds are known to appear in more than one crystalline forms

differing in their melting points. The 1,2,6-isomer can exist in the α− and β− forms

(m. p. 92°C and 40°C respectively), and the 1,3,4-isomer in the α−, β−, and γ− forms

(m. p. 36.3°C, 37.1°C, 28°C).

1-Chloro-2,4-dinitrobenzene

Physical properties. Three crystalline forms of 1-chloro 2,4-dinitrobenzene are

known. A stable α− modification (m. p. 53.4°C) crystallizes from nitric acid (62%)

or from alcohol. An unstable, β− modification (m. p. 43°C) can be precipitated,

as Ostromyslenskii [11] reports, from a fuming nitric acid solution by treating

it with water. It may also be obtained by rapid cooling of the molten substance.
Another unstable modification, γ, melting at 27°C, has also been isolated

(Müller [17]).

The solubilities of 1-chloro-2,4-dinitrobenzene in various solvents are given
(after Dévergnes [18]) in Table 102.