Chlorobenzenes polymorphism

Dinitro-1-chlorobenzene or l,3-Dinitro-4 -chlorobenzene. Three polymorphs exist orthorhmb crysts or alpha(stabile form), mp 53.4°, bp 315°, d 1.697 at 22°/4° vsol in hot ale, eth, benz or CS2 si sol in ale insol in w can be prepd by nitration of chlorobenzene with mixed acid(Refs 1, 2a, 5, 9, 10) rhmb crysts or beta(labile form), mp 4 3°, d 1.680 at 20°/4° solubility same as alpha can be prepd by rapid cooling of the alpha form(Ref 3) and gamma, mp 27°(Refs 1 10). Halpern(Ref 8) reported an expln occurred during distillation of 2 4 -DNCB at 1 mm press... 

In 1996, nine workers from a Mexican chemical plant were evaluated for the effects of chronic exposure to mono-, ortho- and paradichlorobenzenes. They had a mean exposure of 24 working years and worked in all stages of chemical production. Safety equipment was not used, and direct contact with the chlorobenzenes occurred via the skin and respiratory tract. The nine workers had a polymorphic acneiform eruption consisting mainly of comedones and cysts. All had comedones on the face, predominately in the malar area lesions on the nose, axillae, chest, shoulders, arms, buttocks and thighs were also present. Yellow cysts (2-5 mm in diameter) were found on the malar area of the face, eyelids, penis, scrotum, chest, axilla... 

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