Ortho-Chlorobenzamalonitrile

colorless crystals with a melting point of 95°C and a boiling point of 310°C (with decomposition). The structural formula is

Ortho-chlorobenzamalonitrile is readily soluble in benzene and acetone, slightly soluble in alcohol, and poorly soluble in water. It is obtained from the reaction of o-chlorobenzaldehyde, ClC₆H₄CHO, with the dinitrile of malonic acid, CH₂(CN)₂, in the presence of catalysts. The resultant poisonous chemical agent irritates the eyes and the upper respiratory tract. Toxicity is primarily generated by blocking nerve endings through sulfhydryl groups.

The maximum tolerable atmospheric concentration of ortho chlorobenzamalonitrile is estimated at 5 × 10^–4 mg per liter, given an exposure time of 1 min; higher concentrations irritate the skin, especially during perspiration. In some countries outside the USSR this poisonous chemical agent is called CS gas.