Cyanotetrachlorobenzenes, especially ortho- and para- dicyanotetrachlorobenzenes, are prepared by reacting in a liquid medium at 20.degree.-100.degree. C. a corresponding nitrotetrachlorobenzene with, in solution, an inorganic cyanide. Preferably the liquid medium is a two-phase water/water-immiscible organic solvent system, e.g. water/chloroform, a phase transfer catalyst is present and the inorganic cyanide is an alkali metal or alkaline earth metal cyanide.The compounds are useful chemical intermediates in the synthesis of, for instance, pesticidal compounds.