Polymerised Cyanogen Halides

Cyanuric chloride, (CNCl)₃, cyanuric bromide, (CNBr)₃, and cyanuric iodide, (CNI)_n, are known. The two former substances contain the six-membered ring -



being halides of cyanuric acid (CNOH)₃, which has a similar constitution. Cyanuric iodide is not known to be similarly constituted.

Cyanuric Chloride, (CNCl)₃, is formed by the polymerisation of cyanogen chloride, which takes place spontaneously in presence of a little hydrochloric acid. This polymerisation may be accounted for by the chlorimino-structure of cyanogen chloride,:C:N-Cl, whose molecules combine with hydrogen chloride to form the hydrochloride , three molecules of which condense, with elimination of 3HCl thus:

→ + 3HCl

The polymer is also formed when chlorine acts on hydrocyanic acid in presence of sunlight, or upon a chloroform solution of the same substance containing 1 per cent, of alcohol; it also results from the action of phosphorus pentachloride on cyanuric acid, (CNOH)₃.

Cyanuric chloride consists of colourless, monoclinic crystals which melt at 145° C., forming a liquid boiling at 190° C.; the vapour density is 6.35, which corresponds to the formula (CNCl)₃. The heat of formation of (CNCl)₃ from its elements is 107,900 calories; its heat of polymerisation from liquid CNCl is 28,700 calories; its heat of combustion 292,000 calories. Cyanuric chloride dissolves in alcohol, chloroform, and other organic solvents without decomposition; water or moist air hydrolyses it into cyanuric and hydrochloric acids.

Cyanuric Bromide, (CNBr)₃, resembles cyanuric chloride. It is formed from impure cyanogen bromide at 130°-140° C., and in 70-80 per cent, yield by the action of nascent hydrogen bromide on a benzene solution of cyanogen bromide; it is also obtained by the action of bromine on potassium ferricyanide. It is a white, amorphous powder which melts at 300° C., and is hydrolysed by water into cyanuric and hydrobromic acids.

Cyanuric Iodide, (CNI)_n, is formed as a dark-brown amorphous powder by the action of hydriodic acid on cyanuric chloride. It is decomposed above 200° C. into iodine and paracyanogen; consequently its molecular constitution is unknown. Hot water hydrolyses it into cyanuric and hydriodic acids.