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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

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

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

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.

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