Cyanogen Chloride, CNCl

Cyanogen chloride was first obtained by Berthollet by the action of chlorine on hydrocyanic acid; Wohler prepared it by passing chlorine into a saturated solution of mercuric chloride and subsequently distilling; and Gautier saturated aqueous hydrocyanic acid (1HCN:4Aq.) with chlorine, added excess of mercuric oxide and calcium chloride to the well-cooled solution, and afterwards distilled off the cyanogen chloride. Hantzsch and Mai added potassium cyanide to saturated chlorine water at 0° C. till all the chlorine was absorbed, then again saturated the liquid with chlorine and added more cyanide. The cyanogen chloride thus formed was then vaporised and condensed.

Cyanogen chloride has been variously described as a gas and a liquid. Possibly two forms of the liquid exist which boil at -12° C. and +12.7° C. (Regnault) or 15.5° C. (Wurtz) respectively. The vapour density is in either case 2.13, which corresponds to the molecular formula CNCl. The vapour has an irritating smell.

Liquid cyanogen chloride solidifies at -18° C. (Regnault) to a mass of long, transparent prisms which melt at -7° C. or, according to Wurtz, at -12° C. to -15° C.

The heat of formation of cyanogen chloride is +26,900 calories, and its heat of combustion 126,000 calories. This compound dissolves in water without decomposition, also in various organic solvents.

In the pure state cyanogen chloride is stable, though under certain conditions it polymerises into cyanuric chloride (CNCl)₃. Alkalis decompose it into a mixture of cyanate and chloride:

CNCl + 2KOH = KCNO + KCl + H₂O,

and ammonia solution forms cyanamide and ammonium chloride:

CNCl + 2NH₃ = CN-NH₂ + NH₄Cl.

Cyanogen chloride forms the additive compounds BCl₃.CNCl and TiCl₄.CNCl; it is a synthetic agent in organic chemistry.