Cyanogen Bromide (Bromocyanogen), CNBr, resembles Cyanogen Chloride, CNCl in its manner of preparation, being formed by the action of bromine on hydrocyanic acid or a cyanide. It forms transparent prisms by sublimation, which pass into a cubical form; it melts at 52° C., and boils at 61.3° C.; its vapour density is 3.607; it is poisonous, and its vapour is pungent and affects the eyes. The heat of formation of CNBr from its elements is -37,000 calories, and from (CN)2 and Br2 +40,000 calories. It easily polymerises to (CNBr)3.
In dilute aqueous solution cyanogen bromide shows no evidence of ionisation. Hydrogen sulphide reacts quantitatively with it, thus:
CN-Br + H2S = HCN + HBr + S;
and the following reactions are also characteristic:
2KOH + CNBr = KBr + KCNO + H2O
Na2SO3 + CNBr + H2O = NaBr + NaCN + H2SO4
HI + CNBr = IBr + HCN; IBr + HI = HBr + I2
K2S + CNBr = KBr + KSCN.
A theory of the mechanism of these reactions is given by Dixon and Taylor. |