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Cyanamide, CNNH2

Cyanamide, CN-NH2 is formed, according to a common way of preparing amides, by the action of ammonia on the chloride:

CNCl + 2NH3 = CNNH2 + NH4Cl;

it is also conveniently obtained from thiourea by the removal from it of H2S through the agency of precipitated mercuric oxide:

CS(NH2)2 + HgO = CNNH2 + HgS + H2O.

The mercuric oxide is added to an aqueous solution of thiourea until a drop of the liquid ceases to darken ammoniacal silver nitrate solution by formation of Ag2S. The filtered solution is then evaporated and extracted with ether, whence cyanamide crystallises.

Cyanamide melts at 40° C., and can be distilled at 143°-144° C. under 18 mm. pressure. It is deliquescent, is volatile in steam, and is converted by very dilute nitric acid into urea:

CNNH2 + H2O = CO(NH2)2.

Like the amides of other weak acids, cyanamide possesses both basic and acidic properties. The dihydrochloride, CNNH2.2HCl, is formed as a crystalline powder when hydrogen chloride gas is passed into an ethereal solution of cyanamide; on the other hand, the di-silver salt CN-NAg2 is precipitated as a yellow powder when ammoniacal silver nitrate is added to an aqueous solution of cyanamide. Likewise the monosodium salt CN-NHNa is formed when sodium ethoxide reacts with alcoholic cyanamide.

Calcium cyanamide mixed with carbon is produced, rather than calcium cyanide, when nitrogen is passed over calcium carbide heated in an electric furnace:

CaC2 + N2 = CN-NCa + C.

The product known as "Kalkstickstoff" or "Nitrolim" is employed as a nitrogenous manure.

Calcium cyanamide is hydrolysed by cold water with the formation of dicyanamide:

2CaN-NC + 4H2O = 2Ca(OH)2 + NH:C(NH2)(NH-CN)

When carbon dioxide is passed through this solution calcium cyanamidocarboxylate, , is produced.

Under the influence of heat cyanamide polymerises to dicyanamide, NH:C(NH2)(NHCN), and cyanuramide, (CN-NH2)3.

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