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Azidodithiocarbonic Acid, HS.CS.N3

Azidodithiocarbonic Acid, HS.CS.N3, has been prepared by allowing sodium azide, NaN3, dissolved in a little water, to react with carbon disulphide; after keeping the mixture in a stoppered vessel at 40° C. for 48 hours, the resulting solution on treatment with concentrated hydrochloric acid at 0° C. yields a white or very pale yellow crystalline precipitate of the azido-acid. The crystals belong to the monoclinic system. The acid is fairly soluble in water, more soluble in organic solvents. It has the characteristic properties of a strong acid, and it is oxidised by various agents, yielding azido carbon disulphide, (S.CS.N3)2, some sulphate also being formed. At ordinary temperatures the acid undergoes spontaneous decomposition with formation of thiocyanic acid as an intermediate product,

HS.CS.N3 = HCNS + S + N2;

the resulting solid product consists of a mixture of polymerised thiocyanic acid and free sulphur.

The alkali azidodithiocarbonates may be obtained by the action of carbon disulphide vapour on an aqueous solution of the alkali azide at 40° C. With a 1 per cent, solution of sodium azide the action proceeds quantitatively:

NaN3 + CS2 = NaS.CS.N3.

If the SCSN3-group be considered as a unit, azidodithiocarbonic acid may be regarded as a halogenoid hydracid having the same relation to azido carbon disulphide as hydrogen chloride bears to chlorine, and undergoing ionisation in solution in accordance with:

HSCSN3H + SCSN3'.

Azido carbon disulphide, (S.CS.N3)2, may be prepared by the oxidation of the foregoing compound or its salts. It is a white, crystalline solid, very sparingly soluble in water. At ordinary temperatures it decomposes spontaneously, yielding nitrogen, sulphur and a polythiocyanogen:

(S.CS.N3)2 = 2N2 + 2S + (SCN)2.

It reacts with caustic potash in much the same manner as a halogen, forming the potassium salts of azidodithiocarbonic acid and azido-oxydithiocarbonic acid:

(S.CS.N3)2 + 2KOH = KS.CS.N3 + KOS.CS.N3 + H2O.

Potassium azide reacts with iodine in the presence of carbon disulphide to form potassium iodide and nitrogen as the final products, but the reaction appears to proceed according to the following scheme:
  1. KN3 + CS2 = KS.CS.N3,
  2. 2KS.CS.N3 + 2I = (S.CS.N3)2 + 2KI,
  3. 2KN3 + (S.CS.N3)2 = 2KS.CS.N3 + 3N2,
    or (S.CS.N3)2 = 2CS2 + 3N2.
The reaction is facilitated by the presence of alcohol or acetone, and it may be used for the determination of azides. The catalytic effect of sulphides and thiosulphates on this reaction has already been mentioned.

The following formula has been suggested for azido carbon disulphide:

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