Note 28 bis — Chapter VI · TTHE COMPOUNDS OF NITROGEN WITH HYDROGEN AND OXYGEN
George Kamensky translation
Curtius started with benzoylhydrazine, C6H5CONHNH2 (hydrazine, see Note 20 bis). (This substance is obtained by the action of hydrated hydrazine on the compound ether of benzoic acid). Benzoylhydrazine under the action of nitrous acid gives benzoylazoimide and water:
C6H5CONHNH2 + NO2H = C6H5CON3 + 2H2O.
Benzoylazoimide when treated with sodium alcoholate gives the sodium salt of hydronitrous acid:
C6H5CON3 + C2H3ONa = C6H5O2C2H3 + NaN3.
The addition of ether to the resultant solution precipitates the NaN3, and this salt when treated with sulphuric acid gives gaseous hydronitrous acid, HN3. It has an acrid smell, and is easily soluble in water. The aqueous solution exhibits a strongly acid reaction. Metals dissolve in this solution and give the corresponding salts. With hydronitrous acid gaseous ammonia forms a white cloud, consisting of the salt of ammonium, NH4N3. This salt separates out from an alcoholic solution in the form of white lustrous scales. The salts of hydronitrous acid are obtained by a reaction of substitution with the sodium or ammonium salts. In this manner Curtius obtained and studied the salts of silver (AgN3), mercury (HgN3), lead (PbN6), barium (BaN6). With hydrazine, N2H4, hydronitrous acid forms saline compounds in the composition of which there are one or two particles of N3H per one particle of hydrazine; thus N5H5 and N8H6. The first was obtained in an almost pure form. It crystallises from an aqueous solution in dense, volatile, lustrous prisms (up to 1 in. long), which fuse at 50°, and deliquesce in the air; from a solution in boiling alcohol it separates out in bright crystalline plates. This salt, N5H5, has the same empirical composition, NH, as the ammonium salt of hydronitrous acid, N4H4, and imide; but their molecules and structure are different. Curtius also obtained (1893) hydronitrous acid by passing the vapour of N2O5 (evolved by the action of HNO3 on As2O3) into a solution of hydrazine, N2H4. Similarly Angeli, by acting upon a saturated solution of silver nitrite with a strong solution of hydrazine, obtained the explosive AgN3 in the form of a precipitate, and this reaction, which is based upon the equation N2H4 + NHO2 = HN3 + 2H2O, proceeds so easily that it forms an experiment for the lecture table. A thermal investigation of hydronitrous acid by Berthelot and Matignon gave the following figures for the heat of solution of the ammonium salt N3HNH3 (1 grm. in 100 parts of water) -708 C., and for the heat of neutralisation by barium hydrate +10·0 C., and by ammonia +8·2 C. The heat of combustion of N4H4 (+163·8 C. at a constant vol.) gives the heat of formation of the salt N4H4 (solid) as - 25·3 C. and (solution) - 32·3 C.; this explains the explosive nature of this compound. In its heat of formation from the elements N3H = -62·6 C., this compound differs from all the hydrogen compounds of nitrogen in having a maximum absorption of heat, which explains its instability.