Note 44 bis — Chapter XII · SODIUM

Sodamide, NH2Na, (Chapter IV., Note 14), discovered by Gay-Lussac and Thénard, has formed the object of repeated research, but has been most fully investigated by A. W. Titherley (1894). Until recently the following was all that was known about this compound:—

By heating sodium in dry ammonia, Gay-Lussac and Thénard obtained an olive-green, easily-fusible mass, sodamide, NH₂Na, hydrogen being separated. This substance with water forms sodium hydroxide and ammonia; with carbonic oxide, CO, it forms sodium cyanide, NaCN, and water, H₂O; and with dry hydrogen chloride it forms sodium and ammonium chlorides. These and other reactions of sodamide show that the metal in it preserves its energetic properties in reaction, and that this compound of sodium is more stable than the corresponding chlorine amide. When heated, sodamide, NH₂Na, only partially decomposes, with evolution of hydrogen, the principal part of it giving ammonia and sodium nitride, Na₃N, according to the equation 3NH₂Na = 2NH₃ + NNa₃. The latter is an almost black powdery mass, decomposed by water into ammonia and sodium hydroxide.

Titherley's researches added the following data:—

Iron or silver vessels should be used in preparing this body, because glass and porcelain are corroded at 300°–400°, at which temperature ammonia gas acts upon sodium and forms the amide with the evolution of hydrogen. The reaction proceeds slowly, but is complete if there be an excess of NH₃. Pure NH₂Na is colourless (its colouration is due to various impurities), semi-transparent, shows traces of crystallisation, has a conchoidal fracture, and melts at 145°. Judging from the increase in weight of the sodium and the quantity of hydrogen which is disengaged, the composition of the amide is exactly NH₂Na. It partially volatilises (sublimes) in vacuo at 200°, and breaks up into 2Na + N₂ + 2H₂ at 500°. The same amide is formed when oxide of sodium is heated in NH₃: Na₂O + 2NH₃ = 2NaH₂N + H₂O. NaHO is also formed to some extent by the resultant H₂O. Potassium and lithium form similar amides. With water, alcohol, and acids, NH₂Na gives NH₃ and NaHO, which react further. Anhydrous CaO absorbs NH₂Na when heated without decomposing it. When sodamide is heated with SiO₂, NH₃ is disengaged, and silicon nitride formed. It acts still more readily upon boric anhydride when heated with it: 2NH₂Na + B₂O₃ = 2BN + 2NaHO + H₂O. When slightly heated, NH₂Na + NOCl = NaCl + N₂ + H₂O (NHNa₂ and NNa₃ are apparently not formed at a higher temperature). The halogen organic compounds react with the aid of heat, but with so much energy that the reaction frequently leads to the ultimate destruction of the organic groups and production of carbon.