Note 29 — Chapter XI · THE HALOGENS: CHLORINE, BROMINE, IODINE, AND FLUORINE

The hydrochloric acid formed combines with ammonia, and therefore the final result is 4NH3 + 3Cl2 = NCl3 + 3NH4Cl. For this reason, more ammonia must enter into the reaction, but the metalepsical reaction in reality only takes place with an excess of ammonia or its salt. If bubbles of chlorine be passed through a fine tube into a vessel containing ammonia gas, each bubble gives rise to an explosion. If, however, chlorine be passed into a solution of ammonia, the reaction at first brings about the formation of nitrogen, because chloride of nitrogen acts on ammonia like chlorine. But when sal-ammoniac has begun to form, then the reaction directs itself towards the formation of chloride of nitrogen. The first action of chlorine on a solution of sal-ammoniac always causes the formation of chloride of nitrogen, which then reacts on ammonia thus: NCl3 + 4NH3 = N2 + 3NH4Cl. Therefore, so long as the liquid is alkaline from the presence of ammonia the chief product will be nitrogen. The reaction NH4Cl + 3Cl2 = NCl3 + 4HCl is reversible; with a dilute solution it proceeds in the above-described direction (perhaps owing to the affinity of the hydrochloric acid for the excess of water), but with a strong solution of hydrochloric acid it takes the opposite direction (probably by virtue of the affinity of hydrochloric acid for ammonia). Therefore there must exist a very interesting case of equilibrium between ammonia, hydrochloric acid, chlorine, water, and chloride of nitrogen which has not yet been investigated. The reaction NCl3 + 4HCl = NH4Cl + 3Cl2 enabled Deville and Hautefeuille to determine the composition of chloride of nitrogen. When slowly decomposed by water, chloride of nitrogen gives, like a chloranhydride, nitrous acid or its anhydride, 2NCl3 + 3H2O = N2O3 + 6HCl. From these observations it is evident that chloride of nitrogen presents great chemical interest, which is strengthened by its analogy with trichloride of phosphorus. The researches of F. F. Selivanoff (1891–94) prove that NCl3 may be regarded as an ammonium derivative of hypochlorous acid. Chloride of nitrogen is decomposed by dilute sulphuric acid in the following manner: NCl3 + 3H2O + H2SO4 = NH4HSO4 + 3HClO. This reaction is reversible and is only complete when some substance, combining with HClO (for instance, succinimide) or decomposing it, is added to the liquid. This is easily understood from the fact that hypochlorous acid itself, HClO, may, according to the view held in this book, be regarded as the product of the metalepsis of water, and consequently bears the same relation to NCl3 as H2O does to NH3, or as RHO to RNH2, R2NH, and R3N—that is to say, NCl3 corresponds as an ammonium derivative to ClOH and Cl2 in exactly the same manner as NR3 corresponds to ROH and R2. The connection of NCl3 and other similar explosive chloro-nitrogen compounds (called chloryl compounds by Selivanoff; for example, the C2H5NCl2 of Wurtz is chloryl ethylamine), such as NRCl2 (as NC2H5Cl2), and NR2Cl (for instance, N(CH3CO)HCl, chlorylacetamide, and N(C2H5)2Cl, chloryl diethylamine) with HClO is evident from the fact that under certain circumstances these compounds give hypochlorous acid, with water, for instance, NR2Cl + H2O = NR2H + HClO, and frequently act (like NCl3 and HClO, or Cl2) in an oxidising and chloridising manner. We may take chloryl succinimide, C2H4(CO)2NCl for example. It was obtained by Bender by the action of HClO upon succinimide, C2H4(CO)2NH, and is decomposed by water with the re-formation of amide and HClO (the reaction is reversible). Selivanoff obtained, investigated, and classified many of the compounds NR2Cl and NRCl2, where R is a residue of organic acids or alcohols, and showed their distinction from the chloranhydrides, and thus supplemented the history of chloride of nitrogen, which is the simplest of the amides containing chlorine, NR3, where R is fully substituted by chlorine.