The Influence of Substituenta on (1) the Decomposition of Diazo Compounds in Acid and Alkaline Solution, and (2) the Alkaline Reduction of Aromatic Nitro Compounds

Abstract

Conductivity data indicate that diazonium ions in acid solution conatitute the greater part of the diazonium‐diazo equilibrium‐these are stabilimd by kationoid and destabiliaed by anionoid substituenta. Tn alkaline solution, the more complex system‐when disturbed (e.g. by evolution of nitrogen from (I), or by hydrolysis of (IXI), etc.), will them be further upset by the reactivity of (11) with the products from (I) and (111). Kationoid substituents will confer greater reactive power on the diazohydroxides (11) than anionoid aubstituenta, so that the ultimate rate of decomposition of the alkaline system will be enhanced in the revem direction to that in acid solution. This viewpoint explains Jolles' results, on the stability of alkaline diaaoates, and his work on diazo resins is also briefly discussed.(2) Unlike reduction of aromatic nitro compounds direct to aminen in acid solution, the reduction in alkaline media is complicated by the alrlol condelaeation of the second (nitroso) with the third (hydroxylamino) reduction product to form a latively stable azoxy compound. Anionoid substituents will, therefore, tend to inhibit further reduction by making the azoxy compound, and subsequently the azo compound, more anionoid towards the anionoid reducing agent, while kationoid substituents will have the reverse effect. The anomalous caae of the reduction of p‐dinitrobeme by sodium hydrosulphidele mainly to pp′‐dinitroazobenzeneis discussed, and found to depend on solvent ection on the nitro group.