HYDROGENIZATION OF SUBSTITUTED NITRO-, AZOBENZENES, THEIR MIXTURE AND SUBSTITUTED NITROAZOBENZEN ON SKELETAL NICKEL IN AQUEOUS 2-PROPANOL SOLUTIONS

Abstract

The article is devoted to the investigation of the hydrogenation of 4-nitroaniline, 4-amino-2'-hydroxy-5'-methylazobenzene, their mixture and 4-nitro-2'-hydroxy-5'-methylazobenzene on skeletal nickel in an aqueous solution of 2-propanol with azeotropic composition (x2 = 0.68) and this solvent with the addition of acid (0.01 M CH3COOH) or sodium hydroxide (0.01 M NaOH). The elucidation of the reasons and the development of approaches to the selective control of the staged transformations of substituted nitroazobenzenes containing two reactive groups in a molecule under the conditions of hydrogenation are of interest from theoretical and practical points of view. The rate of formation of intermediate products during the hydrogenation of nitroazobenzenes is largely determined by the activation of nitro and azo groups. The aim of the work is to conduct a comparative analysis of the rates of conversion of nitro- and azogroups in individual compounds with the rates of hydrogenation of their mixture and the rate of conversion of nitroazobenzene, which simultaneously contains nitro- and azogroups, to discuss the reasons for the influence of the solvent composition on the conversion rates of mono- and disubstituted benzenes. UV-spectroscopic data indicate that the electronic state of the hydrogenated compounds in the solvent compositions used does not undergo significant changes, since the absorption maxima are shifted by no more than 1 nm, both with the addition of acid and base. On the contrary, the observed rates of hydrogenation of mono- and disubstituted benzenes vary within fairly wide limits. A comparative analysis of the rates of hydrogenation of individual compounds, their mixtures and disubstituted benzene allows us to conclude that the priority of reduction of one or another group in 4-nitro-2'-hydroxy-5'-methyl-azobenzene can be made on the basis of calculating the quantitative ratio of the reaction products. When a mixture of compounds containing nitro and azo groups is hydrogenated, their adsorption rather than reactivity begins to play the primary role.