Influence of sodium hydroxide additives on hydrogenization kinetics of 4-nitro-2'-hydroxy-5'-metylazobenzene on skeletal nickel in aqueous solution of 2-propanol

The elucidation of the sequence of transformations in compounds containing several reactive groups and the development of approaches to controlling the selectivity of the processes with their participation is of interest both from the theoretical and practical points of view. The article is devoted to the analysis of the kinetics of hydrogenation of 4-nitro-2'-hydroxy-5'-methylazobenzene in aqueous solution of 2-propanol with addition of sodium hydroxide on skeletal nickel at different initial amounts of the starting compound. An increase in the initial amount of 4-nitro-2'-hydroxy-5'-methylazobenzene leads to an increase in the rate of conversion of the nitro group in the starting compound and to a decrease in the rate of conversion of the azo-group. The effect of the introduced sodium hydroxide in the neutral solvent 2-propanol-water on the rate of conversion of the nitro and azo-groups to 4-nitro-2'-hydroxy-5'-methylazobenzene is consistent with the nature of the rate changes for the hydrogenation of individual compounds containing nitro and azo-groups, in the quality of which 4-nitroaniline and 4-amino-2'-hydroxy-5'-methylazobenzene were chosen. The results obtained do not contradict the notion of a parallel-sequential scheme of 4-nitro-2'-hydroxy-5'-methylazobenzene transformations. One of the directions involves the conversion of 4-nitro-2'-hydroxy-5'-methylazobenzene due to the hydrogenation of the azo-group to 4-nitroaniline and PC, and the second one is the conversion of 4-nitro-2'-hydroxy-5'-methylazobenzene through 4-amino-2'-hydroxy-5'-methylazobenzene due to the reduction of the nitro group. By the end of the reaction, all the intermediate compounds are restored to PC and 1,4-phenylenediamine. When sodium hydroxide is introduced into the neutral solvent 2-propanol-water, the effect of the direction providing the formation of 4-amino-2'-hydroxy-5'-methylazobenzene to the overall reaction rate increases. It was experimentally established that the amount of 4-amino-2'-hydroxy-5'-methylazobenzene during the hydrogenation of 4-nitro-2'-hydroxy-5'-methylazobenzene in the presence of sodium hydroxide increases by 15%, on the contrary, the amount of 4-nitroaniline decreases by 4 % in comparison with the neutral solvent.FWN – Publicaties zonder aanstelling Universiteit Leide