INFLUENCE OF ADDITIVES OF ACID ON STAGE OF TRANSFORMATIONS OF 4-NITRO-2'-HYDROXY-5'-METHYLASOBENZENE ON SKELETONIC NICKEL IN WATER SOLUTION OF 2-PROPANOL
Authors: Anh Hoang , Lefedova Olga V. , Belova Alexandra.V. 
Published: May 2020

The article is devoted to the analysis of the reaction kinetics of hydrogenation of 4-nitro-2'-hydroxy-5'-methylazobenzene in an aqueous solution of 2-propanol with acetic acid addition on skeletal nickel at different initial quantity of the starting compound. Clarification of the sequence of transformations of compounds containing several reactive groups, and the development of approaches to controlling the selectivity of processes with their participation is a practically significant task. According to the data obtained, at both low and high initial concentrations the hydrogenation of 4-nitro-2'-hydroxy-5'-methylazobenzene on skeletal nickel in a 2-propanol aqueous solution-0.01 M CH3COOH solvent proceeds in two parallel directions. The largest contribution in the first phase of the reaction is made by the azo group conversion of the starting compound, in contrast to the reaction in an aqueous solution of 2-propanol without acid addition. An increase in the initial quantity of the hydrogenated compound above its solubility limit leads to an increase in the rate of conversion of the azo group in 4-nitro- and 2-amino-2'-hydroxy-5'-methylazobenzene. Consequently, optimum quantity of 4-nitroaniline and 2-amino-2'-hydroxy-5'-methylazobenzene in the bulk solution during hydrogenation of the specified quantity of 4-nitro-2'-hydroxy-5'-methylazobenzene practically didn’t change, in contradiction to the hydrogenation on skeletal nickel in a neutral aqueous solution of 2-propanol. In a neutral aqueous solution of 2-propanol, when passing to high concentrations of the hydrogenated compound, the maximum yield of 4-nitroaniline increases twice as long the better, while as 4-amino-2'-hydroxy-5'-methylazobenzene, is reduced conversely. The results obtained do not contradict the concept of a parallel-sequential scheme for the conversion of 4-nitro-2'-hydroxy-5'-methylazobenzene. One of the directions involves the conversion of 4-nitro-2'-hydroxy-5'-methylazobenzene through 4-nitroaniline and 2-amino-4-methylphenol due to the hydrogenation of the azo group, and the second is the conversion of 4-nitro-2'-hydroxy-5'- methylazobenzene via 4-amino-2'-hydroxy-5'-methylazobenzene by reduction of the nitro group. At the end of the reaction, all the intermediate compounds are reduced to 2-amino-4-methylphenol and 1,4-phenylenediamine. When acetic acid is introduced into the composition of the neutral solvent 2-propanol-water, the contribution of the direction that ensures the formation of 4-nitroaniline and 2-amino-4-methylphenol to the overall reaction rate increases. An increase in the initial amount of 4-nitro-2′-hydroxy-5′-methyl-azobenzene leads to an increase in the rate of conversion of the azo group in the starting compound and to a decrease in the rate of conversion of 4-amino-2′-hydroxy-5′-methylazobenzene. The effect of the acid on the change in the conversion rates of nitro and azo groups to 4-nitro-2′-hydroxy-5′-methylazobenzene does not contradict the previously obtained results for the hydrogenation of its analogue, 2-nitro-2′-hydroxy-5-methylazobenzene, as well as individual compounds containing a nitro and azo group.