LIQUID-PHASE HYDROGENATION OF 2-NITRO-2'-HYDROXY-5'-METHYLAZOBENZENE ON SKELETAL NICKEL TO OBTAIN A PHOTO-STABILIZING COMPOSITION

A mixture of 2-2'-hydroxy-5'-methylphenylbenzotriazole and its hydrogenation product 4,5,6,7-tetrahydro-2'-hydroxy-5'-methylphenylbenzotriazole in a molar ratio of 3:2 has a stronger photostabilizing effect than the source components. To prepare such a composition, individual compounds are required, each of which can be obtained as a result of liquid-phase catalytic hydrogenation of the corresponding reagents. 2-2'-Hydroxy-5'-methylphenylbenzotriazole is a product of hydrogenation of 2-nitro-2'-hydroxy-5'-methylazobenzene, and 4,5,6,7-tetrahydro-2'-hydroxy-5'-methylphenylbenzotriazole, as noted above, formed by hydrogenation of 2-2'-hydroxy-5'-methylphenylbenzotriazole. However, it seems more expedient to obtain a mixture of a given composition directly during hydrogenation of the nitroazoderivative without precipitation of the substituted benzotriazole. Thus, the study of the influence of temperature, hydrogen pressure and catalyst amount on the kinetic regularities and selectivity of the 2-nitro-2'-hydroxy-5'-methylazobenzene hydrogenation according to the above compounds is of scientific interest and has practical significance. A skeletal nickel was used as a catalyst, and a 1 M aqueous solution of sodium hydroxide with an additional amount of NaOH necessary to convert the initial reagent into a phenolate was used as a liquid phase. The work considers the dependences of the reaction rate, process time, volume of absorbed hydrogen, and yields of products containing the benzotriazole cycle on the above mentioned process parameters. It is shown that an increase in temperature, hydrogen pressure, and also the amount of catalyst or the mass ratio of catalyst:reagent leads to an increase in the yield of 4,5,6,7-tetrahydro-2'-hydroxy-5'-methylphenylbenzotriazole. The most noticeable effect on the total yield of 2-2'-hydroxy-5'-methylphenylbenzotriazole and its tetrahydroderivative exerts hydrogen pressure. It was established that the dependence of the molar ratio of 2-2'-hydroxy-5'-methylphenylbenzotriazole:4,5,6,7-tetrahydro-2'-hydroxy-5'-methylphenylbenzotriazole on temperature and hydrogen pressure passes through a maximum, and with an increase in the amount of catalyst this ratio decreases. The optimal conditions for obtaining a mixture with a yield of 60-63% at a molar ratio of components within 1-2 are: temperature – 353-363 K, hydrogen pressure – 1.2-1.5 MPa and a catalyst: reagent mass ratio equal to 0.10-0.15. For citation: Lefedova O.V., Nemtzeva M.P. Liquid-phase hydrogenation of 2-nitro-2'-hydroxy-5'-methylazobenzene on skeletal nickel to obtain a photo-stabilizing composition. ChemChemTech [Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol.]. 2025. V. 68. N 9. P. 106-114. DOI: 10.6060/ivkkt.20256809.7267.