Desenvolvimento de uma metodologia para redução de grupamentos nitro utilizando o catalisador Lacob-Pd4

Abstract

Aromatic amines are valuable organic molecules that can be used in the synthesis of bioactive compounds, polymers, drugs, dyes and pharmaceuticals. However, it is worth mentioning that the traditional methods of obtaining these amines have been marked by major obstacles, due to the use of toxic solvents, long reaction times, high catalyst load, among other factors. In this context, reduction reactions via hydrogenation of the nitro group catalyzed by heterogeneous metallic catalysts based on Pd, Pt, Ni, Au, Fe, among others, have become a fast and efficient alternative for obtaining aromatic amines. However, many of these catalysts used in reduction reactions suffer from selectivity problems or need high temperatures to perform their functions. In this sense, the present work developed a methodology based on the principles of green chemistry, selective and efficient, for the reduction of nitro groups to amino used using a palladium-based catalyst (LACOB-Pd4). Therefore, after choosing the solvent (ethanol and water 1:1) and the reducing agent (NaBH4), the methodology was successfully applied to the reduction of nitrobiphenyls. The yields obtained ranged from 56 to >99% for a reaction time of five hours at room temperature, demonstrating the catalytic efficiency of LACOB-Pd4. Finally, the methodology was extended to different substrates (diphenyl ether, methyl benzoate, acetanilide, thiosalicylic acid derivatives, nitrostyrene and imino sugar) containing the nitro group, in order to evaluate the selectivity of the catalyst. The selectivity test results were positive with yields between 50 to >99%. However, it is worth noting that among the advantages of the developed methodology are: the use of ecologically sustainable solvents (a mixture of water/ethanol (1:1)), good yields (56 to >99%), short reaction time (5h), low amount of catalyst mass (0.001 to 0.002 mg) and reactions carried out at room temperature.