Nano-Catalysis in the Selective Oxidation of Alcohols and Anilines

Recently, the development of eco-friendly and sustainable organic redox reactions has attracted considerable attention. In the classification of catalysis, the two categories, homogeneous and heterogeneous catalysis, have their own advantages and limitations. Thus, we need catalytic species that show properties like homogeneous and heterogeneous catalysts. Nano-catalysts fulfill the above requirements as it works as a “linker" between the homogeneous and heterogeneous catalysts. In past years, various heterogeneous nanomaterials have been used in different organic transformations as green catalysts due to their larger surface area and smaller size. Most importantly, nano-catalysts are the modern catalysts that promise green synthesis. Methods: Selective oxidation of alcohols to carbonyl compounds is essential due to the wide applications of carbonyl compounds in pharmaceutical, agrochemical, fragrances, food industries, and electronic industries. Traditional methods for the synthesis of carbonyl compounds require a large number of oxidants; homogeneous catalysts, heavy metal catalysts, and precious metal supports are used. Further, aromatic azo compounds, composed of two phenyl groups interconnected by nitrogen-nitrogen double bonds, are well-known chromophores that have important applications in the synthesis of dyes, pigments, indicators, chemosensors, radical initiators, food additives, and therapeutic, diagnostic, and pro-drug agents as well as building blocks of various polymers and natural products. These compounds exhibited photophysical properties and significant applications in electronics and optics. Several methods have been developed for the preparation of aromatic azo compounds. Moreover, the selective oxidation of aniline is an important and useful organic reaction for the synthesis of oxygenated compound such as azoxybenzenes. Azoxybenzenes have attracted special importance as synthetically useful intermediates, precursors and employed as dyes, reducing agents, chemical stabilizers, and polymerization inhibitors, liquid crystals displays and therapeutic medicines. Here, some green approaches have discussed for the preparation of azoxy compounds. Conclusion: This review focused on the recent green methods for the selective oxidation of alcohols to carbonyl compounds and direct oxidative azo-coupling of anilines to aromatic azo and azoxy compounds using heterogeneous nano-based catalysts.