Uniform Copper Nanoparticles on Tunable Porous N-Doped Carbon Nanospheres for Esterification of Various Aryl Aldehydes with Alcohols

Synthesis of esters as an important intermediate from carboxylic acids or aldehydes is one ofthe popular transformations in organic chemistry [1]. Traditionally base/acid homogeneouscatalysts were applied for the direct esterification of carboxylic acids. In the recent years, heterogeneouscatalysts had also been reported which most of these catalytic systems are presentacidic nature. Metal oxides such as Al2O3, Fe3O4, SnO, ZnO, CaO, ZnO–La2O3, sulfated zirconia,and sulfated carbon were used for catalytic synthesis of esters from carboxylic acidsand alcohols. In the last years, carbon with attractive properties such as porous structure, excellentelectrical conductivity, and high stability find widespread applications as support incatalysts [2]. It is well known that structural modifications on the surface of carbon can effectivelychange the nature of the catalysts. Heteroatom doping strategy can control the intrinsicreactivity of the active metallic sites [3]. Among different dopants, nitrogen is the most intensivelyinvestigated. In this paper, we have prepared highly monodispersed, nitrogen-dopedporous carbon nanospheres as a solid ligand for generation of Cu nanoparticles for esterificationof various aryl aldehydes with primary, secondary and tertiary alcohols (Fig. 1). Generally,nitrogen doping provides basic properties, which can enhance the interaction between substratesand carbon surfaces. Also, nitrogen doping was able to increase the hydrophilicity ofcatalyst which led to the high dispersion ability of catalytic system in aqueous media.