마이크로파 조사 조건에서 H5PW10V2O40과 H5PMo10V2O40을 촉매로 사용하여 알코올로부터 아세트산 알킬을 합성하기(Part 2)

Abstract

Esters are important chemical compounds which can be synthesized via esterification of carboxylic acids with alcohols. The conversion of alcohol to ester as an important industrial functional group transformation is generally catalyzed by usual mineral acids. Considering the importance of environmental health problems in chemical technology, the eco-friendly green approaches have been expanded with the aim to diminish generation of unwanted hazardous and dangerous byproducts. Accordingly, the practical feasibility of microwave assisted solvent-free protocols in various organic transformations by the mediation of inorganic catalysts provided a number of advantages of environmental interest, including easy isolation and recovery from the reaction medium. Keggin-type heteropolyoxovanadates with the general formula of H3+xPM12-xVxO40 (M= W, Mo and x = 0, 1, 2 and 3) are known to exhibit interesting physical and chemical properties with relevance to catalysis, biochemical processes, and materials science. These types of heteropolyoxometalates are strong Bronsted acid and most of them are stronger in acidity than the usual inorganic acids (HCl, H2SO4, HNO3, HBr etc), even stronger than HClO4 and CF3SO3H. This is of fundamental importance for their applications in acid catalysis. The difference in the acid strength between heteropoly acids and typical inorganic acids can be due to the fact that heteropoly anions are large anions bearing high negative charge density than inorganic acids. Therefore, the strength of bonding between the proton and heteropoly anions should be lower, which implies that the dissociation constants should be lower compared to the usual acids. Polyoxometalates show acidity as well as oxidative ability and can be protably used in homogeneous, biphasic, or heterogeneous systems. Herein, in continuation of our ongoing research program on using heteropolyoxometalates in organic synthesis, we wish to describe the protection of alcohols under the environmentally benign microwave approach by the mediation of H5PMo10V2O40 and H5PW10V2O40 as vanadium-containing mixed-addenda heteropolyoxometalates with Keggin primary structure.