Silica Sulphuric Acid Catalyzed Fischer Esterification Reaction under Solventless Condition: A Novel Green Chemical Reaction

Abstract

Objectives: The science of chemistry has matured, and green chemistry emphasizes the creative use and design of chemicals. The main objective of this work is to carryout Fisher esterification reactions using silica sulphuric acid ionic liquid in such a way that they have little or no pollution potential or environmental risk and are both economically and technologically feasible. The aim is to prove the catalytic efficiency of silica sulphuric acid ionic liquid as a green chemical. Study design: Fisher esterification reaction using silica-sulphuric acid ionic liquid as a catalyst under solventless condition. Place and Duration of Study: Department of Chemistry, Sir Theagaraya College, Chennai-21, Tamilnadu, India, between July 2009 and September 2010. Methodology: It involves five stages. First stage is the synthesis of silica sulphuric acid ionic liquid in an eco-friendly way by the reaction of silica gel and chlorosulphonic acid .It is interesting to note that the reaction is easy, clean and not requiring any work-up procedure. Second stage is the Fisher esterification reaction of a variety of carboxylic acids and alcohol utilizing silica sulphuric acid. Third stage is the purification of products by chromatographic techniques. The fourth stage id the characterization of all the products by spectral methods. Fifth stage is the comparison of the catalytic efficiency of silica sulphuric acid with the conventional sulphuric acid catalyst. Results: The silica supported sulphuric acid is bench top reagent which is easy to handle with better accessibility of the reactants to the active sites. Fisher esterification reactions were completed with excellent yields (97 - 99%) within 1.5 - 8 hr at the temperature range of 80-135oC. The reaction does not require any additional catalyst because the ionic liquid itself acts as a catalyst and solvent as well in these experiments, the products were isolated and the remaining catalyst was washed and reloaded with fresh substrates. When similar reactions were carried out in sulphuric acid (conventional acid catalyst), a mixture of products was obtained in poor yields One of the greatest advantages of the reagent sio2.oso3h is that it is recoverable and reusable for several times without potential loss in its catalytic activity. Conclusion: The results indicated that the silica sulphuric acid exhibited excellent catalytic activity for the esterification reaction and better yield (with high degree of purity) under mild reaction conditions than those reactions without ionic liquid. After the reaction was over, the ionic liquid was regenerated and reused with no appreciable change in activity. In conclusion the present method is a very efficient and selective protocol for esterification reactions of carboxylic acids with alcohols and a high yield synthesis of the required ester in the presence of reversible and environmentally benign catalyst. Simple work-up procedure, including washing the mixture followed by evaporation of the solvent is another advantage of this method.