Highly efficient, solvent-free esterification of testosterone promoted by a recyclable polymer-supported tosylic acid catalyst under microwave irradiation

Abstract

Although the classical acylation of testosterone clearly benefits from a broad substrate scope and available catalysts, the requirement of hazardous reagents and the high waste production are its drawbacks. To optimize the process efficiency as well as minimize the environmental impact, we decided to develop a novel method of testosterone esters synthesis, which relies on the usage of recyclable heterogeneous polymer-supported tosylic acid catalyst and microwave-assistance effect in a non-solvent system. Under the established MW-conditions, the acceleration of the process rate was so efficient that the reaction completed within 2.5 min, thus affording the desired esters in the 33–96% yield range without using a work-up procedure. Furthermore, the elaborated catalytic system could be recycled for at least 2 runs not only without a loss of the products yield, but unexpectedly with significant improvement of the reaction efficiency, which may indicate that the reduction of the catalyst loading is possible. We believe that this finding constitutes a very good starting-point for further optimization of the studied process.