Covalently anchored chlorosulfonyl-calix[4]arene onto silica gel as an efficient and reusable heterogeneous system for reduction of ketones using NaBH4

Abstract

The catalytic activities of chlorosulfonyl-calix[4]arene-bonded silica gel (CSC[4]A-SG) as a novel heterogeneous catalyst was illustrated by efficient reduction of various ketones to their corresponding alcohols. To illustrate the promoting effect of the catalyst in the reaction, two more series of parallel experiments were also carried out using bare silica gel and no catalyst. The study suggests that this newly synthesized solid catalyst has high binding tendency toward sodium cations through ion- pair interactions and is consequently effective for the reduction of ketones to alcohols using NaBH4 as a hydrogen donor. Also to demonstrate the high affinity and strong trap capacity of CSC[4]A-SG toward sodium cation, atomic absorption spectrometric measurements were performed. As a result, quantitative reduction of ketones was observed in short time periods, while the catalyst shows high thermal stability (up to 300 °C) and can be recovered and reused for at least five times in a row without loss of its catalytic performance. This is the first report about the application of CSC[4]A-SG as a catalyst in the chemical reactions.