The Selective Synthesis of Di- and Cyclosiloxanes Bearing Several Hidden P-Tolyl-functionalities

This study reports the development of a selective method for the synthesis of p-tolylsiloxanes, namely, symmetrical disiloxanes and cyclotetrasiloxanes, by hydrolytic condensation of p-tolyl-containing mono(ethoxy)silanes and di(ethoxy)silanes in the presence of [Me4N]+OH-. The reaction occurs under mild and simple reaction conditions: at 30 degrees C, under atmospheric pressure, in 1-5 h, in acetone and ethanol medium or in the block (solvent-free), with a loading of 0.25-5 mol.% (per Si-OEt group) of [Me4N]+OH (-), a commercially available and cheap catalyst. The method is well scalable and allows the target products (2a-f) to be obtained in gram amounts (up to 50 g) in 42-85% yields. The structures were confirmed using a set of physicochemical analytical methods: IR, ESI-HRMS, GPC, 3a and 4a H-1/C-13/Si-29 NMR, and X-Ray. (c) 2022 Published by Elsevier B.V.