Selective oxidations of alcohols and aldehydes in a microfluidic electrolysis cell

Abstract

Electrosynthesis uses electrical current to drive reactions as an alternative to stoichiometric reagents that may be toxic, expensive or create substantial waste. Despite the attraction, electrosynthesis has, however, never become routine procedure in the laboratory. The reasons for the apparent underuse are the perception that specialist knowledge and equipment is often required. The recent advances in microflow technology over the past decade have generated a number of electrosynthetic devices that address the perceived problems. Our own research into electrochemical microflow devices has led to the development of a now commercially available electrochemical flow cell.

To fully advertise the benefits of electrochemical microflow technology synthetically useful reactions need to be developed. The optimisation of such reactions has been the focus of this Ph.D. research. The first reaction investigated was a selective electrochemical 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) mediated oxidation of alcohols to aldehydes and ketones. Cyclic voltammetry techniques were used to investigate the mechanism, and optimise the procedure, with 15 examples tested with excellent conversions and yields achieved in a single pass.

We then turned our attention to the development of procedures for an electrochemical oxidative esterification and amidation mediated by N-heterocyclic carbenes (NHCs). The optimisation process was directed by a Design of Experiment (DoE) approach and supported by cyclic voltammetry (CV) experiments. 20 examples of esterification and 23 examples of amidation were demonstrated respectively in excellent yields in a single pass.

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Identifiers

ORCID for Richard Brown: orcid.org/0000-0003-0156-7087

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