High-Productivity Single-Pass Electrochemical Birch Reduction of Naphthalenes in a Continuous Flow Electrochemical Taylor Vortex Reactor

Darren S. Lee, Ashley Love, Zakaria Mansouri, Toby H. Waldron Clarke, David C. Harrowven, Richard Jefferson-Loveday, Stephen J. Pickering, Martyn Poliakoff, Michael W. George

Research output: Journal PublicationReview articlepeer-review

Abstract

We report the development of a single-pass electrochemical Birch reduction carried out in a small footprint electrochemical Taylor vortex reactor with projected productivities of >80 g day-1 (based on 32.2 mmol h-1), using a modified version of our previously reported reactor [Org. Process Res. Dev. 2021, 25, 7, 1619-1627], consisting of a static outer electrode and a rapidly rotating cylindrical inner electrode. In this study, we used an aluminum tube as the sacrificial outer electrode and stainless steel as the rotating inner electrode. We have established the viability of using a sacrificial aluminum anode for the electrochemical reduction of naphthalene, and by varying the current, we can switch between high selectivity (>90%) for either the single ring reduction or double ring reduction with >80 g day-1 projected productivity for either product. The concentration of LiBr in solution changes the fluid dynamics of the reaction mixture investigated by computational fluid dynamics, and this affects equilibration time, monitored using Fourier transform infrared spectroscopy. We show that the concentrations of electrolyte (LiBr) and proton source (dimethylurea) can be reduced while maintaining high reaction efficiency. We also report the reduction of 1-aminonaphthalene, which has been used as a precursor to the API Ropinirole. We find that our methodology produces the corresponding dihydronaphthalene with excellent selectivity and 88% isolated yield in an uninterrupted run of >8 h with a projected productivity of >100 g day-1.

Original languageEnglish
Pages (from-to)2674-2684
Number of pages11
JournalOrganic Process Research and Development
Volume26
Issue number9
DOIs
Publication statusPublished - 16 Sep 2022

Keywords

  • Birch reduction
  • continuous flow
  • dearomatization
  • electrochemistry
  • electroreduction
  • Taylor vortex reactor

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Organic Chemistry

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