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Continuous photochemical benzylic bromination using in situ generated Br2: process intensification towards optimal PMI and throughput

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Abstract

The detailed development of photochemical benzylic brominations using a NaBrO3/HBr bromine generator in continuous flow mode is reported. Optimization of the bromine generator enables highly efficient mass utilization by HBr recycling, coupled with fast interphase transfer within a microstructured photochemical reactor (405 nm LEDs). Intensification of the reaction system, including complete removal of organic solvent, allowed a reduction in PMI from 13.25 to just 4.33. The photochemical transformation achieved exceptionally high throughput, providing complete conversion in residence times as low as 15 s. The organic solvent-free preparation of two pharmaceutically relevant building blocks was demonstrated with outstanding mass efficiency, by monobromination (1.17 kg scale in 230 min, PMI = 3.08) or dibromination (15 g scale in 20 min, PMI = 3.64).

Graphical abstract: Continuous photochemical benzylic bromination using in situ generated Br2: process intensification towards optimal PMI and throughput

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Supplementary files

Article information


Submitted
24 Oct 2019
Accepted
10 Dec 2019
First published
10 Dec 2019

This article is Open Access

Green Chem., 2020, Advance Article
Article type
Paper

Continuous photochemical benzylic bromination using in situ generated Br2: process intensification towards optimal PMI and throughput

A. Steiner, J. D. Williams, O. de Frutos, J. A. Rincón, C. Mateos and C. O. Kappe, Green Chem., 2020, Advance Article , DOI: 10.1039/C9GC03662H

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