Ultrasound-induced CO2 /H2O emulsions as a medium for clean product formation and separation : the Barbier reaction as a synthetic example

Research output: Contribution to journalArticle

Authors

Colleges, School and Institutes

Abstract

Subcritical CO2/H2O (30°C/80 bar) was employed as a renewable solvent mixture in a 1 dm3 ultrasound reactor. As a representative synthetic transformation, the metal-mediated Barbier allylation was used to demonstrate the facility of formation and separation of the homoallylic alcohol product. The chemoselectivity over the competing aldehyde reduction could be improved by deploying the biocompatible nonionic surfactant Tween 80, a saturated salt aqueous phase, or by carrying out the reaction at 60 °C/120 bar. All of these modifications led to an apparent rate increase in the desired allylation. A range of substituted benzaldehydes afforded the corresponding homoallylic alcohols in moderate to high yields. The presence of water constituted a necessary condition for efficient product formation, while CO2 provided an appropriate phase for clean product separation by exploiting a favorable homoallylic alcohol enrichment. In this way, 0.025 mol of homoallylic alcohol product could be isolated from the CO2 phase in 1 h, avoiding further extraction stages that would typically require organic solvents.

Details

Original languageEnglish
Pages (from-to)1280-1288
JournalACS Sustainable Chemistry & Engineering
Volume2
Issue number5
Early online date3 Apr 2014
Publication statusPublished - 5 May 2014

Keywords

  • Carbon dioxide, Mixing, Emulsion, Mass transfer, Allylation, Aqueous media, Biphasic, Sonication, Kinetics