title: Two-Phase Reactions in Microdroplets without the Use of Phase-Transfer Catalysts.
abstract: Many important chemical transformations occur in two-phase reactions, which are widely used in chemical, pharmaceutical, and polymer manufacturing. We present an efficient method for performing two-phase reactions in microdroplets sheared by sheath gas without using a phase-transfer catalyst. This avoids disadvantages such as thermal instability, high cost, and, especially, the need to separate and recycle the catalysts. We show that various alcohols can be oxidized to the corresponding aldehydes and ketones within milliseconds in moderate to good yields (50-75 %). The scale-up of the present method was achieved at an isolated rate of 1.2 mg min-1for the synthesis of 4-nitrobenzylaldehyde from 4-nitrobenzyl alcohol in the presence of sodium hypochlorite. The biphasic nature of this process, which avoids use of a phase-transfer catalyst, greatly enhances synthetic effectiveness.
authors.affiliation: Department of Chemistry, Stanford University, 333 Campus Drive, Stanford, CA, 94305-5080, USA.
authors.forename: Xin
authors.initials: X
authors.lastname: Yan
authors.affiliation: Department of Chemistry, Stanford University, 333 Campus Drive, Stanford, CA, 94305-5080, USA.
authors.forename: Heyong
authors.initials: H
authors.lastname: Cheng
authors.affiliation: Department of Chemistry, Stanford University, 333 Campus Drive, Stanford, CA, 94305-5080, USA.
authors.forename: Richard N
authors.identifier: 0000-0001-5266-4253
authors.initials: RN
authors.lastname: Zare
keywords: Stevens oxidation; liquid-liquid reactions; microdroplet synthesis; phase-transfer catalysis; two-phase reactions