Aqueous microdroplets containing only ketones or aldehydes undergo Dakin and Baeyer-Villiger reactions.

Dan Gao,Richard N Zare,Feng Jin,Jae Kyoo Lee

doi:10.1039/c9sc05112k

Dan Gao, Richard N Zare + Show 2 more

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https://doi.org/10.1039/c9sc05112k

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Journal: Chemical science	Publication Date: Jan 1, 2019
Citations: 75	License type: CC BY 3.0

Affiliation: Stanford University, St Vincent Hospital

Abstract

The Dakin and Baeyer-Villiger (BV) oxidation reactions require addition of peroxides as oxidants and an acid or a base as a catalyst. Reaction times range from hours to days to obtain target products. Previously, we reported that hydrogen peroxide (H2O2) is spontaneously generated in water microdroplets without any added chemicals or applied electrical potential. Here, we report that the Dakin and BV reactions occur in modest yields within milliseconds in aqueous microdroplets at room-temperature without the addition of external peroxides and catalysts. H2O2 generation is the result of the special environment of the microdroplet surface, which promotes water autoionization. We find that increasing the content of water and decreasing the droplet size improve the product yield of the Dakin and BV reactions, supporting the contention that the amount of H2O2 generated in aqueous microdroplets could induce the two reactions and the reactions occur at or near the air-water interface of the microdroplet surface.

Highlights

Many studies have shown that the rates of chemical reactions in microdroplets sprayed in air under ambient conditions can be markedly accelerated compared to the same reactions in bulk solution.[1]
Due to the unique characteristics of aqueous microdroplets, like production of H2O2 and hydrated excess hydronium and hydroxide ions on the microdroplet surface,[11] we present a proof of principle here that the Dakin and BV reactions can be achieved using aqueous microdroplets containing only the carbonyl compound that is desired to be transformed
The Dakin reaction is carried out with excess H2O2 and high concentrations of acid or base at elevated temperatures.[13]. This means that the reaction cannot occur when only the reactant is present in bulk water–organic solvents at room temperature

Summary

Introduction

Many studies have shown that the rates of chemical reactions in microdroplets sprayed in air under ambient conditions can be markedly accelerated compared to the same reactions in bulk solution.[1]. The chemical structures of intermediate 3 and product 5 were con rmed by comparing observed fragment ions from the microdroplet reactions and the corresponding standard samples with tandem mass spectrometry using collision induced dissociation (CID) (see Fig. S1 and S2†).

Results

Conclusion