Spontaneous generation of hydrogen peroxide from aqueous microdroplets

Abstract

We show H2O2 is spontaneously produced from pure water by atomizing bulk water into microdroplets (1 μm to 20 µm in diameter). Production of H2O2, as assayed by H2O2-sensitve fluorescence dye peroxyfluor-1, increased with decreasing microdroplet size. Cleavage of 4-carboxyphenylboronic acid and conversion of phenylboronic acid to phenols in microdroplets further confirmed the generation of H2O2. The generated H2O2 concentration was ∼30 µM (∼1 part per million) as determined by titration with potassium titanium oxalate. Changing the spray gas to O2 or bubbling O2 decreased the yield of H2O2 in microdroplets, indicating that pure water microdroplets directly generate H2O2 without help from O2 either in air surrounding the droplet or dissolved in water. We consider various possible mechanisms for H2O2 formation and report a number of different experiments exploring this issue. We suggest that hydroxyl radical (OH) recombination is the most likely source, in which OH is generated by loss of an electron from OH− at or near the surface of the water microdroplet. This catalyst-free and voltage-free H2O2 production method provides innovative opportunities for green production of hydrogen peroxide.

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

“…As it was suggested by our previous report that H 2 O 2 was formed by hydroxyl radical recombination, 5 we investigated the effects of water and organic solvent ratio in microdroplets on the formation of hydroxyl radicals and thus the amount of H 2 O 2 generated, which will nally inuence the product yield of the Dakin and BV reactions. The BV reaction of reactant 8 to form product 9 was tested as an example.…”

“…Perhaps, the most striking example is the recent discovery that aqueous microdroplets under ambient conditions (room temperature and 1 atmosphere pressure of air) contain a small concentration ($30 mM) of hydrogen peroxide (H 2 O 2 ). 5 In this study, we demonstrate that the H 2 O 2 formed in water microdroplets can be used to carry out the Dakin and Baeyer-Villiger (BV) reactions, which are classic synthetic approaches for the oxidation of carbonyl groups.…”

Visible Light Assisted Selenylative Intramolecular Dearomative Carbo‐Spirocyclisation (IDCS) of Homologated‐Ynones

“…Under a concentrated oxygen atmosphere, in the presence of diaryldiselenide, the intermediate B undergoes a peroxidation and transforms into the peroxy intermediate C, which finally delivers the spiro‐cyclized cyclic enone 3 along with a OH radical. Two OH radicals combined to deliver hydrogen peroxide followed by insitu generations of benzeneperoxyseleninic acid D in the presence of diaryldiselenide, which functions as an epoxidizing agent. The spiro‐cyclized cyclic enone 3 undergoes double epoxidation with the in situ generated epoxidizing agent D facilities the formation towards epoxidation of the adjacent enones to the di‐epoxide 4 .…”

Thermal perturbation of NMR properties in small polar and non-polar molecules

“…Water is a ubiquitous constituent in numerous chemical systems. Despite its vast importance in biological life and societal development, new discoveries in its physical and chemical properties are being made on an ongoing basis, highlighting the vast uncertainties this molecules offers 1 . Its presence in multi-component systems often introduces enhanced complexities in the behavior and interpretation of the chemical system.…”