Solvent-scissors overcoming inert hydrogen bonding enable efficient oxidation of aromatic hydrocarbons under atmospheric oxygen
Hydrogen bonding is a fascinating interaction that controls the outcomes of chemical reactions.However,overcoming the strong deactivation arising from alterations in the polarity and electronic properties of the reactants and intermediates remains a challenge.Herein,we proposed a"sol-vent-scissors"strategy for overcoming the inert hydrogen bonding,enabling the efficient aerobic oxidation of methyl aromatics into aromatic acids under atmospheric oxygen at 25-45 ℃.The hy-drogen bonds between the key intermediate,benzaldehyde(PhCHO),and hexafluoroisopropanol(HFIP)were reconstructed using solvent-scissors(acetic acid(HOAc),ethyl acetate,ethyl chloro-acetate,and methyl chloroacetate),which promoted the release of free PhCHO from its inert hydro-gen-bonded state and enabled the one-step oxidation of toluene to benzoic acid under mild condi-tions.The standard Gibbs free energy changes(△G0)representing the proton acceptance capability of the solvent were of the same order of magnitude as the turnover number(TON)(capacity for promoting benzaldehyde oxidation).This approach affords remarkable benzoic acid selectivity(98.7％)with high toluene conversion(96.8％)at 45 ℃ within 4 h under 0.1 MPa O2 using NHPI/metal acetate/HFIP-HOAc.This strategy opens up a new avenue for regulating hydrogen bonding in a wider range of applications for the planning and development of synthesis protocols.
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