Experimental and computational studies on solvent effects in reactions of peracid–aldehyde adducts

Solvent effects on liquid phase oxidation of aldehydes by dioxygen and m-chloroperbenzoic acid were studied experimentally. The main products were the corresponding carboxylic acid and a formate ester formed by Baeyer–Villiger rearrangement. In alcohol solvents (particularly methanol) substantially higher acid to formate ratios were formed than in solvents not capable of forming hydrogen bonds. Formation of both main products can be rationalised via rearrangement reactions of two epimeric peracid–aldehyde adducts, of which the interactions with methanol were studied computationally employing DFT methods at the DNPP level with the Spartan program (v5.0). The calculations indicate that structures of the adducts rearranging to give two equivalents of acid resemble the transition state of the reaction more than structures of the epimeric adducts rearranging to the acid and formate ester in 1:1 ratio. Therefore, the enhanced favor of the formation of acid in the presence of methanol can be explained in the light of Hammondʹs postulate.