An Excess Acidity Analysis of Acylal and Thioacylal Hydrolysis in Sulfuric Acid. Variation of ρ with Acidity

Article abstract of DOI:10.1021/jo00369a013

The excess acidity method has been applied to the hydrolysis reactions of some acylals and thioacylals in aqueous sulfuric acid mixtures.At low acidities, aryl thioacylals (RCH2OCOCH3, R=ArS) react by an A-2 mechanism involving two water molecules, but for aryl acylals (R=ArO) only one is involved.Both undergo a mechanistic switch to an A-1 pathway at high acidity.Linear free energy relationships for both substrates and both mechanisms were found to give acidity-dependent ρ values.Methoxymethyl (R=CH3O) and (methylthio)methyl acetate (R=CH3S) only show the A-1 reaction.Methylene diacetate (R=CH3COO) has two A-1 hydrolysis pathways, one of them A-2-like, involving attack by an internal nucleophile