Reaction of Hemiacetal Esters, Acetals, and Acylals with Alcohols or Acetic Acid

Article abstract of DOI:10.1021/jo00139a026

Hemiacetal esters undergo rapid exchange with alcohols at room temperature to give mixtures of hemiacetal ester and acetal.The equilibration requires acid catalysis, and equilibrium lies far in favor of the acetal (>95percent).Acetals undergo exchange with carboxylic acids to give the same equilibrium mixtures as that achieved by using the corresponding hemiacetal ester and alcohol.The use of a large excess of carboxylic acid can convert acetals to hemiacetal esters.Under more vigorous conditions, both acetals and hemiacetal esters react with acetic acid to form acetates.The reaction of hemiacetal esters or acetals with anhydrous hydrogen chloride yields α-chloro ethers.The thermolysis of hemiacetal esters is also examined.Acylals do not undergo substitution as observed for acetals and hemiacetal esters.The reaction of acylals with alcohols results in ester formation with no exchange.Under acid conditions, hemiacetal esters are more reactive than either acetals or acylals.