Reaction Pathways of in vivo Stereoselective Conversion of Ethylbenzene to (-)-Mandelic Acid

Abstract

1. Mandelic acid formed in vivo from ethylbenzene as well as from various oxidation intermediates was laevo mandelic acid and was of surprisingly high optical purity.

2. Reaction sequences are proposed for the stepwise oxidation of ethylbenzene to mandelic acid.

3. Although the initial hydroxylation of ethylbenzene to methylphenyl-carbinol is stereoselective, the optical activity of mandelic acid is not established at this point since the optical centre is destroyed in the second step, dehydrogena-tion to acetopheneone.

4. Acetophenone appears to be a precursor of not only mandelic acid and benzoylformic acid but benzoic acid as well.

5. The route from acetophenone involves conversion to eu-hydroxyaceto-phenone and subsequent reduction to glycol and/or oxidation to phenylglyoxal.

6. The configuration of mandelic acid is determined either during reduction of hydroxyacetophenone or reduction of phenylglyoxal.