Chemical Racemization of 5-Benzylhydantoin

Article abstract of DOI:10.1021/jo00302a051

The chemical racemization of L-5-benzylhydantoin (L-5BH) at 37 deg C has been investigated in H2O from pH 6 to 14.The pH-rate profile demonstrates hydroxide catalysis on both the free base and free acid form (or the kinetically equivalent water catalysis on the free base form) of L-5BH.In addition the reaction is subject to buffer catalysis by phosphate, Tris, and carbonate.Evidence is presented for a mechanism involving general base catalysis based upon comparison of the second-order buffer-catalyzed rate constants for L-5BH with those obtained for L-5-benzyl-3-methylhydantoin (L-5B-3MH).A Broensted plot yields a β_gb = 0.59 for L-5BH and β_gb = 0.51 for L-5B-3MH, implying that the proton at carbon 5 is approximately halfway between the hydantoin and the buffer species in the transition state of the racemization reaction.