Dehydration and Enolization Rates of Oxalacetate: Catalysis by Tertiary Amines

Article abstract of DOI:10.1021/ja00393a022

The hydration/dehydration and tautomerization rates of oxalacetate are subject to acid and base catalysis.H2O and OH^- are much more effective for the former process than for the latter, but the opposite holds for tertiary amine catalysis.In buffers comprised of oxyanion bases or unsaturated amines, dehydration is significantly faster than tautomerization and remains so as the buffer concentration is varied.In dilute tertiary amine buffers dehydration rates are also faster, but as the buffer concentration increases, tautomerization rates increase rapidly and eventually surpass those for hydration/dehydration.It is this rate crossover which led earlier workers (ref 9) to propose a carbinolamine mechanism for a tertiary amine-catalyzed tautomerization.After the rate crossover is taken into account, enolization is found to show linear rate-buffer concentration behavior with tertiary amines, vitiating the prime evidence cited for the carbinolamine mechanism.However, tertiary amine catalysis likely operates differently in the tautomerization and dehydration reactions.