Osmium(VIII) Catalyzed Oxidative Cleavage of Pyrrolidine Ring in l-Proline by Hexacyanoferrate(III) in Alkaline Media

Kinetics of oxidation of l-proline by hexacyanoferrate(III) catalyzed by osmium(VIII) in alkaline medium was studied at 30 °C. A mechanism involving free radical path was proposed. Rate law of the reaction was derived as rate=kK1K2[HCF][L-proline][OH−][Os(VIII)]1+K1[OH−]+K1K2[L-proline][OH−] The rate constant k and equilibrium constants K₁ and K₂ were evaluated as 3.79 × 10³ dm³ mol⁻¹ s⁻¹, 0.52 dm³ mol⁻¹, and 3.78 × 10³ dm³ mol⁻¹, respectively. The main reactive species of the catalyst appears to be OsO₅(OH)³⁻. The oxidative product of l-proline was identified as l-glutamic acid which is different from the earlier reports. The literature reveals that 4-amino butyric acid, 4-amino butaraldehyde and keto acids were the oxidative products. Activation parameters were evaluated as E_a = 33.5 ± 2 kJ mol⁻¹, ΔH^⧧ = 31.0 ± 0.2 kJ mol⁻¹, ΔS^⧧ = −24 ± 1.5 J K⁻¹ mol⁻¹, ΔG^⧧ = 38.0 ± 2 kJ mol⁻¹.