Polarographic reduction of aldehydes and ketones. Part XI. Acid–base equilibria accompanying electrolysis of 1-phenylbutane-1,3-dione

Abstract

From the spectrophotometrically determined acid dissociation constant pK_T= 8·84 and from [Enol]/[Keto]= 0·71 it was possible by polarography to calculate k= 1 × 10¹⁰ l. mole^–1 sec.^–1 for the rate constant corresponding to the formation of the keto-form of benzoylacetone (1-phenylbutane-1,3-dione) from the carbanion-enolate. Polarographic reduction at the two-electron step produced 4-hydroxy-4-phenylbutan-2-one. The reduction is facilitated in the sequence: carbanion-enolate (i₄) < unprotonated diketone (i₃) < monoprotonated diketone (i₂) < diprotonated diketone (i₁). In the transitional pH regions the currents are governed by the rate of protonation. Controlled-potential electrolysis of benzoylacetone produces 4-hydroxy-4-phenylbutan-2-one in high yields.