The oxidation of l-valine (l-val) by diperiodatocuprate(III) (DPC) in aqueous alkaline medium at a constant ionic strength of 3.0 × 10⁻³ mol dm⁻³ was studied spectrophotometrically at 298 K and follows the rate law;

$ {\text{Rate}} = - \frac{{{\text{d}}[{\text{DPC}}]}}{{{\text{d}}t}} = \frac{{kK_{4}K_{5} K_{6}[{\hbox{{\sc{l}}-val}}][{\text{DPC}}]}}{{[{\text{OH}}^{ - }][{\text{H}}_{3} {{\text{IO}}_{6}}^{2 - } ] + K_{4}[{\text{H}}_{3} {{\text{IO}}_{6}}^{2 - } ] + K_{4} K_{5} + K_{4}K_{5} K_{6} [{\hbox{{\sc{l}}-val}}]}} $ {\text{Rate}} = - \frac{{{\text{d}}[{\text{DPC}}]}}{{{\text{d}}t}} = \frac{{kK_{4}K_{5} K_{6}[{\hbox{{\sc{l}}-val}}][{\text{DPC}}]}}{{[{\text{OH}}^{ - }][{\text{H}}_{3} {{\text{IO}}_{6}}^{2 - } ] + K_{4}[{\text{H}}_{3} {{\text{IO}}_{6}}^{2 - } ] + K_{4} K_{5} + K_{4}K_{5} K_{6} [{\hbox{{\sc{l}}-val}}]}}

where K ₄, K ₅ and K ₆ are the equilibrium constants for the different steps involved in the mechanism, k is the rate constant for the slow step of the reaction. The appearance of [l-val] term in both numerator and denominator explains the observed less than unit order in [l-val]. Similarly the appearances of [H₃IO₆ ²⁻] and [OH⁻] in the denominator obey the experimental negative less than unit order in [H₃IO₆ ²⁻] and [OH⁻], respectively. The oxidation reaction in alkaline medium proceeds via a DPC-l-valine complex, which decomposes slowly in a rate determining step followed by other fast steps to give the products. The main products were identified by spot test and spectroscopic studies.