Study of Nickel (II) Catalysed Oxidation of Glycylglycine by Heptavalent Manganese: A Kinetic Study

Abstract

Kinetics of the Ni(II) catalysed oxidation of glycylglycine by alkaline KMnO4 has been studied spectrophotometrically over the range 2.0 ≤ 10 3 (Gly-Gly) ≤ 6.0 mol dm -3 ; 1.25 ≤ 10 7 (OH - ) ≤ 10.0mol dm -3 ; 293 ≤ T ≤ 313 K and I = 0.5 mol dm -3 (KNO3). The reaction exhibits first order in (MnO4 - )T and (Ni(II))T but fractional order in both (Gly-Gly)T and (OH - )Trespectively. The rate of reaction is found to increase with increase in (Gly-Gly)T and (OH - )T.For uncatalysed reactionΔH # (kJmol -1 ) and ΔS # (JK -1 mol -1 ) are found to be44.4 ± 1.8 and -182 ± 6.0respectively but for Ni(II) catalysed reaction, the parameters ΔH # (kJ mol -1 ) and ΔS # (JK -1 mol -1 ) are found to be 23.46 ± 2.53 and -159.1 ± 8.43 respectively. The Ni(II) catalysed reaction passes through a new reaction path with less activation energy. The ΔH o (kJ mol -1 )and ΔS o (JK -1 mol -1 ) values for logK1 and logK2 are found to be 42.2& -30.6 and280.1&-37.9. The negative activation entropy is indicative of ordered transition state for electron transfer reaction. The product of the reaction is found to be glyoxalwhich is supported by FTIR data.