Abstract
The kinetics of oxidation of L-asparagine (Asn) by hexacyanoferrate(III) (HCF) has been investigated in alkaline medium in the absence and presence of silver(I) catalyst at a constant ionic strength of 0.5 mol dm−3 and at 20°C. The progress of both uncatalyzed and silver(I)-catalyzed oxidations was followed spectrophotometrically. Both reactions showed a first order dependence with respect to [HCF], whereas the orders with respect to [Asn] and [OH−] were less than unity. The catalyzed reaction exhibited a first order dependence in [AgI]. Increasing both ionic strength and dielectric constant of the reaction medium increased the rate of uncatalyzed reaction and did not affect significantly the rate of catalyzed reaction. Addition of the reaction product, HCF(II) to the reaction mixture had no affect on the rate. Appropriate reaction mechanisms for both uncatalyzed and catalyzed oxidations explaining all of the observed kinetic results has been proposed. The catalyzed reaction has been shown to proceed via formation of a silver(I)-asparagine intermediate complex, which reacted with the oxidant by an inner-sphere mechanism leading to decomposition of the complex in the rate-determining step to yield the final oxidation products which were identified as α-formyl acetamide, ammonia, and carbon dioxide. The rate law expressions associated with the reaction mechanisms were derived.
Highlights
Oxidation reactions are of fundamental importance in nature and are regarded as key transformations in organic synthesis
Numerous kinetic investigations of the oxidation of amino acids have been carried out using various oxidants under different experimental conditions [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23], because of their biological significance, selectivity towards the oxidants and the importance of understanding the mechanism of such biological redox reactions
Kinetic studies on the oxidation reactions of amino acids catalyzed by different metal ions are an important field of chemistry because of the role played by metals in biological systems [5,6,7,8,9, 15,16,17,18,19,20,21,22,23,24]
Summary
Oxidation reactions are of fundamental importance in nature and are regarded as key transformations in organic synthesis. Kinetic studies on the oxidation reactions of amino acids catalyzed by different metal ions are an important field of chemistry because of the role played by metals in biological systems [5,6,7,8,9, 15,16,17,18,19,20,21,22,23,24]. The present study deals with the title reactions in order to examine the selectivity of L-asparagine towards hexacyanoferrate(III) in an alkaline medium, to determine the catalytic activity of the silver(I) catalyst, to understand the kinetically active species of the reactants, to identify the reaction products and to propose appropriate reaction mechanisms
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have