Kinetics and mechanism of oxidation of D‐fructose and D‐glucose by sodium salts of N‐(chloro)‐mono/di‐substituted benzenesulfonamides in aqueous alkaline medium

Abstract

AbstractIn an effort to introduce N‐chloroarylsulfonamides of different oxidizing strengths, nine sodium salts of mono‐ and di‐substituted N‐chloroarylsulfonamides are employed as oxidants for studying the kinetics of oxidation of D‐fructose and D‐glucose in aqueous alkaline medium. The results are analyzed along with those by the sodium salts of N‐chlorobenzenesulfonamide and N‐chloro‐4‐methylbenzenesulfonamide. The reactions show first‐order kinetics each in [oxidant], [Fru/Glu], and [OH−]. The rates slightly increase with increase in ionic strength of the medium. Further, the rate of oxidation of fructose is higher by 4 to 5 times than that of the glucose oxidation, by the same oxidant. Similarly, Ea values for glucose oxidations are higher by about 1.5 times the Ea values for fructose oxidations. The results have been explained by a plausible mechanism, and the related rate law deduced. The significant changes in the kinetics and thermodynamic data are observed with change of substituent in the benzene ring. It is because Cl+ is the effective oxidizing species in the reactions of N‐chloroarylsulfonamides. The oxidative strengths of the latter therefore depend on the ease with which Cl+ is released from them. The ease with which Cl+ is released from N‐chloroarylsulfonamides depends on the electron density of the nitrogen atom of the sulfonamide group, which in turn depends on the nature of the substituent in the benzene ring. The following Hammett equations are valid for the oxidation of fructose and glucose, log kobs = −3.13 + 0.54 σp and log kobs = −3.81 + 0.28 σp, respectively. The enthalpies and entropies of activations for oxidations by all the N‐chloroarylsulfonamides correlate well with isokinetic temperatures of 301 K and 299 K, for fructose and glucose oxidations, respectively. The effect of substitution in the oxidants on the Ea and log A for the oxidations is also considered. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 37: 572–582, 2005