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Kinetics of oxidation of acidic amino acids and their monoamides by N ‐chloroarylsulphonamides in aqueous acidic medium
Author(s) -
Gowda B. Thimme,
Shetty Mahesha
Publication year - 2004
Publication title -
journal of physical organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.325
H-Index - 66
eISSN - 1099-1395
pISSN - 0894-3230
DOI - 10.1002/poc.758
Subject(s) - chemistry , oxidizing agent , kinetics , aqueous solution , reagent , medicinal chemistry , ionic strength , inorganic chemistry , amino acid , organic chemistry , biochemistry , physics , quantum mechanics
Twelve sodium salts of N ‐chloroarylsulphonamides were employed as oxidants for studying the kinetics of oxidation of two acidic amino acids (aspartic and glutamic acid) and their monoamides (aspargine and glutamine) in aqueous acidic medium under various conditions, to see how the oxidative strength of these reagents vary with substitution. The sodium salts of N ‐chloroarylsulphonamides employed are of the general formulae i ‐X‐C 6 H 4 SO 2 NaNCl· x H 2 O (where i ‐X = 4‐C 2 H 5 , 4‐F, 4‐Cl or 4‐Br) and i ‐X‐ j ‐Y‐C 6 H 3 SO 2 NaNCl· x H 2 O [where i ‐X‐ j ‐Y = 2,3‐(CH 3 ) 2 , 2,4‐(CH 3 ) 2 , 2,5‐(CH 3 ) 2 , 2‐CH 3 ‐4‐Cl, 2,4‐Cl 2 and 3,4‐Cl 2 ]. The reactions show second‐order kinetics in [oxidant], fractional order in [amino acid] and an inverse dependence on [H + ]. Addition of the reduced product of the oxidants or variation in ionic strength of the medium has no significant effect on the rates of oxidations. Mechanisms in conformity with the observed kinetics are discussed. The effective oxidizing species of the oxidants is Cl + in different forms. The oxidizing strengths of N ‐chloroarylsulphonamides depend on the ease with which Cl + is released from them. The study reveals that the introduction of electron‐withdrawing groups such as halides to the benzene ring eases the release of Cl + from the reagent and hence increases the oxidizing strengths of the N ‐chloroarylsulphonamides. The effect of substituents on E a of the reactions was analysed by optimising E a with reference to log A , and log A with reference to E a of the parent oxidant. Copyright © 2004 John Wiley & Sons, Ltd.