The aerobic and peroxide-induced coupling of aqueous thiols-II. Reaction mechanisms, model analysis, and a comparison of the model and experimental results

Phooi K. Lim, David W. Giles, John A. Cha

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5 Scopus citations

Abstract

Kinetic results of the preceeding paper are used to formulate the most probable reaction mechanisms for the peroxide-induced and aerobic coupling of aqueous thiols. Parameters in the proposed mechanisms are evaluated for n-propylthiol using the results of independent measurements. A remarkably good agreement is achieved between the model and experimental results. The peroxide reaction, which is not affected by either copper ion or radical scavengers, is shown to be a nucleophilic substitution (SN 2) reaction which proceeds by a two-step mechanism as follows: RS- + H2O2 {A figure is presented} RSOH + OH- rate-determining RS- + RSOH → RSSR + OH- In the reaction the thiolate anion acts as the nucleophile while hydrogen peroxide and the transient sulfenic acid, RSOH, function as electrophiles. The most plausible mechanism for the copper-catalyzed, aerobic coupling reaction is as follows: Cu+ (RSSR)2+ + RS- {A figure is presented} (RSSR)Cu+ (RS-) + RSSR (RSSR)Cu+ (RS-) + RS- {A figure is presented} (RSSR)Cu+ (RS-)2- (RSSR)Cu+ (RS-)2- + O2 {A figure is presented} Cu+(RSSR)2+ + HO2- rate-determining RS- + H2O2 {A figure is presented} RSOH + OH- rate-determining RS- + RSOH → RSSR + OH- For the n-propylthiol substrate, the pertinent parameters in the mechanism are 1n (K1) = -11,000 K/T + 33.6, where K1 is dimensionless, 1n (K2) = 4270 K/T -10.5, where K2 is in 1/mol, 1n (k2) = 30.0 - 5260 K/T, and 1n (k2) = 26.8 - 6190 K/T, where k1 and k2 are in 1/(mol min).

Original languageEnglish (US)
Pages (from-to)3141-3153
Number of pages13
JournalChemical Engineering Science
Volume41
Issue number12
DOIs
StatePublished - 1986

Bibliographical note

Funding Information:
Acknowledgement~Financial support from the U.S. National Science Foundation (Grant No. CPE-8419211) is gratefully acknowledged.

Copyright:
Copyright 2014 Elsevier B.V., All rights reserved.

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