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Kinetics and mechanism of the autoxidation of 2-aminoethanethiol and ethanethiol catalyzed by cobalt(II) 4,4',4",4"'-tetrasulfophthalocyanine in aqueous solution

Leung, Ping Sang K. and Hoffmann, Michael R. (1989) Kinetics and mechanism of the autoxidation of 2-aminoethanethiol and ethanethiol catalyzed by cobalt(II) 4,4',4",4"'-tetrasulfophthalocyanine in aqueous solution. Journal of Physical Chemistry, 93 (1). pp. 434-441. ISSN 0022-3654 . http://resolver.caltech.edu/CaltechAUTHORS:20150814-112038244

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Abstract

The kinetics of autoxidation of 2-aminoethanethiol to 2-aminoethyl disulfide and ethanethiol to ethyl disulfide as catalyzed by cobalt(II) 4,4',4",4"'-tetrasulfophthalocyanine (Co^(II)TSP) were investigated. The following general rate law was found to hold for both substrates over the pH range 8.8-13.5: v = -d[RS-]/dt = k_(obsd)[CoTSP]_T[RS^-]. Evidence for a mechanism that proceeds via a dimeric catalytic center that is bridged by the RS^- anion has been obtained. In the proposed mechanism, electron transfer from the Co(II) metal center to bound dioxygen was considered to be the rate-determining step. Hydrogen peroxide and mercaptan radical were identified as reaction intermediates in the autoxidation of both substrates. These intermediates react further to produce the corresponding disulfide, RSSR, as the final product of the autoxidation. k_(obsd) was found to be of the following general form: k_(obsd) = (k_(31)K_(21) + (k_(32)K_(22)K'_1/ɑH+) + (k_(33)K_(23)K'_1K'_2/ɑ_H^(+2)))/[(1 + (K'_1/ɑ_H^+) + (K'_1K'_2/ɑH^(+2)))(1 + (ɑ_H^+/K'_(a1)^2))], where k_(31) and K_(21) are the rate constants for the electron transfer and the equilibrium constants for substrate complexation of the ith catalytic center, respectively, K'_2 and K'_2 are the apparent acid dissociation constants of the pyrrole groups of Co^(II)TSP-RS^--Co^(II)TSP and Co^(II)TSP^-RS--co^II)TSP-, respectively, and K'_(a1) is the apparent acid dissociation constant of RCH_2CH_2SH


Item Type:Article
Related URLs:
URLURL TypeDescription
http://dx.doi.org/10.1021/j100338a084DOIArticle
http://pubs.acs.org/doi/abs/10.1021/j100338a084PublisherArticle
ORCID:
AuthorORCID
Hoffmann, Michael R.0000-0002-0432-6564
Additional Information:© 1989 American Chemical Society. (Received: August 21, 1987) Support for this research was provided by grants from the U.S. Environmental Protection Agency (R809198-01 and R811612-01-0). We gratefully acknowledge the assistance of the Pollution Control Processes/Environmental Engineering Section (U.S. EPA) and Dr. Donald Carey. We are also grateful to Drs. Detlef Bahnemann and Eric Betteron for their interest in this work and for their extremely valuable assistance.
Funders:
Funding AgencyGrant Number
Environmental Protection Agency (EPA)R809198-01
Environmental Protection Agency (EPA)R811612-01-0
Record Number:CaltechAUTHORS:20150814-112038244
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:20150814-112038244
Official Citation:Kinetics and mechanism of the autoxidation of 2-aminoethanethiol and ethanethiol catalyzed by cobalt(II) 4,4',4",4"'-tetrasulfophthalocyanine in aqueous solution Ping Sang K. Leung and Michael R. Hoffmann The Journal of Physical Chemistry 1989 93 (1), 434-441 DOI: 10.1021/j100338a084
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:59537
Collection:CaltechAUTHORS
Deposited By: Ruth Sustaita
Deposited On:14 Aug 2015 21:07
Last Modified:14 Aug 2015 21:07

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