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Kinetics, mechanism and thermodynamics of the reversible reaction of methylglyoxal (CH_3COCHO) with sulfur (IV)

Betterton, Eric A. and Hoffmann, Michael R. (1987) Kinetics, mechanism and thermodynamics of the reversible reaction of methylglyoxal (CH_3COCHO) with sulfur (IV). Journal of Physical Chemistry, 91 (11). pp. 3011-3020. ISSN 0022-3654. https://resolver.caltech.edu/CaltechAUTHORS:20150817-150959957

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Abstract

At pH ≤ 2 the following rate law for the formation of hydroxyacetylmethaneulfonate (HAMS) from methylglyoxal (MG) and S(IV) (H_2O•SO_2, SO_3^(2-))is obtained: d[HAMS]/dt = ((k_0α_1[H^+]/K_(a0)) + k_1α_1 + k_2α_2)[S(IV)][MG]_0)/(1 + K_d + K_d[H^+]/K_(a0)), where α_1 and α_2 are the fractional concentrations of HSO_3^- and SO_3^(2-), respectively; k_0, is the rate constant for the reaction of HSO_3^- with the carbocation aldehyde species (CH_3COC^+HOH); k_1, and k_2 are the rate constants for the reaction of unhydrated MG with HSO_3^- and SO_3^(2-), respectively; K_d is the dehydration constant of hydrated MG; and K_(a0) is the acid dissociation constant of the carbocation. At pH ≥4 the rate of formation of HAMS is determined by the rate of dehydration of the diol form of (hydrated) MG: d[HAMS]/dt = k_d[MG]/(l + K_d + _Kd [H^+]/K_(a0)), where k_d = k_w + k_H[H^+] + kOH[OH^-] + k_A[A] + kB_[B], and k_w is the intrinsic (water) rate constant; k_H and k_OH) are the specific acid and base rate constants; and k_A and k_B are the general acid (A) and base (B) rate constants. Between pH 2 and 4, biexponential kinetics are observed because, under our conditions, the rates of dehydration and of S(IV) addition become comparable. Over the pH range 0.7-7.0, the dissociation of HAMS follows the rate law: d[S(IV)]/dt = ((k_(-0)[H^+] + k_)-1) + k_(-2)K_(a3)/[H^+])K_(a4)[H^+][HAMS])/[H^+]]^2 + K_(a4)[H^+] + K_(a3)K_(a4)) where k_(-0) k_(-1), and k_(-2) are the reverse of the analogous forward rate constants defined above and K_(a3) and K_(a4) are the acid dissociation constants of the sulfortate anion and the sulfonic acid, respectively. Experiments to determine the effect of temperature on the rate (and equilibrium) constants indicate a marked effect of ΔS^* (and ΔS_(298)) on the relative magnitude of these constants.


Item Type:Article
Related URLs:
URLURL TypeDescription
http://dx.doi.org/10.1021/j100295a074DOIArticle
http://pubs.acs.org/doi/abs/10.1021/j100295a074PublisherArticle
ORCID:
AuthorORCID
Hoffmann, Michael R.0000-0001-6495-1946
Alternate Title:Kinetics, Mechanism, and Thermodynamics of the Reversible Reaction of Methylglyoxal (CH_3COCHO) With S(IV)
Additional Information:© 1987 American Chemical Society. Received: October 27, 1986; In Final Form: January 19, 1987. Publication Date: May 1987. We gratefully acknowledge the financial support of the Electric Power Institute (RP1630-47) and the Environmental Protection Agency (R811496-01-1).
Funders:
Funding AgencyGrant Number
Electric Power Research Institute (EPRI)RP 1630-47
Environmental Protection Agency (EPA)R811496-01-1
Issue or Number:11
Record Number:CaltechAUTHORS:20150817-150959957
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20150817-150959957
Official Citation:Kinetics, mechanism and thermodynamics of the reversible reaction of methylglyoxal (CH3COCHO) with sulfur(IV) Eric A. Betterton and Michael R. Hoffmann The Journal of Physical Chemistry 1987 91 (11), 3011-3020 DOI: 10.1021/j100295a074
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:59658
Collection:CaltechAUTHORS
Deposited By: Ruth Sustaita
Deposited On:18 Aug 2015 15:44
Last Modified:03 Mar 2020 13:01

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