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Kinetics and mechanism of the formation of hydroxymethanesulfonic acid at low pH

Boyce, Scott D. and Hoffmann, Michael R. (1984) Kinetics and mechanism of the formation of hydroxymethanesulfonic acid at low pH. Journal of Physical Chemistry, 88 (20). pp. 4740-4746. ISSN 0022-3654.

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A spectrophotometric kinetic study of the reaction of sulfur dioxide with formaldehyde to form hydroxymethanesulfonic acid in aqueous solution was performed over the pH range 0.0 to 3.5. A kinetic expression of the following form was verified experimentally: -d[S(IV)]/dt = {(k_1α_1 + k_2α_2)K_d/(K_d + l)}[S(IV)][CH_2O]_t where [CH_2O]_t = [CH_2(OH]_2 + [CH_2O] K_d = k_d/k_(-d) = [CH_2O]/[CH_2(OH)_2], [S(IV)] = [SO_2•H_2] + [HSO_3^-] + SO_3^(2-)], α_1 = [HSO_3-]/[S(IV)] = K_(a1)/[H^+]^2 + K_(a1)[H^+][K_(a1)K_(a2),α_2 = [SO_3^(2-)]/S(IV)] = K_(al)K_(a2)/([H+]^2 + K_(a1)[H^+] + K_(a1)K_(a2), K_(a1) = [H^+][HSO_3^-]/[SO_2•H_2O] and K_(a2) = [H^+][SO_3^(2-)]/[HSO_3^-]. The following kinetic parameters were determined at 25 ºC and µ = 1.0 M: k_1 = (7.90 ± 0.32) x 10^2 M^(-1) s^(-1), k_2 = (2.48 ± 0.05) x 10^7 M^(-1) s^(-1), ΔH_1^* = (24.9 ± 0.8) kJ mol^(-1), ΔS_1^* = (-108.0 ± 2.6) J mol^(-1) K^(-1), ΔH_2^* = (20.4 ± 0.5) kJ mol^(-1), and ΔS_2^* = (-31.7 ± 1.6) J mol^(-1) K^(-1) for values of K_d = 5.50 x 10^(-4), K_(a1) = 1.45 X 10^(-2) M, and K_(a2) = 6.31 x 10^(-8) M. Application of the Davies approximation (log γ = -Az^2/{µ^(1/2)- 0.2µ)} to correct for ionic strength effects yielded ^ck_1 = (4.51 ± 0.15) x 10^2 M^(-1) s^(-1) and ^ck_2 = (5.42 ± 0.07) x 10^6 M^(-1) s^(-1) for concentration-dependent equilibrium constants ^cK_(a1) = K_((a1)γ_(SO_2•H_2O)/γ_(H+γ_HSO_2^-) = 2.92 x 10^(-2) M and ^cK_(a2) = K_(a2)γHSO_3^-/γH+γSO_3^(2-)= 2.58 x 10^(-7) M. The reaction proceeds via each of two parallel pathways involving the nucleophilic addition of HSO_3^- and SO_3^(2-) to the carbonyl C-atom of formaldehyde as follows: CH_2(OH)_2 kd/k-d CH_2O + H_2O (fast); SO_2•H_2O K_(a1) H^+ + HSO_3^- (fast); HSO_3^- + CH_2O K_1 CH_2 (OH)SO_3 (slow); SO_3^(2-) + CH_2O k_2 CH_2(O^-)SO_3^- (slow); CH_2(O^-)SO_3^- + H^+ K_(a2)(HMSA) CH_2(OH)SO_3^- (fast). Previous investigations of this reaction have demonstrated that the dehydration of methylene glycol, CH_2(OH)_2 to form CH_2O becomes rate limiting under neutral pH conditions. The experimental data obtained in the present study indicate that rate of CH_2O production from CH_2(OH)_2 is strongly influenced by specific acid catalysis. Application of the aforementioned results to liquid-phase reaction processes occurring in atmospheric microdroplets is discussed.

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Hoffmann, Michael R.0000-0001-6495-1946
Additional Information:© 1984 American Chemical Society. Received: September 20, 1983. The authors gratefully acknowledge the United States Environmental Protection Agency (R808086-01) for providing financial support for this research. Also, we thank the reviewers for offering several constructive suggestions concerning the preparation of the paper.
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Environmental Protection Agency (EPA)R808086-01
Issue or Number:20
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Official Citation:Kinetics and mechanism of the formation of hydroxymethanesulfonic acid at low pH Scott D. Boyce and Michael R. Hoffmann The Journal of Physical Chemistry 1984 88 (20), 4740-4746 DOI: 10.1021/j150664a059
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:59695
Deposited By: Ruth Sustaita
Deposited On:19 Aug 2015 19:23
Last Modified:03 Mar 2020 13:01

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