ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTAzo—Hydrazone Conversion. III. The Autoxidation of Benzaldehyde PhenylhydrazonesH. C. Yao and P. ResnickCite this: J. Org. Chem. 1965, 30, 8, 2832–2834Publication Date (Print):August 1, 1965Publication History Published online1 May 2002Published inissue 1 August 1965https://pubs.acs.org/doi/10.1021/jo01019a504https://doi.org/10.1021/jo01019a504research-articleACS PublicationsRequest reuse permissionsArticle Views339Altmetric-Citations50LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-Alertsclose Get e-Alerts
Bicarbonate ion is an effective activator for hydrogen peroxide in the oxidation of sulfides. Kinetic and spectroscopic results support the formation of peroxymonocarbonate ion (HCO4-) as the oxidant in the catalytic reactions. The reaction of hydrogen peroxide and bicarbonate to form HCO4- occurs rapidly at 25 °C (t1/2 ≈ 300 s) near neutral pH in aqueous solution and alcohol/water mixtures, and an equilibrium analysis of the reaction by 13C NMR leads to an estimate of the electrode potential for the HCO4-/HCO3- couple (1.8 V vs NHE). Solubility of the bicarbonate catalyst is enhanced by the use of NH4HCO3 rather than by the use of group 1 salts, which tend to have lower solubility in the mixed solvents and can lead to phase separation. Rate laws and mechanistic analyses are presented for the oxidation of ethylphenylsulfide and related sulfides. The second-order rate constants for sulfide oxidations by HCO4- are ∼300-fold greater than those for H2O2, and this increase is consistent with expectations based on a Brønsted analysis of the kinetics for other heterolytic peroxide oxidations. At high concentrations of H2O2, a pathway that is second order in H2O2 is significant, and this path is interpreted as a general acid catalysis by H2O2 of carbonate displacement accompanying substrate attack at the electrophilic oxygen of HCO4-. Increasing water content up to 80% in the solvent increases the rate of oxidation. The BAP (bicarbonate-activated peroxide) oxidation system is a simple, inexpensive, and relatively nontoxic alternative to other oxidants and peroxyacids, and it can be used in a variety of oxidations where a mild, neutral pH oxidant is required. Variation of bicarbonate source and the cosolvent can allow optimization of substrate solubility and oxidation rates for applications such as organic synthesis and chemical warfare agent decontamination.
A detailed mechanism for the oxidation of aryl sulfides by peroxymonocarbonate ion in cosolvent/water media is described. Kinetic studies were performed to characterize the transition state, including a Hammett correlation and variation of solvent composition. The results are consistent with a charge-separated transition state relative to the reactants, with an increase of positive charge on the sulfur following nucleophilic attack of the sulfide at the electrophilic oxygen of peroxymonocarbonate. In addition, an average solvent isotope effect of 1.5 +/- 0.2 for most aryl sulfide oxidations is consistent with proton transfer in the transition state of the rate-determining step. Activation parameters for oxidation of ethyl phenyl sulfide in tert-butyl alcohol/water are reported. From the pH dependence of oxidation rates and (13)C NMR equilibrium experiments, the estimated pK(a) of peroxymonocarbonate was found to be approximately 10.6.
The mechanism and kinetics of bicarbonate-catalyzed oxidations of sulfides by H(2)O(2) at the aqueous /cationic micellar interface have been investigated. The general term surfoxidant is introduced to describe the combination of an ionic surfactant with a reactive counterion that is itself an oxidant or activates an oxidant from the bulk solution to form an oxidant counterion. It is shown that the new catalytic cationic surfoxidant CTAHCO(3) (cetyltrimethylammonium bicarbonate) significantly enhances the overall oxidation rates as compared to the addition of bicarbonate salts to CTACl and CTABr, for which the halide counterions must undergo equilibrium displacement by the oxidant anion (peroxymonocarbonate, HCO(4)(-)). General equations based on the classic pseudophase model have been derived to account for the preequilibrium reaction in the aqueous and micellar phases, and the resulting model can be used to describe any micellar reaction with associated preequilibria. Rate constants and relevant equilibrium constants for HCO(4)(-) oxidations of aryl sulfides at micellar surfaces have been estimated for CTAHCO(3), CTACl, and CTABr. The second-order rate constants in the Stern layer (k(2)(m)) for sulfide oxidations by HCO(4)(-) are estimated to be approximately 50-fold (PhSEtOH) and approximately 180-fold (PhSEt) greater than the background rate constant k(m)(0) for oxidation by H(2)O(2) at the micellar surface. The estimated values of k(2)(m) are lower than the corresponding values in water by a factor of 20-70 depending on the substrate, but the high local concentration of the bicarbonate activator in the surfoxidant and the local accumulation of substrate as a result of strong binding to the micelle lead to a net increase in the observed reaction rates. Comparisons of CTAHCO(3)-activated peroxide to other highly reactive oxidants such as peroxymonosulfate (HSO(5)(-)) in aqueous surfactant media suggest a wide variety of potential applications for this green oxidant.
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The kinetics and mechanism of peroxymonocarbonate (HCO4−) formation in the reaction of hydrogen peroxide with bicarbonate have been investigated for the pH 6−9 range. A double pH jump method was used in which 13C-labeled bicarbonate solutions are first acidified to produce 13CO2 and then brought to higher pH values by addition of base in the presence of hydrogen peroxide. The time evolution of the 13C NMR spectrum was used to establish the competitive formation and subsequent equilibration of bicarbonate and peroxymonocarbonate following the second pH jump. Kinetic simulations are consistent with a mechanism for the bicarbonate reaction with peroxide in which the initial formation of CO2 via dehydration of bicarbonate is followed by reaction of CO2 with H2O2 (perhydration) and its conjugate base HOO− (base-catalyzed perhydration). The rate of peroxymonocarbonate formation from bicarbonate increases with decreasing pH because of the increased availability of CO2 as an intermediate. The selectivity for formation of HCO4− relative to the hydration product HCO3− increases with increasing pH as a consequence of the HOO− pathway and the slower overall equilibration rate, and this pH dependence allows estimation of rate constants for the reaction of CO2 with H2O2 and HOO− at 25 °C (2 × 10−2 M−1 s−1 and 280 M−1 s−1, respectively). The contributions of the HOO− and H2O2 pathways are comparable at pH 8. In contrast to the perhydration of many other common inorganic and organic acids, the facile nature of the CO2/HCO3− equilibrium and relatively high equilibrium availability of the acid anhydride (CO2) at neutral pH allows for rapid formation of the peroxymonocarbonate ion without strong acid catalysis. Formation of peroxymonocarbonate by the reaction of HCO3− with H2O2 is significantly accelerated by carbonic anhydrase and the model complex [Zn(II)L(H2O)]2+ (L = 1,4,7,10-tetraazacyclododecane).
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