Deuterium solvent isotope effects on reactions involving the aqueous hydroxide ion

Gold, Victor; Grist, S.

doi:10.1039/p29720000089

Cited by 48 publications

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“…There is a good agreement between the present value and the values reported for the fractionation factor of OH − ion [31][32][33][34]. Rate of reaction decreases with decreasing methanol content.…”

Section: Mechanism and Rate Law Of Os(viii) Catalyzed Oxidation Of Bisupporting

confidence: 89%

“…Kresge and Allred [31] have obtained a value of 0.80 from NMR studies for the isotopic fractionation factor of OH − ion, which was confirmed by the works of Gold and Grist [32]. There is a fair agreement between the present value and the values reported [32][33][34] for the fractionation factor of OH − ion.…”

Section: Mechanism and Rate Law Of Uncatalyzed Oxidation Of Biotinsupporting

confidence: 85%

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Os(VIII)-catalyzed and uncatalyzed oxidation of biotin by chloramine-T in alkaline medium: Comparative mechanistic aspects and kinetic modeling

Ramalingaiah

Jagadeesh

Puttaswamy

2007

Journal of Molecular Catalysis A: Chemical

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Sodium N-chloro-p-toluenesulfonamide (chloramine-T or CAT) is the prominent member of aromatic sulfonyl haloamines and has received considerable attention as a mild oxidant for several organic compounds. d-Biotin, a member of the B-vitamin family, is an essential nutrient in human nutrition as is commonly referred to as Vitamin H. Controlled oxidation of biotin to biotin sulfoxide forms a very important synthetic route in biochemical reactions. Optimum conditions have been developed for the oxidation of biotin to biotin sulfoxide. Literature survey has revealed that no attention has been paid towards the controlled oxidation of biotin to biotin sulfoxide by N-haloamines from the kinetic and mechanistic view points. This prompted us to undertake the title investigation. The kinetics of Os(VIII) catalyzed and uncatalyzed oxidation of biotin by CAT have been studied in NaOH medium at 303 K under identical experimental conditions. The stoichiometry (1:1) and the oxidation product (biotin sulfoxide) are the same for Os(VIII) catalyzed and uncatalyzed reactions. Biotin sulfoxide was confirmed by GC-MS analysis. In Os(VIII) catalyzed oxidation, the rate law is [Biotin] x /[NaOH] −y for uncatalyzed reaction, where x and y are less than unity. The reaction was subjected to changes in: (a) concentration of added reduction product of CAT, p-toluenesulfonamide, (b) ionic strength, (c) dielectric permittivity and (d) halide ions effect in both the cases. Proton inventory studies made in a mixture of H 2 O-D 2 O indicated the participation of OH − ion in the formation of transition state. The reaction fails to initiate polymerization of acrylonitrile. Activation parameters for the composite reaction were deduced from Arrhenius plots. In case of uncatalyzed reactions, the reaction constants involved in the proposed scheme were deduced. Under the identical set of experimental conditions, the kinetics of Os(VIII) catalyzed oxidation of biotin by CAT in alkaline medium has been compared with uncatalyzed reactions, revealing that the catalyzed reactions are eight fold faster than the uncatalyzed reactions. Hence, Os(VIII) acts as an efficient catalyst for the oxidation of biotin by CAT in alkaline medium. The catalytic constant (K C ) has been calculated at different temperatures and the values of activation parameters with respect to catalyst have been evaluated from the plots of log K C versus 1/T. Some spectroscopic evidence for the formation of 1:1 complex between oxidant and Os(VIII) has been obtained. CH 3 C 6 H 4 SO 2 NHCl has been postulated as the reactive oxidizing species in both the cases. The observed experimental results have been explained by plausible mechanisms and the related rate laws have been deduced for both catalyzed and uncatalyzed reactions.

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Section: Mechanism and Rate Law Of Os(viii) Catalyzed Oxidation Of Bisupporting

confidence: 89%

Section: Mechanism and Rate Law Of Uncatalyzed Oxidation Of Biotinsupporting

confidence: 85%

Os(VIII)-catalyzed and uncatalyzed oxidation of biotin by chloramine-T in alkaline medium: Comparative mechanistic aspects and kinetic modeling

Ramalingaiah

Jagadeesh

Puttaswamy

2007

Journal of Molecular Catalysis A: Chemical

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“…It is believed that this is because the hydroxide ion is strongly solvated in aqueous solution through hydrogen bond formation to three water molecules, as shown in 1 (9). Hydrogen bonding is known to lower the vibrational frequencies of bonds to the hydrogens involved, and these solvating water molecules consequently have weaker bonds, with less isotopically sensitive zero-point energy, than do ordinary water molecules in the bulk solvent (10).…”

Section: Discussionmentioning

confidence: 99%

“…3 If hydron transfer from acetaldehyde to the hydroxide ion takes place indirectly through one of the water molecules originally solvating the hydroxide ion, n in eqs. [8] and [9] will be equal to 1. If, on the other hand, hydron transfer is direct, then one of the solvating molecules must be lost before the transition state is reached, and n = 0.…”

Section: Discussionmentioning

confidence: 99%

“…The more remote hydrogens of the water molecules solvating the hydroxide ion are believed to have fractionation factors similar to those of bulk water, 4 = 1.00; the other two kinds of hydrogen have been assigned the values +, = 1.15 and 4, = 0.72 (9). In the transition state these latter hydrogens are on the way to becoming bulk water molecules and their fractionation factors, 4: and +: , should therefore lie between the corresponding initial state values and that for bulk water, i.e., unity.…”

Section: Discussionmentioning

confidence: 99%

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The solvent deuterium isotope effect on the hydroxide-ion-catalyzed conversion of acetaldehyde to its enolate ion

Keeffe¹,

Kresge²

1988

Can. J. Chem.

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. J. Chem. 66, 2440Chem. 66, (1988.Rates of proton transfer from acetaldehyde to the hydroxide ion were measured by iodine scavenging in H 2 0 and in D 2 0 solution at 25OC; the results give the solvent isotope effect kHo-/koo-= 0.73 * 0.02. This value is somewhat more consistent with an estimate, made using fractionation factor theory, for hydron transfer directly from the substrate to the hydroxide ion than with another estimate, made similarly, for hydron transfer through an intervening water molecule. J. R. KEEFFE et A. J. KRESGE. Can. J. Chem. 66, 2440 (1988.On a mesurC les vitesses de transfert du proton de l'acttaldthyde a l'ion hydroxyde en utilisant I'iode comme pikge dans I'eau et dans une solution de D 2 0 a 25°C. On obtient dans ces conditions un effet isotopique du solvant de kHo-/koo-= 0,73 * 0,02.Cette valeur se rapproche davantage de I'tvaluation faite, selon la thCorie du facteur de fractionnement, pour le transfert direct de l'hydron du substrat vers l'ion hydroxyde, que d'une autre Cvaluation faite de la meme faqon, pour le transfert de l'hydron via la participation d'une moltcule d'eau.[Traduit par la revue]There is much current interest in simple enols (for reviews, see ref. 1) and, in our recent examination of some of the chemistry of the simplest en01 of all, vinyl alcohol, we determined the solvent deuterium isotope effect on the hydroniumion-catalyzed formation of this substance from acetaldehyde, eq. [I] (2). We now wish to report the results of a companion study, which provides the solvent isotope effect on the reaction of acetaldehyde with hydroxide ion to give the enolate ion, e q 121. ExperimentalRates of reaction of acetaldehyde with hydroxide ion were measured as before (2) by using iodine to scavenge the enolate ion product as it formed. Initial stoichiometric aldehyde and iodine concentrations in the reaction mixtures were ca. 2 X M and 1 X M respectively. Reactions were followed to completion; the data obeyed the first-order rate law well, and observed first-order rate constants were calculated by least-squares fitting to an exponential function (3). Hydroxide ion concentrations were determined by acidimetric titration of spent reaction solutions.

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Flash photolysis of 4-diazoisochroman-3-one in aqueous solution. Hydration of the carbene produced by loss of nitrogen and ketonization of the enol hydration product

Chiang

Eustace

Jefferson

et al. 2000

J. Phys. Org. Chem.

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Deuterium solvent isotope effects on reactions involving the aqueous hydroxide ion

Cited by 48 publications

References 0 publications

Os(VIII)-catalyzed and uncatalyzed oxidation of biotin by chloramine-T in alkaline medium: Comparative mechanistic aspects and kinetic modeling

Os(VIII)-catalyzed and uncatalyzed oxidation of biotin by chloramine-T in alkaline medium: Comparative mechanistic aspects and kinetic modeling

The solvent deuterium isotope effect on the hydroxide-ion-catalyzed conversion of acetaldehyde to its enolate ion

Flash photolysis of 4-diazoisochroman-3-one in aqueous solution. Hydration of the carbene produced by loss of nitrogen and ketonization of the enol hydration product

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