A General Acid-Catalyzed Anion Breakdown Associated with an E1cB Reaction in the Hydrolysis of Aryl N-(Substituted Phenylsulfonyl)carbamates

Vigroux, Alain; Bergon, Michel; Bergonzi, Catherine; Tisnès, P.

doi:10.1021/ja00105a020

Cited by 20 publications

(24 citation statements)

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“…IR spectra were obtained using a Hitachi 270-50 spectrophotometer on KBr pastille and only diagnostic bands are reported on a cm -1 scale. 1 H NMR and 13 C NMR spectra were recorded at 400 and 100.4 MHz, respectively, in chloroform-d or d 6 DMSO as solvents, and chemical shifts are reported in parts per million (ppm, δ), using as reference the appropriate signal for residual solvent protons. Coupling constants are reported to the nearest 0.1 Hz.…”

Section: Methodsmentioning

confidence: 99%

“…Kinetics and mechanisms of basic hydrolysis of carbamates are well documented in literature, leading to the conclusion that tertiary carbamates hydrolyze always via a B Ac 2 mechanism while secondary ones decompose by a unimolecular elimination, if they have a good leaving group, or via B Ac 2 mechanism if they do not have it. [4][5][6] This paper, which presents unreported kinetic studies on tertiary carbamates, where the nitrogen atom is part of a cycle, involves the synthesis of new carbamates with potential bioactivity and the evaluation of the mechanism of hydrolysis of aryl benzimidazole-1-carbamates (1a-d, 2) over the pH range 1-13.…”

Section: Introductionmentioning

confidence: 99%

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Kinetics and mechanism of hydrolysis of benzimidazolylcarbamates

Norberto¹,

Santos²,

Iley³

et al. 2007

J. Braz. Chem. Soc.

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Através da carbamoilação do 2-aminobenzimidazole com diferentes cloroformatos substituídos, sintetizaram-se novos N- [1-(2-amino)benzimidazolil]carbamatos. Estudouse a hidrólise em meio aquoso destes carbamatos numa gama de pH compreendida entre 1 e 13, a uma temperatura de 25 ºC. Os parâmetros cinéticos avaliados levaram a concluir que até pH 4 a reação se processa por mecanismo que envolve o ataque bimolecular da água ao substrato N-protonado. Esta é a primeira vez que este comportamento é observado em carbamatos, sendo muito provavelmente devido à diferença de basicidade entre um dos azotos do anel de benzimidazolilo e o oxigênio da função carbamato. Para valores mais elevados de pH, os resultados são consistentes com um mecanismo B Ac 2, atuando a água como nucleófilo entre pH 4 e 7 enquanto que em pH superior o íon hidróxido é o nucleófilo.Synthesis of new 2-aminobenzimidazole-1-carbamates was accomplished by carbamoylation of 2-aminobenzimidazole using different substituted phenyl chloroformates. The aqueous hydrolysis of the new compounds was examined in the pH range 1-13 at 25 o C. The evaluated kinetic parameters led to the conclusion that up to pH 4 reaction proceeds by a bimolecular attack of water to the N-protonated substrate. This is the first time this behavior is described for carbamates, and can be ascribed to the higher basicity of the benzimidazolyl moiety when compared with the carbonyl oxygen. For higher values of pH, the results are consistent with a B Ac 2 mechanism with nucleophilic catalysis, but while between pH 4 and pH 7 water acts as the nucleophile, for pH> 7 the hydroxide ion is the acting species.

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Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Kinetics and mechanism of hydrolysis of benzimidazolylcarbamates

Norberto¹,

Santos²,

Iley³

et al. 2007

J. Braz. Chem. Soc.

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“…The values of the constants k a , k p , k OH , and K app required to fit the experimental rate constants k obsd to Equation (1) [7] montre que la valeur a de Brùnsted associeÂe aÁ ce type de reÂaction croît fortement avec leÂnergie de la liaison C À O aÁ rompre (une stabilisation da la liaison C À O denviron 2,3 kcal mol À1 se traduit par une augmentation de a denviron 0,3). Contrairement aÁ la rupture CÀO, les coupures des liaisons SÀO et PÀO mises en jeu dans des systeÁmes apparenteÂs tels que les esters de N-(methoxycarbonyl)sulfamate et les monoesters de phosphate et de sulfate avec de bons groupes partants seffectuent sans catalyse apparente des tampons.…”

Section: Resultsunclassified

“…Buffer catalysis is assumed to be the result of the nonexistence of the zwitterionic species PhOSO 2 N À CO ± O (H)Ph. Comparison with previously studied phenyl N-(phenylsulfonyl)carbamate [7] indicates that the Brùnsted a value associated with such a mechanism increases sharply as the CÀO bond which is cleaved becomes stronger (a change in reactivity of ca. 2.3 kcal mol…”

mentioning

confidence: 89%

“…[8] In the latter case, no buffer catalysis was detected in acid for SÀO cleavage, while the analogous CÀO breaking reaction previously reported for phenyl N-(phenylsulfonyl)-carbamate anion (PhSO 2 N À CO À OPh) was unambiguously demonstrated to be general buffer-acid-catalyzed. [7] The different behaviors observed in acid between the C À O and SÀO cleavage reactions of N-(oxycarbonyl)sulfamate esters are discussed.…”

Section: Introductionmentioning

confidence: 99%

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A General Buffer-Acid-Catalyzed C−O Cleavage Reaction in the Hydrolysis of PhenylN-(Phenoxycarbonyl)sulfamate Ester

Blans

Vigroux

1999

Chem. Eur. J.

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Rate constants and products are reported for the aqueous decomposition (pH 0 ± 14) of phenyl N-(phenoxycarbonyl)sulfamate (pK a 1.18) at 50 8C. The pH ± rate profile indicates a rate law that includes three terms: two pH-independent terms, k a in acid and k p around neutral pH, with k a b k p , and a hydroxide-ion-dependent term, k OH . The observation of non-first-order behavior in the pH range between 1.6 and 4.1 points to the accumulation of a nonsteady-state intermediate that is concluded to be phenyl sulfamate. The latter result, coupled with the observation at low pH of general acid catalysis by buffers, reveals that each of the hydrolytic paths involves i) the anionic form specifically and ii) carbon ± oxygen bond fission. Buffer catalysis is assumed to be the result of the nonexistence of the zwitterionic species PhOSO 2 N À CO ± O (H)Ph. Comparison with previously studied phenyl N-(phenylsulfonyl)carbamate [7] indicates that the Brùnsted a value associated with such a mechanism increases sharply as the CÀO bond which is cleaved becomes stronger (a change in reactivity of ca. 2.3 kcal mol À1gives rise to a change in a of about 0.3). In contrast to CÀO cleavage, SÀO and PÀO fissions involved in related systems such as N-(methoxycarbonyl)sulfamate esters and phosphate and sulfate monoesters with good leaving groups do not exhibit buffer-acid catalysis. It is concluded that unambiguous distinction between inter-and intramolecular general acid catalysis is not currently possible for those compounds.

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