Nonlinear structure-reactivity correlations. The reactivity of nucleophilic reagents toward esters

Jencks, William P.; Gilchrist, Mary.

doi:10.1021/ja01012a030

Cited by 357 publications

(253 citation statements)

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“…Comparison of k 3 for compounds 1a-e give rise to a Hammett plot with a ρ value of 0.99 (r 2 = 0.97) which is also consistent with a B Ac 2 mechanism with nucleophilic catalysis, 8 where the rate determining step is the hydroxide attack on the neutral substrate.…”

Section: Hydrolysis In Basic Mediasupporting

confidence: 67%

“…8 This substituent effect is indicative of a pre-equilibrium protonation of the substrate followed by the rate determining formation of the tetrahedral intermediate, with decomposition occurring by benzimidazole acting as a leaving group. Indeed, there are three basic sites in the carbamate molecule, the exocyclic and endocyclic nitrogens and the acyl oxygen, and so any of the three tautomers can be the starting species in the hydrolysis.…”

Section: Hydrolysis In Acidic Mediamentioning

confidence: 99%

See 1 more Smart Citation

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: Hydrolysis In Basic Mediasupporting

confidence: 67%

Section: Hydrolysis In Acidic Mediamentioning

confidence: 99%

Kinetics and mechanism of hydrolysis of benzimidazolylcarbamates

Norberto¹,

Santos²,

Iley³

et al. 2007

J. Braz. Chem. Soc.

View full text Add to dashboard Cite

show abstract

“…The differences in AC,' values in H 2 0 and D 2 0 for the anhydride and trifluoroacetate series are not inconsistent with the important similarities which have led to both series being classed as reacting by general base catalysis (29). Whether this reaction is to be regarded as a single dominating concerted process (39,40) o r several stages involving pre-equilibria has been argued by several authors (27)(28)(29).…”

Section: Discussionmentioning

confidence: 86%

Neutral Solvolysis of Acyl Carbon and the Temperature Dependence of the Kinetic Solvent Isotope Effect

Rossall¹,

Robertson²

1975

Can. J. Chem.

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The temperature dependence of the rate of hydrolysis of benzoic, phthalic, and succinic anhydrides have been determined in H2O and D2O under "neutral" conditions. Corresponding data have been obtained for methyl trifluoroacetate. While both series supposedly react by the same BAc2 mechanism, remarkable differences are made obvious by this investigation. Possible sources of such differences are proposed.

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“…There are ample experimental data on nucleophilic substitution on p-NPA 2,23,[47][48][49][50] and the available data for p-NPA form a reliable basis for linear free energy relationships (LFERs). 51 Most importantly, however, the change in reaction pathway from general-base catalysed hydrolysis to nucleophilic substitution of 1a is mirrored by p-NPA.…”

Section: 31mentioning

confidence: 99%

General‐base catalysed hydrolysis and nucleophilic substitution of activated amides in aqueous solutions

Buurma

Blandamer

Engberts

2003

J of Physical Organic Chem

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General-base catalysed hydrolysis and nucleophilic substitution of activated amides in aqueous solutions Buurma, NJ; Blandamer, MJ; Engberts, Jan; Buurma, Niklaas J. Other than for strictly personal use, it is not permitted to download or to forward/distribute the text or part of it without the consent of the author(s) and/or copyright holder(s), unless the work is under an open content license (like Creative Commons).Take-down policy If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.Downloaded from the University of Groningen/UMCG research database (Pure): http://www.rug.nl/research/portal. For technical reasons the number of authors shown on this cover page is limited to 10 maximum. ABSTRACT: The reactivity of 1-benzoyl-3-phenyl-1,2,4-triazole (1a) was studied in the presence of a range of weak bases in aqueous solution. A change in mechanism is observed from general-base catalysed hydrolysis to nucleophilic substitution and general-base catalysed nucleophilic substitution. A slight tendency is also observed for the more hydrophobic general bases to show higher reactivity towards 1a. Aspartame is an effective nucleophile, possibly because nucleophilic substitution is subject to intramolecular general-base catalysis. A general conclusion derived from the present results is that unexpected rate effects can only be rationalised provided that the detailed reaction mechanisms are well understood. Copyright  2003 John Wiley & Sons, Ltd.KEYWORDS: hydrolysis; changes in mechanism; general-base catalysis; general-acid catalysis; nucleophilic substitution INTRODUCTIONThe hydrolysis reaction of the activated amide 1-benzoyl-3-phenyl-1,2,4-triazole (1a) is general-base catalysed (Scheme 1). 1In highly aqueous solutions, the concentration of water is sufficiently high for water to act (detectably) as both a general base and a nucleophile. Hence, in the absence of other general bases, the water-catalysed (i.e. pHindependent) hydrolysis is the sole reaction. In the presence of sufficiently basic cosolutes, the watercatalysed reaction is unimportant. More basic cosolutes are much more effective catalysts for hydrolysis than water. Consequently, despite the relatively low molality of added general bases, the general-base catalysed hydrolysis pathway competes with the water-catalysed pathway. It is stressed that even though in the watercatalysed reaction the second water molecule in the activated complex (i.e. B = H 2 O, Scheme 1) acts as a general base, a distinction is drawn between the watercatalysed reaction and general-base catalysed reaction.Increased basicity of cosolutes usually leads to a concomitant increase in nucleophilicity. This increase in nucleophilicity provides an alternative reaction pathway: nucleophilic attack on the carbonyl functionality, followed by loss of the (substituted) 1,2,4-triazole leaving group (Scheme 2).In this mechanism, the nucleophilic water molecule is replaced by a stronge...

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Nonlinear structure-reactivity correlations. The reactivity of nucleophilic reagents toward esters

Cited by 357 publications

References 0 publications

Kinetics and mechanism of hydrolysis of benzimidazolylcarbamates

Kinetics and mechanism of hydrolysis of benzimidazolylcarbamates

Neutral Solvolysis of Acyl Carbon and the Temperature Dependence of the Kinetic Solvent Isotope Effect

General‐base catalysed hydrolysis and nucleophilic substitution of activated amides in aqueous solutions

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