Kinetics and mechanism of the acetate catalysed hydrolysis of 4-methoxyphenyl chloroformate and 4-methoxyphenyl fluoroformate in aqueous dioxan. Evidence for rate-determining attack of acetate ions on an intermediate mixed anhydride

doi:10.1039/P29760000935

Paper

Kinetics and mechanism of the acetate catalysed hydrolysis of 4-methoxyphenyl chloroformate and 4-methoxyphenyl fluoroformate in aqueous dioxan. Evidence for rate-determining attack of acetate ions on an intermediate mixed anhydride

Published 1976 · A. Queen, T. A. Nour

Journal of The Chemical Society-perkin Transactions 1

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Abstract

Esters of fluoroformic acid hydrolyse more rapidly than the corresponding chloroformate esters, suggesting that carbon–halogen bond breaking is not greatly advanced in the rate-determining step. The rate of reaction of 4-methoxyphenyl fluoroformate with aqueous dioxan is markedly decreased in the presence of acetate ions whereas the rate of reaction of 4-methoxyphenyl chloroformate is increased. The rate curves for the latter reaction are sigmoid in shape. The results are interpreted in terms of the formation of an intermediate mixed anhydride for both reactions, which then undergoes nucleophilic attack by acetate ions to yield acetic anhydride and the phenol. This step is rate determining in the case of the fluoroformate.

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Acetate ions catalyze the hydrolysis of 4-methoxyphenyl chloroformate and 4-methoxyphenyl fluoroformate in aqueous dioxan, with the rate-determining attack on an intermediate mixed anhydride being crucial for both reactions.

PopulationOlder adults (50-71 years)

Sample size24

MethodsObservational

OutcomesBody Mass Index projections

ResultsSocial networks mitigate obesity in older groups.

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Paper

Kinetics and mechanism of the acetate catalysed hydrolysis of 4-methoxyphenyl chloroformate and 4-methoxyphenyl fluoroformate in aqueous dioxan. Evidence for rate-determining attack of acetate ions on an intermediate mixed anhydride

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References

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Urazolium diacetate as a new, efficient and reusable Brønsted acid ionic liquid for the synthesis of novel derivatives of thiazolidine-4-ones

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Correlation of the rates of solvolysis of acetic p-toluenesulfonic anhydride (acetyl p-toluenesulfonate) and a comparison with acetyl halides†

Acetyl p-toluenesulfonate solvolysis rates are consistent with an SNl reaction with appreciable nucleophilic solvation or an SN2 reaction with a loose transition state, leading to similar transition state structures.

Correlation of the Rates of Solvolysis of i-Butyl Fluoroformate and a Consideration of Leaving-Group Effects

The specific rates of solvolysis of isobutyl fluoroformate (1) at 40.0°C in 22 solvents correlate well with the extended Grunwald-Winstein equation, with the addition-elimination pathway being rate-determining.

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Neopentyl chloroformate solvolyzes faster in fluoroalcohol-rich solvents due to a 1,2-methyl shift, leading to a tertiary alkyl cation, outweighing weak nucleophilicity solvents.

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