- Kinetics and mechanism of alkaline hydrolysis of Y-substituted phenyl phenyl carbonates
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Second-order rate constants (kOH-) have been measured spectrophotometrically for alkaline hydrolysis of Y-substituted phenyl phenyl carbonates (2a-j) and compared with the kOH- values reported previously for the corresponding reactions of Y-substituted phenyl benzoates (1a-j). Carbonates 2a-j are 8 ~ 16 times more reactive than benzoates 1a-j. The Hammett plots correlated with σ- and σo constants exhibit many scattered points, while the Yukawa-Tsuno plot results in excellent linear correlation with ρ = 1.21 and r = 0.33. Thus, the reaction has been concluded to proceed through a concerted mechanism in which expulsion of the leaving group is advanced only a little. However, one cannot exclude a possibility that the current reaction proceeds through a forced concerted mechanism with a highly unstable intermediate.
- Kim, Song-I,Hwang, So-Jeong,Jung, Eun-Mi,Um, Ik-Hwan
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experimental part
p. 2015 - 2018
(2010/12/19)
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- Nouvelles syntheses de phenyl-4 allophanates
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The synthesis of eighteen alkyl or phenyl 4-phenylallophanates is described.The classical methods used for the preparation of allophanates - namely, condensation between an isocyanate and a carbamate, reaction between a urea and a carbonate, desulphurization of 3-thioallophanic acid esters - proved to be unsuitable for the synthesis of 4-phenylallophanic acid phenyl esters.Variously substituted 4-phenylallophanates can be obtained by reacting a chloroformate with a phenylurea in the presence of pyridine, which promotes the transfer of the carboxylate group.The occurence of electrondonating substituents, such as CH3, at the nitrogen atom receiving the carboxylate group promotes the reaction.The low yields observed for aliphatic esters can be accounted for by the instability of the alkyl chloroformate-pyridine complex.The structures of the derivatives synthesized was corroborated by the analysis of their n.m.r. and u.v. spectra. Non-commercial phenyl chloroformates were prepared by reacting phosgene with a sodium phenolate in the presence of anhydrous benzene.
- Al Sabbagh, Mohamed Mowafak,Calmon, Michelle,Calmon, Jean-Pierre
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