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Influence of substitution on kinetics and mechanism of ring transformation of substituted S-[1-phenylpyrrolidin-2-on-3-yl]isothiuronium salts
Authors: Hanusek Jiří | Hejtmánková Ludmila | Štěrba Vojeslav | Sedlák Miloš
Year: 2004
Type of publication: článek v odborném periodiku
Name of source: Organic & Biomolecular Chemistry
Publisher name: Royal Society of Chemistry
Place: Cambridge
Page from-to: 1756-1763
Titles:
Language Name Abstract Keywords
cze Influence of substitution on kinetics and mechanism of ring transformation of substituted S-[1-phenylpyrrolidin-2-on-3-yl]isothiuronium salts Twelve new substituted S-(1-phenylpyrrolidin-2-one-3-yl)isothiuronium bromides and twelve corresponding 2-imino-5-(2-phenylaminoethyl)thiazolidin-4-ones have been prepared and characterised. Kinetics and mechanism of transformation reaction of S-[1-(4-methoxyphenyl)pyrrolidin-2-one-3-yl]isothiuronium bromide 1a and its N,N-dimethylderivative 5a into corresponding substituted thiazolidin-4-ones 2a and 6a have been studied in aqueous solutions of amine buffers (pH 8.1 ? 11.5) and sodium hydroxide solutions (0.005-0.5 mol?l?1) at 25 °C and at I = 1 mol?l?1 at pseudo-first-order reaction conditions. The kinetics observed shows that the transformation reaction is subject to general acid-base, and hydroxide-ion catalyses. Acid catalysis does not operate in the transformation of 1a; the rate-limiting step of the base-catalysed transformation is the decomposition of bicyclic tetrahedral intermediate In? and the Brřnsted dependence is non-linear (pKa ca 9.8). In the case of derivative 5a both base and acid catalyses make themselves felt. In the base catalysis, the rate-limiting step consists in the decomposition of bicyclic intermediate In, and the Brřnsted dependence is linear (beta = 0.9; pKa > 11.5). The acid-catalysed transformation of 5a also goes via the intermediate In, and the reaction is controlled by diffusion (beta ca 0). With compound 5a in triethylamine and butylamine buffers, the general base catalysis changes into specific base catalysis. The effect of substitution in aromatic moiety of compounds 1a-h and 3a-h on the course of transformation reaction has been studied in solutions of sodium hydroxide (0.005-0.5 mol?l?1) at 25 °C by the stopped-flow method. The electron-acceptor substituents 4-NO2 and 4-CN do not obey the Hammett correlation, which is due to a suppression of cross-conjugation in the ring-closure step of the transformation reaction.
eng Influence of substitution on kinetics and mechanism of ring transformation of substituted S-[1-phenylpyrrolidin-2-on-3-yl]isothiuronium salts Twelve new substituted S-(1-phenylpyrrolidin-2-one-3-yl)isothiuronium bromides and twelve corresponding 2-imino-5-(2-phenylaminoethyl)thiazolidin-4-ones have been prepared and characterised. Kinetics and mechanism of transformation reaction of S-[1-(4-methoxyphenyl)pyrrolidin-2-one-3-yl]isothiuronium bromide 1a and its N,N-dimethylderivative 5a into corresponding substituted thiazolidin-4-ones 2a and 6a have been studied in aqueous solutions of amine buffers (pH 8.1 ? 11.5) and sodium hydroxide solutions (0.005-0.5 mol?l?1) at 25 °C and at I = 1 mol?l?1 at pseudo-first-order reaction conditions. The kinetics observed shows that the transformation reaction is subject to general acid-base, and hydroxide-ion catalyses. Acid catalysis does not operate in the transformation of 1a; the rate-limiting step of the base-catalysed transformation is the decomposition of bicyclic tetrahedral intermediate In? and the Brřnsted dependence is non-linear (pKa ca 9.8). In the case of derivative 5a both base and acid catalyses make themselves felt. In the base catalysis, the rate-limiting step consists in the decomposition of bicyclic intermediate In, and the Brřnsted dependence is linear (beta = 0.9; pKa > 11.5). The acid-catalysed transformation of 5a also goes via the intermediate In, and the reaction is controlled by diffusion (beta ca 0). With compound 5a in triethylamine and butylamine buffers, the general base catalysis changes into specific base catalysis. The effect of substitution in aromatic moiety of compounds 1a-h and 3a-h on the course of transformation reaction has been studied in solutions of sodium hydroxide (0.005-0.5 mol?l?1) at 25 °C by the stopped-flow method. The electron-acceptor substituents 4-NO2 and 4-CN do not obey the Hammett correlation, which is due to a suppression of cross-conjugation in the ring-closure step of the transformation reaction. Kinetics, mechanism, ring transformation, substituted S-[1-phenylpyrrolidin-2-on-3-yl]isothiuronium salts

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