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Kinetic investigatins of the reactions of hindered phenols with N-fluoro-1,4-diazoniabicyclo[2.2.2]octane salt analoguesStavber, Stojan ; Jereb, Marjan, kemik ; Zupan, Marko, 1947-The kinetics of reactions of hindered phenols (2,4,6-trimethylphenol, 2,6-di-tert-butyl-4-methylphenol and 2,4,6-tri-tert-butylphenol) with 1-fluoro-4-chloromethyl-1,4-diazoniabicyclo [2.2.2]octane ... bis(tetrafluoroborate) (SelectfluorTM, F-TEDA-BF4) in acetonitrile in the absence or presence of various sources of external nucleophile (alcohols, water, trifluoroacetic acid) were studied. The reactions exhibitedoverall second-order kinetics, whereas products formation was strongly dependent on reaction conditions. Fluorination took place in neat MeCN; in the presence of water or alcohols, para quinols or para quinol ethers were formed exclusively; under acidic conditions (TFA), Ritter-type amidation was found to be the predominant process. Values for second-order rate constants k2 were found to be dependent on the structure of the target phenol and decreased with bulkiness of the substrate. Methanol slightly increased the rate, whereas water decreased it considerably. Activation enthalpies (between 72 and 78 kJ mol-1) and activation entropies (between -5 and -42 J mol-1 K-1) were obtained. Activation entropies were found to be higher for less-hindered substrates, indicating that the rate-determining steps were mainly regulated by steric factors. Grunwald-Winstein correlation of log k2 with solvent ionizing power Y revealed a relatively small correlation factor m. An electron-transfer-type process following the rate-determining formation of substrate-reagent complex was postulated as the key step of the reaction pathway.Source: Journal of physical organic chemistry. - ISSN 0894-3230 (Vol. 15, 2002, str. 56-61)Type of material - article, component partPublish date - 2002Language - englishCOBISS.SI-ID - 16352039
Author
Stavber, Stojan |
Jereb, Marjan, kemik |
Zupan, Marko, 1947-
Topics
hindered phenols |
kinetics |
octane salts |
electron transfer
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Database name | Field | Year |
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Links to authors' personal bibliographies | Links to information on researchers in the SICRIS system |
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Stavber, Stojan | 06058 |
Jereb, Marjan, kemik | 19177 |
Zupan, Marko, 1947- | 01317 |
Source: Personal bibliographies
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