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Kinetics and Mechanism of Acetoxymercuration and Acid-Catalysed Hydration of α-Alkylstyrenes
Joint Laboratory of Solid State Chemistry, Academy of Sciences of the Czech Republic, University of Pardubice, 532 10 Pardubice, Czech Republic
Department of Physical Chemistry, Palacky University, 771 46 Olomouc, Czech Republic
Department of Organic Chemistry, University of Pardubice, 532 10 Pardubice, Czech Republic
* Author to whom correspondence should be addressed.
Received: 15 April 2004; in revised form: 10 January 2005 / Accepted: 10 January 2005 / Published: 31 January 2005
Abstract: Nine α-alkylstyrenes carrying the following substituents have been synthesised: methyl, ethyl, propyl, butyl, pentyl, isobutyl, isopropyl, sec-butyl and tert-butyl. Kinetics has been measured for the reaction of these compounds with mercuric acetate in anhydrous acetic acid at 25 °C. The rate constants are very sensitive to inductive effects (ρI = –49.5 in AISE theory) and steric effects (ψ = –1.59 according to Charton). These results support the presumed existence of an intermediate with an asymmetrically bound acetylmercuric cation to carbon atoms of the vinyl group of styrene. The kinetics of an acid-catalysed hydration of the above-mentioned α-alkylstyrenes were also measured in aqueous sulphuric acid at 25 °C. The derivatives exhibited kinetically a consecutive isomerisation reaction giving the more stable substituted styrenes. The values of the slope m‡m* of the dependence upon the excess acidity function (X) were evaluated, and exceptionally low values were found for the butyl and pentyl substituents (1.02 and 0.73, respectively), while on the other hand tert-butyl showed an exceptionally high value (3.28). On the basis of the facts, a mechanism has been suggested for the acid-catalysed hydration, involving the reaction of a relatively stable and sterically hindered carbocation with water as the rate-limiting step of the reaction.
Keywords: Styrenes; methoxymercuration; hydration; substituent effects
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Svoboda, J.; Pelcová, M.; Nevěčná, T.; Pytela, O. Kinetics and Mechanism of Acetoxymercuration and Acid-Catalysed Hydration of α-Alkylstyrenes. Int. J. Mol. Sci. 2005, 6, 30-44.
Svoboda J, Pelcová M, Nevěčná T, Pytela O. Kinetics and Mechanism of Acetoxymercuration and Acid-Catalysed Hydration of α-Alkylstyrenes. International Journal of Molecular Sciences. 2005; 6(1):30-44.
Svoboda, Jan; Pelcová, Monika; Nevěčná, Taťjana; Pytela, Oldřich. 2005. "Kinetics and Mechanism of Acetoxymercuration and Acid-Catalysed Hydration of α-Alkylstyrenes." Int. J. Mol. Sci. 6, no. 1: 30-44.