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.
Highlights
Styrenes and their derivatives are often studied compounds
Particular attention has been focused on electrophilic addition reactions to the double bond in the side chain of the aromatic ring
Within their research work on kinetics and mechanism of methoxymercuration of styrenes [1,2,3,4,5,6,7,8] and other alkenes [8,9,10,11,12,13,14,15,16], the authors have focused their attention especially on substituent effects [2, 3, 6, 8, 10, 12], including the steric ones [10, 12]; to salt effects [14, 15], temperature dependences of the reaction rate constant [1, 2, 6] and in the context with the abovementioned areas, to the structure of the addition intermediate [3, 4, 8,9,10, 13,14,15,16]. From these studies it follows that methoxymercuration is an electrophilic reaction, whose rate-limiting step involves formation of an intermediate with an acetylmercuric cation asymmetrically bound to the carbon atoms of the styrene vinyl group
Summary
Styrenes and their derivatives are often studied compounds. Besides their industrial applications, particular attention has been focused on electrophilic addition reactions to the double bond in the side chain of the aromatic ring. The aim of this paper is, on the basis of kinetic measurements and evaluation of substituent effects, to verify and/or suggest mechanisms of acetoxymercuration and acidcatalysed hydration of the title α-alkylstyrenes, and to compare the results obtained here with those obtained elsewhere for other styrene derivatives.
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
