Elevated reaction order of 1,3,5-tri-tert-butylbenzene bromination as evidence of a clustered polybromide transition state: a combined kinetic and computational study
The kinetics and mechanism of concurrent bromo-de-protonation and bromo-de-tert-butylation of 1,3,5-tri-tert-butylbenzene at different bromine concentrations were studied experimentally and theoretically. Both reactions have high order in bromine (experimental kinetic orders ~5 and ~7, respectively). According to quantum chemical DFT calculations, such high reaction orders are caused by participation of clustered polybromide anions Br2n?1- in transition states. Bromo-de-tert-butylation has a higher order due to its bigger reaction center demanding clusters of extended size. A significant primary deuterium kinetic isotope effect (KIE) for bromo-de-protonation is measured indicating proton removal is rate limiting, as confirmed by computed DFT models. The latter predict a larger value for the KIE than measured and possible explanations for this are discussed.
Shernyukov, Andrey V.,Genaev, Alexander M.,Salnikov, George E.,Shubin, Vyacheslav G.,Rzepa, Henry S.
Derivatives of m-di-tert-butylbenzene. Part VI. The preparation of miscellaneous halogenated compounds
The preparation of seven series of dihalogenated and monohalogenated derivatives of m-di-tert-butylbenzene, comprising twenty three new compounds, is described.
Koning, Adrianus Jan de
p. 421 - 425
(2007/10/02)
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