Elevated reaction order of 1,3,5-tri-tert-butylbenzene bromination as evidence of a clustered polybromide transition state: a combined kinetic and computational studyElectronic supplementary information (ESI) available. See DOI: 10.1039/c9ob00607a

• Main Authors: Shernyukov, Andrey V, Genaev, Alexander M, Salnikov, George E, Shubin, Vyacheslav G, Rzepa, Henry S
• Format: Article
• Language: English
• ISSN: 1477-0520; 1477-0539
• DOI: 10.1039/c9ob00607a

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 Br 2 n −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. 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.