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

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 Full article

Journal

Organic and Biomolecular Chemistry
ISSN: 1477-0520 , E-ISSN: 1477-0539

Output data

Year: 2019, Volume: 17, Number: 15, Pages: 3781-3789 Pages count : 9 DOI: 10.1039/c9ob00607a

Authors

Shernyukov Andrey V. ^1,2 , Genaev Alexander M. ¹ , Salnikov George E. ^1,2,3 , Shubin Vyacheslav G. ¹ , Rzepa Henry S. ⁴

Affiliations

1	(Данные Web of science) Russian Acad Sci, Siberian Branch, NN Vorozhtsov Novosibirsk Inst Organ Chem, Acad Lavrentiev Ave 9, Novosibirsk 630090, Russia
2	(Данные Web of science) Novosibirsk State Univ, Pirogova 2, Novosibirsk 630090, Russia
3	(Данные Web of science) Int Tomog Ctr, Inst Skaya 3a, Novosibirsk 630090, Russia
4	(Данные Web of science) Imperial Coll London, MSRH, Dept Chem, 80 Wood Lane, London W12 0BZ, England

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 similar to 5 and similar to 7, respectively). According to quantum chemical DFT calculations, such high reaction orders are caused by participation of clustered polybromide anions Br-2n-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 A.V. , Genaev A.M. , Salnikov G.E. , Shubin V.G. , Rzepa H.S.
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
Organic and Biomolecular Chemistry. 2019. V.17. N15. P.3781-3789. DOI: 10.1039/c9ob00607a WOS Scopus РИНЦ

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