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Contrasting kinetic behaviour of allyl and crotyl alcohols towards N ‐bromosuccinimide in aqueous methanol
Author(s) -
Karunakaran C.,
Ganapathy K.
Publication year - 1990
Publication title -
journal of physical organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.325
H-Index - 66
eISSN - 1099-1395
pISSN - 0894-3230
DOI - 10.1002/poc.610030405
Subject(s) - chemistry , alcohol , allyl alcohol , methanol , n bromosuccinimide , medicinal chemistry , leaving group , organic chemistry , reaction rate , halogenation , catalysis
The reactions of N ‐bromosuccinimide (NBS) with allyl and crotyl alcohols in aqueous methanol are first order in NBS. Allyl alcohol displays a zero‐order dependence whereas crotyl alcohol exhibits a Michaelis–Menten‐type dependence on substrate concentration. The NBS–allyl alcohol reaction is inhibited by H + whereas the NBS–crotyl alcohol reaction is independent of [H + ]. However, both are fast in the absence of acid. The rates are unaffected by the addition of neutral salt and succinimide. The reaction of NBS with crotyl alcohol exhibits a positive dielectric effect whereas allyl alcohol displays no such effect. Inhibition by Hg II is observed in the crotyl alcohol reaction but not with allyl alcohol. 3‐Bromo‐2‐methoxypropan‐1‐ol is the product of the allyl alcohol reaction but a mixture of 2‐bromo‐3‐methoxybutan‐1‐ol and 2‐bromobutane‐1,3‐diol in the crotyl alcohol reaction. In the allyl alcohol reaction the formation of solvated bromonium ion and of HOBr is suggested as rate‐limiting steps. In the crotyl alcohol reaction, rate determining breakdown of an NBS–crotyl alcohol complex, formed in a fast pre‐equilibrium, is proposed.