HYDROXYBROMINATION OF CINNAMYL ALCOHOL BY N-BROMOSUCCINIMIDE - A KINETIC-STUDY

The reaction of N- bromosuccinimide (NBS) with cinnamyl alcohol in aqu eous t-butanol is hydroxybromination, and is first order each in [NBS] and substrate. While the reaction is Independent of [H+] at high [H+] the rate increases with decrease in [H+] at low [H+], and in absence cf acid the reaction becomes fast. Succinimide has no influence on the reaction rate. There is no primary salt effect, and the dielectric ef fect is positive. The reaction is shown to proceed via two paths: (i) rate-limiting transfer of Br+ from molecular NBS to the substrate resu lting to a bromocarbocation which takes up a water molecule in a fast step to yield the ]product, and (ii) fast interaction between the subs trate and HOBr formed by the rate-determining hydrolysis of NBS.