CHEM01200604012 Dibakar Goswami - Homi Bhabha National ...

precursor to partially replenish the lost allyl bromide (Scheme II.3.5, eq. 2). The amount
of alkene trapped by Br 2 was very less since very little amount of 1,2-dibromopropane was
isolated. This suggested that most of propene or its precursor gets converted to allyl
bromide. It is most likely that [bmim][Br] would react with propene precursor (allyl
radical), producing less amount of propene.
Our 1 H NMR studies also suggested the operation of eq. 2, since there was a builtup
of the peak at δ 3.8 at ~1.5-2 h. This was confirmed by a time-dependent GLC analysis
(Fig. II.3.6) of the reaction mixture that showed a sharp decline (60-110 min), followed by
a gradual rise of the concentration of allyl bromide, which finally became steady.
Evidently, at the initial stage, formation of II was very fast due to the high concentration of
allyl bromide, and the growth of the latter could only be seen at a latter stage. A steady
concentration of II at ~3 h (NMR results) was also in consonance with these results.
Fig. II.3.6. GLC analysis of the time dependent concentration variation of allyl
bromide
51