CHEM01200604012 Dibakar Goswami - Homi Bhabha National ...

The standard reduction potential of [bmim][Br], measured using cyclic
voltammetry (std. Calomel electrode as reference) was found to be 0.641 V. This also
supported the possibility of CT between In and the RTIL. Regeneration of the RTIL on
addition of allyl bromide also confirmed that the CT generated an activated In transient
species. This facilitates its subsequent reaction with allyl bromide to furnish the active
allylating species II. Although the allyl-In species I has been reported to be more reactive
than the species II, our results revealed otherwise. This might be due to the polar nature of
[bmim][Br]. The reduction potential of [bmim][Br] also suggested that In metal may got
oxidized by [bmim][Br] to generate InBr 3 , which would for 62 by reaction with
[bmim][Br] (Scheme II.3.4). This was isolated and characterized by comparing the 1 H and
13 C NMR spectra with those reported 82 for the analogous chloride compound, as well as
from the elemental analysis data. Addition of demineralized water to the above mixture
produced In(OH) 3 , which also indicated the presence of In(III) in the mixture.
H
H
H
H
Br
N +
+ InBr 3
N N + N InBr 4
C4 H 9 C4 H 9
H
H
62
Scheme II.3.4
The formation of the species II and the catalytic role of In could be partially
rationalized considering the reactions shown in Scheme II.3.5. In the 1st path, the reaction
of allyl bromide with the ([bmim][Br]—In) species directly produced the active species II
along with propene or its precursor (eq. 1). Formation of the alkene was confirmed by
trapping it with Br 2 /CCl 4 to produce 1,2-dibromopropane that was characterized by 1 H
NMR spectrum. The RTIL subsequently reacts with the evolved propene or most likely its
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