A kinetic, product and kinetic isotope effect investigation of the bromination of 1,1-diphenylethylenes and of their 2,2-dideuterio derivatives
作者:Giuseppe Bellucci、Cinzia Chiappe
DOI:10.1039/a605390d
日期:——
The kinetics of bromination of 1,1-diphenylethylene (1a),
4-trifluoromethyl-1,1-diphenylethylene (1b), and
1-(3-trifluoromethylphenyl)-1-(4-trifluoromethylphenyl)ethylene
(1c) and of their 2,2-dideuterio derivatives have been
investigated in 1,2-dichloroethane. The rate law was always
second-order in Br2 and first-order in olefin, with
the following k3: 1a (L = H),
1.7 (0.1) × 107; 1b
(L = H), 8.0
(0.1) × 104; 1c
(L = H), 52 (2) dm6
mol-2 s-1. Olefin 1a
(L = H) gave dibromide 4a and vinyl bromide 3a in
a ratio changing from 99∶1 at 10-2 mol
dm-3 to 5∶95 at 10-4 mol
dm-3 Br2 and olefin. The
k3 was independent of the reagent
concentrations and of the extent of proton loss from the
intermediate, showing that the last step was not rate limiting
and the formation of the intermediate was completely rate
determining. In the whole investigated concentration range, only
dibromides 4b and 4c were instead obtained from 1b and 1c,
respectively. A negligible KIE, 0.97 (0.01) was found for 1a,
whether the dibromide or the vinyl bromide was the main product,
while significant inverse KIEs were obtained for 1b, 0.75 (0.05),
for 1c, 0.70 (0.05), on deuteriation of the methylene group, and
for cis-1,2-diphenylethylene, 2. The kinetic and product
distribution data are discussed in terms of nature of the
intermediates, depending on substituent effect and reagent
concentration.
,2-二氯乙烷。