R. Ambrosetti et al., DETAILED KINETIC-ANALYSIS OF THE ELECTROPHILIC BROMINATION OF 2-CYCLOHEXEN-1-OL BENZOATE USING A NEWLY DEVELOPED MULTICHANNEL STOP-FLOW APPARATUS, Journal of physical chemistry, 98(6), 1994, pp. 1620-1625
A new stop-flow instrument is presented. It is equipped with a 32-chan
nel parallel diode-array detector and a data-acquisition system interf
aced to a standard MS-DOS PC, yielding a total throughput of 10 000 sp
ectra/s. The apparatus includes a program capable of fitting simultane
ously data taken over a range of wavelengths, concentrations, and temp
erature. The program can be adapted quickly to any kinetic model. This
apparatus allowed a comprehensive kinetic analysis of the electrophil
ic addition reaction of molecular bromine to 2-cyclohexen-1-ol benzoat
e in 1,2-dichloroethane. Under the employed reagent concentrations, th
e formation of the expected olefin-bromine charge-transfer complex cou
ld not be detected. Data were taken over the 300-480-nm range. We foun
d k(3)(1) = 368 (25) and k(3)(2) = 215 (30) M(-2) s(-1) for the third-
order (second order in bromine) reactions leading respectively to the
trans-dibromo adducts (1 and 2) and to the intermediate hexano-cis-1,2
-(2'-phenyl-1',3'-dioxolan-2'-ylium) tribromide (5). The species 5 the
n collapses to the cis-bromo adducts 3 and 4 with k(1) = 0.282 (0.006)
s(-1). The ratio k(3)(1)/k(3)(2) = 1.7 is in agreement with that prev
iously reported for the yields of the trans- and cis-dibromo adducts.