5405-28-7Relevant articles and documents
Equilibria and UV-spectral characteristics of BrCl, BrCl2-, and Br2Cl- species in 1,2-dichloroethane - Stereoselectivity and kinetics of the electrophilic addition of these species to alkenes
Chiappe, Cinzia,Moro, Federica Del,Raugi, Marco
, p. 3501 - 3510 (2007/10/03)
UV/Vis spectrophotometric measurements have been used to determine the equilibrium constants and the absorption spectra of Bu4N+Br2Cl- and Bu4N+BrCl2- species in 1,2-dichloroethane (DCE) at 25°C. The formation constants and the absorption spectra of BrCl from Br2 and Cl2 and of Bu4N+Cl3- species from Bu4N+Cl- and Cl2 were also determined in this solvent at 25°C. The kinetics and the products of bromochlorination of several aryl-substituted olefins with BrCl, with Br2 in the presence of an excess of Bu4N+Cl- (Br2/Cl-), and with BrCl in the presence of an excess of Bu4N+Cl- (BrCl/Cl-) were investigated in DCE at different temperatures. The kinetics and product distribution data for the reactions with Br2/Cl- or BrCl/Cl- are interpreted on the basis of a mechanism involving a product- and rate-determining nucleophilic attack by chloride on the olefin-halogen (Br2 or BrCl) π complex. The data relating to the electrophilic addition of BrCl are interpreted in terms of the initial formation of a 1:1 olefin-BrCl π complex, the ionization of which, catalyzed by a second halogen molecule, gives a bromonium (or β-bromocarbenium) BrCl2- ion pair able to collapse to the corresponding bromochloro adducts. A significant proportion of the ion pair intermediates may, however, actually be present as bromonium (or β-bromocarbenium) Br2Cl- and Br3- ion pairs, and the collapse of these should be responsible for the formation of the dibromides in BrCl addition.
Formation of Bromocarbenium Bromide Ion Pairs in the Electrophilic Bromination of Highly Reactive Olefins in Chlorinated Aprotic Solvents
Bellucci, Giuseppe,Chiappe, Cinzia,Moro, Giacomo Lo
, p. 3176 - 3182 (2007/10/03)
The kinetics and the products of bromination of several substituted stilbenes with tetrabutylammonium tribromide (TBAT) have been investigated in aprotic solvents at different temperatures. Stilbenes bearing electron-withdrawing or moderately electron-donating substituents gave stereospecifically the anti addition products. The reactions followed a second-order rate law, and an inverse kinetic isotope effect (KIE), kH/kD = 0.85(0.05), was found for the bromination of cis-stilbene. The reactions of cis- and trans-4,4-dimethoxystilbenes yielded mixtures of meso and d,l dibromides both in chloroform and 1,2-dichloroethane. The rate constants (kBr3-) measured for the latter olefins deviated considerably from the Hammett correlations, and added bromide had a significant effect on the rates. The reactions of these activated stilbenes with molecular Br2, carried out at low Br2 concentration, followed a mixed second/third-order rate law. The kinetic and product distribution data for the reaction, with TBAT, of stilbenes bearing electron-withdrawing or moderately electron-donating substituents are interpreted on the basis of the known mechanism involving a product-and rate-determining nucleophilic attack by bromide on the olefin-Br2 π-complex. The data related to the bromination of the more activated methoxystilbenes are rationalized considering that, for these olefins, even in aprotic solvents, the ionization of the initially formed 1:1 π-complex to a bromocarbenium bromide ion pair can compete both with the formation of a bromonium-tribromide ion pair and with the nucleophilic attack by Br-. For this second-order process (first order in Br2), the kinetic constants and the activation parameters have been measured in chloroform and 1,2-dichloroethane and the activation parameters have been compared with those related to the third-order Br2 addition and to the reaction with TBAT.
