Kinetics of Electrophilic Bromination L. Second order reactions Rate Law: -d[Bradt= k(Olefin Br2] a Reactions run with dilute bromine in water or alcohol solvents No relationship between rate and product composition so the product forming stages follow the rate a There is a large solvent effect tent with a highly polarized transition state, and a large solvent deuterium isotope effect k(Br2, MeOH)/k(Br2, Me Br…H-OR ll. Third Order reactions a Rate li d[Bral/dt= k(Olefin J(Br22 a Reactions run with higher concentrations of Br2 in aprotic solvents Proposed that second molecule of Br2 catalyzes the heterolytic bond cleavage in rate determining step which forms br- Alternatively, one Br2 may be acting as the nucleophile and one acts as an electrophile(not as likely) l. Higher order reactions a Reactions that are third order in Br2 have been proposed, but there is no conclusive evidence for this s lodination reactions have been shown to react with overall fourth order kinetics de la Mare, P B D: Bolton, R. Electrophilic Additions to Unsaturated Systems, 2nd Ed, Elsevier Publishing, New York 1982 Yates, K.J. Org. Chem., 1973 38, 2460 BA-Bromination 02 10/4/00 4: 34 PMδ− δ+ . de la Mare, P. B. D.; Bolton, R. Electrophilic Additions to Unsaturated Systems, 2nd Ed., Elsevier Publishing, New York 1982 Yates, K. J. Org. Chem., 1973 38, 2460 . . . . . Reactions that are third order in Br2 have been proposed, but there is no conclusive evidence for this Iodination reactions have been shown to react with overall fourth order kinetics III. Higher order reactions Rate Law: -d[Br2]/dt = k[Olefin][Br2]2 Reactions run with higher concentrations of Br2 in aprotic solvents Proposed that second molecule of Br2 catalyzes the heterolytic bond cleavage in rate determining step which forms Br3-. Alternatively, one Br2 may be acting as the nucleophile and one acts as an electrophile (not as likely). II. Third Order Reactions . Rate Law: -d[Br2]/dt = k[Olefin][Br2] Reactions run with dilute bromine in water or alcohol solvents No relationship between rate and product composition so the product forming stages follow the rate determining step There is a large solvent effect consistent with a highly polarized transition state, and a large solvent deuterium isotope effect k(Br2, MeOH)/k(Br2, MeOD) = 1.4. . . . I. Second order reactions: Kinetics of Electrophilic Bromination Br H OR Br 09A-Bromination 02 10/4/00 4:34 PM