Positive Halogens from Halides and Hydrogen Peroxide with Organotellurium Catalysts
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- 作者：Michael R. Detty ; Feng Zhou ; and Alan E. Friedman
- 刊名：Journal of the American Chemical Society
- 出版年：1996
- 出版时间：January 17, 1996
- 年：1996
- 卷：118
- 期：2
- 页码：313 - 318
- 全文大小：320K
- 年卷期：v.118,no.2(January 17, 1996)
- ISSN：1520-5126
文摘
The oxidations of sodium bromide, sodium chloride, andsodium iodide to positive halogen with hydrogenperoxide in two-phase systems of dichloromethane and pH 6 phosphatebuffer were catalyzed by organotelluriumcatalysts 1-3. The positive halogens weretrapped by cyclohexene for bromine and chlorine to give mixtures ofthe1,2-dihalocyclohexane (4) and 2-halocyclohexanol(5). For the bromination(4a)/hydrobromination (5a) ofcyclohexene, unoptimized turnover numbers of 1010 mol of product permole of catalyst for 1, 960 for 2, and820for 3 were measured with 4a/5a ratiosof 55:45, 53:47, and 52:48, respectively. In cyclohexane, theturnover numberfor 1 was 150 and the 4a/5a ratio was68:32. In the uncatalyzed process and in the reaction of aqueousbrominewith cyclohexene, the 4a/5a ratio is 55:45 indichloromethane and 67:33 in cyclohexane. The relative ratesofcatalysis for equimolar amounts of 1-3 werenearly identical to the relative second-order rate constants foroxidationof the organotellurium compounds with hydrogen peroxide, which suggeststhat oxidation of the catalyst is therate-determining step of the process. Stopped-flow studiesindicated a rapid reaction (k = 22.5 ± 0.3M-1 s-1foriodide and 13.9 ± 0.5 M-1s-1 for bromide) between halide and oxidized3 to regenerate catalyst 3. Relativeratesof catalysis with 0.1 mol % of 1-3 (relativeto cyclohexene) were 4.6 for 1, 2.0 for 2, 1.0for 3, and 0.11 for thecontrol reaction with no catalyst at 296.1 ± 0.1 K. Oxidation ofchloride with hydrogen peroxide with 1 as acatalyst was much slower but the unoptimized turnover number was 100with a 4b/5b ratio of 7:93 (10:90 intheuncatalyzed process) in a two-phase cylohexane/aqueous system.Oxidized 3 reacts rapidly with both sodiumchlorideand sodium bromide to give products from oxidative addition of halogento the catalyst. Stronger Te-Cl bondsrelative to Te-Br bonds slow down the release of the Te(II) stateof the catalyst. Positive iodine from catalysis with1 was trapped by 4-pentenoic acid to give iodomethyl lactone6.