THERMAL-DECOMPOSITION AND COBALT CARBON BOND-DISSOCIATION ENERGIES OF ORGANOCOBALAMINS - NEOPENTYL, (CYCLOPENTYLMETHYL), (CYCLOHEXYLMETHYL), (TETRAHYDROFURFURYL) AND ((TETRAHYDRO-2H-PYRYL)METHYL)COBALAMIN
THERMAL-DECOMPOSITION AND COBALT CARBON BOND-DISSOCIATION ENERGIES OF ORGANOCOBALAMINS - NEOPENTYL, (CYCLOPENTYLMETHYL), (CYCLOHEXYLMETHYL), (TETRAHYDROFURFURYL) AND ((TETRAHYDRO-2H-PYRYL)METHYL)COBALAMIN
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DOI：
10.1021/ja00218a021
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发表时间：
1988-05-11
影响因子：
15
通讯作者：
HALPERN, J
中科院分区：
文献类型：
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作者：
KIM, SH;CHEN, HL;HALPERN, J
制备并表征了标题化合物，并研究了它们在不同pH、不同浓度cob(II)alamin （B12r）和双（二甲基乙氧基）钴（II）， [Co（DH2]）的水溶液中的热分解反应。根据以下方案，通过竞争性捕获产生的自由基，确定了钴碳键解离的均裂途径：R。+ B12r;R。+ Co(DH)2。R-Co (DH) 2。这些反应的动力学测定（在对碱对碱的平衡进行校正后）得到了以下活化参数值：R = neopentyl, . delta . h .dbldag。= 26.7 .+-。1.2千卡/摩尔，δ δ s。= 1.5 .+-。5 cal/(mol K)；R =环戊基甲基；= 26.8 .+-。2千卡每摩尔;.DELTA.S.dbldag。= 3 .+-。6cal /(mol K)。从这些测量结果中，我们可以看到。新戊基- b12和环戊基-甲基- b12的碱基形式的C键离解能约为24千卡/摩尔。在乙二醇中。delta。h。用于Co .sbd的均解离解。新戊基- b12的C键比水溶液中高约4千卡/摩尔。
The title compounds were prepared and characterized and their thermal decomposition reactions were studied in aqueous solutions of varying pH and containing varying concentrations of cob(II)alamin (B12r) and of bis(dimethylglyoximato)cobalt (II), [Co(DH2]. Homolytic cobalt-carbon bond dissociation pathways were identified through competitive trapping of the resulting free radicals according to the following scheme: R-B12 .dblarw. R . + B12r; R . + Co(DH)2 .fwdarw. R-Co(DH)2. Determination of the kinetics of these reactions yielded (after correction for the base on-base off equilibria) the following values of the activation parameters: R = neopentyl, .DELTA.H.dbldag. = 26.7 .+-. 1.2 kcal/mol, .DELTA.S.dbldag. = 1.5 .+-. 5 cal/(mol K); R = cyclopentylmethyl, .DELTA.H.dbldag. = 26.8 .+-. 2 kcal/mol; .DELTA.S.dbldag. = 3 .+-. 6 cal/(mol K). From these measurements the Co .sbd. C bond dissociation energies of the base-on forms of neopentyl-B12 and cyclopentylmethyl-B12 were deduced to be ca. 24 kcal/mol. In ethylene glycol .DELTA.H.dbldag. for homolytic dissociation of the Co .sbd. C bond of neopentyl-B12 was found to be about 4 kcal/mol higher than in aqueous solution.