Kinetic study of the hydrogen abstraction reaction of the benzotriazole-N-oxyl radical (BTNO) with H-donor substrates
Kinetic study of the hydrogen abstraction reaction of the benzotriazole-N-oxyl radical (BTNO) with H-donor substrates
复制标题
DOI：
10.1021/jo051615n
复制
发表时间：
2005-11-11
影响因子：
3.6
通讯作者：
Gentili, P
中科院分区：
文献类型：
--
作者：
Brandi, P;Galli, C;Gentili, P
在MeCN中，1-羟基苯并三唑（HBT; > N-OH）与Ce-IV盐氧化生成了氨基自由基（> n -o -中心点）BTNO（苯并三唑- n -氧）。BTNO具有宽吸收带，最大吸收峰为474 nm，是1840 M-1 cm（-1）的元素，在25℃时在MeCN中自发衰减，一阶速率常数为6.3 x 10(-3) s（-1）。BTNO的自发衰变在h供体底物（如烷基芳烯、苯醇和烯醇和烷醇）的存在下被强烈加速，并且BTNO从许多底物中提取h的速率常数在25℃下被光谱研究。动力学同位素效应证实了h的提取步骤是决定速率的。活化参数在15-40℃范围内与选定的底物进行了测量。根据Evans-Polanyi方程，得到了一小部分h给体e与BDE(C-H) （C-H键离解能）之间的关系，alpha = 0.44。从该图可以推断出实验中无法得到的苯甲醇BDE（C-H）约为79千卡/摩尔。在H提取步骤中，烷基烯（ArC(H)R-2）和苯甲醇(ArC（H)(OH)R）在AS参数上出现了特殊的差异。将BTNO的吸氢活性数据与最近报道的n -羟基邻苯二胺（HPI）生成的氨基自由基PINO （phthalimide-N-oxyl）的吸氢活性数据进行了比较。自由基PINO的高反应活性是基于HPI的NO-H键能量高于HBT（分别为88 kcal/mol和85 kcal/mol），这是由RH底物的h萃取形成的。
The aminoxyl radical (> N-O-center dot) BTNO (benzotriazole-N-oxyl) has been generated by the oxidation of 1-hydroxybenzotriazole (HBT; > N-OH) with a Ce-IV salt in MeCN. BTNO presents a broad absorption band with gimel(max) 474 nm and is an element of 1840 M-1 cm(-1), and spontaneously decays with a first-order rate constant of 6.3 x 10(-3) s(-1) in MeCN at 25 degrees C. Characterization of BTNO radical by EPR, laser flash photolysis, and cyclic voltammetry is provided. The spontaneous decay of BTNO is strongly accelerated in the presence of H-donor substrates such as alkylarenes, benzyl and allyl alcohols, and alkanols, and rate constants of H-abstraction by BTNO from a number of substrates have been spectroscopically investigated at 25 degrees C. The kinetic isotope effect confirms the H-abstraction step as rate-determining. Activation parameters have been measured in the 15-40 degrees C range with selected substrates. A correlation between E. and BDE(C-H) (C-H bond dissociation energy) for a small series of H-donors has been obtained according to the Evans-Polanyi equation, giving alpha = 0.44. From this plot, the experimentally unavailable BDE(C-H) of benzyl alcohol can be extrapolated, as ca. 79 kcal/mol. With respect to the H-abstraction step, peculiar differences in the AS' parameter emerge between an alkylarene, ArC(H)R-2, and a benzyl alcohol, ArC(H)(OH)R. The data acquired on the H-abstraction reactivity of BTNO are compared with those recently reported for the aminoxyl radical PINO (phthalimide-N-oxyl), generated from N-hydroxyphthalimide (HPI). The higher reactivity of radical PINO is explained on the basis of the higher energy of the NO-H bond of HPI, as compared with that of HBT (88 vs ca. 85 kcal/mol, respectively), which is formed on H-abstraction from the RH substrate.