Absolute kinetics of amidyl radical reactions
Absolute kinetics of amidyl radical reactions
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DOI：
10.1021/ja981244a
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发表时间：
1998-08-12
影响因子：
15
通讯作者：
Newcomb, M
中科院分区：
文献类型：
--
作者：
Horner, JH;Musa, OM;Newcomb, M
通过直接激光闪光光解(LFP)和间接竞争动力学研究相结合的方法，建立了酰胺基反应的绝对动力学标度。用LFP方法研究了6个酰胺基自由基。测定了N-丁基-6，6-二苯基-5-己烯胺自由基(2)和N-butyl-6-(trans-2-phenylcyclopropyl)-5-hexenamidyl自由基(5)的6-外环化反应和N-(6，6-二苯基-5-己烯基)乙酰胺基(3)的1，5-氢转移反应的Arrhenius参数；这些反应在20℃时的速率常数分别为3.0×10(7)S(-1)(2)，5.5×10(6)S(-1)(3)和1×107 S(-1)(5)。用LFP方法建立了N-甲基-5，5-二苯基-4-戊烯胺自由基(1)和N-甲基-5-(反式-2-苯基环丙基)-4-戊酰胺自由基(4)(k>；2×10(8)S(-1))在48℃时的快速环化反应和N-(2，2-二苯乙基)乙酰胺基(6)(k=2×10(4)S(-1))的快速环化反应的动力学极限。用竞争动力学方法测定了氨基自由基与Bu3SnH和PhSH反应的速率常数，20℃时的速率常数分别为1.3×10(9)M-1 S(-1)和23℃时的9×10(7)M-1 S(-1)。N-丁基-4-戊烯胺自由基和N-(4-戊烯基)丁胺自由基的5-外环化反应和N-乙基-5-己烯胺自由基的6-外环化反应的速率常数ac65℃分别为3×10(9)S(-1)，7×10(8)S(-1)和1.0×10(7)S(-1)。本工作所确定的动力学数值可用于涉及酰胺基的合成规划，而简单的酰胺基钟可用于测量双分子反应的速率常数。综述了氮自由基与Bu3SnH和PhSH的环化反应和双分子反应的动力学。
An absolute kinetic scale for amidyl radical reactions was established by a combination of direct laser flash photolysis (LFP) and indirect competition-kinetic studies. Six amidyl radicals were studied by LFP. Arrhenius parameters were determined for 6-exo cyclizations of the N-butyl-6,6-diphenyl-5-hexenamidyl radical (2) and the N-butyl-6-(trans-2-phenylcyclopropyl)-5-hexenamidyl radical (5) and for 1,5-hydrogen transfer in the N-(6,6-diphenyl-5-hexenyl)acetamidyl radical (3); rate constants for these reactions at 20 degrees C are 3.0 x 10(7) s(-1) (2), 5.5 x 10(6) s(-1) (3), and 1 x 107 s(-1) (5). Kinetic limits were established by LFP for the fast cyclizations of the N-methyl-5,5-diphenyl-4-pentenamidyl radical (1) and the N-methyl-5 -(trans-2-phenylcyclopropyl)-4-pentenamidyl radical (4) (k > 2 x 10(8) s(-1) at ambient temperature) and for the slow fragmentation of the N-(2,2-diphenylethyl)acetamidyl radical (6) (k = 2 x 10(4) s(-1) at 48 degrees C). Rate constants for amidyl radical reactions with Bu3SnH and PhSH were determined by competition kinetics; respective rate constants are 1.3 x 10(9) M-1 s(-1) at 20 degrees C and 9 x 10(7) M-1 s(-1) at 23 degrees C. Cyclizations of simple amidyl radicals were determined from competition kinetic studies by employing Bu3SnH and N-(phenylthio)amide radical precursors using data from the literature and from studies in this work. Rate constants ac 65 degrees C for 5-exo cyclizations of the N-butyl-4-pentenamidyl radical and the N-(4-pentenyl)butanamidyl radical and for 6-exo cyclization of the N-ethyl-5-hexenamidyl radical are 3 x 10(9) s(-1), 7 x 10(8) s(-1), and 1.0 x 10(7) s(-1), respectively. The kinetic values determined in-this work can be employed in synthetic planning involving amidyl radicals, and the simple amidyl radical clocks can be used for measuring rate constants of bimolecular reactions. A compilation of the kinetics of nitrogen-centered radical cyclizations and bimolecular reactions of nitrogen radicals with Bu3SnH and PhSH is presented.