Colley Christopher S, Grills David C, Besley Nicholas A, Jockusch Steffen, Matousek Pavel, Parker Anthony W, Towrie Michael, Turro Nicholas J, Gill Peter M W, George Michael W
School of Chemistry, University of Nottingham, University Park, Nottingham, NG7 2RD, United Kingdom.
J Am Chem Soc. 2002 Dec 18;124(50):14952-8. doi: 10.1021/ja026099m.
A series of substituted benzoyl radicals has been generated by laser flash photolysis of alpha-hydroxy ketones, alpha-amino ketones, and acyl and bis(acyl)phosphine oxides, all of which are used commercially as photoinitiators in free radical polymerizations. The benzoyl radicals have been studied by fast time-resolved infrared spectroscopy. The absolute rate constants for their reaction with n-butylacrylate, thiophenol, bromotrichloromethane and oxygen were measured in acetonitrile solution. The rate constants of benzoyl radical addition to n-butylacrylate range from 1.3 x 10(5) to 5.5 x 10(5) M(-1) s(-1) and are about 2 orders of magnitude lower than for the n-butylacrylate addition to the counterradicals that are produced by alpha-cleavage of the investigated ketones. Density functional theoretical calculations have been performed in order to rationalize the observed reactivities of the initiating radicals. Calculations of the phosphorus-centered radicals generated by photolysis of an acyl and bis(acyl)phosphine oxide suggest that P atom Mulliken spin populations are an indicator of the relative reactivities of the phosphorus-centered radicals. The alpha-cleavage of (2,4,6-trimethylbenzoyl)phosphine oxide was studied by picosecond pump-probe and nanosecond step-scan time-resolved infrared spectroscopy. The results support a mechanism in which the alpha-cleavage occurs from the triplet excited state that has a lifetime less than or equal to the singlet excited state.
通过对α-羟基酮、α-氨基酮、酰基膦氧化物和双（酰基）膦氧化物进行激光闪光光解，生成了一系列取代苯甲酰基自由基，所有这些化合物在商业上都用作自由基聚合反应中的光引发剂。已通过快速时间分辨红外光谱对苯甲酰基自由基进行了研究。在乙腈溶液中测量了它们与丙烯酸正丁酯、苯硫酚、三氯溴甲烷和氧气反应的绝对速率常数。苯甲酰基自由基加成到丙烯酸正丁酯的速率常数范围为1.3×10⁵至5.5×10⁵ M⁻¹ s⁻¹，比丙烯酸正丁酯加成到由所研究酮的α-裂解产生的反自由基的速率常数低约2个数量级。进行了密度泛函理论计算，以解释引发自由基的观察到的反应活性。对酰基膦氧化物和双（酰基）膦氧化物光解产生的以磷为中心的自由基的计算表明，P原子的穆利肯自旋布居是磷中心自由基相对反应活性的一个指标。通过皮秒泵浦-探测和纳秒步进扫描时间分辨红外光谱研究了（2,4,6-三甲基苯甲酰基）膦氧化物的α-裂解。结果支持了一种机制，即α-裂解发生在寿命小于或等于单重激发态的三重激发态。
