Photoprocesses of p-naphthoquinones and vitamin K_1: effects of alcohols and amines on the reactivity in solution
Photoprocesses of p-naphthoquinones and vitamin K_1: effects of alcohols and amines on the reactivity in solution
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DOI：
10.1039/b306670n
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发表时间：
2004-01
影响因子：
3.1
通讯作者：
H. Görner
中科院分区：
文献类型：
--
作者：
H. Görner
用时间分辨紫外-可见光谱法研究了1，4-萘醌（NQ）及其2-甲基、2，3-二氯和2-溴衍生物和维生素K_1在非水溶剂中的光化学反应。NQs的三重态与醇和胺反应，例如三乙胺（TEA）和DABCO，产生半醌自由基（HQ stec/Q stec ^−）。它们是主要的中间体，它们的二级衰减动力学取决于添加剂和介质的性质。瞬态电导率的测量表明，发生光诱导的电子转移胺的三重态的NQs在乙腈中。在不同浓度的电子和氢原子给体存在和不存在的情况下，测量了NQs到1，4-二羟基萘（H_2Q）的光转换（λ irr = 254 nm），发现量子产率随电子或质子给体浓度的增加而增加。异丙醇和TEA在乙腈中光还原NQs的机理表现出许多相似之处。氧猝灭三重态，从而形成单重态分子氧。氧也与半醌自由基反应，从而形成HO_2 stec/O_2 stec ^−自由基，并与H_2Q反应，从而重新形成醌。维生素K_1则有一个不同的模式，涉及分子内氢原子转移，在乙腈中观察到1，3-醌甲基化物（1，3-QM）双自由基，然后形成两个1，2-QM互变异构体，但没有三重异构体。由于质子转移反应，在醇和胺的存在下，1，3-QM中间体的衰变变得更快。
The photochemistry of 1,4-naphthoquinone (NQ), the 2-methyl, 2,3-dichloro and 2-bromo derivatives, and vitamin K_1 was studied in non-aqueous solvents by time-resolved UV-vis spectroscopy after ns laser pulses at 248 and 308 nm. The triplet state of the NQs reacts with alcohols and amines, e.g. triethylamine (TEA) and DABCO, yielding semiquinone radicals (HQ˙/Q˙^−). They are the major intermediates and their second-order decay kinetics depend on the properties of the additives and the medium. Transient conductivity measurements suggest the occurrence of photoinduced electron transfer from amines to the triplet state of NQs in acetonitrile. The photoconversion ( λ _irr = 254 nm) of NQs to the 1,4-dihydroxynaphthalenes (H_2Q) was measured in the absence and presence of varying concentrations of electron and H-atom donors, and the quantum yield was found to increase with increasing electron- or proton-donor concentration. The mechanisms of photoreduction of NQs by propan-2-ol and TEA in acetonitrile exhibit a number of similarities. Oxygen quenches the triplet state, thereby forming singlet molecular oxygen. Oxygen also reacts with the semiquinone radical, thereby forming HO_2˙/O_2˙^− radicals, and reacts with H_2Q, thereby re-forming the quinone. A different pattern, involving intramolecular H-atom transfer, holds for vitamin K_1, where 1,3-quinone methide (1,3-QM) diradicals were observed in acetonitrile prior to formation of two 1,2-QM tautomers, but a triplet was not. The decay of the 1,3-QM intermediates becomes faster in the presence of alcohols and amines due to proton-transfer reactions.