School of Pharmacy and Molecular Sciences, James Cook University, Townsville, QLD 4811, Australia.
J Phys Chem A. 2011 Jan 27;115(3):280-5. doi: 10.1021/jp108832x. Epub 2010 Dec 17.
The photoinduced oxidation of 1-naphthol to 1,4-naphthoquinone and of 5-hydroxy-1-naphthol to 5-hydroxy-1,4-naphthoquinone was studied by steady-state and time-resolved techniques. The direct photooxidation of naphthols in methanol or water takes place by reaction of the naphoxyl radical ((•)ONaph) with the superoxide ion radical (O(2)(•-)), the latter of which results from the reaction of the solvated electron with oxygen after photoionization. The sensitized oxidation takes place by energy transfer from the xanthene triplet state to oxygen. From the two oxygen atoms, which are consumed, one is incorporated into the naphthol molecule giving naphthoquinone and the second gives rise to water. The effects of eosin, erythrosin, and rose bengal in aqueous solution, pH, and the oxygen and naphthol concentrations were studied. The quantum yield of the photosensitized transformation was determined, which increases with the naphthol concentration and is largest at pH > 10. The quantum yield of oxygen uptake is similar. The pathway involving singlet molecular oxygen is suggested to operate for the three sensitizers. The alternative pathway via electron transfer from the naphthol to the xanthene triplet state and subsequent reaction of (•)ONaph with O(2)(•-), the latter of which is formed by scavenging of the xanthene radical anion by oxygen, does also contribute.
通过稳态和时间分辨技术研究了 1-萘酚氧化为 1,4-萘醌和 5-羟基-1-萘酚氧化为 5-羟基-1,4-萘醌的光诱导氧化。甲醇或水中萘酚的直接光氧化是通过萘氧基自由基((•)ONaph)与超氧离子自由基(O(2)(•-))反应发生的，后者是在光致电离后溶剂化电子与氧反应产生的。敏化氧化是通过呫吨三重态向氧的能量转移发生的。从两个消耗的氧原子中，一个与萘酚分子结合生成萘醌，另一个生成水。研究了曙红、赤藓红和玫瑰红在水溶液中的作用、pH 值以及氧和萘酚浓度的影响。确定了光致转化的量子产率，其随萘酚浓度的增加而增加，在 pH > 10 时最大。氧气吸收的量子产率相似。建议三种敏化剂都通过单重态分子氧的途径起作用。通过萘酚向呫吨三重态的电子转移和随后的(•)ONaph 与 O(2)(•-)反应的替代途径也有贡献，后者是由氧对呫吨自由基阴离子的清除形成的。
