Oxidation of phenols by triplet aromatic ketones in aqueous solution
Oxidation of phenols by triplet aromatic ketones in aqueous solution
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DOI：
10.1021/jp9930550
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发表时间：
2000-02-17
影响因子：
2.9
通讯作者：
Wirz, J
中科院分区：
文献类型：
--
作者：
Canonica, S;Hellrung, B;Wirz, J
芳香酮有效地介导了充气水溶液中苯酚的光氧化降解，这一过程可能与阳光照射的天然沃茨有关。用纳秒激光闪光光解法测定了9种酚类化合物对三种模型酮三联体的猝灭反应的绝对双分子速率常数，这些酚类化合物具有不同的取代基，从供电子的烷基和烷氧基到吸电子的氰基。三聚体二苯甲酮（BP）以接近扩散控制的速率（2.6-5.6 X 10（9）M-1 s（-1））淬灭。三重态猝灭的3 ′-甲氧基苯乙酮（3 ′-MAP）和2-苯乙酮（2-AN）由同一组酚发生更有选择性的，与速度常数的范围跨越1和超过2个数量级，分别。猝灭速率常数与电子从苯酚到酮三聚体的转移自由能之间存在一个很好的关系。通过比较的猝灭常数与整体光氧化速率通过固定照射在空气饱和的水溶液中，酚轴承供电子取代基被发现被耗尽的量子产率一般超过0.5，而母体苯酚，据推测，受体取代的酚转化仅在类似于0.1的效率。本猝灭数据被用来解释的效率光敏氧化的酚类溶解天然有机物（DNOM），一个重要的太阳光吸收剂存在于表面沃茨。DNOM中反应性激发三重态的有效还原电位估计为至少1.36 V vs NHE。
Aromatic ketones efficiently mediate the photo-oxidative degradation of phenols in aerated aqueous solution, a process likely to be relevant in sunlit natural waters. Absolute bimolecular rate constants for the quenching of three model ketone triplets by nine phenols bearing various substituents, from electron-donating alkyl and alkoxy groups to the electron-withdrawing cyano group, were measured by nanosecond laser flash photolysis. Tripler benzophenone (BP) is quenched at nearly diffusion-controlled rates (2.6-5.6 x 10(9) M-l s(-1)). Triplet state quenching of 3'-methoxyacetophenone (3'-MAP) and 2-acetonaphthone (2-AN) by the same set of phenols occurs more selectively, with rate constants spanning a range of I and more than 2 orders of magnitude, respectively. Quenching rate constants obey a Rehm-Weller relationship to the free energy of electron transfer from the phenol to the ketone tripler. By comparison of the quenching constants with overall photo-oxidation rates obtained by stationary irradiation in air-saturated aqueous solution, phenols bearing electron-donating substituents were found to be depleted with quantum yields generally exceeding 0.5, whereas parent phenol and, presumably, acceptor-substituded phenols are transformed at only similar to 0.1 efficiency. The present quenching data were used to interpret the efficiency of photosensitized oxidation of phenols by dissolved natural organic matter (DNOM), an important sunlight absorber present in surface waters. The effective reduction potential of reactive excited tripler states in DNOM was estimated to be at least 1.36 V vs NHE.