Canle López Moisés, Fernández M Isabel, Rodríguez Santiago, Santaballa J Arturo, Steenken Steen, Vulliet Emmanuelle
Grupo de Reactividade Química e Fotorreactividade, Departamento de Química Física e Enxeñería Química I, Universidade da Coruña, Rúa Alejandro de la Sota 1, 15008A Coruña, Galicia, Spain.
Chemphyschem. 2005 Oct 14;6(10):2064-74. doi: 10.1002/cphc.200500004.
Phenylurea herbicides undergo low-yield (phi(PI) <15 %) monophotonic photoionisation upon 193-nm laser flash excitation. The so-formed radical cations (phenylurea.+) are highly acidic (-1.5 < pKa <0.5) and deprotonate readily to yield the corresponding neutral radical (phenylurea.). Pulse radiolysis experiments allowed limitation of the reduction potential of phenylurea.+ within 2.22 V versus the normal hydrogen electrode (NHE) < E degrees (phenylurea.+/phenylurea) < 2.43 V versus NHE. The main photoproducts of UVC (lambda=193 nm) photodegradation of phenylureas correspond to a photo-Fries rearrangement. One-electron reduction with e-(aq) yields the corresponding radical anions (phenylurea.-), for which 4.3< pKa < 5.33. The rate constants for reaction with e-(aq) show that in photocatalysis the generation of phenylurea.- and O2.- on the surface of the photocatalyst may be competitive. High reactivity toward e-(aq) is predicted from linear free-energy relationships (LFER) for phenylureas bearing electron-withdrawing groups. Reaction with HO. takes place mainly via addition to the aromatic ring and/or H. abstraction from a saturated carbon atom (98 %), rather than one-electron oxidation (2 %). High reactivity toward oxidation by HO. is predicted from LFER for phenylureas bearing electron-donating groups. Adsorption studies for TiO2 in its polymorphic forms of rutile and anatase, as well as with the commercial mixture Degussa P-25, show photocatalysis is independent of the specific area of the catalyst. A variety of compounds are generated during the photocatalytic degradation of Diuron, while only two hydroxychloro derivatives are observed upon prolonged direct 365 nm irradiation. The photocatalytic degradation proceeds mainly by oxidation of the Me group of the side chain, hydroxylation of the aromatic ring, and dechlorination. The photoproducts of photocatalytic degradation differ from one polymorphic form of TiO2 to another.
苯基脲类除草剂在193 nm激光闪光激发下会发生低产率（φ(PI) <15%）的单光子光电离。如此形成的自由基阳离子（苯基脲.+）具有高酸性（-1.5 < pKa <0.5），很容易去质子化生成相应的中性自由基（苯基脲.）。脉冲辐解实验将苯基脲.+的还原电位限制在相对于标准氢电极（NHE）为2.22 V < E°(苯基脲.+ /苯基脲) < 2.43 V相对于NHE范围内。苯基脲类化合物在UVC（λ = 193 nm）光降解中的主要光产物对应于光弗里斯重排。用e-(aq)进行单电子还原会产生相应的自由基阴离子（苯基脲.-），其pKa为4.3 < pKa < 5.33。与e-(aq)反应的速率常数表明，在光催化中，光催化剂表面上苯基脲.-和O2.-的生成可能存在竞争。从带有吸电子基团的苯基脲的线性自由能关系（LFER）预测，其对e-(aq)具有高反应活性。与HO.的反应主要通过加成到芳环和/或从饱和碳原子上夺取H.进行（98%），而不是单电子氧化（2%）。从带有供电子基团的苯基脲的LFER预测，其对HO.氧化具有高反应活性。对金红石和锐钛矿多晶型形式的TiO2以及商业混合物德固赛P-25的吸附研究表明，光催化与催化剂的比表面积无关。在敌草隆的光催化降解过程中会生成多种化合物，而在长时间直接365 nm照射下仅观察到两种羟基氯衍生物。光催化降解主要通过侧链甲基的氧化、芳环的羟基化和脱氯进行。光催化降解的光产物因TiO2的不同多晶型形式而异。
