Hirose Kensaku, Ohkubo Kei, Fukuzumi Shunichi
Department of Material and Life Science, Graduate School of Engineering, Osaka University and SENTAN (Japan) Science and Technology Agency (JST), Suita, Osaka, 565-0871, Japan.
Division of Applied Chemistry, Graduate School of Engineering, Osaka University, Suita, Osaka, 565-0871, Japan.
Chemistry. 2016 Aug 26;22(36):12904-9. doi: 10.1002/chem.201602856. Epub 2016 Jul 28.
Hydroxylation of benzene by molecular oxygen (O2 ) occurs efficiently with 10-methyl-9,10-dihydroacridine (AcrH2 ) as an NADH analogue in the presence of a catalytic amount of Fe(ClO4 )3 or Fe(ClO4 )2 with excess trifluoroacetic acid in a solvent mixture of benzene and acetonitrile (1:1 v/v) to produce phenol, 10-methylacridinium ion and hydrogen peroxide (H2 O2 ) at 298 K. The catalytic oxidation of benzene by O2 with AcrH2 in the presence of a catalytic amount of Fe(ClO4 )3 is started by the formation of H2 O2 from AcrH2 , O2 , and H(+) . Hydroperoxyl radical (HO2 (.) ) is produced from H2 O2 with the redox pair of Fe(3+) /Fe(2+) by a Fenton type reaction. The rate-determining step in the initiation is the proton-coupled electron transfer from Fe(2+) to H2 O2 to produce HO(.) and H2 O. HO(.) abstracts hydrogen rapidly from H2 O2 to produce HO2 (.) and H2 O. The Fe(3+) produced was reduced back to Fe(2+) by H2 O2 . HO2 (.) reacts with benzene to produce the radical adduct, which abstracts hydrogen from AcrH2 to give the corresponding hydroperoxide, accompanied by generation of acridinyl radical (AcrH(.) ) to constitute the radical chain reaction. Hydroperoxyl radical (HO2 (.) ), which was detected by using the spin trap method with EPR analysis, acts as a chain carrier for the two radical chain pathways: one is the benzene hydroxylation with O2 and the second is oxidation of an NADH analogue with O2 to produce H2 O2 .
在298K下，以10-甲基-9,10-二氢吖啶（AcrH₂）作为NADH类似物，在催化量的Fe(ClO₄)₃或Fe(ClO₄)₂以及过量三氟乙酸存在的情况下，于苯和乙腈的混合溶剂（1:1 v/v）中，分子氧（O₂）能有效地使苯发生羟基化反应，生成苯酚、10-甲基吖啶鎓离子和过氧化氢（H₂O₂）。在催化量的Fe(ClO₄)₃存在下，O₂与AcrH₂对苯的催化氧化反应是由AcrH₂、O₂和H⁺生成H₂O₂引发的。通过Fenton型反应，H₂O₂与Fe(3⁺)/Fe(2⁺)氧化还原对反应生成氢过氧自由基（HO₂(.)）。引发反应中的速率决定步骤是质子耦合电子从Fe(2⁺)转移至H₂O₂，生成HO(.)和H₂O。HO(.)迅速从H₂O₂中夺取氢，生成HO₂(.)和H₂O。生成的Fe(3⁺)被H₂O₂还原回Fe(2⁺)。HO₂(.)与苯反应生成自由基加合物，该加合物从AcrH₂中夺取氢，生成相应的氢过氧化物，同时生成吖啶基自由基（AcrH(.)），从而构成自由基链反应。通过电子顺磁共振（EPR）分析的自旋捕集法检测到的氢过氧自由基（HO₂(.)），作为两条自由基链途径的链载体：一条是O₂对苯的羟基化反应，另一条是O₂对NADH类似物的氧化反应以生成H₂O₂。
