Yamada Mihoko, Karlin Kenneth D, Fukuzumi Shunichi
Department of Material and Life Science, Graduate School of Engineering, Osaka University, ALCA and SENTAN, Japan Science and Technology (JST), Suita, Osaka 565-0871, Japan.
Department of Chemistry, The Johns Hopkins University, Baltimore, Maryland, 21218, United States.
Chem Sci. 2016 Apr 1;7(4):2856-2863. doi: 10.1039/C5SC04312C. Epub 2016 Jan 5.
Benzene was hydroxylated with hydrogen peroxide (HO) in the presence of catalytic amounts of copper complexes in acetone to yield phenol at 298 K. At higher temperature, phenol was further hydroxylated with HO by catalysis of copper complexes to yield -benzoquinone. The kinetic study revealed that the rate was proportional to concentrations of benzene and HO, but to the square root of concentration of a copper(II) complex ([Cu(tmpa)]: tmpa = tris(2-pyridylmethyl)amine). The addition of a spin trapping reagent resulted in formation of a spin adduct of hydroperoxyl radical (HO), as observed by EPR spectroscopy, inhibiting phenol formation. HO produced by the reaction of [Cu(tmpa)] with HO acts as a chain carrier for the radical chain reactions for formation of phenol. When [Cu(tmpa)] was incorporated into mesoporous silica-alumina (Al-MCM-41) by a cation exchange reaction, the selectivity to production of phenol was much enhanced by prevention of hydroxylation of phenol, which was not adsorbed to Al-MCM-41. The high durability with turnover number of 4320 for the hydroxylation of benzene to phenol with HO was achieved using [Cu(tmpa)] incorporated into Al-MCM-41 as an efficient and selective catalyst.
在丙酮中，在催化量的铜配合物存在下，苯与过氧化氢（HO）在298K下发生羟基化反应生成苯酚。在较高温度下，苯酚在铜配合物的催化下进一步与HO发生羟基化反应生成对苯醌。动力学研究表明，反应速率与苯和HO的浓度成正比，但与铜（II）配合物（[Cu(tmpa)]：tmpa = 三（2-吡啶甲基）胺）浓度的平方根成正比。通过电子顺磁共振光谱观察到，添加自旋捕获试剂会导致氢过氧自由基（HO）的自旋加合物形成，从而抑制苯酚的形成。[Cu(tmpa)]与HO反应生成的HO作为自由基链式反应的链载体用于苯酚的形成。当通过阳离子交换反应将[Cu(tmpa)]掺入介孔硅铝酸盐（Al-MCM-41）中时，通过防止未吸附到Al-MCM-41上的苯酚羟基化，苯酚生产的选择性大大提高。使用掺入Al-MCM-41中的[Cu(tmpa)]作为高效选择性催化剂，实现了以HO将苯羟基化为苯酚的高耐久性，周转数为4320。
