由TiO 2和酚类形成的表面电荷转移复合物在可见光光催化中显示出巨大的潜力。然而,背电子转移限制了电荷转移效率和表面络合物中酚类的活化。在此,我们揭示了通过引入碱来有效活化表面复合物中的酚类。同源偶联反应和丁基化羟基甲苯捕获的实验都清楚地证明了从各种木质素衍生的底物中产生酚自由基。碱的加入引起了表面配合物的蓝移吸收,同时增加了可见光诱导的从衬底到TiO 2的电子激发。振动光谱表明酚盐和 TiO 2之间的相互作用更强高于中性苯酚。这种碱基触发策略可能有助于通过表面复合物对酚进行有用的转化或降解。
The reaction of the 2,6-di-tert-butyl-4-methylphenoxy radical with phenols
作者:Kanji Omura
DOI:10.1021/jo00003a006
日期:1991.2
Dimer 3 dissociates in solution to give the phenoxy radical 4. When solid 3 is dissolved in a solution of phenol 11a, radical 4 dehydrogenates the phenol to afford phenol 5 and phenoxy radical 12. Radical 12 couples with more 4 to afford principally bis(cyclohexadienone) 16a and a minor amount of the dimeric bis(cyclohexadienone) 13. The preferential formation of 16a over 13 is explained as the result of a solvent-cage reaction. Compounds 13 and 16a are isomerized in the presence of silica gel or triethylamine to 4,4'-dihydroxybiphenyl 14 and phenolic dienone 17a, respectively. Compound 13 is relatively stable in hexane at 30-degrees-C, while 16a slowly dissociates under these conditions to afford parent radicals 4 and 12. If 11a is present, radical 4 either recombines with 12 or dehydrogenates the phenol. Two radicals of 12 generated by the dissociation of 16a and the subsequent dehydrogenation of 11a couple to give 13. Therefore, dissolving 3 in hexane containing excess 11a and keeping the resulting solution at 30-degrees-C results in the preferential formation of 13. Dissolving 3 in triethylamine containing phenols 11 or 21 similarly affords dienones 17 or 23. The yields of these dienones increase with increasing electron-donating capability of the substituent on the phenol ring.
OMURA, KENJI, J. ORG. CHEM., 56,(1991) N, C. 921-926