Olah G A, Hashimoto I, Lin H C
Institute of Hydrocarbon Chemistry, Department of Chemistry, University of Southern California, Los Angeles, California 90007.
Proc Natl Acad Sci U S A. 1977 Oct;74(10):4121-5. doi: 10.1073/pnas.74.10.4121.
The mercuration and thallation of benzene and substituted benzenes was studied with mercuric and thallic trifluoroacetate, respectively, in trifluoroacetic acid. With the shortest reaction time (1 sec) at 0 degrees , the relative rate of mercuration of toluene compared to that of benzene was 17.5, with the isomer distribution in toluene of: ortho, 17.4%; meta, 5.9%; and para, 76.7%. The isomer distribution in toluene varied with the reaction time, significantly more at 25 degrees than at 0 degrees . The competitive thallation of benzene and toluene with thallic trifluoroacetate in trifluoroacetic acid at 15 degrees showed the relative rate, toluene/benzene, to be 33, with the isomer distribution in toluene of: ortho, 9.5%; meta, 5.5%; and para, 85.0%. With increasingly higher reaction temperatures in both mercuration and thallation reactions of aromatics, isomerization (both intramolecular and intermolecular) within the relevant ortho- and para-metallated intermediate ions and/or of the isomers becomes more important. Competitive rates and isomer distributions of mercuration and thallation of benzene and substituted benzenes were also determined. The predominant para substitution in both mercuration and thallation of methylbenzenes reflects, besides some steric factors, the strong stabilizing effect of para methyl groups on the arenium ion intermediates. Under predominantly kinetically controlled conditions, no anomalous increase in the amount of meta substitution was observed.
分别用三氟乙酸汞和三氟乙酸铊在三氟乙酸中研究了苯和取代苯的汞化反应和铊化反应。在0℃下反应时间最短（1秒）时，甲苯与苯的汞化相对速率为17.5，甲苯中的异构体分布为：邻位，17.4%；间位，5.9%；对位，76.7%。甲苯中的异构体分布随反应时间而变化，在25℃时的变化比在0℃时显著得多。在15℃下，用三氟乙酸铊在三氟乙酸中对苯和甲苯进行竞争铊化反应，甲苯/苯的相对速率为33，甲苯中的异构体分布为：邻位，9.5%；间位，5.5%；对位，85.0%。在芳烃的汞化和铊化反应中，随着反应温度的不断升高，相关邻位和对位金属化中间体离子内的异构化（分子内和分子间）和/或异构体的异构化变得更加重要。还测定了苯和取代苯的汞化和铊化反应的竞争速率和异构体分布。甲苯的汞化和铊化反应中主要的对位取代，除了一些空间因素外，还反映了对位甲基对芳鎓离子中间体的强烈稳定作用。在主要动力学控制条件下，未观察到间位取代量的异常增加。
