Mercura tion

Until a few years ago, no quantitative comparison of overall reactivities in electrophilic substitution of the fundamental five-membered rings was available. Only the reactivity of thiophene relative to benzene had been measured quantitatively in several electrophilic substitutions bromination,72 chlorination,72 nitration,121 hydrogen exchange,57 protodesilylation,174 and mercura-tion.121... 

A dimercurihydroxy naphthoic acid cannot be obtained, and mercura-tion of -hydroxynaphthoic-4 7-disulphoiiic acid has not been very successful. 

The kinetics and mechanisms of these aromatic mercurations are known, e.g., for Hg(OCOCF3)2 ° and Hg(OAc)2 . The most straightforward for kinetic purposes is the Hg(0C0CF3)2-CF3C02H system. Clean second-order reactions (first order in Hg salt and in aromatic) are found at all concentrations. For the Hg(02CCHj)2-CH3C02H system (with or without HCIO4.), there is departure from second-order kinetics at other than low concentrations. Another problem with reaction in AcOH is solvent mercura-tion. 

Remarkably, some C-electrophilic substitutions such as bromination, mercura-tion and even Mannich reactions " (but not nitration) can be achieved, though the mechanisms for these substitutions may not be of the conventional type. 

Substituent Bromina- tion Chlorina- tion Detritia- tion Dedeuter- iation Acetyla- tion-f Trilluoro- acetylation Mercura- tion ... 

Gunstone, F.D., and R.P Inglis, Neighbouring Group Participation in the Ox mercura-tion-Demercuration Reaction, Chem. Phys. Lipids 10 89-104 (1973). 

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