Deoxymercuration, catalysis

Nucleophilic catalysis by halide ion would be most reasonable, and such possibilities have been realized in studies H8g) on deoxymercuration, and suggested by the late Professor Hughes for apparent S l processes involving scission of the c—hg bond in some -COCH2HgX compounds 107). 

Kreevoy studied in depth the deoxymercuration of CH3CH(OR)CH2HgI with perchloric and acetic acids in methanol, and found that the process was pseudo-first order in mercurial, with ka. [HA]. Specific hydronium ion catalysis was involved, and solvent HOH/DOD isotope effects were those predicted by the Butler equations for a pre-rate-determining proton transfer. Further studies on what had been termed - and /9-2-methoxy-cyclohexylmercuric iodides under similar conditions, led to similar findings concerning the solvent isotope effects, and correlation of log k with — Hq. This suggested that the transition state differs from substrate only by a proton. 

Deoxymercuration, and hence oxymercuration, still presents many pitfalls to broad generalizations. Kreevoy and Turner 118g) have shown that by judicious choice of substrate deoxymercuration can be solvolytic in nature, or involve acid catalysis with conucleophilic catalysis (or assistance)... 

Lambert, J. B., Emblidge, R. W. (1993). Nucleophilic catalysis in deoxymercuration the beta effect of mercury. Journal of Physical Organic Chemistry, 6,555—560. 

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