Mercat reaction

The term Mercat reaction refers to the use of mercury photosensitization to perform reactions on a preparatively useful, multigram scale. Typically these reactions involve CH activation, for example the conversion of methanol to ethylene glycol or indeed almost any organic compound to its dehydro dimer. 

Mercury also gives the synthetically useful transformation of R—H to R2 in the Mercat reaction (Eqs. 12.37 and 12.39) the weakest C—H bond in the molecule is selectively cleaved. The product shown in Eq. 14.33 is a useful ligand, but very difficult to make by conventional routes. 

Other photochemical reactions have been reported as in the Mercat process involving gas-phase mercury-catalyzed oxidative homo- and cross-couplings (Equation (16)) 25>2Sa>2Sb... 

The critical property of the Mercat process [3-8] that gives it its selectivity is that only Hg atoms in the vapor phase undergo reaction, because their absorption line is narrow and matched with the sharp emission line of the lamp. Mercury dissolved in the liquid phase has a broadened and shifted absorption band and Hg in solution has a short excited-state lifetime, so the liquid phase undergoes no significant reaction. In the vapor, Eqs. (2)—(5) produce the dehydro dimer, which condenses. 

The major characteristic of the catalysts described above is that they deactivate—a complex able to attack C—H bonds is also able to attack itself or the solvent. In the Mercat process, the catalyst, a Hg atom, is completely stable to the reaction conditions. There is no solvent because this is a rare example of organometallic chemistry in the gas phase. The system easily... 

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See also in sourсe #XX -- [ ]

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