Mercat process

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... 

---