2,2''-Bis(2-chlorophenyl)-4,4'',5,5''-tetraphenyl-1,2''-biimidazole (CAS# 7189-82-4) is a hexaarylbiimidazole (HABI), a visible light thiol-ene photoinitiator, such as in the polymerization of 1,6-hexanediol diacrylate by hexaarylbisimidazoles and heterocyclic mercapto compounds.
Preparation of a bisimidazole photoinitiator (BCIM):
1. BCIM monomer wet cake is oxidatively coupled using HO in a biphasic system (aqueous alkali/dichloromethane) with a quaternary ammonium salt as phase-transfer catalyst.
2. Work-up: separation of organic phase, washing, and distillation to recover dichloromethane.
3. Isopropanol is added and distilled until turbidity. Water is added to crystallize the product, which is filtered, washed with isopropanol, and dried.