Radical Dissociation of 2,2′-Bis(2-aryl-3-benzothiophenonyl)s by Mechanical Energy

Article abstract of DOI:10.1246/bcsj.69.2355

On applying pressure with a press in the solid state, the title compounds undergo homolysis of the central C-C bond to give green-colored radicals. X-Ray structure analysis for p-chloro derivative showed that the central C(2)-C(2′) bond was not elongated but had a normal distance (1.576 A) as a hexa-substituted C_sp³-C_sp³ bond. The amount of the radical formed by mechanical energy depended on the substituents on the 2-phenyl rings and on the solvent of crystallization. As for the crystals containing no solvent, p-bromo and p-chloro derivatives showed higher reactivity than the unsubstituted compound, probably due to smaller dissociation enthalpy. The radical dissociation was suppressed by the presence of some solvent of crystallization. In the solvated crystals, the excess energy supplied by external mechanical energy would be transferred mainly to vibrational modes of the solvent molecules rather than to the substrate.