Solid-state solvolysis of thiophene-substituted trityl-type alcohols: Nucleophilic substitution induced by gas-solid contact

The nucleophilic substitution reaction by gas-solid contact has been invest igated. When 9-thienothienylfluoren-9-ol derivatives were coground with dic hlorodicyanoquinone (DDQ) and then exposed to methanol vapor, the correspon ding 9-methoxyfluorenes were obtained in 15-70% yields. Throughout the whol e procedure the solid state was retained. The generation of a radical catio n in the coground solids via charge-transfer interaction between the substr ate alcohol and DDQ was suggested by the ESR spectrum. The mechanism involv ing the collapse of the radical cation to generate a proton, which acts as a catalyst to afford the carbocation, was deduced based on the electrochemi cal oxidation of the substrate in solution. The propagation of the substitu tion reaction in the solid state has been shown for the carbocation upon co ntact with methanol vapor. The crystalline inclusion compounds of 9-thienot hienylfluoren-9-ol derivatives incorporating methanol as a guest were expos ed to HCl gas. This gas-solid reaction also led to the formation of the cor responding methoxy compounds maintaining the solid state. Through this work a new consequence of solid-state cogrinding is deduced.