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 investigated. When 9-thienothienylfluoren-9-ol derivatives were coground with dichlorodicyanoquinone (DDQ) and then exposed to methanol vapor, the corresponding 9-methoxyfluorenes were obtained in 15-70% yields. Throughout the whole procedure the solid state was retained. The generation of a radical cation in the coground solids via charge-transfer interaction between the substrate alcohol and DDQ was suggested by the ESR spectrum. The mechanism involving the collapse of the radical cation to generate a proton, which acts as a catalyst to afford the carbocation, was deduced based on the electrochemical oxidation of the substrate in solution. The propagation of the substitution reaction in the solid state has been shown for the carbocation upon contact with methanol vapor. The crystalline inclusion compounds of 9-thienothienylfluoren-9-ol derivatives incorporating methanol as a guest were exposed to HCl gas. This gas-solid reaction also led to the formation of the corresponding methoxy compounds maintaining the solid state. Through this work a new consequence of solid-state cogrinding is deduced.