SYNTHESIS OF FLUOROCYCLOHEXADIENES BY THE ELECTROCHEMICAL FLUORINATION OF P-FLUOROBENZENES ON A PREPARATIVE SCALE

摘要

Fluorine containing-cyclohexadienes (FCHDs), 3,3,6,6,-tetrafluoro-1,4-cyclohexadiene (1a), 1-chloro-3,3,6,6-tetrafluoro-1,4-cyclohexadiene (3a) and 1-bromo-3,3,6,6-tetrafluoro-1,4-cyclohexadiene (4a), were isolated in pure states with high yields (ca. 80%) by the preparative scale electrochemical fluorination of 1,4-difluorobenzene (1), 1-chloro-2,5-difluorobenzene (3) and 1-bromo-2,5-difluorobenzene (4), respectively, in Et(4)NF . mHF (Et = C2H5: m = 4.0, 4.45 and 4.7) at a platinum anode, followed by extraction and fractional distillation. The electrochemical fluorination of 1,2,4-trifluorobenzene (2) yielded both 1,3,3,6,6-pentafluoro-1,4-cyclohexadiene (2a) and 2,5,5,6,6-pentafluoro-1,3-cyclohexadiene (2b) with high yield (ca. 90%). Some of (2a) was also isolated in a pure state by fractional distillation. Each substrate compound (1-4) was fluorinated to the corresponding FCHDs with an almost quantitative yield when 2.0-2.1 faraday (per mol of substrate) of electricity was passed. [References: 18]