Fluorocarbon-aluminium compounds. IV. Reactions of some chloropolyfluorobenzenes with lithium tetrahydroaluminate

Abstract

The reaction of lithium tetrahydroaluminate with chloropentafluorobenzene yields mainly p-chlorotetrafluorobenzene. The nature of the solvent influences the formation of other fluorocarbon compounds in the reaction. p-Chlorotetrafluoro-benzene reacts further with LiAlH₄ in tetrahydrofuran, but not in diethyl ether, to give predominantly 1-chloro-2,3,5-trifluorobenzene and 1-chloro-2,3,6- trifluorobenzene. In turn, the trifluorobenzene compounds react with LiAlH₄ in tetrahydrofuran to give mainly 1-chloro-2,5-difluorobenzene. The major products are formed by a combination of (i) direct nucleophilic displacement of fluorine in the chloropolyfluorobenzene compounds by hydride, and (ii) hydrolysis of the compounds LiAl(C₆F₄Cl)H₂F, LiAl(C₆F₃HCl)H₂F, and LiAl(C₆F₂H₂Cl)H₂F. The fluorocarbon- aluminium compounds have not been isolated from solution but they were characterized by quantitative determination of the products of hydrolysis and by ¹H and ¹⁹F N.M.R. spectroscopy.