Fluorocarbon-aluminium compounds. II. Reactions of hexafluorobenzene, pentafluorobenzene, and 1,2,4,5-tetrafluorobenzene with lithium tetrahydroaluminate

Abstract

Reaction of lithium tetrahydroaluminate with hexafluorobenzene yields pentafluorobenzene. Pentafluorobenzene reacts further with LiAlH₄ to give 1,2,4,5-tetrafluorobenzene. The products are formed by a combination of (i) reduction (hydride for fluoride replacement) of the fluoroaromatic compound, and (ii) hydrolysis of one of the compounds LiAl(C₆F₄H)H₂F or LiAl(C₆F₅)H₂F that are formed in the reactions. These competing reactions take place to a similar extent and are much faster in tetrahydrofuran than in diethyl ether.     In tetrahydrofuran, 1,2,4,5-tetrafluorobenzene is metalated by LiAlH₄. The compounds LiAl(C₆F₄H)H₃, LiAl(C₆F₄H)₂H₂, and LiAl(C₆F₄H)₃H are proposed as products of the reaction.     The fluorocarbon-aluminium compounds have been characterized by quantitative determination of the products of hydrolysis and by ¹H and ¹⁹F N.M.R. spectroscopy.