Synthesis and bromodemercuration of some permercurated arenes

Abstract

Pentabromonitrobenzene, pentabromobenzoic acid, pentabromobenzamide, pentabromoacetanilide, barium pentabromobenzenesulphonate, 1,2,4,5 - tetrabromo -3-chloro-6-(trifluoromethyl)benzene, 2,3,5,6-tetrabromo-4-methoxytoluene 2,3,5,6-tetrabromo-4-methoxybenzamide, methyl 2,3,5,6-tetra- bromo-4-methoxybenzoate, and 1,2,5-tribromo-3,4-dichloro-6-fluorobenzene have been synthesized in good yield by bromodemercuration of the corresponding fully mercurated (permercurated) arenes, e.g. C₆(HgO₂CCF₃)₅NO₂, which were prepared by reaction of an excess of molten mercuric tri- fluoroacetate with suitable arenes at c. 180-245º. Permercuration of p-methoxybenzoic acid was accompanied by complete decarboxylation giving, after bromodemercuration, pentabromo(methoxy)- benzene, which was also obtained in low yield from preparations of methyl 2,3,5,6-tetrabromo-4- methoxybenzoate and 2,3,5,6-tetrabromo-4-methoxybenzamide. Conditions have been devised for conversion of phenylmercuric chloride into either a pentamercurated or a hexamercurated benzene derivative, and hence into pentabromo-or hexabromobenzene. The results establish permercuration/bromodemercuration as a simple and versatile route to polybromobenzene.