Mercuration of boiling 1, 2, 4-trichlorobenzene ith mercuric trifluoroacetate yields complex species, which were shown to contain mainly μ-(2, 5, 6-trichloro-1, 3-pheny1ene)dimercury bridging units and 2, 3, 6-trichlorophenylmercury terminal groups by halogenodemercuration reactions, and bis(2, 3, 6-tri-chlorophenyl)mercury, which was independently synthesized from 2, 3, 6-trichlorophenyllithium and mercuric chloride. The organolithium compound was formed regiospecifically on reaction of 1, 2, 4-trichlorobenzene with butyllithium. Mercuration of 1, 2, 4-trichlorobenzene with mercuric trifluoroacetate (mole ratio 1:1) in trifluoroacetic acid results in regiospecific monomercuration giving 2, 4, 5-trichlorophenylmercuric trifluoroacetate. This compound undergoes rearrangement in boiling 1, 2, 4-trichlorobenzene to give a 2, 3, 6-trichlorophenylmercurial, and is considered to be an intermediate in the mercuration synthesis of bis(2, 3, 6-trichloropheny1)mercury. Thus, in 1, 2, 4-trichlorobenzene, the kinetically and thermodynamically favoured mercuration positions differ by contrast with the reported behaviour of 1, 2, 3-trichlorobenzene. Formation of the complex mercuration products is considered to involve μ-(2, 5, 6-trichloro-1, 3-phenylene)bis(trifluoroacetato)dimercury and bis(2, 3, 6-trichloropheny1)mercury as intermediates. The new mercurials, bis(2, 3, 5-trichloro-pheny1)-, bis(3, 4, 5-trichloropheny1)- and bis(2, 4-dichloropheny1)-mercury, have been prepared from the appropriate polychloroanilines by the diazonium route.