The bistetrachloronitrophenylmercurials R2Hg (R = o-, m- or p-O2NC6Cl4) have been prepared by mercuration of the appropriate tetrachloronitrobenzenes with mercuric trifluoroacetate under forcing conditions. Bis(2,3,5,6-tetrachloro-4-nitrophenyl)mercury could not be obtained analytically pure by this method, but pyrolysis of mercuric 2,3,5,6-tetrachloro-4-nitrobenzenesulphonate gave the pure mercurial. Sodium 2,3,5,6-tetrachloro-4-nitrobenzenesulphonate was prepared by reaction of 2,3,5,6- tetrachloro-1,4-dinitrobenzene with sodium sulphite, and was converted into the mercuric salt via the barium salt and free sulphonic acid. Cleavage of the bistetrachloronitrophenylmercurials with iodine in N, N-dimethylformamide gave the corresponding tetrachloroiodonitrobenzenes. When the mercurials were cleaved with triiodide ions, the resulting tetrachloroiodonitrobenzenes contained impurities, e.g. tetrachloronitrobenzenes or tetrachlorodiiodobenzenes, which were formed by reaction of iodide ions (derived from I3−) either with the mercurials or with their cleavage products.