ABSTRACT
In this chapter, biphenyl syntheses are discussed which have been used for the preparation of chlorobiphenyls including labeled compounds. Decompositions of aroyl peroxides in appropriate substrates are also useful synthetic reactions in which high yields of chlorobiphenyls have been obtained, particularly in the presence of electron acceptors. A method for the one-step homolytic decarboxylation of aromatic carboxylic acids has been described and this source of aryl radicals has been used for the preparation of several chlorobiphenyls. Mono- and dichlorobiphenyls have been prepared using new phenylating agents: iodoso-benzene dibenzoate, lead tetrabenzoate, and silver iodide (bromide) dibenzoate. The preparation of a number of symmetrical and unsymmetrical polychlorobiphenyls by the Ullmann reaction has recently been reported. 4,4'-Dichlorobiphenyl and 2,4'-dichlorobiphenyl were easily separated from the mixture and 2,2'-dichlorobiphenyl was collected in a fraction together with monochlorobiphenyls. A complete bibliography on chlorobiphenyls until 1949 can be found in Beilsteins Handbuch.
