Synthesis of halogenated diphenyl ethers and dibenzofurans - A discussion of specific isomers available

Polychlorinated diphenyl ethers—A review

“…6 Studies conducted in Finland have detected PCDEs in fresh salmon, white-tailed eagles, and in commercial fish liver oil. 10 PCDEs have been shown to be relatively stable in the environment, 12 and coupled with the fact that they physicochemically similar to the PCBs, it was suggested that leakage of PCDEs into the biosphere may cause bioaccumulation problems similar to those caused by PCBs. 13 Furthermore, studies indicate that the rate of degradation of PCDEs depends upon their concentration.…”

“…The nitro group can then be transformed to the desired PCDE congener using one of the reactions described above. 12 Howie et al 20 used direct conversion of a nitro group into a chloro group by treatment with dichlorophenylphosphine, chlorine gas, and phenylphosphonic dichloride. They synthesized various PCDEs with an overall yield > 40%.…”

“…Of 209 possible congeners, 143 can be synthesized using this method. 12 Direct halogenation of diphenyl ether is another method for the synthesis of PCDEs, and this reaction is catalyzed by Lewis acids such as A1C1 3 . This synthetic route is of limited utility because it results in the formation of a complex mixture from which only a limited number of isomers can be isolated.…”

“…By altering the substitution pattern on the phenol and the benzene, different congeners can be synthesized. 12 The Ponomarkenko reaction, which is carried out by treating a nitro-or a sulfonyl-substituted diphenyl ether with a high boiling halogenated aliphatic hydrocarbon at high temperature, can also be used to synthesize PCDEs. 12 Using the Sandmeyer reaction, the nitro group on a substituted diphenyl ether can be reduced to an amino group which in turn can be replaced by a chlorine or hydrogen via diazotization.…”

“…This synthetic route is of limited utility because it results in the formation of a complex mixture from which only a limited number of isomers can be isolated. 12 Additionally, PCDEs can be synthesized via the Ullmann reaction by coupling a phenolic salt with a halogenated benzene. By altering the substitution pattern on the phenol and the benzene, different congeners can be synthesized.…”