We have investigated the elementary reaction path on the 3,3′,4,4′,5,5′-hexachlorinated biphenyl (HxCB) formation from two 1,2,3,5-tetrachlorobenzenes (TCBz) and the catalytic role of copper on this formation using ab initio molecular orbital calculation. The elementary reaction path on the 3,3′,4,4′,5,5′-HxCB formation from two 1,2,3,5-TCBzs has been shown to occur as follows: Step 1 - the dissociation of Cl atom substituted at 5-position in 1,2,3,5-TCBz, Step 2 - the association between Cl atom substituted at 5-position in another 1,2,3,5-TCBz and the Cl radical formed in Step 1, Step 3 - the elimination of Cl2 molecule from the intermediate species formed in Step 2, and Step 4 - the 3,3′,4,4′,5,5′-HxCB formation from the direct condensation of two 1,2,3-trichlorophenyl radicals formed in Step 1 and Step 3. The geometric factor, which decides the reactivity of this formation, is the C-Cl bond strength of 1,2,3,5-TCBz. The catalytic roles of copper are to stabilize the total energy in the adsorption of 1,2,3,5-TCBz onto the copper surface and to weaken the C-Cl bond strength due to the charge transfer from the 1,2,3,5-TCBz to the copper surface. Moreover, we have achieved the prediction of the minimum energy path on the formation of non- and mono-ortho polychlorinated biphenyls congeners for which TEFs have been determined.
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