Polymerization of aromatic nuclei. XII. Oligomerization of halobenzenes by aluminum chloride‐cupric chloride

Polymerization of chloro‐ and fluorobenzene by aluminum chloride‐cupric chloride produced highly colored oligomers. Chlorobenzene reacted under the standard conditions, i.e., 6/1/0.5 (molar ratio) of aromatic/catalyst/oxidant at 60°C. for 1 hr., to give a red solid in 14% yield. Evidence concerning the structure was obtained from elemental analyses, infrared and ultraviolet spectra, dechlorination, oxidation, solubility, molecular weight, and color. The data indicate that the backbone chain consists of an o‐polyphenyl structure with chlorine atoms situated at the 4‐positions. Polynuclear regions presumably comprise part of the structure. Molecular weight data pointed to an average of 10–12 units per chain. The coupled product from fluorobenzene was very similar to the chlorobenzene oligomer in most respects. In contrast to the chlorobenzene case, there was evidence of propagation occurring to some extent by attack ortho to the fluorine. Bromobenzene produced brominated p‐polyphenyl apparently by disproportionation to benzene which then functioned as the monomer. An oxidative cationic mechanism (σ polymerization) is proposed for the nuclear coupling.