The halogenation of aromatics: Part V. Gas‐phase chlorination of phenoxybenzene

The gas‐phase chlorination of phenoxybenzene was studied at 300‐500°, using the experimental methods described earlier. The results obtained are in contrast with those found in liquid‐phase chlorination: there the product was mainly para‐chlorophenoxybenzene, while in the present investigation, at temperatures above 350°, monochlorinated products were mainly the meta‐isomer; they did not contain any ortho‐compound. Instead, dibenzofuran was formed. Between 300 and 350°, appreciable proportions of para‐chlorophenoxybenzene were also formed, presumably owing to the occurrence of electrophilic substitution in the liquid‐phase afterchlorination or at the walls of the reactor. The high‐temperature halogenation of phenoxybenzene therefore leads to substitution at the carbon atom carrying the highest positive charge, i.e. the position corresponding to the highest Hammett σ‐value, in the same way as in our earlier gas‐phase halogenations of halobenzenes and of benzonitrile.