Tetrabromo-o-xylene
# Tetrabromo-o-xylene

α,α,α',α'-Tetrabromo-o-xylene is an organobromine compound with the formula $C_6H_4(CHBr_2)_2.$ Three isomers of α,α,α',α'-Tetrabromoxylene exist, but the ortho derivative is most widely studied. It is an off-white solid. The compound is prepared by the photochemical reaction of o-xylene with elemental bromine:

    $C_6H_4(CH_3)_2$ + 4 $Br_2$ → $C_6H_4(CHBr_2)_2$ + 4 HBr

Reaction of α,α,α',α'-tetrabromo-o-xylene with sodium iodide affords α,α'-dibromo-o-xylylene, which can be trapped with dienophiles to give naphthylene. In the absence of trapping agents, the xylylene relaxes to α,α'-dibromobenzocyclobutane:

    $C_6H_4(CHBr_2)_2$ + 2 NaI → $C_6H_4(=CHBr)_2$ + 2 NaBr + $I_2$
    $C_6H_4(=CHBr)_2$ → $C_6H_4(CHBr)_2$

Cycloadditions of these xylylenes provides a pathway to acenes.

