o-Xylene (ortho-xylene) is an aromatic hydrocarbon, based on benzene with two methyl substituents bonded to adjacent carbon atoms in the aromatic ring (the ortho configuration).It is a constitutional isomer of m-xylene and p-xylene.o-Xylene is largely used in the production of phthalic anhydride, and is generally extracted by distillation from a mixed xylene stream in a plant primarily designed for p-xylene production.