This mass quantity of xylenes is reagent grade and can be used as a precursor for mass manufacturing various industrially significant substances such as terephthalic acid and dimethyl terephthalate. Both of these xylene based monomers are used extensively in the production of polyethylene terephthalate (PET) plastic bottles and polyester textiles. Around 98 percent of all p-xylene produced in the world is expended to make polyester or PET plastic bottles. O-xylene is also in high demand due to its nature as a precursor for phthalic anhydride, the anhydrous form of phthalic acid, an important plasticizer in manufacturing numerous types of plastic derived from vinyl chloride. Phthalic acid is produced by the catalytic oxidation of o-xylene or naphthalene, but o-xylene is the preferred compound due to the superior purity of the phthalic acid produced by catalytic oxidation. X-xylene is generally used as an industrial solvent for the printing, leather, and rubber industries.