P 1835 (OTTO) Phthalic acid, 98% Cas 88-99-3 - used as plasticizers for polyvinyl chloride and other polymers. It is also useful in the production of anthraquinone, phenolphthalein and phthalocyanine pigments. It serves as an organic reagent in the production of phthalates. It is used to prepare 1,3-cyclohexadiene by reduction using sodium amalgam.