A method of preparing a purified oxydiphthalic anhydride, said method comprising: a) providing a first mixture comprising: an organic solvent, oxydiphthalic anhydride, phase transfer catalyst selected from the group consisting of guanidinium salts, aminopyridinium salts, phosphazenium salts, and mixtures thereof, and at least 10,000 parts per million of a metal halide salt relative to the total weight of the oxydiphthalic anhydride; b) combining the first mixture with water in an amount substantially in excess of the amount of water needed to effect complete hydrolysis of the dianhydride and dissolution of the metal halide salt and at least one inorganic acid to form a second mixture; c) heating said second mixture until substantially all of said oxydiphthalic anhydride is converted to a tetraacid formed as an ingredient in a third mixture, said third mixture comprising an organic layer and an aqueous layer; d) subjecting the third mixture to at least one operation selected from the group consisting of: (i) removing substantially all of the organic solvent to produce an aqueous slurry of the tetraacid; (ii) removing the organic layer from the aqueous layer to form a mixture comprising the tetraacid and the organic solvent; and (iii) filtering to form a tetraacid wet cake; and e) subjecting the product formed in step (d) to at least one operation selected from the group consisting of: (i) filtering to provide a tetraacid wet cake; (ii) combining a tetraacid wet cake with at least one organic solvent to produce a mixture comprising a tetraacid and an organic solvent; and (iii) effecting ring closure of a tetraacid ingredient; to provide a purified oxydiphthalic anhydride comprising less than 50 parts per million of said metal halide salt and less than 30 parts per million of phase transfer catalyst. a) providing a first mixture comprising: an organic solvent, oxydiphthalic anhydride, phase transfer catalyst selected from the group consisting of guanidinium salts, aminopyridinium salts, phosphazenium salts, and mixtures thereof, and at least 10,000 parts per million of a metal halide salt relative to the total weight of the oxydiphthalic anhydride; b) combining the first mixture with water in an amount substantially in excess of the amount of water needed to effect complete hydrolysis of the dianhydride and dissolution of the metal halide salt and at least one inorganic acid to form a second mixture; c) heating said second mixture until substantially all of said oxydiphthalic anhydride is converted to a tetraacid formed as an ingredient in a third mixture, said third mixture comprising an organic layer and an aqueous layer; d) subjecting the third mixture to at least one operation selected from the group consisting of: (i) removing substantially all of the organic solvent to produce an aqueous slurry of the tetraacid; (ii) removing the organic layer from the aqueous layer to form a mixture comprising the tetraacid and the organic solvent; and (iii) filtering to form a tetraacid wet cake; and (i) removing substantially all of the organic solvent to produce an aqueous slurry of the tetraacid; (ii) removing the organic layer from the aqueous layer to form a mixture comprising the tetraacid and the organic solvent; and (iii) filtering to form a tetraacid wet cake; and e) subjecting the product formed in step (d) to at least one operation selected from the group consisting of: (i) filtering to provide a tetraacid wet cake; (ii) combining a tetraacid wet cake with at least one organic solvent to produce a mixture comprising a tetraacid and an organic solvent; and (iii) effecting ring closure of a tetraacid ingredient; (i) filtering to provide a tetraacid wet cake; (ii) combining a tetraacid wet cake with at least one organic solvent to produce a mixture comprising a tetraacid and an organic solvent; and (iii) effecting ring closure of a tetraacid ingredient;