3-(Dimethylamino)benzoic acid → 2-(Bis(4-(dimethylamino)phenyl)methyl)-5-(dimethylamino)benzoic acid

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A process for preparing 3,3-bis(4-dimethylaminophenyl)-6-dimethylaminophthalide which comprises reacting one mole proportion of tetramethyl-4,4'-diaminobenzhydrol with from about 0.9 to about 1.2 mole proportions of 3-dimethylaminobenzoic acid in aqueous sulfuric acid at a temperature of 65°-100° C. to form 2-[4,4'-bis(dimethylamino)benzhydryl]-5-dimethylaminobenzoic acid, adding sodium hydroxide to the reaction mixture to form the sodium salt of the said benzoic acid therein, contacting the reaction mixture at a temperature of about 40°-90° C. with a solvent selected from a liquid aromatic hydrocarbon and a mixture of liquid aromatic hydrocarbon and a water-immiscible alkane, whereby impurities present in said solution are extracted therefrom; separating the organic extract phase from the aqueous reaction mixture phase, treating the reaction mixture phase with an inorganic oxidizing agent to oxidize the sodium salt of the 2-[4,4'-bis(dimethylamino)benzhydryl]-5-dimethylaminobenzoic acid to the 3,3-bis-(4-dimethylaminophenyl)-6-dimethylaminophthalide product and recovering said product from the reaction mixture.

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