Process for the preparation of dimethyl succinylosuccinate, the disodium salt thereof, dianilinodihydroterephthalic acids, the dimethyl esters and salts thereof, and dianilinoterephthalic acids, and the dimethyl esters and salts thereof

Process for the preparation of dimethyl dianilinodihydroterephthalates of the formula (I), ##STR26## the rings A and B optionally being substituted by 1 to 4 substituents from the group comprising C.sub.1 -C.sub.4 -alkyl, chlorine, fluorine, C.sub.1 -C.sub.4 -alkoxy, carbamoyl which is optionally monosubstituted or disubstituted by C.sub.1 -C.sub.4 -alkyl, trifluoromethyl, carboxyl or nitro, or optionally an aromatic ring is fused thereto, characterized in that the suspension of the disodium salt of dimethyl succinylosuccinate, which suspension is obtained by condensation of dimethyl succinate in a 35-45 percent by weight solution of 120-180 percent of theory of sodium methylate in methanol, is acidified, the liberated dimethyl succinylosuccinate is condensed with at least two mols of a compound of the formula ##STR27## in which A has the meaning given under formula (I), or with, altogether, at least 2 mols of a mixture of a compound of the formula (II) and a compound, which differs therefom, of the formula (III) ##STR28## in which B has the meaning given under formula (I), or with salts of the amines (III) and/or (II), and the dimethyl esters are isolated.