| abstract |
The present invention provides a process for the preparation of a compound of the formula n nwherein n Y represents —O—, —S— or —N(R 2 )—, n R 2 being hydrogen, C 1 -C 10 alkyl or aralkyl; Z represents a 2,5-furanyl, 2,5-thiophenyl, 4,4′-stilbenyl or a 1,2-ethylenyl residue and n R 1 represents hydrogen, halogen, C 1 -C 10 alkyl, C 1 -C 10 alkoxyl, cyano, COOM or SO 3 M, n nM being hydrogen or an alkaline or alkaline earth metal, characterized by reacting a compound of the formula n nwith a dicarboxylic acid of the formula n nHOOC-Z-COOH (3) n nor an ester thereof, Y, Z and R 1 being as previously defined, in N-methylpyrrolidone or N,N-dimethylacetamide, in the presence of an acidic catalyst and, optionally, in the presence of a secondary solvent capable of removing water from the reaction mixture, which are useful as optical whitening agents for natural and synthetic materials. |