Abstract: A process to prepare (2E)-2-cyano-3-(3, 4-dihydroxy-5-nitrophenyl)-N,N-diethyl-2-propenamide (Entacapone) eliminating corrosive acids in the purification, with more than 99.5% purity with a Z-isomer content of less than 0.1% comprising condensation of e,4-Dihydroxy{5-nitrobensaldehyde with N,N-diethyl cyanoacetamide in the presence of a base selected from cyclic and acyclic secondary amines and a mixture of solvents, to obtain a crude product, stirring the crude product in a halogenated solvent, filtering and finally crystallization of polymorph A of Entacapone in a solvent.