A new process for manufacturing entacapone comprising reacting 3,4-dihydroxy-5-nitrobenzaldehyde with N,N-diethyl-2-cyanoacetamide in the presence of acatalyst in a C 4 to 8 alcohol at reduced pressure and at a temperature of atleast 70 ~C, cooling the mixture to a temperature of 30 ~C or below, seedingthe mixture with N,N-diethyl-2-cyano-3-(3,4-dihydroxy-5-nitrophenyl)acrylamidecomprising at least 10 % of the Z-isomer by weight in the seeding crystals,cooling the mixture to a temperature of 5 ~C or below, isolating thecrystallized product and converting the obtained mixture of the E- and Z-isomers of N,N-diethyl-2-cyano-3-(3,4-dihydroxy-5-nitrophenyl)acrylamide tothe E-isomer (entacapone).
