Continuous process for the manufacture of 3,5,5-trimethylcyclohexa-3-en-one(β-isophorone)

A continuous process for the manufacture of 3,5,5-trimethyl-cyclohexa-3-en-1-one (β-isophorone) by isomerization under homogeneous catalysis of 3,5,5-trimethylcyclohexa-2-en-1-one (α-isophorone), obtained by trimerization of acetone in an alkaline medium, said process comprising:

• a) continuously introducing α-isophorone and a solution of an alkaline hydroxide into a reaction region,
• b) heating the reaction mixture,
• c) continuously and simultaneously removing from said reaction mixture:
• 1) by distillation, a fraction comprising an amount by weight of β-isophorone ranging from 30% to 90%;
• and
• 2) drawing off, heavy products, so that their content is at most equal to 7% by weight in the reaction mixture,
• d) rectifying the fraction distilled in c) 1) so as to obtain β-isophorone with a purity as defined by the β-isophorone/α-isophorone ratio of greater than 99% and,
• e) continuously returning the bottoms from the rectification to the reaction region.