Abstract: For the continuous manufacture of &bgr;-isophorone by isomerization under homogeneous catalysis of &agr;-isophorone, the steps of introducing the &agr;-isophorone and a solution of an alkaline hydroxide into a reaction region, bringing the reaction mixture to reflux at a temperature at least equal to 150° C. under a equal P1 of less than or equal to atmospheric pressure, continuously and simultaneously removing from the reaction mixture: &bgr;-isophorone vapor, by distillation under a pressure P2 less than P1 and at a temperature at most equal to 150° C., and heavy products, at a rate, so that their content by weight is at most equal to 7% in the reaction mixture, and continuous returning the distillation to the reaction region.

Abstract: This invention relates to improved hydroformylation reactors of the "loop" type comprising two parallel vertical tubes, one of said tubes having a supply tube at its base and acting as the ascending branch and the other of said tubes acting as the descending branch, and means connecting said tubes to one another at their top and bottom ends, the improvement comprising a tubular loop connecting said tubes at their upper ends, and an evacuation orifice for synthesis gases and excess liquid phase from said tubular loop, said orifice having a smaller diameter than the internal diameter of said tubular loop.