Process for preparing piperonal

#The present invention relates to a process for producing piperonal, more specifically to a process for producing a high quality piperonal with high yield by using 1,2-methylenedioxybenzene as a starting material and without taking 3,4-methylenedioxymandelic acid which is an intermediate in the course of the reaction as a crystal.

#Piperonal is a base material for preparing a heliotrope type perfume and has widely been used as a perfume for general cosmetics, and in addition, it is a useful compound as a starting material for synthesis of medical and agricultural chemicals and a brightener for metal plating.

#As a method for producing piperonal, it has been generally known a method of oxidizing 3,4-methylenedioxy-mandelic acid with nitric acid (for example, P. S. Raman Current Science, 27, 22 (1958), Perfumer & Flavourist, 14, 13 (1989), EP 429316, etc.). Also, it has been known that 3,4-methylenedioxymandelic acid can be produced by reacting 1,2-methylenedioxybenzene and glyoxylic acid in the presence of sulfuric acid, etc. (for example, Japanese Provisional Patent Publication No. 95573/1979, Perfumer & Flavourist, 14, 13 (1989), etc.).

#Next, the present invention will be explained by referring to Examples, but the scope of the present invention is not limited by these ranges. Incidentally, a yield of the formed piperonal was calculated out in terms of mole.

#In a flat bottom separable flask having an inner volume of 7 liters, 500.0 g (4.09 mol) of 1,2-methylenedioxybenzene and 250 ml of 4-methyl-2-pentanone were charged under nitrogen atmosphere, and the mixture was cooled to −5° C. while stirring. Then, a mixture comprising 833.4 g (4.44 mol) of a 40% by weight aqueous glyoxylic acid solution and 857.8 g (8.40 mol) of 96% by weight sulfuric acid was gradually added dropwise, and then, the mixture was stirred at −5° C. for 21 hours.

#Then, 3000 ml of 4-methyl-2-pentanone was added, and 1030.0 g (16.9 mol) of 28% by weight aqueous ammonia was gradually added to the mixture while maintaining the liquid temperature to −10 to 5° C. to effect neutralization. After the neutralization, the mixture was heated to 80° C., and 3,4-methylenedioxymandelic acid was extracted in a 4-methyl-2-pentanone layer (an organic solvent layer). At this time, the reaction mixture was separated into two layers of an organic solvent layer and an aqueous layer.