Purification of pseudo-ionone

Psuedo-ionone is purified by reacting the impure compound with an alkali metal or ammonium bisulphite, the molar ratio of bisulphite to pseudo-ionone being less than 2 but sufficient to convert a substantial proportion of the pseudo-ionone into a monosulphonic acid derivative, separating the impurities, and then decomposing the monosulphonic acid derivative to liberate the purified pseudo-ionone. The preferred molar ratio of bisulphite to pseudo-ionone is 1,5. The bisulphite probably reacts at the a :b unsaturated bond of the pseudo-ionone with the formation of a b -sulphonic acid salt. In an example, lemongrass oil, containing 74% citral, is heated with acetone in the presence of finely-divided barium hydroxide. After removal of baryta with ammonium chloride, the excess acetone is evaporated from the reaction-product. The crude pseudo-ionone is then heated under reflux with a solution of sodium metabisulphite in aqueous industrial methylated spirit. The spirit is distilled off; and the cooled mixture is extracted with isopropyl ether to remove non-ketonic impurities. The aqueous bisulphite complex is decomposed with sodium hydroxide; and the purified pseudo-ionone is extracted from the mixture by means of isopropyl ether. After evaporation of the ether; the pseudo-ionone is finally distilled at 1 m.m. pressure.