Sulfuric Acid → 2-Cyclohexen-1-one, 3,5-dimethyl-, oxime

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375 g of 3,5-dimethylcyclohexenone, 99% pure, (= 372 g of 100% pure product = 3 moles) are added to 1,080 g (= 923 ml) of a 25% strength technical grade hydroxylamine sulphate solution (d = 1.17) which additionally contains about 20 g of sulphuric acid and 20 g of ammonium sulphate, the mixture is heated to 70° C. and stirred at this temperature for one hour. The resulting solution can be worked up as follows: (a) 300 g of sodium chloride are added to the hot solution at 70° C. and the mixture is stirred without cooling until the temperature has reached 20° C. 3,5-Dimethylcyclohexenone oxime hydrochloride thus precipitates. It is filtered off and washed with 20% strength sodium chloride solution. After drying, this gives 600 g of hydrochloride with a content of pure compound of 85.1%, corresponding to 97% of theory. (b) After cooling the hot solution from 70° C. to 20° C., the latter is exhaustively extracted with an extracting agent, for example methylene chloride. The solvent is distilled off. A brown oil remains which consists of a mixture of oxime and oxime sulphate in a ratio of 2:1; yield 95%. (c) After cooling the hot solution from 70° C. to +10° C., the pH value is adjusted at this temperature to 5-5.5 with sodium hydroxide solution. This gives a thick white precipitate of 3,5-dimethylcyclohexenone oxime. It is filtered off and washed with water. This gives 510.4 g of oxime with a content of pure compound of 98%, corresponding to 95% of theory.

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