Hydrochloric Acid → chrysanthemic acid d-trans-form

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62 g. of chrysanthemic acid (consisting of 18% cis and 82% trans isomer) prepared as described in Example (3a) and enriched in the trans isomer were dissolved at 70°-75° C. in 70 ml. of a 20% aqueous sodium hydroxide solution, cooled to room temperature and set aside overnight. The precipitated crystals were filtered by thorough suction and dissolved in 330 ml. of water, 240 ml. of petroleum ether (b.p. 40° C.) were added to the solution of the sodium salt obtained and the mixture was acidified to pH 1 by concentrated hydrochloric acid while stirring. The organic phase was separated and the aqueous solution was again extracted with 75 ml. of petroleum ether. After combination, the organic solution was washed with 3×100 ml. of water, dried over anhydrous sodium sulphate, then evaporated to one-fourth its volume. The obtained solution was slowly cooled to 25° C. and stirred at this temperature for one hour. After filtering out a little amount of the crystals rich in the cis isomer, the mother liquor was further cooled to -10° C. and the precipitated crystals were separated. Thus 23.1 g. of dl-trans-chrysanthemic acid were obtained with a purity of 99.8% which was resolved according to the Example (3b).

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