Hydrochloric Acid → (R)-(+)-citronellic acid

Participants

Reaction Steps

44.3 g of HCl gas (measured by determining the weight gain) were passed into 187.2 g (1.045 mol) of technical (85% pure) (R)-pulegone (or R-(+)-p-menth-4(8)-en-3-one) while cooling in ice. After the reaction solution had stood overnight, it was poured into 2.0 l of 5% strength KOH solution and stirred at RT (=room temperature) for 2 h. It was subsequently extracted 5 times with 200 ml of diethyl ether each time. The extract contains pulegone and isopulegone, which can be reused. On addition of concentrated HCl to the aqueous phase (to pH=2), the citronellic acid separated out as a yellowish oil. The acid was extracted by shaking 5 times with 200 ml of diethyl ether each time, the organic phase was dried with Na2SO4 and, after the solvent had been stripped off, was distilled under reduced pressure (boiling point 105°-110° C. under 0.04 mbar). 84.6 g (0.486 mol=45.5% of theory) and, on reuse of the extracted ketones under similar conditions conditions [sic], a further 44.4 g (0.255 mol) of (R)-(+)-citronellic acid were obtained as a clear liquid.

Provenance & Evidence