and stirred together with 36 hydrochloric acid until the measured ph value of the solution fell below 3 the solvent was then stripped out and the product recrystallised from isopropanol tramadol hydrochloride was obtained 50 g of a diastereomeric base mixture of u00b1 cis trans 2 dimethylamino methyl 1 3 methoxyphenyl cyclohexanol cis trans isomer ratio 63 37 were dissolved in 100 ml of acetone 20 ml of water were then added and the reaction mixture stirred at 20 u00b0 c crystallisation began after approx 30 minutes the suspension was stirred for a further 90 minutes the crystals were separated from the mother liquor using a filter were washed twice with an acetone water mixture volume ratio 10 2 and suction filtered dry the hydrate of the cis diastereomer was obtained at a yield of 36 and a purity of greater than 95 the isomer ratio in the crystal fraction was 97 cis isomer to 3 trans isomer 20 g of a diastereomeric base mixture of u00b1 cis trans 2 dimethylamino methyl 1 3 methoxyphenyl cyclohexanol cis trans isomer ratio 75 25 were dissolved in 20 g of ethanol at 22 u00b0 c and combined with 20 vol of water the solution was cooled to 6 u00b0 c and left to stand for 6 hours the resultant crystals were removed by suction filtration and washed twice with 10 ml portions of ethanol water after drying the hydrate of the cis diastereomer is obtained at a yield of 34 and a purity of greater than 95 the isomer ratio.