Synthesis

A solution of 233 g (5.83 mol) of NaOH in 930 mL of water was added to 345 g of the raw diethyl ester 15 ina 3-L one-neck flask, and the mixture was stirred a troom temperature for 2 h, after which 30 g of activated carbon was added, and stirring was continued for an additional 30 min and filtered on a Buchner funnel tor remove the activated carbon. The filtrate was made acidic (pH 4) by adding 545 mL of conc. HCl and stirred for 1 h. The precipitate was filtered off (Schott filter no. 3), washed with water (3 × 600 mL), suspended in 750 mL of water, acidified to pH 4 with 65 mL of conc. HCl, and immediately neutralized to pH 8 with 90 mL of 40% NaOH. Activated carbon, 13 g, was then added, and the mixture was stirred for 30 min, the activated carbon was removed by filtration, and the filtrate was acidified to pH 4 with conc. HCl. The precipitate was filtered off, washed with water (3 × 500 mL), and dried at 55 °C and a vacuum of 40 mmHg for 12 h to obtain 129 g (70%) of the target product, purity by HPLC 99.61%, main substance content by titration 80% (water 21%).