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Under an inert atmosphere, 1.9 g of the previous compound are dissolved in 20 ml of anhydrous ethyl acetate and 5 ml of anisole and 20 ml of a 5N solution of HCl in ethyl acetate are added slowly at 5° C. The mixture is allowed to attain room temperature and after being stirred for 2 hours is cooled to about 5° C. before a 5N aqueous solution of NaOH is added to give a basic pH. The organic phase is then separated, dried and concentrated at about 70° C. under reduced pressure. The residual oil is dissolved in 60 ml of isopropanol and decolorized by means of 50 mg of active charcoal and 50 ml of a 0.5M solution of oxalic acid dihydrate in isopropanol are added; the precipitated salt is isolated by filtration. 1.5 g of oxalate hemihydrate are thus obtained (containing two molecules of oxalic acid), M.p.=130° C.

1. customto attain room temperature
2. additionis added
3. customto give a basic pH
4. customThe organic phase is then separated
5. customdried
6. concentrationconcentrated at about 70° C. under reduced pressure
7. dissolutionThe residual oil is dissolved in 60 ml of isopropanol
8. additionare added
9. customthe precipitated salt is isolated by filtration