To a stirred solution of aq. NaOH (25%, 200 mL), the quinoline ester 9 (54 g, 0.241 mol, 1.0 equiv.) was added. The reaction mixture was heated at 95-97 °C for 2 h, during which all the ester dissolved to form a brown solution. The reaction mixture was cooled to room temperature and neutralised to pH 8.2 by slow addition of 10% aq. H2SO4 solution. The reaction mixture was heated at 45 °C for 1 h (maintaining pH 8.2). The precipitate was collected by filtration while warm and washed with water (2x 200 mL). The filter cake was suspended in 250 mL water, stirred vigorously, and the pH adjusted to 4 by slow addition of 10% aq. H2SO4 solution.