1.5 g (4.3 mmol) of the compound from Step 5.3 was dissolved in 30 mL of water and 1.3 g of 32% hydrochloric acid solution. At 0 to 5° C., 0.31 g (4.5 mmol) of sodium nitrite in 3 mL of water was added dropwise without allowing the temperature to exceed 5° C. After one hour of additional agitation in the ice bath, excess sodium nitrite was decomposed with sulfaminic acid, and the mixture was poured with agitation into a solution of 0.65 g (4.3 mmol) of 2-naphthol in 8 mL of isopropanol. To this mixture was added a saturated solution of sodium carbonate until the pH reached a value of 9. The mixture was then allowed to agitate for an additional 30 min after which it was neutralized with dilute hydrochloric acid and suction-filtered. The resulting crude product was suspended in 20 mL of 2-normal hydrochloric acid at room temperature for 15 minutes after which the mixture was suction-filtered and dried.
