20.35 g of quinizarin, 20.38 g of dihydroquinizarin (contains 0.47 g of quinizarin), 10.8 g of trimethyl borate and 8.71 g of 90% by weight lactic acid were introduced into 159.7 g of 2,6-diethyl-4-methylaniline under nitrogen. The mixture was heated to 115 C. over 1 h, in the course of which the resulting methanol was distilled off. Without delay, the temperature was then raised to 145 C. over 2.5 h, and the mixture was stirred at 145 C. for 8 h, during which resulting water was distilled off. Completeness of reaction was checked via a thin layer chromatogram. The mixture was then cooled down to 125 C. and air was passed into it for 3 h. After cooling to 80 C., 20.6 g of potassium hydroxide powder were added and air was again passed into it at 80 C. for 4 h. 290 ml of methanol were added dropwise in the course of 2 h at 70 C., followed by 1 h of stirring under gentle boiling. Finally, the suspension was cooled down to room temperature, filtered off with suction, washed with 200 ml of cold methanol and then with 11 of hot water (at 80 C.) in portions. Vacuum drying at 80 C. left 72.9 g (82.0% of theory) of a blue crystalline powder of the formula Heating time: 3.5 h Condensation time: 8 h
