Yield:116-75-6 83.9%

Reaction Conditions:

with LACTIC ACID;2,3-dihydro-1,4-dihydroxyanthraquinone;boric acid at 50 - 145; for 13 h;Product distribution / selectivity;

Steps:

4
20.0 g of quinizarin, 23.0 g of dihydroquinizarin (contains 1.5 g of quinizarin), 5.84 g of boric acid were introduced into 153 g of 2,4,6-trimethylaniline under nitrogen. After heating to 50° C., 7.84 g of 90% by weight lactic acid were added. The mixture was heated to 115° C. over 1 h and maintained at 115° C. for 4 h. If this time is not adhered to, severe foaming will take place in the course of continued heating and can lead to overfoaming into the distillation receiver. This is followed by heating to 145° C. over 2 h and stirring at 145° C. for 6 h, during which resulting water was distilled off. Completeness of reaction was checked via a thin layer chromatogram. This was followed by cooling to 100° C. and air introduction for 3 h. After cooling to 70° C., 17.35 g of potassium hydroxide powder were added and after heating to 100° C. again air introduced for 3 h. The mixture was cooled to 80° C. 220 ml of methanol were added dropwise. Finally, the suspension was filtered off with suction at 60° C., washed with 220 ml of hot methanol (at 60° C.) and then with 11 of hot water (at 80° C.) in portions. Vacuum drying was carried out at 50° C. to obtain 71.1 g (83.9% of theory) of a blue crystalline powder of the formula of Example 1.Heating time: 7 h Condensation time: 6 h It needed 7 hours to reach the ultimate reaction temperature because of the foaming. In Examples 1 to 3 this took just one hour. In addition, the same yields as in Examples 1 to 3 took 6 hours to achieve instead of 3.5 hours. In addition, in Examples 2 and 3 the amount of dihydroquinizarin and boric ester used was distinctly reducible without disadvantage.

References:

LANXESS Deutschland GmbH US2008/139830, 2008, A1 Location in patent:Page/Page column 5