SUPRACET BRILLIANT RED BD synthesis

Yield:-

Reaction Conditions:

Stage #1: 6-methoxybenzothiazol-2-ylaminewith nitrosylsulfuric acid;sulfuric acid in water at -7 - -5; for 4.25 h;
Stage #2: 2,2'-(phenylimino)bis[ethanol] in water at -5 - 20; for 16.5 h;

Steps:

A4.1 Example A4:

Step 1: A mixture of conc. H₂SO₄ (57ml) and water (47ml) is introduced in a 500 ml 3-necked round bottom flask under external cooling.2-amino-6-methoxybenzothiazole (22.2 g) is added slowly under vigorous stirring to this solution.The white suspension is cooled to -7°C. The ice-cold solution of nitrosylsulfuric acid is then added over a period of 15min maintaining the temperature in the range of -7 to -5°C.The reaction mixture is further stirred for 4 hours at -5°C.Urea (1.8 g) is added to the reaction mixture under stirring to decompose the traces of excess nitrous acid.The cold diazo-solution is then poured onto to crushed ice (72g) over a period of 5-10 min under mechanical stirring. Crushed ice (123 g) is added To this and the temperature is maintained at -5°C. N-phenyl diethanolamine (22.38 g) is added in portion over a period of 15min under stirring to the above solution. The temperature is maintained at -5°C by addition of ice (123 g) and stirring is continued for 15min.The stirring is stopped and reaction mixture kept at room temperature overnight (16h). A sodium hydroxide (36%, ca. 200 ml) solution is added to the reaction mixture (which is cooled externally) till the pH reaches adjustes in the range of 3-4. The reaction mixture is then neutralized (pH 6 to 7) by addition of saturated solution of NaHCO₃.The filtration of the solid followed by washings with water (100ml x 4) affords brown-red colored solid, which can be crystallized from methanol.

References:

EP2029674,2013,B1 Location in patent:Paragraph 0155