Farbreaktionen zur Identitätsprüfung von Natriumcromoglicat

Chromone-2-carboxylic acid (3) reacts with aminopyrazolone (2) in methanolic hydrochloric acid to yield the orange-red polymethine dye 4. Treating dimethyl cromoglicate (6) with compound 2 and perchloric acid leads to the tetraperchlorate 7 of the red azamerocyanine 8. The phenol 9 , obtained from alkaline hydrolysis of sodium cromoglicate (la), couples with diazotized sulfanilic acid to form the red azo dye 10. The chromone 6 condenses with 1,3-dimethylbarbituric acid (DMBA) in acetic anhydride/acetic acid to the red oxonole 12. Cromoglicinic acid (1b) reacts under these conditions to yield the yellow polymethine dye 14, whose structure is elucidated by X-ray analysis.