Schmidt reaction of some constrained aromatic acids, and related topics

Abstract

Schmidt reaction of phthalic acid in 90–98% sulfuric acid gives anthranilic acid and anthranilazide (major products) by a process considered to involve 3,1-benzoxazin-2,4(1H)-dione as intermediate. Benzimidazol-2-one is produced in this reaction by a secondary process from anthranilazide; it is also produced by photolysis of anthranilazide. Under Schmidt reaction conditions, 1,2,3-benzotriazin-4(3H)-one gives o-azidobenzamide. Under similar conditions, the lactol of 4-formyl-5-phenanthroic acid gives 1-azapyren-2(1H)-one and phenanthrene-4,5-dicarboximide, while phenanthrene-4,5-dicarboxylic acid gives l-azapyren-2(1H)-one. Diphenic acid yields phenanthridone and 2,2′-diaminobiphenyl in proportions dependent on the sulfuric acid concentration.