Indazole, acidity solubility

The preceding method is that of Huisgen and Nakaten and is based on the preparation of indazole (ca. 40% yield) from N-nitroso-fl-benzotoluidide discovered by Jacobson and Huber. Mechanistic studies showed this reaction to be an intramolecular azo coupling with an initial acyl shift as the determining step. The yield of indazole from N-nitroso-o-benzotoluidide can be made almost quantitative. Since the low solubility of o-benzo-toluidide makes large quantities of acetic acid and acetic anhydride necessary, the method using the N-acetyl compound described here is more convenient. 

Iron(II) complexes of 7-nitroso-6-hydroxyindazoIes (203) are sufficiently soluble in water to permit the dyeing of wool and polyamide fibres in green to olive shades having good fastness properties from weakly acidic dyebaths. Cationic ironfll) complexes (204) have also been prepared from quatemized indazoles of this type but have found little or no commercial application. 

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