INDAZOLES (B ENZOPYRAZOLES), organic substances con- /N /CH taming the ring system I I I > NH. The parent substance N/N N indazole, C7H6N2, was obtained by E. Fischer (Ann. 1883, 221, p. 280) by heating ortho-hydrazine cinnamic acid, C 6 H4 CH=CH[[Cooh=C 0 +C, ? Nh]]-NH2 It has also been obtained by heating ortho-diazoaminotoluene with acetic acid and benzene (F. Heusler, Ber., 1891, 24, p. 4161).
C6H4 HN.NHC7H7 = C7H7NH2+C7H6N2.
It crystallizes in needles (from hot water), which melt at 146.5° C. and boil at 269°-270° C. It is readily soluble in hot water, alcohol and dilute hydrochloric acid. Nitrous acid converts it into nitrosoindazole; whilst on heating with the alkyl iodides it is converted into alkyl indazoles.
A series of compounds isomeric with these alkyl derivatives is known, and can be considered as derived from the ring system / NH N. N/NCH7 be prepared by the reduction of the nitroso-ortho-alkylaminoacetophenones with zinc dust and water or acetic acid. The indazoles are weak bases, which crystallize readily. Phenyl indazole, on reduction with sodium and absolute alcohol, gives a dihydro derivative (K. L. Paal, Ber., 1891, 24, p. 963).
For other derivatives, see E. Fischer and J. Tafel, Ann. 1885, 227, p. 314.
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