1911 Encyclopædia Britannica/Indazoles

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INDAZOLES (Benzopyrazoles), organic substances containing the ring system

Hexagon, point up.jpg CH Rangle.svgNH.
|
BSlash45.png N

The parent substance indazole, C7H6N2, was obtained by E. Fischer (Ann. 1883, 221, p. 280) by heating ortho-hydrazine cinnamic acid,

C6H4Langle.svg CH = CH·COOH =C2H4O2+C7H6N2.
NH·NH2

It has also been obtained by heating ortho-diazoaminotoluene with acetic acid and benzene (F. Heusler, Ber., 1891, 24, p. 4161).

C6H4Langle.svg CH3 =C7H7NH2+C7H6N2.
N:N·NHC7H7

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

Hexagon, point up.jpg NH GreaterThanOrEqual.svgN.
 
BSlash45.pngCH

These isomers are called isindazoles, and may be prepared by the reduction of the nitroso-ortho-alkylamino-acetophenones 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.