1911 Encyclopædia Britannica/Indazoles
INDAZOLES (Benzopyrazoles), organic substances containing the ring system
 |
∕CH |  NH.
|
| | | ||
 N
|
The parent substance indazole, C7H6N2, was obtained by E. Fischer (Ann. 1883, 221, p. 280) by heating ortho-hydrazine cinnamic acid,
C6H4 |
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).
| C6H4 |
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
|
∕NH |  N.
|
| CH
|
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.