The hydrazones are crystalline substances which are of value in the characterization of the aldehydes.
Both oximes and hydrazones, on boiling with dilute acid, regenerate the parent aldehyde.
The hydrazones are best prepared by mixing the aldehyde with phenylhydrazine in dilute acetic acid solution, in the absence of any free mineral acid.
Cane sugar has no reducing power and does not form an hydrazone or osazone; the other varieties, however, reduce Fehling's solution and form hydrazones and osazones, behaving as aldoses, i.e.
They may also be obtained by the reduction of nitroso compounds and of hydrazo compounds and of hydrazones (J.
As being quinone hydrazones, type R NH N: R l: 0.
Chem., 1896, 21, p. 355; Ber., 1900, 33, p. 1302)examined the questionfromthe physico-chemical standpoint by determining the freezing-point depressions, the result being that the para-oxyazo compounds give abnormal depressions and the ortho-oxyazo compounds give normal depressions; Auwers then concluded that the para compounds are phenolic and the ortho compounds are quinone hydrazones or act as such.
Hantzsch (Ber., 18 99, 3 2, pp. 59 o, 3089) considers that the oxyazo compounds are to be classed as pseudoacids, possessing in the free condition the configuration of quinone hydrazones, their salts, however, being of the normal phenolic type.
Bamberger (Ber., 1898, 31, p. 455) has shown that the nitro-alkyl derivatives behave as though they possess the constitution of hydrazones, for on heating with dilute alkalies they split more or less readily into an alkaline nitrite and an acid hydrazide: C 6 H 5 NH N: C(N02)CH3+NaOH=NaN02+C6H5NH NH CO CH3.
They combine with hydrocyanic acid to form nitriles, which on hydrolysis furnish hydroxyacids, (CH3)2C0 -> (CH 3) 2 C OH CN - (CH3)2 C OH C02H; with phenylhydrazine they yield hydrazones; with hydrazine they yield in addition ketazines RR' C:N N:C RR' (T.