Hydrazines
Hydrazines are a family of compounds with two nitrogen atoms connected by an N−N bond and up to four hydrocarbon groups attached. They are derivatives of inorganic hydrazine (H2N−NH2) where some hydrogens are replaced by carbon groups.
They are divided into three groups by how many substituents they have:
- Monosubstituted hydrazines and asymmetrically disubstituted hydrazines (two carbon groups on the same nitrogen): colorless liquids. Aliphatic ones are very water soluble, strongly basic, and good reducing agents. Aromatic ones are less soluble in water, less basic, and weaker reducing agents.
- Symmetric disubstituted hydrazines (one substituent on each nitrogen): also liquids, but with higher boiling points. Aliphatic symmetric disubstituted hydrazines are basic, reducing, and water soluble; aromatic symmetric disubstituted hydrazines are not water soluble.
- Tri- or tetrasubstituted hydrazines: aliphatic ones are water-insoluble and weakly basic; arylhydrazines are solid, colorless, insoluble in water, and scarcely basic.
How they are made:
- Aliphatic hydrazines: by reacting hydrazine with alkyl halides or by reducing nitroso compounds.
- Aromatic hydrazines: by reducing aromatic diazonium salts.
- Symmetric disubstituted hydrazines: by reducing nitro compounds under basic conditions or by reducing azines.
Other notes:
- Some hydrazines form colored reactions with concentrated sulfuric acid.
- Notable examples include unsymmetrical dimethylhydrazine, phenylhydrazine, 2,4-dinitrophenylhydrazine, 1,2-diphenylhydrazine, and tetraphenylhydrazine.
- Phenylhydrazine and 2,4-dinitrophenylhydrazine were historically used in analytical chemistry to detect carbonyl compounds. Phenylhydrazine was used to study sugars, because aldehyde groups react to form well-crystallizing phenylhydrazones or osazones.
- Organohydrazines and their derivatives are numerous, especially when hydrazones are included.
This page was last edited on 2 February 2026, at 05:20 (CET).