Hydrazines

Unsymmetrical dimethylhydrazine Phenylhydrazine 2,4-Dinitrophenylhydrazine 1,2-Diphenylhydrazine Tetraphenylhydrazine Hydrazines (R2N−NR2) are a class of chemical compounds with two nitrogen atoms linked via a covalent bond and which carry from one up to four alkyl or aryl substituents.

Aliphatic monosubstituted and asymmetrically disubstituted hydrazines are very water soluble, strongly alkaline and good reducing agents.

Aromatic monosubstituted and asymmetrically disubstituted hydrazines are poorly soluble in water, less basic and weaker reducing agents.

Phenylhydrazine and 2,4-dinitrophenylhydrazine had been used historically in analytical chemistry to detect and identify compounds with carbonyl groups.

Phenylhydrazine was used to study the structure of carbohydrates, because the reaction of the sugar's aldehyde groups lead to well crystallizing phenylhydrazones or osazones.