Hydralazine hydrochloride is a direct-acting smooth muscle relaxant used to treat hypertension by acting as a vasodilator primarily in arteries and arterioles. By relaxing vascular smooth muscle, vasodilators act to decrease peripheral resistance, thereby lowering blood pressure.
Chemical IUPAC Name: 1(2H)-Phthalazinone hydrazone hydrochloride
Synonyms: Hydralazine hydrochloride, Apresoline, 1-Hydrazinophthalazine monohydrochloride
Chemical Formula: C8H8N4
Molecular Weight: 160.178 g/mol
CAS Registry Number: 86-54-4 (Hydralazine), 304-20-1 (Hydralazine hydrochloride)
Melting Point: 275 C
Solubility in water: 1 g/125 ml
Solubility in ethanol: 1g/ 500 ml
Canonical SMILES: C1=CC=C2C(=C1)C=NN=C2NN
InChIKey Identifier: RPTUSVTUFVMDQK-WXRBYKJCCB
Hydralazine has the following structural formula:

Synthesis Reference:
1) Druey and Ringier, “Hydrazinderivate der Phtalazin- und Pyridazinreihe” Helvetica Chimica Acta, vol. 34(21), 195-210 (1951).
2) Butula et al, “Eine neue Methode zur Gewinnung von 1-Hydrazino-phthalazin” Croatica Chemica Acta, vol. 52(1), 43-45 (1979).