Studies on Aromatic Dihydrazines (I). Synthesis of p-Phenylenedihydrazine via Tetrazonium Salt and Formation of Dihydrazones

A practical method applicable to the synthesis of aromatic dihydrazines was proposed by reducing tetrazonium salt in strong mineral acid media. By diazotizing p-phenylenediamine with sodium nitrite in a medium of concentrated hydrochloric acid or 45 % perchloric acid at and reducing the tetrazonium salt with stannous chloride, p-phenylenedihydrazine (PPDH) was separated in the form of hydrochloride as colorless fine needles. Since PPDH was subject to oxidation and unstable, the free base could not be isolated. PPDH2HCl was decomposed at without showing sharp melting point. It behaved largely as aromatic monohydrazines, and reacted immediately with aldehydes and ketones in acetate buffer, giving generally yellow to brownish condensation products, dihydrazones. This suggests that PPDH will react with dicarbonyl compounds producing high molecular polymers or cyclization products