208 PRACTICAL ORGANIC CHEMISTRY melt at 98°, the molten material decomposing vigorously above this temperature: the crystalline material darkens on exposure to light and most specimens are therefore of a yellowish-brown colour. Aminoazobenzene. C 6 H 5-N :N • C 6 H 4-NH 2 . When diazoaminobenzene is added to a warm aqueous solution of hydro-chloric acid, it tends to break up into its original components, i.e., to benzene-diazonium chloride and aniline, and an equilibrium is thus established. The diazonium chloride and the aniline, however, in addition to recombining to form diazoaminobenzene, also undergo direct condensation at the />-hydro-C 6 H 5 N a NHC 6 H 6 +HCl^C 6 H B N 2 CH-H 8 NC 6 H 6->C 6 H 6 N:NC fl H 4 NH 2-fHCl gen atom of the aniline molecule, giving aminoazobenzenc. Since this re-action is irreversible, whilst the former is freely reversible, the final result is the complete conversion of the diazoaminobenzene into the aminoazobenzene. (The intermediate formation of the benzenediazonium chloride can be demon-
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