Since 1960s, 1,4-phenylenediamine (PPD) has been surfaced to a raw material for para-aramid fiber having superior mechanical strength and thermal resistance under harsh condition. Recently, aromatic amination of 1,4-diiodobenzene using Cu(II) compounds as a catalyst has been started for commercial development of PPD process. Substitution of two iodine through amination of NH3
have sparked the cheap and efficient production of high purity 1,4-phenylenediamine. However, to the best knowledge of known processes, the incomplete removal of mono-substituted benzene derivatives and iodide salts has determined the mechanical strength, molecular weight, viscosity and polymerization rate of synthesized polymers. Therefore, separation of iodine salts and side products is one of key operations in improving the economic feasibilities of developing process.
In the present work, drowning-out crystallization was applied to separate highly pure NH4I from NH4I/1,4-phenylenediamine mixture. Solubilities of NH4I and 1,4-phenylenediamine were measured isothermally in various organic solvents. Yield and solubility of NH4I was the primary criterion for selecting appropriate solvent/anti-solvent pairs in drowning-out crystallization. Thus, we tested the reduction of iodine salts into the recovery of elemental iodine by reducing agents. Purity and yield were achieved to 99% and 93% at 65 °C, respectively. XRD pattern reveals that pure NH4I was precipitated without containing other crystalline structures.