2.4- Diamino-13-benzenediol

Equimolar quantities of 2,4-diamino-l,5-benzenediol dihydrochloride and isophthalic acid were mixed in fresh poly (phosphoric acid) using a high-shear stirrer under a slow stream of nitrogen gas. The system was heated at 40°C for 6 hours, at CG°C for 18 hours, at 120°C for 6 hours, at 160°C for 8 hours, and at 220°C for 24 hours. The resultant mixture was dark brown. The polymer was precipitated from water. After filtration and washing with water and methanol, the solid product was then dissolved in methane-sulfonic acid, filtered and precipitated by the addition of methanol. The solid was washed with concentrated ammonium hydroxide, water, methanol, methanol/benzene mixtures (with a volume ratio of 1/1), and finally benzene. The final product was dark brown. 

Polymerization of terephthalic acid with 4,6-diamino-l,3-benzenediol via oxazole formation (Eq. 2-219) proceeds with a sharp and continuous decrease in reaction rate with increasing polymer molecular weight [Cotts and Berry, 1981]. Reaction becomes progressively more diffusion-controlled with increasing molecular size due to the increasing rigid-rod structure of the growing polymer. 

SYNTHESIS Polycondensation of a terephthalic acid with 4,6-diamino-1,3-benzenediol dihydrochloride in poly(phosphoric acid). Processing is primarily limited to variations of wet extrusion. 

The first challenge to be overcome in the production of PBO is the high purity synthesis of the monomer 4,6-diamino-l,3-benzenediol dihydrochloride (DABDO) (Scheme 9.6). The long-established method developed by Wolfe et al. [46] involved reacting diacetyl-1,3-benzenediol with concentrated nitric acid containing less than 2% water. This method required multiple recrystallizations to remove undesirable byproducts. The expense of the starting materials and the purification process has lead to the abandonment of this method of DABDO production in favor of a process developed by Lysenko [47] at the Dow Chemical Company. This method involves nitrating 1,2,3-trichlorobenzene under acid conditions to produce l,2,3-trichloro-4,6-dinitrobenzene. Sodium hydroxide is... 

Scheme 9.6 Synthesis of 4,6-diamino-l,3-benzenediol dihydrochloride (DABDO).

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