Integrated process for the preparation of polybenzimidazole precursors

An integrated process for preparing 2,3,5,6-tetraminotoluene or a 2,3,5,6-tetraminotoluene salt comprising the sequential steps under exclusion of oxygen:

• a) nitrating 2,6-dihalotoluene (II)
• wherein each Z is independently Cl or Br, in a reaction mixture comprising oleum or SO3, nitric acid, and H2SO4
• wherein
• (iv) the concentration of nitric acid is about 2.0 to about 2.3 moles per mole of 2,6-dihalotoluene;
• (v) the concentration of SO3 is about 1 to about 3 moles per mole of 2,6-dihalotoluene;
• (vi) the concentration of 2,6-dihalotoluene in the reaction mixture is between about 12 and about 24 weight percent;
• and
• wherein the temperature of the reaction mixture does not exceed 120° C.;
• thereby producing 2,6-dihalo-3,5-dinitrotoluene;
• b) directly separating the 2,6-dihalo-3,5-dinitrotoluene from the reaction mixture by filtration, while recycling the sulfuric acid mother liquor;
• c) washing the 2,6-dihalo-3,5-dinitrotoluene with water or acid then water, then with NH4OH, and then mixing it with glycol as a suspension;
• d) aminating the 2,6-dihalo-3,5-dinitrotoluene by heating the suspension formed in step (c) to a temperature in the range of about 100° C. to about 160° C. and contacting it with NH3(g), thereby converting the 2,6-dihalo-3,5-dinitrotoluene to 2,6-diamino-3,5-dinitrotoluene
• e) directly separating the 2,6-diamino-3,5-dinitrotoluene from the reaction mixture by filtration, washing with glycol, then washing with water,
• f) forming a slurry of the 2,6-diamino-3,5-dinitrotoluene with water and transferring the slurry to a hydrogenation reactor containing a hydrogenation catalyst to form a reaction mixture;
• g) hydrogenating the 2,6-diamino-3,5-dinitrotoluene by contacting the reaction mixture formed in step (f) with hydrogen at a pressure in the range of about 0.31 to about 3.45 MPa and a temperature in the range of about 20° C. to about 100° C. for sufficient time to hydrogenate the 2,6-diamino-3,5-dinitrotoluene, thereby producing 2,3,5,6-tetraminotoluene;
• h) contacting the 2,3,5,6-tetraminotoluene produced in (g) with an aqueous solution comprising 1 to 6 equivalents of acid per mol of 2,3,5,6-tetraminotoluene, optionally heating the solution, thereby dissolving the 2,3,5,6-tetraminotoluene;
• i) filtering the reaction mixture, thereby removing the spent hydrogenation catalyst;
• j) forming and precipitating the salt by adding an acid to the filtered reaction mixture, and
• k) cooling, filtering, and washing the precipitated 2,3,5,6-tetraminotoluene salt.