Integrated processes for the preparation of polybenzimidazole precursors
AssigneeE.I.Du Pont De Nemours and Company
InventorsRajiv Dhawan, Annalisa Hargis, Joachim C. Ritter
Life of this patent
Estimating the term…
Abstract
An integrated process is provided for efficiently preparing 2,4,5-triaminophenol, starting with nitration of 2,6-dihalobenzene; high purity salts thereof; and complexes of 2,4,5-triaminophenol aromatic diacids, which are precursors for making polybenzimidazole polymer for high performance fibers. The process design eliminates several costly intermediate drying and recrystallization steps. The handling of solid materials with possible skin sensitizing properties and toxicity is avoided, thereby eliminating human and environmental exposure.
Claims15
A process comprising the sequential steps under the substantial exclusion of oxygen:
- (o) nitrating 1,3-dihalobenzene (II)
- wherein each Z is independently Cl or Br, comprising contacting 1,3-dihalobenzene in a reaction mixture comprising with 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 1,3-dihalobenzene;
- (v) the concentration of SO3 is about 1 to about 3 moles per mole of 1,3-dihalobenzene;
- (vi) the concentration of 1,3-dihalobenzene 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 1,3-dihalo-4,6-dinitrobenzene (III);
- (p) separating the 1,3-dihalo-4,6-dinitrobenzene from the reaction mixture, while recycling the sulfuric acid mother liquor;
- (q) washing the 1,3-dihalo-4,6-dinitrobenzene with water or acid then water, then with aqueous ammonia, and then mixing it with solvent as a suspension;
- (r) monoaminating the 1,3-dihalo-4,6-dinitrobenzene by heating the suspension formed in step (c) to a temperature in the range of about 60° C. to about 140° C. and contacting it with at least 2.0 equivalents NH3, thereby converting the 1,3-dihalo-4,6-dinitrobenzene to 1-amino-3-halo-4,6-dinitrobenzene (IV);
- (s) separating the 1-amino-3-halo-4,6-dinitrobenzene from the reaction mixture, washing with solvent, then washing with water;
- (t) forming a slurry of the 1-amino-3-halo-4,6-dinitrobenzene with benzyl alcohol and at least 1.0 equivalent of NaOH or of sodium benzyloxide;
- thereby converting the 1-amino-3-halo-4,6-dinitrobenzene to 1-benzyloxy-3-amino-4,6-dinitrobenzene (V);
- (u) separating the 1-benzyloxy-3-amino-4,6-dinitrobenzene formed in step (f) from the reaction mixture
- (v) forming a slurry of the 1-benzyloxy-3-amino-4,6-dinitrobenzene formed in step (f) with water and transferring the slurry to a hydrogenation reactor containing a hydrogenation catalyst to form a reaction mixture;
- (w) hydrogenating the 1-benzyloxy-3-amino-4,6-dinitrobenzene in water by contacting the reaction mixture formed in step (h) 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 1-benzyloxy-3-amino-4,6-dinitrobenzene, thereby producing 2,4,5-triaminophenol and toluene;
- (x) contacting the reaction mixture (i) with an aqueous solution comprising 1 to 2 equivalents of acid per mol of 2,4,5-triaminophenol and, optionally, heating the solution, thereby dissolving the 2,4,5-triaminophenol;
- (y) removing the spent hydrogenation catalyst from the reaction mixture;
- (z) extracting toluene from the reaction mixture;
- (aa) adjusting the pH of the extracted reaction mixture to a value base does not increase 2,4,5-triaminophenol solubility, thereby precipitating 2,4,5-triaminophenol product;
- and
- (bb) isolating the 2,4,5-triaminophenol product.
Dependencies are inferred from the claim text.