Preparation of polyaspartic acid

Details Preparation of polyaspartic acid Preparation of polyaspartic acid

1997-02-12

1998-11-03

Truong, Duc

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

From carboxylic acid or derivative thereof

528363, 530333, 530339, 530340, C08G 6910

Patent

active

058309853

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

1. Field of the Invention
The present invention relates to a process for preparing polyaspartic acid by polycondensation of fine-particle aspartic acid at temperatures above 150 .degree. C. in the presence of acids as catalysts.
2. Discussion of the Background
The use of phosphoric acid as catalyst in the polycondensation of aspartic acid is known, compare Journal of Medicinal Chemistry, 16 (1973) 893 and DE-A-4 023 463. The polycondensation temperature is at least 120.degree. C. and, in most cases, is in the range from 140.degree. to 250.degree., preferably 160.degree. to 240.degree. C. U.S. Pat. No. 5,219,986 discloses a process for the thermal polycondensation of aspartic acid in a fluidized bed under reduced pressure.
U.S. Pat. No. 5,221,733 discloses a process for preparing polysuccinimide in which powdered L-aspartic acid is first rapidly heated to about 188.degree. C. in a rotary evaporator, and then the temperature of the mixture is rapidly increased to at least 227 .degree. C., and condensation is continued at this temperature until the conversion is at least 80%. Salts of polyaspartic acid are prepared by hydrolyzing the resulting poly succinimide with bases.
One problem in the polycondensation of fine-particle aspartic acid in the presence of acids such as phosphoric acid is that the phosphoric acid acting as catalyst must be distributed as uniformly as possible on the aspartic acid crystals before the polycondensation. If phosphoric acid is used in amounts of about 5-20% of the weight of aspartic acid, sticky phases are produced on the aspartic acid crystals during the polycondensation. This leads to agglomeration of aspartic acid crystals so that the polymerizing mixture becomes virtually impossible to stir.


SUMMARY OF THE INVENTION

It is an object of the present invention to provide a process for preparing fine-particle polyaspartic acid by polycondensation of aspartic acid powder in the presence of acidic catalysts in which virtually no, or slight at the most, agglomeration of polymer particles occurs.
We have found that this object is achieved by a process for preparing polyaspartic acid by polycondensation of fine-particle aspartic acid having an average particle diameter of 5 .mu.m-5 mm at temperatures above 150.degree. C. in the presence of acidic catalysts when the first contact between the acidic catalysts and the fine-particle aspartic acid takes place in the reaction zone where the polycondensation takes place.


A DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

It is possible to use as aspartic acid L-, DL- or D-aspartic acid besides mixtures of said aspartic acids. Aspartic acid can be prepared, for example, by thermal addition of ammonia onto maleic acid, by enzymatically catalyzed addition of ammonia onto fumaric acid or by fermentation of glucose and ammonium salts with micro-organisms. The size of the crystals and the method of preparation of aspartic acid have no effect on the polycondensation. The fine-particle aspartic acid used for the polycondensation can have average particle diameters of, for example, 5 .mu.m-5 mm, preferably 50 .mu.m-400 .mu.m.
The polycondensation of the fine-particle aspartic acid takes place at temperatures above 150.degree. C., preferably at 160.degree.-200.degree. C.
Suitable acidic catalysts are inorganic and organic acids and compounds with an acidic reaction. Examples of acids are:


______________________________________ Benzenesulfonic acid pKa = 0.70 Naphthalenesulfonic acid pKa = 0.57 Ortho-phosphoric acid pKa1 = 2.12 Pyrophosphoric acid pKa1 = 0.85 Pyrophosphoric acid pKa2 = 1.49 Phosphorous acid pKa1 = 2.00 Sulfuric acid pKa2 = 1.92 Sulfuric acid pKa1 below 0.7 Hydrochloric acid pKa below 0.7 Sulfurous acid pKa1 = 1.81 Dichloroacetic acid pKa1 = 1.48 Bromoacetic acid pKa1 = 2.69 Chloroacetic acid pKa1 = 2.85 Chloropropionic acid pKa = 2.83 Cyanoacetic acid pKa = 2.45 Dichloroacetic acid pKa = 1.48 Dihydroxymaleic acid pKa1 = 1.92 Dihydroxytartaric acid pKa1 = 1

REFERENCES:
patent: 5142062 (1992-08-01), Knebel et al.
patent: 5219986 (1993-06-01), Cassata
patent: 5221733 (1993-06-01), Koskan et al.
Journal of Medicinal Chemistry, vol. 16, No.8 (1973) Paolo Neri, et al., Plasma Expander.

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