U.S. patent application number 13/345996 was filed with the patent office on 2012-05-10 for synthesis of diaminodinitropyridine.
This patent application is currently assigned to E. I. DU PONT DE NEMOURS AND COMPANY. Invention is credited to HASAN DINDI, James Arnold Schultz.
Application Number | 20120116046 13/345996 |
Document ID | / |
Family ID | 40336707 |
Filed Date | 2012-05-10 |
United States Patent
Application |
20120116046 |
Kind Code |
A1 |
DINDI; HASAN ; et
al. |
May 10, 2012 |
SYNTHESIS OF DIAMINODINITROPYRIDINE
Abstract
A process for the preparation of diaminodinitropyridine or
diaminodinitrobenzene by contacting an aminopyridine or
aminobenzene with oleum and nitric acid, wherein the improvement
comprises adding at least about 1% molar excess of nitric acid,
based upon the aminopyridine or aminobenzene, with stirring for at
least two hours to form first the intermediate sulfonic acid, and
then diaminodinitropyridine or diaminodinitrobenzene, and use of
such products in the preparation of rigid rod polymers is
disclosed.
Inventors: |
DINDI; HASAN; (Wilmington,
DE) ; Schultz; James Arnold; (Swedesboro,
NJ) |
Assignee: |
E. I. DU PONT DE NEMOURS AND
COMPANY
Wilmington
DE
|
Family ID: |
40336707 |
Appl. No.: |
13/345996 |
Filed: |
January 9, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11986877 |
Nov 27, 2007 |
8115007 |
|
|
13345996 |
|
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Current U.S.
Class: |
528/208 |
Current CPC
Class: |
C07D 213/73 20130101;
C08G 73/18 20130101; C07C 209/76 20130101; C07C 209/76 20130101;
C07C 211/52 20130101 |
Class at
Publication: |
528/208 |
International
Class: |
C08G 73/06 20060101
C08G073/06 |
Claims
1-13. (canceled)
14. A process for the preparation of
poly(2,3,5,6-tetraaminopyridine-co-2,5-dihydroxyterephthalate)
having an inherent viscosity of at least 25 dL/g comprising A)
hydrogenation of diaminodinitropyridine which contains less than
about 0.1% by weight of 2,6-diamino-3-nitropyridine-5-sulfonic acid
to yield tetraaminopyridine, B) coupling of said tetraaminopyridine
with dipotassium dihydroxyterephthalate to yield a
tetraaminopyridinium dipotassium dihydroxyterephthalate complex,
and C) polymerization of said tetraaminopyridinium dipotassium
dihydroxyterephthalate complex to yield
poly(2,3,5,6-tetraaminopyridine-co-2,5-dihydroxyterephthalate)
having an inherent viscosity of at least 25 dL/g.
15. The process of claim 14 wherein the
poly(2,3,5,6-tetraaminopyridine-co-2,5-dihydroxyterephthalate) has
a tenacity of at least 35 g(force)/denier.
16. The process of claim 14 wherein the diaminodinitropyridine
contains less than about 0.05% by weight of
2,6-diamino-3-nitropyridine-5-sulfonic acid.
17. The process of claim 14 wherein the diaminodinitropyridine
contains less than about 1% by weight of
2-hydroxy-6-amino-3,5-dinitropyridine.
18. A process for the preparation of
poly(2,3,5,6-tetraaminobenzene-co-2,5-dihydroxyterephthalate)
having an inherent viscosity of at least 25 dL/g comprising A)
hydrogenation of diaminodinitrobenzene which contains less than
about 0.1% by weight of 2,6-diamino-3-nitrobenzene-5-sulfonic acid
to yield tetraaminobenzene, B) coupling of said tetraaminobenzene
with dipotassium dihydroxyterephthalate to yield a
tetraaminobenzene dipotassium dihydroxyterephthalate complex, and
C) polymerization of said tetraaminobenzene dipotassium
dihydroxyterephthalate complex to yield
poly(2,3,5,6-tetraaminobenzene-co-2,5-dihydroxyterephthalate)
having an inherent viscosity of at least 25 dL/g.
19. The process of claim 18 wherein the diaminodinitrobenzene
contains less than about 0.05% by weight of
2,6-diamino-3-nitrobenzene-5-sulfonic acid.
Description
BACKGROUND OF THE INVENTION
[0001] 2,6-Diamino-3,5-dinitropyridine and diaminodinitrobenzene
are intermediates for the preparation of precursors for the
manufacture of "rigid rod" polymers used in fabricating films,
filaments, and yarns. An example of such rigid rod polymers,
poly[pyridobisimidazole-2,6-diyl(2,5-hydroxy-p-phenylene) or
poly(2,3,5,6-tetraaminopyridine-co-2,5-dihydroxyterephthalate) is
described by Sikkema et al. in U.S. Pat. No. 5,674,969.
2,6-Diamino-3,5-dinitropyridine can also be used as an insensitive
(safe) explosive and as a multifunctional organic reagent.
[0002] 2,6-Diamino-3,5-dinitropyridine is prepared by nitration of
2,6-diaminopyridine. The nitration of 2,6-diaminopyridine by
reaction with a mixture of nitric acid and sulfuric acid is known
from German Patent 3,920,336. The drawback to this process is that
it gives a 2,6-diamino-3,5-dinitropyridine yield of not more than
50% of theory.
[0003] Sikkema et al. in U.S. Pat. No. 5,945,537 describe an
improved process for the conversion of 2,6-diaminopyridine to
2,6-diamino-3,5-dinitropyridine in a single step reaction using
oleum (fuming sulfuric acid).
[0004] The diaminopyridine is added to the oleum, and then
concentrated nitric acid is added, and the product isolated. A
yield improvement to more than 90% was obtained.
[0005] The prior art processes for the production of
2,6-diamino-3,5-dinitropyridine and the corresponding
diaminodinitrobenzene are prone to yield product containing
variable amounts of heretofore-unidentified impurities. The
composition of the impurities and the effect of these impurities on
products made using the 2,6-diamino-,5-dinitropyridine and the
corresponding diaminodinitrobenzene are unknown.
[0006] It is desirable to find a nitration process for the
preparation of diaminodinitropyridine and diaminodinitrobenzene
that provides a high yield free of impurities. It is also desirable
to identify the composition of the impurities. It is also desirable
to find a process of making rigid rod polymers having a minimum
inherent viscosity of about 25 dL/g. The present invention
identifies one of the major impurities and provides such
processes.
SUMMARY OF THE INVENTION
[0007] The present invention comprises a process for the
preparation of 1) diaminodinitropyridine or 2)
diaminodinitrobenzene by contacting 1) an aminopyridine or 2) an
aminobenzene, respectively, with oleum and nitric acid, wherein the
improvement comprises adding at least about 1% molar excess of
nitric acid based upon the aminopyridine or aminobenzene
respectively, with stirring for at least two hours to form first 1)
aminonitropyridine sulfonic acid or 2) aminonitrobenzene sulfonic
acid, respectively, and then 1) diaminodinitropyridine or 2)
diaminodinitrobenzene respectively.
[0008] The present invention further comprises a composition
comprising 2,6-diamino-3-nitropyridine-5-sulfonic acid.
[0009] The present invention further comprises a process for
purification of 1) diaminodinitropyridine which contains
2,6-diamino-3-nitropyridine-5-sulfonic acid or 2)
diaminodinitrobenzene which contains
2,6-diamino-3-nitrobenzene-5-sulfonic acid comprising contacting 1)
said diaminodinitropyridine or 2) said diaminodinitrobenzene
respectively with oleum and at least about 1% molar excess of
nitric acid based upon the diaminodinitropyridine or
diaminodinitrobenzene, with stirring for at least two hours to
yield 1) diaminodinitropyridine having less than about 0.1% by
weight of 2,6-diamino-3-nitropyridine-5-sulfonic acid or 2)
diaminodinitrobenzene having less than about 0.1% by weight of
2,6-diamino-3-nitrobenzene-5-sulfonic acid respectively.
[0010] The present invention further comprises a process for the
preparation of
poly(2,3,5,6-tetraaminopyridine-co-2,5-dihydroxyterephthalate)
having an inherent viscosity of at least 25 dL/g comprising [0011]
A) hydrogenation of diaminodinitropyridine which contains less than
about 0.1% by weight of 2,6-diamino-3-nitropyridine-5-sulfonic acid
to yield tetraaminopyridine, [0012] B) coupling of said
tetraaminopyridine with dipotassium dihydroxyterephthalate to yield
a tetraaminopyridinium dipotassium dihydroxyterephthalate complex,
and [0013] C) polymerization of said tetraaminopyridinium
dipotassium dihydroxyterephthalate complex to yield
poly(2,3,5,6-tetraaminopyridine-co-2,5-dihydroxyterephthalate)
having an inherent viscosity of at least 25 dL/g.
[0014] The present invention further comprises a process for the
preparation of
poly(2,3,5,6-tetraaminobenzene-co-2,5-dihydroxyterephthalate)
having an inherent viscosity of at least 25 dL/g comprising [0015]
A) hydrogenation of diaminodinitrobenzene which contains less than
about 0.1% by weight of 2,6-diamino-3-nitrobenzene-5-sulfonic acid
to yield tetraaminobenzene, [0016] B) coupling of said
tetraaminobenzene with dipotassium dihydroxyterephthalate to yield
a tetraaminobenzene dipotassium dihydroxyterephthalate complex, and
[0017] C) polymerization of said tetraaminobenzene dipotassium
dihydroxyterephthalate complex to yield
poly(2,3,5,6-tetraaminobenzene-co-2,5-dihydroxyterephthalate)
having an inherent viscosity of at least 25 dL/g.
DETAILED DESCRIPTION
[0018] Trademarks are denoted herein by capitalization. Chemical
abbreviations used herein are shown in Table 1.
TABLE-US-00001 TABLE 1 Chemical Abbreviations Abbreviation Chemical
name DADNP 2,6-diamino-3,5-dinitropyridine DANPS
2,6-diamino-3-nitropyridine-5-sulfonic acid DAP 2,6-diaminopyridine
DAPH 2,6-diaminopyridine hemisulfate DAPSA
2,6-diaminopyridine-3-sulfonic acid HADNP
2-hydroxy-6-amino-3,5-dinitropyridine K.sub.2-DHTA dipotassium
dihydroxyterephthalate M5 Monomer Tetraaminopyridinium dipotassium
dihydroxyterephthalate complex M5 Polymer
poly(2,3,5,6-tetraaminopyridine-co- 2,5-dihydroxyterephthalate) TAP
2,3,5,6-tetraaminopyridine TAP/K.sub.2-DHTA Tetraaminopyridinium
dipotassium complex dihydroxyterephthalate complex, Synonym for M5
Monomer DMAC Dimethylacetamide THF Tetrahydrofuran
[0019] The present invention comprises a process for the
preparation of aminonitropyridines and aminonitrobenzenes from
aminopyridines and aminobenzenes respectively. Specifically,
2,6-diamino-3,5-dinitropyridine is prepared from
2,6-diaminopyridine or its neutralization product with sulfuric
acid, 2,6-diaminopyridine hemisulfate. The reaction is conducted by
contacting 2,6-diaminopyridine (DAP) or 2,5-diaminopyridine
hemisulfate (DAPH) with oleum and concentrated nitric acid with
stirring for at least two hours. The
2,6-diamino-3,5-dinitropyridine produced by the method of the
present invention is purer than that produced by the method of the
prior art, free of a harmful byproduct, and yields purer
2,3,5,6-tetraaminopyridine, an intermediate in the preparation of
rigid rod polymers, such as
poly(2,3,5,6-tetraaminopyridine-co-2,5-dihydroxyterephthalate) (M5
Polymer). The M5 Polymer thereby produced has a higher inherent
viscosity (IV) and increased tenacity, measured as g (force)/denier
or g (force)/tex. For high strength fiber a high tensile strength
is desired. For M5 Polymer a value of 35-40 g (force)/denier is
desired.
[0020] The improved nitration process of the present invention can
also be utilized for the nitration of m-diaminobenzene to provide
diamino-dinitrobenzene. Hydrogenation of the latter product forms
1,2,4,5-tetraamino benzene, the intermediate for a similar rigid
rod copolymer,
poly(1,2,4,5-tetraaminobenzene-co-2,5-dihydroxyterephthalate).
Improvements in the tetraaminobenzene and end product copolymer
result from the use of the process of the present invention, as is
the case with the 2,6-diaminopyridine process.
[0021] In the following discussion and examples, the
diaminodinitropyridines will be detailed. All such details also
apply to the preparation and use of diaminodinitrobenzenes.
[0022] It has been found that the process involves a sequence of
reactions starting from 2,6-diaminopyridine (DAP) to form a first
sulfonic acid intermediate, 2,6-diaminopyridine-3-sulfonic acid
(DAPSA) that is readily nitrated to a second sulfonic acid
intermediate, 2,6-diamino-3-nitropyridine-5-sulfonic acid (DANPS).
While the initial formation of 2,6-diaminopyridine hemisulfate
(DAPH) during the nitration of DAP is known, the fact that this
nitration proceeds through the intermediate compound
2,6-diamino-3-nitropyridine-5-sulfonic acid (DANPS) in the
synthesis of 2,6-diamino-3,5-dinitropyridine (DADNP) has not been
previously recognized or reported. The relatively rapid formation
of DANPS is followed by a slower nitration of DANPS to DADNP. For
this last reaction to be completed, the reaction mixture must be
stirred at ambient temperature for about 2 to about 4 hours,
preferably about 4 hours. The reactions are shown in Reaction
Sequence 1.
##STR00001##
[0023] 2,6-Diaminopyridine-3-sulfonic acid (DAPSA) is formed when
2,6-diaminopyridine (DAP), or 2,6-diaminopyridine hemisulfate salt
(DAPH) is contacted with cold oleum. The oleum concentration is
from about 10% to about 30% oleum and preferably about 20%. The
oleum is added at a temperature of from about -5.degree. C. to
about 25.degree. C., and preferably at from about 0.degree. C. to
about 10.degree. C. Previously, it was incorrectly believed that
this was a simple dissolution of the 2,6-diaminopyridine
hemisulfate salt (DAPH) in the oleum. In the process of the present
invention as concentrated (98%) nitric acid is added slowly to
2,6-diaminopyridine-3-sulfonic acid (DAPSA) in oleum solution,
first 2,6-diamino-3-nitropyridine-5-sulfonic acid (DANPS) is
readily formed from the first stoichiometric amount of nitric acid.
As the second stoichiometric amount of concentrated (98%) nitric
acid is added, a second nitro group replaces the sulfonic acid
group to form 2,6-diamino-3,5-dinitropyridine (DADNP). The second
nitration is a slower step. In the process of the present
invention, a small excess of nitric acid is used but the reaction
is stirred for a time sufficient for the sulfonic acid group to be
totally displaced. Typically this is from about 2 to about 4 hours
at a temperature of from about 5.degree. C. to about 30.degree. C.,
and preferably from about 20.degree. C. to about 25.degree. C. The
nitric acid can be added in increments or in a single or continuous
addition. Only a small excess of nitric acid (about 1 to 3%) is
necessary to completely remove the sulfonic acid group. Prolonged
stirring at ambient temperature is employed.
[0024] The importance of the formation of this intermediate is that
DANPS as a residual contaminant in DADNP adversely affects the
quality of subsequent products made using the DADNP. In the prior
art, the importance of the length of the stirring period was not
recognized, consequently the 2,6-diamino-3,5-dinitropyridine
(DADNP) product contained various residual amounts of
2,6-diamino-3-nitro-5-sulfonic acid (DAPSA). In turn M5 Polymer
prepared from such compounds was highly variable and relatively
poor quality. For the purposes of this patent, the appearance and
quality of the M5 Polymer is a light purple color polymer having an
inherent viscosity (IV) of at least 25 dL/g. Such higher IV values
of the M5 Polymer provide higher quality fibers having higher
breaking strength, (tenacity) measured as g(force)/denier. The
DANPS content of the DADNP prepared by the method of the present
invention is less than about 0.1%, and preferably less than about
0.05% by weight. The detection limit for DANPS by HPLC is
approximately 0.05% by weight.
[0025] A second impurity that can occur when making
diaminodinitropyridine (DADNP) by prior art methods is
2-hydroxy-6-amino-3,5-dinitropyridine (HADNP), formed by the
hydrolysis of an amine group, a reaction enhanced by higher
temperatures. While not desired, HADNP is typically removed during
the hydrogenation and during the coupling steps employed to make M5
Polymer. HADNP is also sufficiently soluble in aqueous solutions of
sulfuric acid and ammonium hydroxide that it is readily removed in
filtration and washing steps. The HADNP content of the DADNP
prepared by the method of the present invention is less than 1%,
and preferably less than 0.5%, by weight. However, if the HADNP
content after sulfuric acid and ammonium hydroxide treatment should
still exceed 1%, this impurity can also reduce the inherent
viscosity and fiber strength of the M5 Polymer made therefrom. High
residual levels (greater than about 1%) of HADNP in DADNP are
readily reduced below the 1% level either by recrystallizing the
DADNP from hot dimethylacetamide (DMAC) or by treating the aqueous
DADNP slurry with a 5% aqueous solution of potassium carbonate,
followed by a water wash and drying of the relatively insoluble
DADNP. An aqueous ammonium hydroxide solution can be substituted
for the potassium carbonate solution. Example 3 hereinafter
demonstrates the removal of residual HADNP. HADNP content is
quantified by .sup.1H NMR.
[0026] Similarly, residual sulfuric acid, mainly present as the
pyridinium salt, is removed after neutralization with ammonium
hydroxide in the subsequent hydrogenation step. Quantification of
residual sulfuric acid as the pyridinium salt is conducted by
proton NMR or base titration. Base titration results also include
the sulfate equivalent of sulfonic acid impurities.
[0027] The process of the present invention provides a yield of
about 90% to about 96%. The process of the present invention does
not require the preparation and isolation of 2,6-diaminopyridine
hemisulfate salt intermediate, although this remains as an option.
The 2,6-diamino-3-nitro-sulfonic acid (DANPS) intermediate,
undesired in the final diaminodinitropyridine product, need not be
isolated as the prolonged stirring results in its reaction with
nitric acid to form the desired diaminodinitropyridine product.
Thus the process of the present invention does not have such
intermediates present as impurities in the product that can
contaminate downstream polymers and products made therefrom. In
making rigid rod polymers, such as the M5 Polymer, DADNP is
hydrogenated to form tetraaminopyridine, which is then coupled with
dipotassium dihydroxyterephthalate to form a complex, followed by
polymerization of the complex. It has also been found that DANPS in
DADNP poisons the precious metal catalyst used in the hydrogenation
step of 2,6-diamino-3,5-dinitropyridine to
2,3,5,6-tetraaminopyridine. While not wishing to be bound by
theory, it is believed that the presence of even small amounts
(less than 0.25%) of the sulfonic acid intermediate DANPS during
the hydrogenation causes the formation of dye-like diazo compounds,
resulting from N--N dimerization of hydroxylamines during the
reduction of 2,6-diamino-3,5-dinitropyridine to
2,3,5,6-tetraaminopyridine. Once formed, removal of these diazo
impurities is at best extremely difficult. The diazo impurities are
believed to lead to a colored 2,3,5,6-tetraaminopyridine solution,
then to an orange-colored complex of 2,3,5,6-tetraaminopyridine and
dipotassium 2,5-dihydroxyterephthate (TAP/K.sub.2-DHTA complex).
The DANPS impurity also has the potential to act as a chain
terminating or chain transfer agent, resulting in weak points in
the polymer chain, and thus a weaker fiber with a low inherent
viscosity (IV). Using the process of the prior art, IV values from
about 4 dL/g to only as high as about 21 dL/g are obtained. The
higher values in this prior art IV range are obtained only after
the removal of DANPS before polymerization by purification steps
using solvents such as tetrahydrofuran (THF), acetone, or
dimethylformamide. Firstly, DADNP having IV values of 25 dL/g or
greater are preferred and necessary for the preparation of high IV
M5 Polymer; secondly, avoiding the need for the DANPS purification
steps is strongly preferred. In the preparation of rigid rod
polymer and fiber using 2,6-diamino-3,5-dinitropyridine prepared by
the process of the present invention, the hydrogenation step to
2,3,5,6-tetraaminopyridine proceeds faster, more completely, and
with a smaller precious metal catalyst requirement. As indicated
above, the presence of even small amounts of DANPS also appears to
poison the supported platinum or rhodium precious metal catalyst.
Polymer from 2,3,5,6-tetraaminopyridine, prepared by the process of
the present invention, has consistently resulted in high inherent
viscosity values of 30 dL/g or more.
[0028] The process of the present invention is conducted in a
suitably agitated reaction vessel made of glass, or other materials
that are compatible with the reaction mixture. Stainless steel,
such as SS304 or SS316 stainless steel, becomes passivated by the
excess nitric acid and can be used. The reaction vessel is
optionally equipped with a reflux condenser to condense sulfur
trioxide. A dryer device is installed to preventingress of
moisture. In larger scale processes, a closed, slightly
pressurized, and nitrogen-purged reactor is used. The reaction
vessel further comprises methods of heating and cooling, and a
means for measuring the temperature of the reaction mass. The
2,6-diaminopyridine is slurried in an excess of 20% oleum at a
temperature of about 5.degree. C. to about 15.degree. C., then
cooled to about 0.degree. C., in preparation for the next
exothermic nitration reaction. The amount of 20% oleum is an amount
sufficient to provide about a 10% excess of sulfur trioxide over
the amount required to react with all the water in the 98% nitric
acid and the water produced during the nitration reaction. A small
excess of concentrated (98%) nitric acid is added slowly with
stirring at a temperature not exceeding 15.degree. C. The amount of
nitric acid is an amount sufficient to provide about a 2% to about
a 5% excess molar proportion of nitric acid based on the
stoichiometric amount required for the nitration of the
aminopyridine and the degree of substitution required. The reaction
mass is stirred at 5.degree. C. to 15.degree. C. until the solids
dissolve to give a homogeneous dark brown solution (for at least 15
minutes). The reaction mass is allowed to reach ambient temperature
and stirred for from about 2 hours to about 4 hours (4 hours is
preferred) to effect the second nitration. The reaction mass is
then drowned in chilled (-10.degree. to -20.degree. C.) 20%
sulfuric acid (about 25 to about 35 times the weight of the initial
2,6-diaminopyridine) at a temperature not exceeding 5.degree. C.,
and preferably not exceeding 0.degree. C. Deionized water (about 5
to about 10 times the weight of the initial 2,6-diaminopyridine) is
added at room temperature, and the mix stirred for 1 hour. The
drowned mass is then filtered at room temperature and the filter
cake washed sequentially with deionized water, 5% aqueous NH.sub.3
solution, and then deionized water. Each wash is between about 5 to
about 10 times the weight of the initial 2,6-diaminopyridine). The
solid product is dried by any suitable method, including but not
limited to nitrogen blow and vacuum suction, centrifugation and the
like. The yield of 2,6-diamino-3,5-dinitropyridine is about
95%.
[0029] Quenching the reaction mix in 20% H.sub.2SO.sub.4 is
preferred for the precipitation of the
2,6-diamino-3,5-dinitropyridine since the 20% H.sub.2SO.sub.4 gives
a larger particle size versus quenching in water, facilitating the
filtration, washing, and drying.
[0030] In a second embodiment, the present invention further
comprises the composition 2,6-diamino-3-nitropyridine-5-sulfonic
acid (DANPS). This is the intermediate formed during the process of
the present invention described above, which is undesirable in the
diaminodinitropyridine product.
2,6-Diamino-3-nitropyridine-5-sulfonic acid is prepared by
dissolving 2,6-diaminopyridine or 2,6-diaminopyridine hemisulfate
salt in oleum to form 2,6-diaminopyridine-3-sulfonic acid and
treating the resulting solution with one stoichiometric amount of
concentrated (98%) nitric acid. The resulting
2,6-diamino-3-nitropyridine-5-sulfonic acid is isolated by slowly
drowning the reaction mix in an excess of 20% sulfuric acid
followed by filtration, and washing the filter cake with water and
5% aqueous ammonium hydroxide solution and drying.
2,6-Diamino-3-nitropyridine-5-sulfonic acid is useful as a chemical
intermediate, for instance as a dye intermediate.
[0031] The present invention further comprises
2,6-diamino-3,5-dinitropyridine prepared by the process of the
present invention as described above, containing (i) less than
0.1%, and preferably less than 0.05%, DANPS; and (ii) less than 1%,
and preferably less than 0.5%, HADNP.
[0032] The present invention further comprises a process for
purification of 1) diaminodinitropyridine which contains
2,6-diamino-3-nitropyridine-5-sulfonic acid or 2)
diaminodinitrobenzene which contains
2,6-diamino-3-nitrobenzene-5-sulfonic acid comprising contacting 1)
said diaminodinitropyridine or 2) said diaminodinitrobenzene
respectively with oleum and at least about 1% molar excess of
nitric acid based upon the diaminodinitropyridine or
diaminodinitrobenzene, with stirring for at least two hours to
yield 1) diaminodinitropyridine having less than about 0.1% by
weight of 2,6-diamino-3-nitropyridine-5-sulfonic acid or 2)
diaminodinitrobenzene having less than about 0.1% by weight of
2,6-diamino-3-nitrobenzene-5-sulfonic acid respectively.
[0033] Thus the process of the present invention as described above
can be used for renitration of diaminodinitropyridine which is
contaminated with or contains
2,6-diamino-3-nitropyridine-5-sulfonic acid (DANPS), or renitration
of diaminodinitrobenzene which is contaminated with or contains
2,6-diamino-3-nitrobenzene-5-sulfonic acid. Such contaminated
diaminodinitropyridine or diaminodinitrobenzene is used as the
starting material in the process using the same conditions as
previously described above. The renitration or purification process
of the present invention typically yields diaminodinitropyridine
containing less than 0.1%, and preferably less than 0.05%, of
DANPS, or diaminodinitrobenzene containing less than 0.1%,
preferably less than 0.05%, of
2,6-diamino-3-nitrobenzene-5-sulfonic acid.
[0034] The present invention further comprises a process for making
rigid rod polymers, in particular M5 Polymer, using
diaminodinitropyridine prepared using the processes of the present
invention as described above. Because such diaminodinitropyridine
is free of, or contains less than 0.1% of, DANPS the rigid rod
polymer obtained has an inherent viscosity of at least 25 dL/g. The
process of the present invention for making M5 Polymer comprises:
[0035] A) hydrogenation of diaminodinitropyridine which contains
less than about 0.1% by weight of
2,6-diamino-3-nitropyridine-5-sulfonic acid to yield
tetraaminopyridine, [0036] B) coupling of said tetraaminopyridine
with dipotassium dihydroxyterephthalate to yield a
tetraaminopyridinium dipotassium dihydroxyterephthalate complex,
and [0037] C) polymerization of said tetraaminopyridinium
dipotassium dihydroxyterephthalate complex to yield
poly(2,3,5,6-tetraaminopyridine-co-2,5-dihydroxyterephthalate)
having an inherent viscosity of at least 25 dL/g.
[0038] The complex formed in step B) above is also called the M5
Monomer and has the following structure of Formula 1. The final M5
Polymer has the structure of Formula 2 below wherein n is the
degree of polymerization.
##STR00002##
[0039] Tetraaminopyridinium dipotassium dihydroxyterephthalate
complex (M5 Monomer) is prepared by adding an aqueous solution of
tetraaminopyridine to an alkaline solution of dipotassium
2,5-dihydroxyterephthate. The preparation is performed with
rigorous exclusion of oxygen, using de-aerated deionized water and
a nitrogen purge. The M5 Monomer precipitates and is filtered. The
preparation of the M5 Monomer is completed by washing the wet cake
with deaerated deionized water, and, finally, flushing with hot
nitrogen and drying. The M5 Monomer when dry typically has very
good quality and stability. Using this monomer,
poly(2,3,5,6-tetraaminopyridine-co-2,5-dihydroxyterephthalate) (M5
Polymer) is prepared using the following steps. A slurry is
prepared from the tetraaminopyridinium dihydroxyterephthalate and
polyphosphoric acid. The slurry so obtained is homogenized at about
100.degree. C. for about 1 hour. Stirring of the mixture is
continued at about 140.degree. C. for about 1 hour. The temperature
is rapidly increased to about 180.degree. C. to dissolve the
remaining dipotassium 2,5-dihydroxyterephthalic acid, then is
polymerized at about 180.degree. C. for about 0.3 to about 2.5
hours, preferably for about 1 to about 2.5 hours. The polymer is
prepared in concentrations in the range of from about 10 to about
21 weight %. For higher molecular weight, the concentration of the
polymer in the polyphosphoric acid solution is preferably lower,
such as from about 14 to about 18 weight %. For subsequent spinning
of yarns, the concentration is preferably in the range of from
about 12 to about 19 weight %.
[0040] The mixture obtained from the polymerization reaction is
used directly for spinning or extrusion into fibers, films, or
tapes. To obtain a solution that can be spun or extruded directly
it is desired that the concentration of P.sub.2O.sub.5 in the
P.sub.2O.sub.5/H.sub.2O solvent system is at least 79.5% by weight
to 84% by weight after the reaction has ended. At a concentration
of more than 84% by weight it can be necessary to under some
circumstances to have a chain terminator such as benzoic acid
present during the polymerization reaction in order to prevent the
viscosity from rising too high. The final step involves extraction
of the fibers, films, or tapes using sequentially water, ammonium
hydroxide solution, and water. Further details on preparation of
fibers, films or tapes are provided in U.S. Pat. No. 5,674,969.
[0041] While batch processes are described above, and in the
Examples below, for the processes of the present invention, the
invention further includes continuous processes for the manufacture
of larger product quantities. Continuous processes typically
provide tighter control of reaction conditions, for instance
temperature. Continuous processing thus results in improved product
quality, improved product consistency, and economic benefits.
[0042] In a further embodiment, the nitration process of the
present invention is applicable to other nitrations. For instance,
it is also beneficial to the nitration of diaminobenzenes,
particularly m-diaminobenzene. In the case of m-diaminobenzene,
there are similar improvements in the quality of the
1,3-diamino-4,6-dinitrobenzene produced. The latter compound can be
similarly reduced to 1,2,4,5-tetraaminobenzene, an intermediate for
the preparation of a similar rigid rod copolymer,
poly(1,2,4,5-tetraaminobenzene-co-2,5-dihydroxyterephthalate). The
end-product copolymer thus produced has improved tenacity and
inherent viscosity.
[0043] The processes of the present invention are useful to prepare
diaminodinitropyridine and diaminodinitrobenzene that contains less
than about 0.1% by weight of undesired intermediates. Such
diaminodinitropyridine and diaminodinitrobenzene are useful in the
process of the present invention to make rigid rod polymers having
an inherent viscosity of less than about 25 dL/g.
Materials and Test Methods
[0044] The following materials and test methods were used in the
Examples herein.
[0045] 1) Nitric acid (98%) was obtained from El Dorado Chemical
Company, El Dorado Ark.
[0046] 2) 2,6-Diaminopyridine (DAP) was obtained from Alkali
Metals, Inc. of Hyderabad, India.
[0047] 3) 20% Oleum was obtained from E. I. du Pont de Nemours and
Company, Wilmington Del.
[0048] 4) Dipotassium 2,5-dihydroxyterephthalate
[0049] Dipotassium 2,5-dihydroxyterephthalate was prepared in the
known "Kolbe-Schmidt" type reaction from hydroquinone. Hydroquinone
was mixed with potassium carbonate and potassium formate, the
latter which acted as a solvent when molten. The mixture was heated
to 200.degree. C. with stirring to provide a homogeneous solution.
Excess carbon dioxide was bubbled through the stirred solution for
about 8 h. Excess carbon dioxide optionally may be recycled. The
reaction mass was drowned in water, and filtered. When the drowned
and stirred reaction mass was filtered, the sparingly soluble
dipotassium 2,5-dihydroxyterephthalate was separated from
water-soluble potassium formate and potassium carbonate.
[0050] 5) 2,6-Diaminopyridine hemisulfate (DAPH)
[0051] 2,6-Diaminopyridine hemisulfate (DAPH) was prepared as
follows. To a 5-L round-bottomed flask equipped with a means of
temperature control and a liquid addition funnel was added water
(deionized, 2 L) and 2,6-diaminopyridine (DAP 500 g) and the
mixture stirred to form a solution. Sulfuric acid (96%, 334 g) the
stoichiometric amount) was added at a rate to raise and then to
maintain a temperature of 45.degree. to 55.degree. C. An exotherm
resulted when the sulfuric acid was added. The solution became
brown during the reaction, probably due to the generation of small
quantities of water-soluble oxidation products of DAP. Off-white
crystals of 2,6-diaminopyridene hemisulfate (DAPH or
DAP.1/2H.sub.2SO.sub.4) precipitated out as the sulfuric acid was
added. The end-point pH was adjusted to between about pH 3 to about
pH 5, preferably to a pH about 4. Any necessary final adjustment
was by small supplemental additions of sulfuric acid to lower the
pH or by small supplemental additions of DAP to raise the pH. The
reaction mixture was then cooled to room temperature and filtered.
The wet crystalline filter cake was washed once with water (800 mL)
and once with industrial denatured 2T ethanol (ethanol denatured
with 7.5% toluene and containing 7.5% water) or water (800 mL). The
crystals were then dried in a vacuum oven at 75.degree. C. and 30.5
kPa. At 25.degree. C., the solubility of DAP Hemisulfate in water
was about 1.5% and in ethanol less than 0.15%. Thus, in a series of
preparations, the water filtrate and washes, which contained small
amounts of dissolved DAPH, optionally may be reused in subsequent
preparations to maximize yield. With this recycle, the yield of
DAPH was 98-99%.
[0052] 6) DARCO G60 is an activated carbon powder for removing
colors from liquids and was obtained from Sigma-Aldrich, Milwaukee,
Wis.
[0053] 7) The water used in all examples was deionized water.
Test Method 1. Measurement of Inherent Viscosity
[0054] The inherent viscosities (IV) of M5 Polymers were determined
using viscosity measured with a Viscotek Forced Flow Viscometer
Y900 (Viscotek Corporation, Houston, Tex.) for the polymer
dissolved in 50/50 weight % trifluoroacetic acid/methylene chloride
at a 4 g/L concentration at 19.degree. C. following an automated
method based on ASTM D 5225-92. The measured IV values of M5
Polymer were correlated to IV values measured manually in 60/40
weight % phenol/1,1,2,2-tetrachloroethane following ASTM D
4603-96.
Test Method 2. Tenacity
[0055] The physical properties of the yarns reported in the
following examples were measured using an Instron Corp. Tensile
Tester, Model No. 1122 (Instron Corp., Canton Mich.). Specifically,
tenacity was measured according to ASTM D-2256.
EXAMPLES
Example 1
[0056] To a 3-L round-bottomed flask, equipped with a mechanical
stirrer, a moisture trap, a thermocouple, and a dry-ice/acetone
bath for cooling, was added 20% oleum (containing 20% sulfur
trioxide in sulfuric acid, 1350 g). The acid in the flask was
cooled to 10.degree. C. 2,6-diaminopyridine hemisulfate (DAPH,
316.4 g, 2 mole, prepared from DAP) was added in portions over 30
min., maintaining the temperature at 15-25.degree. C. The reaction
mass was then stirred at 15.degree. C. until the solids dissolved
to give a dark brown homogeneous solution. The solution was then
cooled to 0.degree. C. and 98% nitric acid (270 g, 5% excess), was
added drop-wise while maintaining the temperature below 15.degree.
C. The nitration product was stirred for 2 hours at 21.degree. C.
after the completion of the nitric acid addition, and then quenched
in dilute sulfuric acid solution as described below.
[0057] To a 12-L round-bottomed flask equipped with a mechanical
stirrer, an overhead condenser, a thermocouple, a dry-ice/acetone
bath for cooling, and an addition funnel, was added 20% sulfuric
acid (6.7 kg). When practical, the 20% sulfuric acid was prepared
by recycling and diluting the mother liquor from the previous
nitration. This acid solution was cooled to -5.degree. C. to
-10.degree. C. and the nitration product prepared above was added
drop-wise through the addition funnel while maintaining the
temperature in the 12-L flask below -5.degree. C. Bright yellow
crystals of 2,6-diamino-3,5-dinitropyridine (DADNP) precipitated.
After the completion of this addition, de-ionized water (1 L) was
added, the mixture was brought to room temperature, and stirred at
room temperature for 1 h. The DADNP slurry was filtered in a
fritted glass filter and the wet cake was washed with water (1 L)
at room temperature three times. The filter cake was washed
sequentially with deionized water, 5% aqueous NH.sub.3 solution,
and then deionized water. Each wash was between about 5 to about 10
times the weight of the initial 2,6-diaminopyridine). The crude
DADNP (360 g, 90% yield) contained 1.05% HADNP and non-detectable
(less than 0.05%) DANPS by HPLC.
[0058] The crude DADNP sample was combined with another smaller
sample from a similar experiment and the combined DADNP sample (474
g) and was again purified by stirring it in THF (1 L) and aqueous
ammonia (1.3 L, 7% ammonia) at 50.degree. C. over the weekend (2
days). The wet cake was washed with water (two 500-mL portions) and
dried in a vacuum oven at 85.degree. C. to a constant weight to
obtain bright yellow, fluffy DADNP (460 g, 97% purification yield).
An HPLC analysis gave 0.5% HADNP, DANPS was undetectable, whereas
.sup.1H NMR analysis showed no HADNP or sulfuric acid.
[0059] A sample of the purified DADNP (97 g, 0.49 mole), prepared
as described above, was converted to 2,3,5,6-tetraaminopyridine
(TAP) by hydrogenation. The DANDP was placed in a 1-L autoclave
with de-aerated and deionized water (500 g), 5% supported Pt
catalyst (Degussa F101, 1 g dry basis), and ammonia gas (10 g).
After closing and inerting the autoclave, the slurry was warmed to
65.degree. C. and treated with hydrogen gas bubbled into the
reaction mass at 65.degree. C. and 125 psig (kPa) until hydrogen
uptake stops (typically 1 to 2 h). The highly oxygen-sensitive
aqueous TAP solution (10 to 12%) was purified under a nitrogen
blanket in situ using activated carbon (DARCO G60, 10 g) and was
filtered into a basic aqueous (pH 9-10) solution of dipotassium
2,5-dihydroxyterephthalate (K.sub.2-DHTA, 126 g, 0.47 mole, in 2.2
L deaerated deionized water). The autoclave was rinsed twice, each
rinse using deaerated deionized water (100 g), and the washings
added to the filtrate.
[0060] The entire following process steps of titration, filtration,
washing, and drying, were conducted under a nitrogen atmosphere
free of oxygen. The basic TAP/K.sub.2-DHTA solution (3 L) and 25%
phosphoric acid (200 mL) solution were slowly and simultaneously
fed to a jacketed and agitated glass reactor containing water (700
mL), maintaining the pH at 4.5 and the temperature at 50.degree. C.
This titration resulted in the instantaneous formation of bright
yellow crystals of the TAP/K.sub.2-DHTA complex (the M5 Monomer for
making the M5 Polymer). The TAP/K.sub.2-DHTA complex slurry was
filtered in a sintered glass filter and washed sequentially with
de-aerated water (three 400 mL portions) and de-aerated ethanol
(two 100 mL portions). The wet cake was dried on the filter
overnight under a nitrogen purge to obtain pale yellow
TAP/K.sub.2-DHTA complex (151 g, 93% yield).
[0061] A portion of the TAP/K.sub.2-DHTA complex was then
polymerized. Using this complex, the M5 Polymer was prepared using
the following steps. (i) A slurry was prepared from the
tetraaminopyridinium dihydroxy terephthalate complex (23 g) and
polyphosphoric acid (135 g). (ii) The slurry so obtained was
homogenized at about 100.degree. C. for 1 h. (iii) Stirring of the
mixture was continued at 140.degree. C. for 1 h. (iv) The
temperature was rapidly increased to 180.degree. C. to dissolve the
remaining dipotassium 2,5-dihydroxyterephthalic acid, then
polymerized at about 180.degree. C. for 0.3 to 2.5 h, to obtain an
M5 Polymer with an inherent viscosity (IV) of 32 dL/g.
[0062] Another portion of the purified DADNP (97 g) was
hydrogenated and then coupled with K.sub.2-DHTA (126 g) to obtain
pale yellow TAP/K.sub.2-DHTA complex (154 g, 94% yield). A small
portion (23 g) of this TAP/K.sub.2-DHTA complex was again
polymerized to obtain M5 Polymer having an IV of 31 dL/g. The
remaining of the two TAP/K.sub.2-DHTA complex samples (250 g) were
combined and the combined sample was polymerized as a large batch
in the presence of 0.7% chain terminator (o-phenylenediamine) to
obtain M5 Polymer having an IV of 26 dL/g and a tenacity of 32 g
(force)/denier. Note that the intentional use of a chain terminator
reduces the IV of the polymer, but the resulting fiber is of
superior quality. Example 1 showed the formation of DADNP which was
free of DANPS from DAPH by the process of the present invention,
resulting in good quality TAP and thus good quality M5 Polymer, the
latter having an IV higher than 25 dL/g and a tenacity greater than
30 g (force)/denier.
Comparative Example A
[0063] In Comparative Example A, DADNP was prepared from DAPH using
a prior art method. To a 3-L round-bottomed flask, equipped with a
mechanical stirrer, a moisture trap, a thermocouple, and a
dry-ice/acetone bath for cooling, was added 20% oleum (containing
20% sulfur trioxide in sulfuric acid, 1350 g). The acid in the
flask was cooled to 10.degree. C. 2,6-diaminopyridine hemisulfate
(DAPH, 237.3 g, 1.5 mole, prepared as described above from DAP) was
added in portions over 30 min., maintaining the temperature at
15-25.degree. C. The reaction mass was then stirred at 15.degree.
C. until the solids dissolved to give a dark brown homogeneous
solution. The solution was then cooled to 0.degree. C. and 98%
nitric acid (197 g, 2.06 mole, 2% excess), was added drop-wise
while maintaining the temperature below 15.degree. C. The nitration
product was stirred only for 15 min. and then quenched in dilute
sulfuric acid solution as described below.
[0064] To a 12-L round-bottomed flask equipped with a mechanical
stirrer, an overhead condenser, a thermocouple, a dry-ice/acetone
bath for cooling, and an addition funnel, was added 20% sulfuric
acid (5.0 kg). When practical, the 20% sulfuric acid was prepared
by recycling and diluting the mother liquor from the previous
nitration. This acid solution was cooled to -5.degree. C. to
-10.degree. C. and the nitration product prepared above was added
drop-wise through the addition funnel while maintaining the
temperature in the 12-L flask below -5.degree. C. Bright yellow
crystals of 2,6-diamino-3,5-dinitropyridine (DADNP) precipitated.
After the completion of this addition, de-ionized water (1 L) was
added, the mixture was brought to room temperature, and stirred at
room temperature for 1 h. The DADNP slurry was filtered in a
Buchner filter and the wet cake was washed with water (1 L) at room
temperature. The wet cake in the Buchner filter was partially dried
by vacuum suction under a nitrogen atmosphere and then dried to a
constant weight in a vacuum oven at 75.degree. C. and 30.5 kPa to
obtain yellow solids of crude DADNP (293 g, 98% yield). .sup.1H NMR
analysis showed the sample contained 2.2%
2-hydroxy-6-amino-3,5-dinitropyridine (HADNP) and 2.2%
H.sub.2SO.sub.4. A base titration showed that the DADNP obtained in
this experiment contained 3.5% H.sub.2SO.sub.4. As described
previously, the higher titration analysis, but not the NMR
analysis, includes the sulfate equivalent of any contaminating
DANPS. In a similar repeated example, yellow solid crude DADNP (285
g, 95% yield) was obtained. .sup.1H NMR analysis showed the sample
contained 2.7% HADNP and 4.5% H.sub.2SO.sub.4, demonstrating the
reproducibility of the synthesis. Based on analysis of a composite
sample from several repeated syntheses, the average DANPS content
was about 2 to about 4%.
[0065] A composite sample of crude DADNP from above (830 g,
containing about 3% HADNP) was placed in a 12-L round-bottomed
flask. Tetrahydrofuran (2.2 L) and 30% aqueous ammonia (600 mL)
were added to the composite sample. The mix was stirred to form a
slurry and stirred overnight at 45.degree. C. before filtering in a
Buchner filter at room temperature. The wet cake on the filter was
washed with water (four portions of 250 mL) at room temperature and
partially dried by vacuum suction under a nitrogen atmosphere. The
cake was then dried to a constant weight in a vacuum oven at
75.degree. C. and 30.5 kPa to obtain bright yellow solids of
purified DADNP (800 g, 96% purification yield). .sup.1H NMR
analysis showed the sample contained 0.1% HADNP and 0.05%
H.sub.2SO.sub.4. A base titration showed that the sample contained
0.4% H.sub.2SO.sub.4. Another analysis by HPLC showed the sample
contained 0.3% HADNP and 0.8% DANPS.
[0066] A sample of the purified DADNP (100 g), prepared as
described above, was converted to 2,3,5,6-tetraaminopyridine (TAP)
by hydrogenation. DANDP (100 g) was placed in a 1-L autoclave with
de-aerated and deionized water (500 g), 5% supported Pt catalyst
(Degussa F101, 1 g dry basis), and ammonia gas (10 g). After
closing and inerting the autoclave, the slurry was warmed to
65.degree. C. and treated with hydrogen gas bubbled into the
reaction mass at 65.degree. C. and 125 psig (963 kPa) until
hydrogen uptake stops (typically 1 to 2 h). The highly
oxygen-sensitive aqueous TAP solution (10 to 12%) was purified
under a nitrogen blanket in situ using activated carbon (DARCO G60,
10 g) and was filtered into a basic aqueous (pH 9-10) solution of
di-potassium 2,5-dihydroxyterephthalate (K.sub.2-DHTA, 126 g in 2.2
L deaearated deionized water). The autoclave was rinsed twice, each
rinse using deaerated DI water (100 g), and the washings added to
the filtrate.
[0067] The entire following process steps of titration, filtration,
washing, and drying, were conducted under a nitrogen atmosphere
free of oxygen. The TAP/K.sub.2-DHTA complex was oxygen sensitive
and discolored to orange and then light brown within a week if
exposed to air. The basic TAP/K.sub.2-DHTA solution (3 L) and 25%
phosphoric acid (200 mL) solution were slowly and simultaneously
fed to a jacketed and agitated glass reactor containing water (700
mL), maintaining the pH at 4.5 and the temperature at 50.degree. C.
This titration resulted in the instantaneous formation of bright
yellow crystals of the TAP/K.sub.2-DHTA complex (the M5 Monomer for
making the M5 Polymer). The TAP/K.sub.2-DHTA complex slurry was
filtered in a sintered glass filter and washed sequentially with
de-aerated water (three 400 mL portions) and de-aerated ethanol
(two 100 mL portions). The wet cake was dried on the filter
overnight under a nitrogen purge to obtain pale yellow
TAP/K.sub.2-DHTA complex (157 g, 96% yield). The ratio of TAP to
K.sub.2-DHTA contained about a 3% to about a 5% excess of TAP. This
small excess of TAP was removed in the washing step, and prevented
the presence of any excess DHTA (free acid) that would otherwise
precipitate out with the TAP/K.sub.2-DHTA complex.
[0068] The TAP/K.sub.2-DHTA complex was then polymerized using the
procedure described in Example 1. Using this complex, the M5
Polymer was prepared using the following steps. (i) A slurry was
prepared from the tetraaminopyridinium dihydroxyterephthalate (23
g) and polyphosphoric acid (135 g). (ii) The slurry so obtained was
homogenized at about 100.degree. C. for 1 h. (iii) Stirring of the
mixture was continued at 140.degree. C. for 1 h. (iv) The
temperature was rapidly increased to 180.degree. C. to dissolve the
remaining dipotassium 2,5-dihydroxyterephthalic acid, then
polymerized at about 180.degree. C. for 0.3 to 2.5 h, to obtain an
M5 Polymer with an inherent viscosity (IV) of 22 dL/g. The presence
of measurable quantities of DANPS resulted in poor quality TAP, and
poor quality M5 Polymer. In a similar example, the same purified
DADNP was used to obtain another TAP/K.sub.2-DHTA complex sample
that was initially light orange in color when dried (152 g, 93%
yield) that yielded M5 Polymer with a lower IV of 17 dL/g. The
discoloration and lower IV, believed to be due to inadvertent
contact with air, emphasizes importance of oxygen exclusion. As
indicated above, acceptable M5 Polymer has an IV not less than 25
dL/g.
Comparative Example B
[0069] In Comparative Example B DADNP was prepared from DAP using a
prior art process. The nitration experiment described in
Comparative Example A was repeated except for replacing the DAPH
(1.5 mole) with DAP (2,6-diaminopyridine, 163.7 g, 1.5 mole, to
obtain yellow crude DADNP (277 g, 93% yield). .sup.1H NMR analysis
showed the sample was identical to that obtained using DAPH in
Comparative Example A and contained 2% HADNP and 1.4%
H.sub.2SO.sub.4. A subsequent HPLC analysis showed that this sample
contained 2.8% DANPS.
[0070] Comparative Example B was duplicated at one-third scale
(DAP, 54.55 g, 0.5 mole) in 1-L (nitration) and 3-L flasks
(quench), respectively. The yellow crude DADNP (94 g, 94%) obtained
in this smaller scale experiment contained 2.6% HADNP and 1%
sulfuric acid as determined by .sup.1H NMR. HPLC analysis showed
that the sample contained 2.5% DANPS.
[0071] Crude DADNP samples prepared from DAP were combined and
purified using THF and aqueous ammonia as described in Comparative
Example A to obtain purified DADNP (950 g) containing 0.3% HADNP
and 0.7% H.sub.2SO.sub.4. An HPLC analysis showed that it also
contained 0.5% DANPS.
[0072] Purified DADNP (100 g) from above was used as described in
Comparative Example A to make sequentially pale yellow
TAP/K.sub.2-DHTA complex (152 g, 91%) and M5 Polymer. The M5
Polymer had an IV of 23 dL/g.
Example 2
[0073] DADNP (400 g), prepared according to the procedure of
Example 1 and containing 1.1% DANPS and 0.3% HADNP as determined by
HPLC, was dissolved in portions in a mixture of 96% H.sub.2SO.sub.4
(1.125 kg) and 20% oleum (1.125 kg) in a 3-L round-bottomed flask.
The temperature was maintained between 0.degree. to 10.degree. C.
The mixture was stirred until all solids dissolved. To this
solution was added 98% HNO.sub.3 (15 g) drop-wise at 0-10.degree.
C. The brown to burgundy color solution was stirred for an
additional 4 h at 10.degree. C. The mixture was added to a 20%
H.sub.2SO.sub.4 solution (10.4 kg) at 0.+-.2.degree. C. in a 12-L
round-bottomed flask as described in Example 1. A bright yellow
slurry was obtained. The slurry was stirred, diluted with 1.67 kg
deionized water, filtered and washed with three 1.67 kg washes, the
first and third washes being deionized water, the second wash was
again 5% aqueous ammonia, using a fritted-glass filter as described
in Example 1. Bright yellow DADNP (389 g) was obtained after
drying. HPLC analysis showed the sample contained 0.7% HADNP and no
detectable DANPS.
[0074] The crude DADNP sample from above was combined with other
similar DADNP samples and again purified by stirring it in
proportional amounts of THF and aqueous ammonia as described in
Example 1, and was dried to obtain bright yellow, fluffy DADNP. An
HPLC analysis gave 0.4% HADNP, undetectable DANPS, whereas .sup.1H
NMR analysis showed 0.5% HADNP and 0.07% sulfuric acid.
[0075] A portion of the purified DADNP from above (130 g, 0.65
mole) was hydrogenated according to the hydrogenation procedure of
Example 1. The resulting aqueous TAP solution was first color
treated with DARCO G60 (15 g), then complexed with K.sub.2-DHTA
(165 g, 0.60 mole, prepared as in Example 1 to obtain pale yellow
TAP/K.sub.2-DHTA complex (209 g, 98% yield). A portion of this
TAP/K.sub.2-DHTA complex was polymerized as described in Example 1
to obtain M5 Polymer having an IV of 31 dL/g. Another portion of
the same purified DADNP (130 g) was hydrogenated and then coupled
with K.sub.2-DHTA (165 g) to obtain pale yellow TAP/K.sub.2-DHTA
complex (209 g, 98% yield). A small portion of this
TAP/K.sub.2-DHTA complex was polymerized to obtain a high quality
M5 Polymer with an IV of 29 dL/g.
[0076] Using the procedure described above, the starting DADNP for
this example containing 1.1% DANPS and 0.3% HADNP was also
hydrogenated and then coupled with K.sub.2-DHTA to make
TAP/K.sub.2-DHTA complex. A portion of that TAP/K.sub.2-DHTA
complex was polymerized as described in Example 1 to obtain M5
Polymer with a sub-standard IV of 23 dL/g, demonstrating the
increase in IV associated with the purification of the DADNP.
Example 2 demonstrated that DADNP, containing DANPS in excess of
0.1%, can be further nitrated to convert the DANPS impurity to
DADNP, resulting in good quality TAP and thus good quality M5
Polymer
Example 3
[0077] The same procedure of removing DANPS by re-nitration as
described in Example 2 was repeated using DADNP (500 g) containing
1%) DANPS and 1.5% HADNP to obtain crude re-nitrated DADNP (473 g,
95%) containing 2.2% HADNP and no detectable DANPS. A portion of
this re-nitrated crude DADNP (53 g) was again hydrogenated and the
resulting aqueous TAP solution was coupled with K.sub.2-DHTA (63 g,
0.23 mole) to obtain pale yellow TAP/K.sub.2-DHTA complex (80 g,
98% yield) using the procedure as described in Example 1. A portion
of this TAP/K.sub.2-DHTA complex was polymerized as in Example 1 to
obtain M5 Polymer having an IV of 24 dL/g. A portion of the
re-nitrated crude DADNP (200 g) was then dissolved in hot DMAC (1.2
L) and then treated with 5% aqueous K.sub.2CO.sub.3 solution (100
mL) to remove HADNP. A purified DADNP (187 g, 96%), containing 100%
DADNP and no HADNP and no DANPS was obtained. A portion of this
pure DADNP (50 g) was hydrogenated and then coupled with
K.sub.2-DHTA (63 g, 0.23 mole) as described in Example 1 to obtain
pale yellow TAP/K.sub.2-DHTA complex (78 g, 95% yield). A portion
of this TAP/K.sub.2-DHTA complex was polymerized as described in
Example 1 to obtain M5 Polymer IV of 31 dL/g. For comparison, the
starting DADNP containing 1% DANPS and 1.5% HADNP, when eventually
converted to TAP/K.sub.2-DHTA complex and then polymerized, had
yielded an IV of 17 dL/g. Example 3 demonstrated that DADNP
containing DANPS in excess of 0.1% that resulted in M5 Polymer with
IV less than 25 dL/g, can be renitrated to remove the contaminating
DANPS. Renitrated DADNP can be converted to M5 Polymer with
acceptable IV.
Example 4
[0078] The same procedure of removing DANPS by re-nitration as
described in Example 2 was repeated a third time using DADNP (400
g) containing 4% DANPS and 3.5% HADNP to obtain crude re-nitrated
DADNP (380 g, 95%) containing 3.2% HADNP and no detectable DANPS.
This re-nitrated crude DADNP (379 g) was treated with 5% aqueous
K.sub.2CO.sub.3 solution (100 mL) to remove HADNP, and a purified
DADNP (356 g, 94%), containing 99.7% DADNP, 0.2% HADNP and no
DANPS, was obtained. A portion of this pure DADNP (50 g) was
hydrogenated and then coupled with K.sub.2-DHTA (63 g, 0.23 mol) as
described in Example 1 to obtain pale yellow TAP/K.sub.2-DHTA
complex (798 g, 97% yield). A portion of this TAP/K.sub.2-DHTA
complex was then polymerized as described in Example 1 to obtain M5
Polymer having an IV of 31 dL/g. Example 4 demonstrated that DADNP
containing DANPS in excess of 0.1% that resulted in M5 Polymer with
IV less than 25 dL/g, can be renitrated to remove the contaminating
DANPS. Renitrated DADNP can be converted to M5 Polymer with
acceptable IV.
Example 5 and Comparative Example C
[0079] The nitration of DAPH, as described in Example 1, was
repeated using half the recipe of ingredients. For example, DAPH
(158.2 g, 1 mole), prepared as described above using DAP, was used.
Similarly, 20% oleum (900 g), 98% HNO.sub.3 (135 g) were used in
the same equipment. The same procedure described in Example 1 was
used until the end of nitration. After the nitration, the reaction
mixture (1.19 kg) was stirred for 15 minutes and then split into
two halves. The first half (Comparative Example C, 596 g) of the
nitration reaction product was quenched immediately at
0.+-.2.degree. C. into 1.675 kg of 20% H.sub.2SO.sub.4 solution. To
this solution was then added 250 g of deionized water to complete
the DADNP product precipitation. The product was then filtered and
washed three times using water (300 g), 5% NH.sub.3 solution (300
g), and then water (300 g). The crude DADNP (82 g, 82% yield)
contained 1.2% HADNP and 10.3% DANPS by HPLC. The second half of
the nitration reaction mixture (Example 5, 596 g) was stirred at
20-23.degree. C. for an additional 2.5 h. The same procedure, as in
the first half of the reaction mixture, was used to obtain crude
DADNP (93 g, 93% yield) containing 0.5% HADNP and non-detectable
(less than 0.05%) DANPS by HPLC.
Example 6 and Comparative Example D
[0080] The experiment described in Example 5 was repeated using DAP
(109.1 g, 1 mole) instead of DAPH. Otherwise, the same equipment
and procedure were used. After the nitration, the reaction mass
(1.144 kg) was stirred for 30 minutes to provide a nitration
product and then split into two halves. The first half (Comparative
Example D, 570 g) of the nitration product was quenched immediately
at 0.+-.2.degree. C. into 1.675 kg of 20% H.sub.2SO.sub.4 solution.
To this solution was then added 250 g of deionized water to
complete the DADNP product precipitation. The product was then
filtered and washed three times using water (300 g), 5% NH.sub.3
solution (300 g), and then water (300 g). The crude DADNP (87 g,
88% yield) contained 0.9% HADNP and 5.1% DANPS by HPLC. The second
half of the nitration product (Example 6, 596 g) was stirred at
20-23.degree. C. for an additional 2 h. The same procedure, as in
the first half of the reaction mixture, was used to obtain crude
DADNP (92 g, 92% yield) containing 0.3% HADNP and undetectable
(less than 0.05%) DANPS by HPLC.
[0081] A portion of the crude DADNP (50 g, 0.25 mole), from the
first half (Comparative Example D) of the nitration product
described above (with 30-min stirring), was hydrogenated and the
resulting aqueous TAP solution was first color treated with DARCO
G60 (5 g) and then coupled with K.sub.2-DHTA (63 g, 0.23 mole) as
described in Example 1 to obtain pale yellow TAP/K.sub.2-DHTA
complex (74 g, 91% yield). A portion of this TAP/K.sub.2-DHTA
complex was polymerized as described in Example 1 to obtain a low
polymer IV of 16 dL/g.
[0082] A portion of the crude DADNP (51 g, 0.26 mole), from the
second half (Example 6) of the nitration product described above (a
total of 2.5 h of stirring), was hydrogenated and the resulting
aqueous TAP solution was first color treated with DARCO G60 (5 g)
and then coupled with K.sub.2-DHTA (63 g, 0.23 mole) as described
in Example 1 to obtain pale yellow TAP/K.sub.2-DHTA complex (78 g,
96% yield). A portion of this TAP/K.sub.2-DHTA complex was
polymerized as described in Example 1 to obtain an excellent M5
Polymer with an IV of 32 dL/g. In strength tests, polymer samples
with IV of 32 dL/g resulted in high quality fiber, exceeding
breaking strength of 40 g (force)/denier.
Example 7 and Comparative Example E
[0083] The procedure of Example 5 was repeated using DAP (163.65 g,
1.5 mole). The same procedure and proportionately same amounts of
20% oleum (1.35 kg) and 98% nitric acid (202.5 g, 3.15 mole, 5%
excess) were used.
[0084] After the nitration, the nitration product (1.716 kg) was
stirred for 35 minutes and then split into two halves. The first
half (Comparative Example E, 850 g) of the nitration product was
quenched immediately at 0.+-.2.degree. C. into 2.5 kg of 20%
H.sub.2SO.sub.4 solution. To this solution was then added 375 g of
deionized water to complete the DADNP product precipitation. The
product was then filtered and washed three times using water (500
g), 5% NH.sub.3 aqueous solution (500 g) and then water (500 g).
The crude DADNP (136 g, 92% yield) contained 0.6% HADNP and 2.5%
DANPS by HPLC. The second half of the nitration product (Example 7,
858 g) was stirred at 5-10.degree. C. for an additional 2 h. The
same procedure, as for the first half of the nitration product, was
used to obtain crude DADNP (140 g, 93% yield) containing 0.5% HADNP
and 0.3% DANPS by HPLC. The crude DADNP (135 g) from the second
half of the nitration product (Example 7 with 2.5 h of stirring)
was purified by dissolving it in a 3-L round-bottom flask using 1.2
L of hot DMF (140.degree. C.) and then re-precipitating it by
cooling the solution to obtain purified DADNP (130 g, 96% yield)
with 0.2% HADNP, no DANPS, and 99.7% DADNP. A portion of the crude
DADNP (50 g, 0.25 mole), from the first half (Comparative Example
E) of the nitration product described above (35-min. stirring), was
hydrogenated and the resulting aqueous TAP solution was first color
treated with DARCO G60 (5 g) and then coupled with K.sub.2-DHTA (63
g, 0.23 mole) as described in Example 1 to obtain pale yellow
TAP/K.sub.2-DHTA complex (76 g, 93% yield). A portion of this
TAP/K.sub.2-DHTA complex was polymerized as described in Example 1
to obtain a polymer with a low IV of 17 dL/g.
[0085] A portion of this Example 7 DMF-purified DADNP (50 g, 0.25
mole) was hydrogenated and the resulting aqueous TAP solution was
first decolorized with DARCO G60 (5 g) and then coupled with
K.sub.2-DHTA (63 g, 0.23 mole) as described in Example 1 to obtain
pale yellow TAP/K.sub.2-DHTA complex (78 g, 96% yield). A portion
of this TAP/K.sub.2-DHTA complex (25 g) was polymerized as
described in Example 1 to obtain an excellent M5 Polymer with an IV
of 33 dL/g. In strength tests, polymer samples with IV of 33 dL/g
resulted in high quality fiber, exceeding a breaking strength of 42
g (force)/denier.
[0086] Table 2 summarizes the data from Examples 1 to 7 and
Comparative Examples A to E.
TABLE-US-00002 TABLE 2 M5 Polymer IV Ex. # Method DANPS (dL/g)*
Tenacity** A Prior art nitration of DAPH 0.8% 22 (a) B Prior art
nitration of DAP 0.5% 23 (a) 1 Nitration of DAPH by the ND 26 32
process of the present invention 2 Renitration of poor quality ND
29 (a) DADNP prepared according to the process of Comparative
Example A, contaminated with 1.1% DANPS 3 Renitration of DADNP ND
31 (a) contaminated with 1% DANPS 4 Renitration of DADNP ND 31 (a)
contaminated with 4% DANPS C Short (0.25 h) nitration mix 10.3 Not
polymerized time for DAPH 5 Long (2.75 h) nitration mix ND Not
polymerized time for DAPH D Short (0.5 h) nitration mix 5.1 16 (a)
time for DAP 6 Long (2.5 h) nitration mix ND 32 (a) time for DAP E
Short (0.5 h) nitration mix 2.5 17 -- time for DAP 7 Long (2.5 h)
nitration mix ND 33 42 time for DAP *Acceptable quality M5 Polymer
has an IV of at least 25 dL/g. **Tenacity in g (force)/denier. (a)
not measured. ND not detectable (detection limit for DANPS by HPLC
is about 0.05%)
[0087] The data in Table 2 demonstrates the following. Comparative
Examples A and B showed that the nitration method of the prior art
forms sufficient DANPS in the DADNP to adversely affect the quality
of M5 Polymer prepared therefrom in terms of low IV. Example 1
showed the longer nitration process of the present invention
provides DADNP with much lower DANPS content and, subsequently,
high quality M5 Polymer. Examples 2, 3, and 4 showed that DADNP
containing harmful levels of DANPS can be renitrated to reduce the
DANPS content and yield high quality M5 Polymer. Duplicating the
nitration step, however, is not preferred. The short nitration
times used in Comparative Examples C, D and E were compared with
the longer nitration times of the present invention used in
Examples 5, 6 and 7. The longer nitration times correlated with
decreased DANPS contamination and higher IV values in the resulting
M5 Polymer.
Example 8
[0088] Example 8 demonstrated the preparation of DANPS from DAPH.
To a 1-L round-bottomed flask, equipped with a mechanical stirrer,
a moisture trap, a thermocouple, and a dry-ice/acetone bath for
cooling, was added 20% oleum (fuming sulfuric acid containing 20%
dissolved SO.sub.3, 450 g). The acid in the flask was cooled to
0.degree. C. 2,6-diaminopyridine hemi-sulfate (DAPH, 79.1 g, 0.5
mole), prepared in-house using 2,6-diaminopyridine (DAP) was added
in portions over 30 minutes while maintaining the temperature at
0-10.degree. C. The reaction mass was stirred at 15.degree. C.
until the solids dissolved to give a dark brown homogeneous
solution. The solution was then cooled to 0.degree. C. and 98%
nitric acid (33 g, 0.51 mole, 2% excess), was added drop-wise over
45 minutes while maintaining the temperature below 10.degree. C.
The sample was stirred for an additional 2 h and was quenched in
dilute sulfuric acid solution as described below.
[0089] To a 3-L round-bottomed flask equipped with a mechanical
stirrer, an overhead condenser, a thermocouple, and a
dry-ice/acetone bath for cooling, was added 20% sulfuric acid (1.7
kg) solution. This acid solution was cooled to 0.degree. C. and the
nitration reaction mass from the 3-L round-bottom flask from above
was added drop-wise over 1.5 h through a liquid-addition funnel
while maintaining the temperature in the 3-L flask below 2.degree.
C. Bright yellow crystals of product precipitated in the 3-L flask.
After the completion of this addition, de-ionized water was added
(250 mL), the mixture was brought to the room temperature, and was
stirred at room temperature for 1 h. The bright yellow slurry was
filtered in a fritted-glass filter and the wet cake was washed
three times at room temperature, first with water (300 g), the
second time with 5% aqueous NH.sub.3 solution (300 g) and the third
time with water again (300 g). Each wash involved making slurry of
the wet cake, stirring for 15 min. and then filtering. The wet cake
in the filter was partially dried by nitrogen blow and vacuum
suction and then dried to a constant weight in a vacuum oven to
obtain yellow solids of product (112 g, 96% yield, based on the
sample being DANPS, MW=234).
[0090] An LC/MS analysis conducted on this sample showed the
presence of two peaks, a minor DADNP peak having a molecular weight
of 199 and a major peak having a molecular weight of 234. The
isotopic distribution of the parent ion suggested the presence of
sulfur in this impurity. Based on this LC/MS analysis, the most
logical explanation of the 234 molecular ion peak would be
2,6-diamino-3-nitropyridine-5-sulfonic acid (DANPS). Subsequently,
two-dimensional .sup.13C NMR confirmed that this peak was indeed
DANPS. A subsequent HPLC analysis showed that the sample contained
3% DADNP, no HADNP, and 97% DANPS.
[0091] No attempt was made to hydrogenate or polymerize this sample
since samples containing only a few percent DANPS resulted in
severe catalyst poisoning and an unsuccessful TAP formation.
Example 9
[0092] In Example 9 DANPS was prepared from DAP. The procedure
described in Example 8 was employed using the same equipment,
procedure, and chemicals except for replacing DAPH (79.1 g, 0.5
mole) with DAP (54.6 g, 0.5 mole). Also, the wash size was
increased to 500 g from 300 g in each of the three washes of the
wet cake.
[0093] After the washes, the wet cake in the filter was partially
dried by nitrogen blow and vacuum suction and then dried to a
constant weight in a vacuum oven to obtain yellow solids of product
(91 g, 86% yield, based on the sample being DANPS, MW=234). A HPLC
analysis showed that the sample contained 3% DADNP, no HADNP, and
97% DANPS. No attempt was made to hydrogenate or polymerize this
sample.
* * * * *