Organic compounds -- part of the class 532-570 series – Organic compounds – Oxygen containing
Reexamination Certificate
2000-11-29
2002-07-16
Parsa, Jafar (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Oxygen containing
C568S928000, C568S930000
Reexamination Certificate
active
06420616
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to the preparation of a dinitronaphthalene isomer mixture having an increased proportion of 1,5-dinitronaphthalene by direct nitration of naphthalene. 1,5-Dinitronaphthalene is a key compound for the preparation of 1,5-diaminonaphthalene. This is, inter alia, the starting compound for the preparation of 1,5-diisocyanato-naphthalene (trade name Desmodur 15®). 1,5-Diisocyanato-naphthalene is used as an isocyanate component in polyurethane production.
The preparation of nitrated aromatics has been known for a long time (G. A. Olah et al.,
Nitration: Methods and Mechanism
, VCH, New York, 1989). For decades, nitroaromatics have been prepared industrially by nitration using a mixture of sulfuric and nitric acids (known as mixed or nitration acid).
The nitration of naphthalene in mixed acid at elevated temperatures of from 80 to 100° C. gives a mixture of various dinitronaphthalenes. This mixture comprises mainly 1,5- and 1,8-dinitronaphthalene in a ratio of about 1:2. In addition, the mixture contains about 5% of other isomers, for example 1,6- and 1,7-dinitronaphthalene. The unfavorable selectivity of the reaction thus leads to a high and undesirable proportion of 1,8-dinitronaphthalene being preferentially formed in the preparation of 1,5-dinitronaphthalene.
German Offenlegungsschrift 11 50 965 describes the preparation of 1,5-dinitronaphthalene starting from 1-nitronaphthalene. An increase in the selectivity in favor of the desired of 1,5 isomer is achieved by rapid and intensive mixing of the 1-nitronaphthalene dissolved in sulfuric acid with nitration acid. Disadvantages of this process are the considerable amount of sulfuric acid and its complicated and costly work-up. In addition, this process can form considerable amounts of trinitrated products that not only significantly reduce the yield of 1,5-dinitronaphthalene but also are critical in terms of safety, particularly under the adiabatic reaction conditions described in this prior art.
WO 99/12887 describes a process for preparing a dinitronaphthalene isomer mixture having an increased proportion of 1,5-dinitronaphthalene, likewise starting from 1-nitronaphthalene. Here, the reaction of the nitronaphthalene with nitric acid takes place in the presence of a solid perfluorinated strong acid ion exchanger. This process generally has the disadvantage that the resulting dinitronaphthalene isomer mixture must be separated from the catalyst by extraction with dioxane at 900° C. The dioxane subsequently must be removed by means of an additional distillation step. The best selectivities in respect of the desired 1,5 isomer are obtained when sulfolane or nitromethane is added as solvent. However, the conversion in the reaction is then only 31-44% and the reaction forms considerable amounts of other dinitro isomers and trinitrated naphthalenes, which are more difficult to separate from the isomer mixture.
German Offenlegungsschrift 24 53 529 describes the preparation of dinitronaphthalenes from naphthalene by nitration using nitric acid in organic solvents (for example, dichloroethane) and removal of the water of reaction by azeotropic distillation. This process gives dinitronaphthalene in high yields, but the isomer ratio is not influenced.
WO 94/19310 describes nitrations of nitroaromatics over aluminum silicates that are sometimes doped with heavy metals, known as claycops, as solid catalyst, giving high yields of dinitrated products with small amounts of trinitroaromatics. However, nitrations of naphthalene carried out by this process give isomer ratios similar to those in classic nitrations using mixed acid.
It is therefore an object of the invention to provide a process for preparing a dinitronaphthalene isomer mixture by nitration of naphthalene that gives a high conversion and a low proportion of by-products and at the same time forms a mixture of 1,5- and 1,8-dinitronaphthalene that contains an increased proportion of 1,5 isomer.
It has now surprisingly been found that the presence of ionic liquids in the nitration of naphthalene in an excess of nitric acid or a mixture of nitric acid and sulfuric acid and/or phosphoric acid makes it possible to shift the isomer ratio in favor of 1,5-dinitronaphthalene.
SUMMARY OF THE INVENTION
The invention accordingly provides a process for preparing a dinitronaphthalene isomer mixture having an increased proportion of 1,5-dinitronaphthalene comprising nitrating naphthalene with a molar excess of nitric acid in the presence of at least one ionic liquid.
DETAILED DESCRIPTION OF THE INVENTION
The dinitronaphthalene isomer mixtures prepared according to the invention contain, in addition to 1,8-dinitronaphthalene, a surprisingly high proportion of 1,5-dinitronaphthalene. The 1,5-dinitronaphthalene content is preferably above 30% by weight, based on the conversion, particularly preferably in the range from 35 to 40% by weight. The content of by-products, in particular 1,6- and 1,7-dinitronaphthalene and more highly nitrated products, is low.
In the process of the invention nitric acid is preferably used in a 1-to 22-fold molar excess, particularly preferably in a 2- to 20-fold molar excess, very particularly preferably in a 4- to 16-fold molar excess, based on the nitro groups to be introduced into naphthalene.
The concentration of the nitric acid used in the process of the invention is preferably from 50 to 100%, particularly preferably from 60 to 100%, very particularly preferably from 67 to 98%.
In a further embodiment of the process of the invention, the nitric acid can be used in admixture with sulfuric acid and/or phosphoric acid.
If sulfuric acid is used in the process of the invention, its concentration is preferably from 90 to 100%, particularly preferably from 96 to 100% and very particularly preferably from 98 to 100%. If phosphoric is used in the process of the invention, its concentration is preferably from 50 to 99%, particularly preferably from 65 to 99% and very particularly preferably from 85 to 99%.
If a mixture of nitric acid and sulfuric acid and/or phosphoric acid is used in the process of the invention, this mixture preferably contains from 1 to 20 molar parts of nitric acid and 1 molar part of sulfuric acid and/or phosphoric acid, particularly preferably from 1 to 10 molar parts of nitric acid and 1 molar part of sulfuric acid and/or phosphoric acid, very particularly preferably from 1 to 5 molar parts of nitric acid and 1 molar part of sulfuric acid and/or phosphoric acid.
The ionic liquids used in the process of the invention are liquid salts of the formula Q
+
A
−
that preferably form liquid salts at temperatures below 90° C., in particular at temperatures below 80° C. and particularly preferably at temperatures below 50° C.
In the formula Q
+
A
−
, Q
+
preferably represents a quaternary ammonium and/or phosphonium ion. Q
+
is particularly preferably a compound selected from the group consisting of
R
1
R
2
R
3
R
4
N
+
, R
1
R
2
R
3
R
4
P
+
, R
1
R
2
N
+
═CR
3
R
4
, and R
1
R
2
P
+
═CR
3
R
4
wherein R
1
to R
4
are, independently of one another, hydrogen (with the proviso that R
1
R
2
R
3
R
4
N
+
cannot be NH
4
+
), saturated or unsaturated C
1
-C
12
-alkyl, C
3
-C
8
-cycloalkyl, C
6
-C
10
-aryl, or C
7
-C
11
-aralkyl.
Q
+
is particularly preferably an ammonium and/or phosphonium ion derived from a nitrogen- and/or phosphorus-containing heterocycle containing 1, 2, or 3 nitrogen and/or phosphorus atoms and corresponding to the following formulas
wherein the ring contains from 4 to 10 atoms (preferably 5 or 6 atoms) and R
1
and R
2
are as defined above.
Furthermore, Q
+
preferably represents quaternary ammonium and/or phosphonium ions selected from the group consisting of
R
1
R
2
N
+
═CR
3
—R
5
—R
3
C═N
+
R
1
R
2
and R
1
R
2
P
+
═CR
3
—R
5
—R
3
C═P
+
R
1
R
2
wherein
R
1
, R
2
, and R
3
are identical or different and are as defined above, and
R
5
represents a C
1
-C
6
-alkylene or phen
Gürtler Christoph
Jautelat Manfred
Schelhaas Michael
Bayer Aktiengesellschaft
Gil Joseph C.
Henderson Richard E. L.
Parsa Jafar
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