Organic compounds -- part of the class 532-570 series – Organic compounds – Oxygen containing
Reexamination Certificate
2000-04-26
2001-06-05
Barts, Samuel (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Oxygen containing
C568S939000, C568S940000, C568S929000, C568S706000, C564S441000
Reexamination Certificate
active
06242657
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a process for preparing aromatic nitro compounds by reacting aromatic compounds with nitrating acids comprising HNO
3
and, if appropriate, H
2
SO
4
and/or H
3
PO
4
and/or H
2
O, the said process being carried out in the presence of surface-active substances.
Nitro compounds of the most varied types are important intermediates for preparing plastics, dyes, auxiliaries, pharmaceuticals and other chemicals.
There is abundant technical and scientific literature, including patent literature, on the preparation of nitro aromatic compounds by various processes involving isothermic or adiabatic conditions, batchwise or continuous operation and various reactors. Products required in small amounts are preferably prepared in batchwise operation, whereas mass products, such as nitrobenzene, nitrotoluene and nitrochlorobenzene, are preferably prepared by continuous operation. Suitable reactors for batchwise operation are, in general, stirred tanks, whereas, for example, tubular reactors are preferred for continuous operation. In the case of products produced in great quantities, there has been no lack of attempts to recover the considerable heat of reaction at a high temperature level and to utilize it for other purposes, for example for concentrating the waste acid. More recent and promising adiabatic operations have been described, inter alia, in EP-A 668 263 and EP-A 675 104. Whereas the processes of the EP patent applications just mentioned already have a high level of successful resource utilization (high material yields and high energy recovery), it is still important, especially for mass products, to attempt to increase resource utilization even more.
In the context of the preparation of 1-nitroanthraquinone, JP 06/293709 mentions the use of di-(2-ethylhexyl)-sulphosuccinic acid Na salt. This process is characterized by a purely organic reaction medium (1,2-dichlorethane) and the use of NO
2
or N
2
O
4
in combination with SO
3
as nitrating agent. The di-(2-ethylhexyl)-sulphosuccinic acid Na salt is employed in an amount of 0.17 g, based on the nitrating agent, consisting of 4.1 g of SO
3
and 4 g of NO
2
. The 1- and 2-nitroanthraquinone yield obtained does not exceed that of other examples without the use of the di-(2-ethylhexyl)-sulphosuccinic acid Na salt mentioned. In Ind. Eng. Chem. Res. 34 (1995), 4305, it is noted in the context of an investigation of the role of surface reactions in heterogenic nitrations of aromatic compounds that addition of amphiphilic impurities to the organic phase slows down the reaction; this effect was confirmed using cetyl-trimethylammonium bromide as deactivator (p. 4305, left-hand column, below FIG.
15
). In this publication, the reaction conditions involve a mixed acid of 41.41% by weight of H
2
SO
4
, 1% by weight of HNO
3
and the remainder to 100% by weight of water. When the reaction is realized on an industrial scale, this phenomenon of reaction slow-down leads to a drastic reduction in the space-time yield.
Surprisingly, it has now been found that, in contrast to the observations in Ind. Eng. Chem. Res., a considerable increase in reaction rate and yield is obtained under the conditions according to the invention described further below when surface-active substances are employed. These surprising results have the following advantages: for mixing the reaction mixture, the expenses required for apparatus are lower, thus reducing the investment costs of a nitration process. The cheap surface-active substances which are prepared as detergents in mass production can be used, in particular. The surface-active substances are employed in the ppm range. It is possible to select surface-active substances having a wide range of properties, and it is likewise possible to select a wide range of other reaction conditions.
DESCRIPTION OF THE INVENTION
The invention relates to a process for preparing aromatic nitro compounds by reacting nitratable aromatic compounds with nitrating acids comprising HNO
3
and, if appropriate, H
2
SO
4
and/or H
3
PO
4
and/or H
2
O at normal to elevated temperature with constant mixing of the aromatic compounds and the nitrating acids, characterized in that the reaction mixture comprises one or more surface-active substances from the group of the anionic, cationic, zwitterionic or nonionic surface-active substances in an amount of from 0.5 to 20,000 ppm.
Surface-active substances which are suitable for the process according to the invention can be from the group of the anionic, cationic, zwitterionic or nonionic surface-active substances. Anionic surface-active substances are, for example, lignosulphonic acids, formaldehyde condensates with aromatically attached sulphonic acid groups, protein condensates, alkanesulphonates, alkylarylsulphonates and alkyl sulphates. Cationic surface-active substances are, for example, the quaternary ammonium salts. Zwitterionic surface-active substances are betaines and sulphobetaines. Nonionic surface-active substances are polyethers which are formed by alkoxylation of compounds having a mobile H atom with ethylene oxide, propylene oxide or butylene oxide, or a mixture of two or more of these. Compounds having a mobile H atom of this type are, for example, alcohols, alkylphenols, phenols, alkylamines, carboxylic acids and carboxamides. Such surfactants, their structure and their preparation are known to the person skilled in the art working in this field.
From among the surface-active substances mentioned, those from the group of the anionic or cationic surface-active substances are preferably suitable for use in the process according to the invention, particularly preferably those from the group of the anionic surface-active substances. Very particularly preferably, these are alkanesulphonates or alkyl sulphates having 10 to 22 C atoms.
It is possible to use a mixture of one or more surface-active substances. The amount of surface-active substances in the reaction mixture at the reactor inlet, for example, is from 0.5 to 20,000 ppm, preferably from 1 to 2000 ppm, particularly preferably front 1 to 200 ppm, very particularly preferably from 5 to 150 ppm.
Surface-active substances from the groups mentioned are suitable for the process according to the invention independently of the degree of their stability. The following configurations are, for example, feasible here:
The surface-active substance or a mixture of two or more surface-active substances is stable and remains in the HNO
3
-depleted waste acid and becomes reuseable according to the invention during reconcentration and recycling of the waste acid.
The surface-active substance or a mixture of two or more surface-active substances is stable under the reaction conditions according to the invention, but migrates into the organic phase of the aromatic nitro compound and is, during various washing and other treatment processes, removed from the process according to the invention and accordingly has to be replaced, for example at the reactor inlet.
The surface-active substance or a mixture of two or more surface-active substances is not entirely stable under the process conditions according to the invention; it does, however, act in the sense according to the invention during the nitration reaction, but has to be replaced to the extent of its degradation/its destruction.
The surface-active substances can be introduced into the reaction mixture in various ways: Thus, it is possible to feed the surface-active substances into the feed stream of the organic compounds to be nitrated and/or into the feed stream of the nitrating acid. It is also possible to add the surface-active substances to the reaction mixture as a separate feed stream, for example at the reactor inlet.
The nitration process according to the invention which is characterized by the use of surface-active substances can otherwise be applied to all customary processes operating with nitrating acids of HNO
3
and optionally H
2
SO
4
and/or H
3
PO
4
and/or H
2
O. Thus, it is possible, for example, to operate
Dühr Johannes
Kaczorowski Manfred
Konig Bernd-Michael
Raatz Hans-Joachim
Barts Samuel
Bayer Aktiengesellschaft
Eyl Diderico van
Gil Joseph C.
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