Process for the preparation of nitrotoluenes

Details Process for the preparation of nitrotoluenes Process for the preparation of nitrotoluenes

2002-03-20

2003-09-16

Shippen, Michael L. (Department: 1621)

Organic compounds -- part of the class 532-570 series

Organic compounds

Oxygen containing

Reexamination Certificate

active

06620981

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a process for the preparation of nitrotoluenes. More particularly, the present invention relates to a process for the preparation of nitrotoluenes with high para -selectivity from toluene using zeolite beta with different binders as a catalyst
BACKGROUND OF THE INVENTION
Nitration process is used for the production of many large-volume chemicals such as nitrotoluenes, nitrochlorobenzenes and other nitroarenes which are vital intermediates for dyes, pharmaceuticals, perfumes and pesticides. Nitration of arenes is performed classically with a mixture of nitric acid and sulfuric acids. Major disadvantages in this method are formation of by-products of polynitration and environmental pollution during in disposal of spent acid.
Reference is made to U.S. Pat. No. 4,418,230 wherein a method for nitration of toluene with HNO
3
and H
2
SO
4
at 0 to 52° C. is described (o:m:p 55:2.3:38.9). The drawbacks are the use of sulfuric acid and also the formation of more of o-isomer.
Reference is made to another U.S. Pat. No. 1,12,006 wherein a process for the nitration of toluene with HNO
3
and 10% H
2
SO
4
impregnated Al
2
O
3
and 1% Mo at 135-145° C./20 torr is described (o:m:p 34.0:3.5:62.5). The drawbacks of this disclosure are the use of sulfuric acid in the preparation of the catalyst and the deactivation of the catalyst on each cycle.
Although it is known that benzene and its homologues can be nitrated with HNO
3
alone without using sulfuric acid, little or no progress has been made in this direction on a commercial scale. The disadvantage of this method is low productivity and the use of large excess of nitric acid (molar ratio of nitric acid to benzene 2:1to 4:1) which increases the possibility of formation of polynitro compounds and affects the economics of the project. Recently attention has been focussed on the development of environmentally friendly solid acid catalysts such as Nafion especially in Friedel-Crafts reactions to replace environmentally hazardous sulfuric acid in nitration reactions.
Reference is made to U.S. Pat. No. 4,234, 470 wherein a method for nitration of benzene, chlorobenzene and toluene with HNO
3
in presence of Nafion catalyst is described. The drawbacks are the use of expensive Nafion resin whose activity decreases on each cycle and offers nearly identical isomer selectivity (o:m:p 56:4:40) as that of mixed acid.
Reference is also made to
Chem. Commun
, 469, 1996 wherein benzene, alkylbenzenes and halobenzenes are nitrated in quantitiative yields and with high para-selectivity in a solvent free process by using stiochiometric quantity of nitric acid and acetic anhydride at 0 to 20° C. in the presence of zeolite. beta, a recyclable catalyst.
Reference is made to
Chem. Commun
. 613, 1997 wherein aromatics are nitrated in good yields in dichloromethane solvent by using stiochiometric quantities of 69% nitric acid at reflux temperature of the solvent in the presence of lanthanide (111) triflates as recyclable catalysts. The drawbacks are the slowness of the reaction, more time being required for completion of the reaction, the use of expensive catalysts and low productivity of the process. The isomeric ratio is also identical with that of mixed acids.
Reference is made to U.S. Pat. No. 6,034,287 and publication
Chem. Commun
. 25, 2000, wherein process for the production of nitroarenes with high para-selectivity from monosubstituted aromatic hydrocarbons using aluminosilicates as catalysts is described. The drawbacks are the catalyst is in powder form and can not be used in the fixed bed.
OBJECTS OF THE INVENTION
It is an object of the present invention to provide a simple and an ecofriendly process for production of substituted nitroarenes.
It is another object of the invention to provide a simple method for obtaining nitrotoluenes with high para-selectivity.
It is still another object of the invention to provide a process for obtaining nitrotoluenes using a zeolite beta catalyst with binders to impart robustness to the zeolite beta catalyst to withstand vagaries of the reacting substrate and nitric acid on a catalytic fixed bed.
It is another object of the invention to provide a process for the preparation of nitrotoluenes wherein the use of sulfuric acid, a hazardous chemical and expensive acetic anhydride which forms an explosive mixture in conjunction with nitric acid is dispensed with.
It is still another object of the invention to provide a process for the preparation of nitrotoluenes wherein the problem of effluent disposal is obviated.
SUMMARY OF THE INVENTION
The above and other objects are achieved by the present invention wherein nitrotoluenes are produced with high para-selectivity using a zeolite beta catalyst in an inorganic/organic matrix in the absence of acetic anhydride and sulfuric acid.
Accordingly, the present invention provides a process for the preparation of nitrotoluenes with high para selectivity from toluene which comprises nitrating toluene with nitric acid in the presence of a catalyst system comprising Zeolite beta and an inorganic/organic matrix, and recovering the desired product.
In one embodiment of the invention the zeolite beta catalyst has an Si/Al ratio in the range of 15/1 to 22/1.
In another embodiment of the invention, the catalyst system is used in the form of powder, pellets, extrudates or spherules.
In another embodiment of the invention, the nitration of toluene is carried out in the absence of sulfuric acid.
In another embodiment of the invention, the nitration of toluene is carried out in the absence of acetic anhydride.
In still another embodiment of the invention, the inorganic matrix is selected from the group consisting of montmorillonite, silamanite and kaolin clay.
In a further embodiment of the invention, the inorganic/organic matrix comprises one or more of graphite, gelatin, acetic acid, polyvinyl alcohol (5-10%), sodium silicate, TEOSI, alumina, stearic acid and acrylate.
In another embodiment of the invention, sodium silicate is used as a binder along with clay in the inorganic matrix.
In another embodiment of the invention, the binder system comprises of graphite and acetic acid.
In another embodiment of the invention, the zeolite beta and binder catalyst system is used in the form of pellets after mixing with the binders.
In another embodiment of the invention, the amount of the inorganic matrix in the catalyst system is in the range of 1.5-20% of the weight of the catalyst system.
In a further embodiment of the invention, the catalyst system pellets measure 6-8 mm diameter and 4-6 mm long.
In a further embodiment of the invention, the pellet bulk density is in the range of 0.25-0.55 gm/cc.
In a further embodiment of the invention, the pellet crushing strength ranges between 0.5-5 kg.
In another embodiment of the invention, the temperature of the nitration reaction is in the range of 100-200° C. preferably 100 -160° C.
In a further embodiment of the invention, the selectivity to para-nitrotoluene is >60%.
In another embodiment of the invention, the molar ratio of nitric acid and aromatic is in the range from 0.25 to 2.5, desirably 0.5 to 2.0.
In another embodiment of the invention, nitration is carried out in continuous mode.
In another embodiment of the invention, the nitration is carried out in batch mode. In a further embodiment of the invention, the nitration is carried out over a fixed catalyst bed.
In another embodiment of the invention, the selectivity to para-nitrotoluene ranges from 59-68 in batch mode and 55-61 on a catalytic fixed bed depending on the binder used.
In another embodiment of the invention, the zeolite beta with binder acts as a bifunctional catalyst generating electrophile, nitronium ion as well as instant adsorbent for water formed during the reaction to facilitate electrophilic substitution on toluene.
DETAILED DESCRIPTION OF THE INVENTION
The present invention provides a process for the production of nitrotoluenes with high para-selectivity from toluene by beta zeolite with a Si/Al ratio in the range of 15

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