FORM 2
THE PATENTS ACT, 1970 (39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
[See section 10, Rule 13]
A PROCESS FOR PREPARATION OF PARA-ALKOXYANILINE;
DEEPAK NITRITE LTD., A COMPANY INCORPORATED UNDER THE COMPANIES ACT, 1956, WHOSE ADDRESS IS 9/10, KUNJ SOCIETY, ALKAPURI, VADODARA - 390007, INDIA.
THE FOLLOWING SPECIFICATION
PARTICULARLY DESCRIBES THE INVENTION AND THE MANNER IN WHICH IT IS TO BE PERFORMED.

FIELD OF THE INVENTION:
The present invention relates to a process for the preparation of para-alkoxyaniline, more particularly to a process for preparing substituted para-alkoxyaniline from nitro compounds.
BACKGROUND OF THE INVENTION:
4-Alkoxyanilines are important intermediate products for the preparation of dyes and medicines. In particular, 2-methyl-4-methoxyaniline is useful as an intermediate of fluoran series black dyes.
Traditionally, the 4-alkoxyanilines have been produced from nitrobenzenes through a number of steps and the total yield of the products and the economy of the processes practiced have proved to be very unsatisfactory.
Generally, the 4-alkoxyanilines have been produced by reducing nitrobenzenes with hydrogen in presence of hydrogenation catalyst in aliphatic alcohol and sulfuric acid. However, commercial grade acid degrades the catalyst and hence generally not use for the reaction.
JP05331115 discloses the process for preparation of 2-methyl-4-methoxyaniline by catalytically reducing the nitro compound in the presence of a noble metal catalyst with lower alcohol and sulfuric acid. The deterioration of catalytic activity is suppressed by washing a recovered catalyst with hot water and reusing the washed catalyst for the preparation of 2-methyl-4-methoxyaniline. This Japanese patent provides a post treatment to a catalyst which will not remove all the impurities on the metal surface of the catalyst and hence life of the catalyst decreases with each recycles.

SUMMARY OF THE INVENTION
It is another object of the present invention to provide a cost efficient process for producing para-alkoxyanilines or substituted para-alkoxyanilines.
The present invention provides a process for the preparation of para-alkoxyaniline or substituted para-alkoxyanilines comprising pretreatment of sulfuric acid. Accordingly, the process comprises the steps of pre-treating sulfuric acid with air and reducing nitrobenzene with hydrogen in presence of a hydrogenation catalyst in aliphatic alcohol in the pretreated sulfuric acid wherein pre-treating of the sulfuric acid reduces poisoning of the catalyst and enables recycling of the catalyst.
According to the present invention, pre-treating step includes passing air through the sulfuric acid and then flushing or bubbling of nitrogen compound through the sulfuric acid.
According to one embodiment of the present invention, the sulfuric acid is preferably pretreated with air.
According to another embodiment of the present invention, the impurities in sulfuric acid are oxidized with air at room temperature.
DETAILED DESCRIPTION OF THE INVENTION
According to the present invention, the process for preparing para-alkoxyaniline or substituted para-alkoxyaniline comprises the steps of reducing a nitro compound with a pre-treated sulfuric acid in the presence of a noble metal catalyst in aliphatic alcohol.

According to the present invention, the sulfuric acid is pretreated with air. The pre-treating step includes passing air through the sulfuric acid and then flushing or bubbling of nitrogen gas through the sulfuric acid. The pretreatment of the acid with air oxidizes all the catalyst poisons present in the acid. Further, flushing or bubbling with inert gas or nitrogen removes the gases which may act as poisons to catalyst after the treatment with air. This treatment safeguard the catalyst poisoning and allows for the recycling or reuse of the catalyst again in the reaction even any grade of the sulfuric acid including commercial grade sulfuric acid is used in the process for preparing para-alkoxyaniline or substituted para-alkoxyaniline.
The process uses the aliphatic alcohol preferably selected from methanol, ethanol, and isopropyl alcohol.
According to the present invention, the sulfuric acid is pretreated with air for 0.5 to 5 hours depending on the grade of the sulfuric acid for example good quality sulfuric acid such as laboratory grade, analytical, battery grade requires less time about 1 hr and the commercial or technical grade sulfuric acid requires about 3 hrs.
According to the present invention, the catalyst used is a noble metal catalyst and is preferably selected from platinum on activated carbon, palladium on activation carbon or a combination of both. The nitro compound used is nitrobenzene.
In another embodiment of the invention, the nitro compound is selected from a group including but not limited to Nitrobenzene, 2-Nitrotoluene, 2,3-

dimethyl-1-nitro benzene, 1-chloro-2-nitrobenzene or substituted thereof to produce substituted para-alkoxyaniline.
According to the present invention the reaction is carried out a temperature in the range of 20 to 80 deg C, preferably at 40 to 60 deg C and at a pressure of 0.3 to 2.0 kg/cm2, preferably 0.5 to 1 kg/cm2. The reaction takes place under vigorous stirring for 10 to 18 hrs, preferably 11 to 14 hours.
The pretreatment of sulfuric acid with air prevents the deactivation of platinum on carbon catalyst used in the process. This treatment benefits in the catalyst recycling, which can be used in the reaction for more than twenty times. The recycling of the catalyst does not decrease the yield of the product as no phase transfer reagent or a catalyst activity moderator is used thereby this recycling of the catalyst has a direct impact on the economic viability of the process. Further, this method uses air and allows use of any grade of the sulfuric acid hence it is very cost effective. It is also safer and easy to perform.
The present invention can be understood better with the help of the following examples. While the present invention has been described herein with respect to the various exemplary embodiments, it will be apparent to one of the ordinary skill in the art that many modifications, improvements and sub combinations of the various embodiments, adaptations and variations can be made to the invention without departing from the spirit and the scope thereof.

Example: 1
To a round bottom flask, 700g 98% commercial grade sulfuric acid is charged. This acid was stirred at 600 rpm and air was bubbled at the bottom of mass through dip pipe. The flow rate of air was kept at 20liter / hour and at a temperature of 25 to 30deg C. This air bubbling / treatment was continued for 1hour. This air pre-treated acid was subjected to flushing or bubbling of nitrogen gas. This operation of flushing or bubbling with inert gas or nitrogen removes the gases from sulfuric acid. These gases if remain in the acid may act as poisons to catalyst.
700g (5.08mole) 2-Nitrotoluene, 2227g methanol, 700g 98% sulfuric acid (treated with air) and 1.2g 3% platinum on carbon (dry) catalyst was added to a pressure reactor. The contents were flushed with nitrogen gas for 2 times and heated to 40°C. Hydrogen gas was then introduced to the reactor to attain a total pressure of 0.3 to 1.0 kg/cm2. The mass was mixed using intensive stirring at 1000 rpm. The total pressure in the reactor was maintained constant by introducing hydrogen gas as it gets consumed in the reaction. The temperature was maintained constant by circulating cold water through the internal coils in the reactor. After 12hrs, the reaction mass analysis by gas chromatography (GC) shows following result
2-methyl-4-methoxyaniline 72%, ortho-toluidine 26% and 4-amino-meta cresol 2%.

The catalyst was recovered by filtration, washed and was recycled. The same process was carried out more 20 times and every time catalyst recovered used for the next process.
Example: 2
700g (5.08mole) 2-Nitrotoluene, 2227g methanol, 700g 98% sulphuric acid (treated with air as given in example 1) and catalyst recovered from example 1 with 5% top up fresh catalyst was added to a pressure reactor. The contents were flushed with nitrogen gas for 2 times and heated to 40°C. Reaction was earned out using the procedure as presented in Example 1. After 12hrs, the reaction mass analysis by GC shows following result
2-methyl-4-methoxyaniline 72%, ortho-toluidine 26% and 4-amino-meta cresol 2%
The catalyst was recovered by filtration, washed and was recycled more than 20 times.
Example: 3
383.9g (2.54 mole) of 2,3-dimethyl-1-nitro benzene, 1105g methanol, 317.5g 98% sulphuric acid (treated with air as in example 1) and 0.58 g 3% Platinum on Carbon (dry) catalyst was heated to 40°C in a reactor. Reaction was carried out using the procedure as presented in Example 1. After 10 hrs, the reaction mass analysis by GC shows following result 2,3-dimethyl-4-methoxyaniline 79.7% and 2,3-dimethylaniline 17.8%. The catalyst was recovered by filtration, washed and was recycled more than 20 times.

Example: 4
625.4 g (5.08mole) of nitrobenzene, 2211 g methanol, 635g 98% sulphuric acid (treated with air as in example 1), and 0.94 g 3% Platinum on Carbon (dry) catalyst was heated to 40°C in a reactor. Reaction was carried out using the procedure as presented in Example 1. After 12 hrs, the reaction mass analysis by GC shows following result p-anisidine 27.5%, o-anisidine 6.3 and aniline 63%. The catalyst was recovered by filtration, washed and was recycled many times.
Example: 5
400g (2.54mo!e) of 1-chloro-2-nitrobenzene, 1105 g methanol, 317.5g 98% sulphuric acid (treated with air as in example 1) and 0.6 g 3% Platinum on Carbon (dry) catalyst was heated to 40°C in a reactor. Reaction was carried out using the procedure as presented in Example 1. After 16 hrs, the reaction mass analysis by GC shows following result 2-chloro-4-methoxyaniline 49.7% and o-chloroaniline 43.4%. The catalyst was recovered by filtration, washed and was recycled many times.
Example: 6
700g (5.08mole) 2-Nitrotoluene, 2227g methanol, 700g sulphuric acid used was not treated with air, 1.2g 3% Platinum on Carbon (dry) catalyst was added to an autoclave. The reaction mixture was flushed and then heated to 40°C in a reactor. Reaction was carried out using the procedure as presented in Example 1. After 16 hrs, the reaction mass analysis by GC

shows large amount of unreacted 2-nitrotoluene. The recovered catalyst gets deactivated and recycle of this catalyst in the next batches was not possible.

WE CLAIM
1. A process for preparing para-alkoxyaniline or substituted para-
alkoxyaniline, the process comprising step of:
pre-treating sulfuric acid with air; and
reducing nitrobenzene with hydrogen in presence of a hydrogenation catalyst in aliphatic alcohol in the pretreated sulfuric acid;
wherein pre-treating of the sulfuric acid reduces poisoning of the catalyst and enables recycling of the catalyst.
2. The process as claimed in claim 1 wherein pre-treating step includes passing air through the sulfuric acid and then flushing or bubbling of nitrogen compound through the sulfuric acid.
3. The process as claimed in one of the preceding claims wherein the sulfuric acid is pretreated with air at room temperature.
4. The process as claimed in any one of the claims 1 or 3, wherein the sulfuric acid is pretreated with air for 0.5 to 5 hours depending on the grade of the sulfuric acid.
5. The process as claimed in claim 1, wherein the nitro compound is selected from a group including but not limited to Nitrobenzene, 2-Nitrotoluene, 2,3-dimethyl-1-nitro benzene, 1-chloro-2-nitrobenzene or substituted thereof to produce substituted para-alkoxyaniline.
6. The process as claimed in claim 1, wherein the catalyst is selected from the group consisting of platinum on activated carbon, palladium on

activated carbon, and a mixture of platinum and palladium on activated carbon.
7. The process as claimed in claim 1, wherein the process is carried out at a temperature of 20 to 80 deg C,
8. The process as claimed in claim 1, wherein the process is carried out at a pressure upto 2 kg/cm2.
9. The process as claimed in claim 1, wherein the process is camied out under vigorous stirring for 10 to 18 hrs.