Claims:1. A catalyst for preparation of N, N-dialkyl aromatic amines comprising ?-alumina treated with ammonia or aliphatic amine.

2. A process for preparing the catalyst as claimed in claim 1, comprising the steps of dipping ?-alumina in ammonia or aliphatic amine solution at 250-300C, filtering, and drying the catalyst.

3. The process as claimed in claim 2, wherein the catalyst is dried at 1500C.

4. The process as claimed in claim 2, wherein concentration of the ammonia or aliphatic amine solution is 0.2-20% (w/w) and preferably 1 - 10% (w/w).

5. The process as claimed in any one of preceding claims, wherein the carbon contents of the aliphatic amine is between C1 to C4.
, Description: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 N, N-DIALKYL AROMATIC AMINES AND A CATALYST THEREOF AND PREPARATION PROCESS OF THE CATALYST

DEEPAK NITRITE LIMITED, A COMPANY INCORPORATED UNDER COMPANIES ACT 1956, WHOSE ADDRESS IS CORPORATE OFFICE, DEEPAK COMPLEX, NATIONAL GAMES ROAD, YERWADA, PUNE – 411 006, MAHARASTRA, 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 preparation of N, N-dialkyl aromatic amines by the vapor-phase catalytic reaction of an aromatic amine with alcohol.
BACKGROUND OF THE INVENTION
Traditionally, to prepare N, N-dialkyl aromatic amines, alkylation of aromatic amines with alcohol or halide is conducted in a batch reactor. Either sulfuric acid or phosphoric acid is used as the catalyst in the liquid-phase reaction that took place at a temperature of about 2000C and under a pressure of from 30 to 50 kg/cm2. This traditional route suffers from the disadvantages of high capital cost, corrosion of the reactor and also needs a waste acid treatment. To avoid this vapor phase technology was invented.
U.S. 4801752 discloses a vapor phase process for the production of N-alkyl and N, N-dialkylaniline by alkylation of aniline with an alcohol, preferably methanol and ethanol, in the presence of a ZSM-5 catalyst. The reactants are contacted in the presence of the catalyst at a temperature of from about 3000C to 5000C, at a pressure of from about 1 to 3 atmospheres, and at a molar ratio of alcohol to aniline of from about 1 to 6. However, this reaction requires high temperature and pressure. Further, this invention uses a specially designed expensive catalyst.

SUMMARY OF THE INVENTION:
An object of the present invention is to provide a simple and inexpensive vapor phase catalytic process for preparation of N, N-dialkyl aromatic amines.
Accordingly, the present invention in the first embodiment provides a process for preparation of N, N-dialkyl aromatic amines comprising step of reacting aromatic amine with alcohol in vapor phase at an elevated temperature in presence of a catalyst ?-alumina treated with ammonia or aliphatic amine.
In the second embodiment, the present invention provides a catalyst for preparation of N, N-dialkyl aromatic amines comprising ?-alumina treated with ammonia or aliphatic amine.
In third embodiment, the present invention provides a process for preparing said catalyst comprising steps of dipping ?-alumina in ammonia or aliphatic amine solution at about 25-300C, filtering and then drying the catalyst.

DETAILED DESCRIPTION OF THE INVENTION
In accordance with this invention, there is provided a process for preparation of N, N-dialkyl aromatic amines from an aromatic amine which comprises contacting a reaction mixture of an aromatic amine and an alcohol in the vapor-phase at an elevated temperature in the presence of catalyst ?-alumina treated with ammonia or aliphatic amine. The catalysts of the present invention promote a high and selective conversion of aromatic amines to their N,N-dialkyl derivatives.
According to the present invention, the catalyst is prepared by dipping ?-alumina in ammonia or aliphatic amine solution at about 25-300C, filtering and then drying the catalyst preferably at about 1500C. The catalyst has life more than 400 hours.
According to the present invention, concentration of the ammonia or aliphatic amine solution is 0.2-20% (w/w) and preferably 1 - 10% (w/w) for preparation of the catalyst.
According to the present invention, the aliphatic amines contain carbon contents for preparation of catalyst between C1 to C4 for example methylamine, ethylamine, propyl amine and butyl amine.
The process of the present invention can be carried out in any type of reactor used for vapor-phase reaction in which the reactants and catalysts are brought into intimate contact for a sufficient length of time to accomplish the desired reaction. For example, a conventional fixed-bed tubular reactor, a fluidized bed reactor, or a moving bed reactor may be employed. It is generally preferred to employ a tubular reactor; for example, a glass or metal tube which is filled with a static bed of the catalyst. The reactor can be heated by any conventional means such as, for example, by surrounding the reactor with an electrical heater, a heated gas, or a liquid, which can be conveniently maintained at the reaction temperature.
The reaction products which are in the form of vapor from the reactor are collected, condensed and separated in any known manner such as, for example, by distillation. Since the reaction is preferably run at atmospheric pressure, no expensive pressure equipment is needed for the collection and separation of the reaction products. To achieve maximum yields it is desirable for any reactant which is passed through the reaction zone unchanged to be collected and recycled.
The pressure at which the process is operated is not narrowly critical and can range from sub-atmospheric pressure to super-atmospheric pressure in addition to normal atmospheric pressure. Since the reaction of this invention proceeds smoothly at atmospheric pressure thereby eliminating the need for overly expensive equipment which is required for operations for carrying out at other pressures. The process of this invention is preferably carried out at atmospheric pressure for economic reasons.
The mechanics of the process consist of contacting the reactants of the aromatic amine and alcohol with the selected catalyst of this invention in the reaction zone at a temperature between about 2000C to 3000C. The process may be effected in a batch, intermittent, or continuous manner. However, since the reaction is carried out in the vapor-phase, and since it is necessary to maintain the reactants at the reaction temperature for a predetermined limited period of time, it is generally preferred to carry out the process in a continuous manner till the end of catalyst life that is atleast 400 hours in which case the starting materials may be vaporized in a separate chamber of the front section of the reaction chamber and then passed through the reaction zone at the optimum temperature and the desired space velocity. Advantageous weight hourly space velocity (WHSV) of the reactants according to the present invention is about 0.8 to 1.0 hr-1. As an alternative, the liquid reactants may be vaporized in the reaction chamber.
The molar ratio of aromatic amine to alcohol reactants can be varied from unity to about 1:4 to give the desired admixture. The formation of an intermediate, mono N-alkylated product may be controlled within limits by adjusting temperature of reaction and/or the ratio of alcohol to aromatic amine in the feed. Advantageously it is realized that the use of molar ratios of aromatic amine to alcohol about 1:4 improves the selectivity to product N, N-dialkyl aromatic amine.
Examples of aromatic amines which may be alkylated by the process of this invention are aniline, o-, m-, or p-toluidine, o-, m-, and p-xylidine, o-, m-, and p-anisidine, alpha- and beta, naphthylamines, any other e.g., naphthalene amines, and the like. Suitable alkylating alcohols useful in the process of this invention are methanol, ethanol, butanol, isopropanol, pentanol and the like. In a preferred embodiment of this invention, the reactant aromatic amine is p-toluidine, and the alcohol used is methanol to prepare the product N,N-dimethyl-p-toluidine. The process of this invention provides the desired product in high chemical and space-time yields.
The conversion of the aromatic compound according to the present invention is 99% as the ammonia or aliphatic amine treated catalyst of the process of the present invention is highly active and selective for the N, N-dialkylation of aromatic amines and the selectivity is about 93-95% to dialkyl amines along with formation of 3-5% N-alkyl aromatic amines. The N-alkyl aromatic amine can be separated by distillation and recycled with aromatic amine to increase the overall yield. Further, the catalyst of the present invention is cheaply and easily manufacture as the ?-alumina, ammonia, and aliphatic amine solution are easily available and are cheap. Moreover, as the process is carried out as vapor phase, it is environmentally pollution free, continuous and does not produce salts. Furthermore, the process does not require special material of construction.
The following examples are merely illustrative of preferred embodiments of the invention. Many variations thereon may be made without departing from the spirit of the disclosed invention, as will be evident to those skilled in the art, and such variations are intended to come within the scope of what is claimed:
Example 1:
Catalyst preparation:
100 g ?-alumina extrudates (surface area BET 250m2/g, Density 0.65g/cc, Pore volume 0.55cc/g) were dipped in 300 g 5 % ammonia solution at 25-300C for 10 min, filtered and then dried at 1500C for 2 hours.
Example 2:
Catalyst preparation:
100 g ?-alumina extrudates (surface area BET 250m2/g, Density 0.65g/cc, Pore volume 0.55cc/g) were dipped in 300 g 5% ethylene diamine solution at 25-300C for 10 min, filtered and then dried at 1500C for 2 hours
Example 3:
The catalyst prepared as per the Example 1 was filled in a SS tubular reactor between inert materials such as glass beads. This inert material acts as a preheater for the reactants entering in the reactor. The premixed solution of p-toluidine and methanol in a mole ratio of 1:4 were passed over the catalyst bed at a temperature of 260±50C with WHSV of 0.8 hr-1. The contents were passed through a condenser and liquid organic products were analyzed by gas chromatography. The conversion of p-toluidine was >99% and shoed p-toluidine 0.2%, N, N-dimethyl p-toluidine 94%, and N-alkyl p-toluidine 5.8% and trace of other products.
The catalyst showed stable activity for more than 400 hours.
Example 4:
The experimental procedure of Example 3 was repeated except that the catalyst made in Example 2 was used for the reaction. The products were analyzed by gas chromatography showed p-toluidine 0.28, N,N-dimethyl p-toluidine 92.1, and N-alkyl p-toluidine 5.85 and trace of other products.
Example 5:
The experimental procedure of Example 3 was repeated except that the aromatic amine was aniline. The analysis of the product showed N,N-dimethylaniline 91.28% with > 99 % conversion of aniline.
Example 6:
The experimental procedure of Example 3 was repeated except that the aromatic amine was m-toludine. The analysis of the product showed N,N-dimethyl-m-toluidine 81.39% with >99 % conversion of m-toluidine.