The present process relates to the preparation of a versatile pre-emergence and preplanting herbicide Pendimethalin (1). It is particularly effective against weeds having broad leaves like Parthenium hysterophorous, Commelina benghalenses, etc.

The process for the preparation of Pendimethalin involves various stages as given below
STAGE I
3,4-xylidine (II) is condensed with diethyl ketone (111) and then reduced to give xylidine derivative (IV).


The xylidine derivative (IV) is nitrated to give nitroso derivative (V).

The Nitroso derivative is refluxed with concentrated hydrochloric acid and sulfamic acid to give pendimethalin.

The preparation of various intermediates and the title compound are described in the following examples.
EXAMPLE 1


catalyst and 0.3 g of p-toluene sulphonic acid are also charged. The reactor is pressurised by hydrogen to 7-15 kg/cm2.
The reactants are stirred and the temperature maintained between 50-80°C for 5-8 hrs. After the reaction the contents are cooled and the solvent distilled off to give intermediate (IV).
Yield: 17.5 g of IV (92%)
EXAMPLE 2
Preparation of N-Nitroso NM-Ethvipropvl) 3,4- dimethyl 2.6- dinitro aniline:
15.3 g of N(1-Ethyl propyl)-3, 4-dimethyl aniline is charged into a flask along with 40 ml of 1,1,2,2,tetrachloroethane. The reaction mixture is cooled to 15°C. To this, nitrating mixture containing 10.2 ml concentrated sulphuric acid and 2.7 ml of 60% nitric acid is added under stirring maintaining the temperature between 15-20°C. After the addition of the nitrating mixture, the contents of the flask are stirred for another 3 hrs. Then the reaction is poured onto crushed ice. The organic layer separated, washed with alkali and water and dried over anhydrous sodium sulphate. To give N-Nitroso N-(1-Ethylpropyl)3, 4-dimethyl 2,6-dinitroaniline (V).
EXAMPLE 3
Preparation of N-(1-Ethvl propvl) 3.4 Dimethvl 2.6-Dinitro aniline :
The intermediate (V) from the above step is placed in a flask containing 1 ml of concentrated hydrochloric acid and 1.0 g of sulfamic

acid and 100 ml of 1,1,2,2-tetrachioroethane. The contents are stirred at 70-90O C for 8-10 hrs. Then the reaction mixture is poured Into crushed Ice. The organic layer is separated, washed well with 5% NaOH solution and dried over anhydrous sodium sulphate, solvent is removed under reduced pressure. On cooling solid separates out.
Yield : 20 g (88.8%)
Dated this....'.-?.
day of .. .B:W.tt!*^j!i... 1^*15


BACKGROUND OF INVENTION
The present process relates to the preparation of Pendimethalin (I) which is a versatile pre- emergence and preplanting herbicide. It is particularly effective against weeds having broad leaves like Parthenium hysterophorous, Commelina benghalenses, etc.

As per U.S. Patent No.4,124,639. Pendimethalin is prepared from 3,4-dimethyl-2,6-dinitro aniline. Dinitroaniline is diazotised and converted into the corresponding chloro compound. This is further reacted with appropriate substituted amine and converted into pendimethalin. In this process preparation of dinitro dimethylaniline is done by nitrating the corresponding xylidines. This results in the formation of a mixture of nitro compounds. However, this problem is overcome by a Dutch Patent No.2,429,958 where 3,4 xylidine is condensed with diethyl ketone, reduced and then nitrated to give pendimethalin. Under the experimental conditions the vields are verv low.

With a view to improve upon the yields the present process has been developed to give pendimethalin in high yields of 88%.
SUMMARY OF INVENTION
This invention relates to the development of a process, for the preparation of Pendimethalin (I).
First stage of the process involves the condensation of 3,4 xylidine with Diethyl ketone in presence of solvents like benzene, toluene, etc. and a phase transfer catalyst like p-toluene sulphonic acid. The reaction is carried out at various temperatures ranging from 50°C to HCC. Best results are obtained using toluene as the solvent and refluxing the reaction mixture at HCC. The water formed during the reaction is removed azeotropically using a Dean Stark apparatus. This azeotropic removal of water reduces the deactivation of the reduction catalyst used in the next step.
The Schiff base is charged Into a pressure reactor and palladium on charcoal is used as a catalyst. The reactor is pressurised with hydrogen to a pressure of 6-15 kg/cm2 and the temperature maintained at 50-80°C. Reaction is faster at 60-65°C and a pressure of 6-8 kg/cm2. At lower temperatures the reaction is very slow.
In the second stage N(1-Ethyl propyl)-3,4 dimethyl aniline is nitrated using concentrated nitric acid. The reaction is carried out using chlorinated solvents like dichloromethane 1,1,2,2, tetrachloro ethane

chloroform and dichloroethane at different temperatures ranging from 5 to 20°C. Best results are obtained using 1,1,2,2, tetrachloroethane as solvent and when the temperature is between 18-20°C.
In the third stage the mixture of N-nitroso pendimethalin and pendimethalin is refluxed in the presence of substituted sulphonic acids like p-toluene sulfonic acid, 2-Napthalene sulfonic acid and Amino sulphonic acid, etc. and concentrated hydrochloric acid to give pendimethalin. Amino sulphonic acid gives better results.
ABSTRACT
The process for the preparation of pendimethalin involves following stages.
STAGE I
3,4-xylidine (II) is condensed with Diethylketone (III) to give Schiffs base (Ilia) which is reduced to give N(1-Ethyl propyl)- 3,4 dimethyl aniline (IV).

The preparation of various intermediates and pendimethalin are described in the following examples.
EXAMPLE I
STAGE I
PREPARATION OF SCHIFF BASE
12.1g of 3,4-xylidine, diethyl ketone and 0.3 g of p-toluene sulphonic acid are charged into a round bottom flask, 50 ml of toluene is added. The contents of the flask are refluxed at HCC for 3-4 hrs until theoretical amount of water is removed. Then the solvent is removed and the product is passed through anhydrous sodium sulphate. This is directly charged into a pressure reactor with 200 ml xylene, 0.43 g 5% Pd/c catalyst. The reactor is pressurised to 7-15 kg by hydrogen. Reactants are stirred and maintained between 50-80°C for 5-8 hrs. After the reaction the contents are cooled and the solvent distilled off to give N-(1-Ethyl propyl) 3,4-dimethyl aniline.
Yield: 17.5 g (92%)
EXAMPLE 11
PREPARATION OF N(1-ETHYLPROPYL)-3.4-DIMETHYL 2.6-DINITROBENZENEAMINE AND N-NITR0S0.Nf1-ETHYLPR0PYL) 3.4 DIMETHYL 2.6 DINITROBENZENEAMINE MIXTURE :
15.3 g of N(1-Ethylpropyl)3,4 dimethylaniline is charged into a flask, along with 1,1,2,2,tetrachloroethane (40 ml). Reaction mixture is cooled to

We Claim:
1. A process for the preparation of Pendimethalln (I) as shown in the accompanying drawing sheets in which 3,4-xylidine is condensed with Diethylketone in presence of a solvent, catalyst, under a temperature range of 50-110°C, which would enable the azeotropic distillation of

water to give Schiff base, which is then reduced using a reduction catalyst and a pressure of 6-15 kg/cm2 to give N(1-Ethylpropyl)3,4 dimethyl aniline, which is then nitrated in presence of chlorinated solvents to give a mixture of N-Nitroso,N-(1-Ethylpropyl) 3,4 dimethyl 2,6-dini- troaniline and N(1-Ethylpropyl)3,4 dimethyl 2,6 dinitroaniline, this mixture is refluxed with concentrated hydrochloric acid and substituted sulphonic acid to give pendimethalin.
The process as claimed in Claim 1 wherein in the condensation reaction of 3,4-xylidine and Diethylketone the solvent used is toluene.
The process as claimed in Claim 1 wherein in the condensation reaction of 3,4 xylidine and diethyl ketone the catalyst used is p-toluene sulphonic acid.
The process as claimed in Claim 1 wherein in the condensation reaction of 3,4 xylidine and diethylketone the temperature is 110oC.
The process as claimed in Claim 1 wherein the catalyst used for reducing Schiff base is 5% Palladium on charcoal.
The process as claimed in Claim 1 wherein the pressure applied for reducing Schiff base is 6-8 kg/cm2.
The process as claimed in Claim 1 wherein the chlorinated solvent used in the nitration reaction is 1,1,2,2-tetrachloroethane.

8. The process as claimed in Claim 1 wherein the substituted sulphonic acid used is Amino sulphonic acid.
Dated this .15th
day of february 1996