FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
&
The Patents Rules, 2003
COMPLETE SPECIFICATION
(See section 10; rule 13)
1. Title of the invention. - AN IMPROVED PROCESS FOR PREPARATION OF
SUBSTANTIALLY PURE CRYSTALLINE
PENDIMETHALIN.
2. APPLICANT(S)
(a) NAME: RALLIS INDIA LIMITED
(b) NATIONALITY : INDIAN
(c) ADDRESS: 15 A, MIDC, Thane-Belapur Road, MIDC, Turbhe, Navi
Mumbai-400703, Maharashtra, INDIA.
3. PREAMBLE TO THE DESCRIPTION
The following specification particularly describes the invention and the manner in which it is to be performed:

FIELD OF INVENTION
The present invention relates to an improved process for the preparation of substantially pure crystalline pendimethalin. More particularly the present invention relates to the conversion of crude pendimethalin to substantially pure crystals of pendimethalin by the method of melt crystallization employing melt crystallizer.
BACKGROUND OF THE INVENTION
Pendimethalin which is chemically known as N-(l-ethylpropyl)-3,4--dimethyl-2, 6-dinitrobenzenamine [pendimethalin] are known as selective herbicides generally used for pre-emergence control of annual broad-leaved weeds and grasses in cotton, soybeans, rice, barley, beans, alliums, vines, ornamentals and orchards of fruit and nut trees. It has the following structural formula:

US5 705698 relates to an improved process for the production of pendimethalin and i so-pendimethalin. US patent in Example 1 teaches a method of preparation of pendimethalin. In this method pendimethalin in a reaction mixture was cooled with an ice-water bath to afford crystallization of the product which was then filtered off and air dried yielding 8.22 g (91% yield) of more than 99% pure pendimethalin in the form of orange crystals with the melting point 56°-57°C.
The following are the disadvantages of the process disclosed in US5705698:
a. Yield of the process is not to the expected level of more than 95 % for the
second and the third cut.
b. Time taken for the process is very lengthy.
c. No of equipments required are quite high and require more space.

Most of the prior art processes for preparation of pure crystals of Pendimethalin were capable of delivering only a Product purity of 94%-95% alongwith sedimentation in solution with xylene to the extent of 5 ml/100 ml. The present invention has given a purity of 99% with almost 0-01 ml/100 ml sedimentation in solution with xylene.
The present inventors have found that melt crystallization method provide an economic and efficient alternative method of crystallization of pendimethalin which yield crystals of Pendimethalin having high purity.
The present inventors have developed an improved process for the preparation of substantially pure crystalline Pendimethalin which ameliorates the drawbacks of the prior art. The present inventors have surprisingly found that conducting the crystallization of pendimethalin in a melt crystallizer and employing the process of the present invention yields crystals of pendimethalin having high purity in good yield.
The present inventors have found that carrying out crystallization of crude pendimethalin (technical grade) having purity 94% by the method of melt crystallization employing melt crystallizer, according to the process of present invention yield crystals of pendimethalin having 98%-99% purity.
The present inventors have surprisingly found that the crystallization process of the present invention can be carried out at safe operating temperatures below 90°C. The advantage of the ahove approach is that there is no alteration of the chemical structure of Pendimethalin by any thermal decomposition.
The present inventors have further found that temperatures of the product during the heating and the cooling cycles of crystallization and gradual chilling of the solution is essential to crystallize the crude product of Pendimethalin by the process of the present invention based on the Higher purity to lower purity factor.

OBJECT OF INVENTION
It is an object of the present invention to provide an improved process for the crystallization of pendimethalin by melt crystallization method employing a melt crystallizer.
It is another object of the present invention to provide an improved process for the crystallization of Pendimethalin which can be carried out at safe operating temperatures below 90°C.
It is another object of the present invention to provide an improved process for the preparation of crystals of pendimethalin having high purity in good yield.
SUMMARY OF INVENTION
According to an aspect of the present invention there is provided an improved process for crystallizing Pendimethalin in a melt crystallizer comprising the steps of:
i. Introducing uniformly melted crude pendimethalin mass into the melt
crystallizer; ii. heating the pendimethalin mass to attain the temperature in the range of
80°C to 85°C; iii. cooling the pendimethalin mass until the compound attains the
temperature of 65°C; iv. start controlled cooling of the pendimethalin mass at the rate of 0,5°C to
1.0°C per hour until compound attains the temperature in the range of 37°C
to 38°C; v. stop controlled cooling and start controlled heating at the rate of 1°C per
hour until the material attains the temperature 44°C; vi. remove the crystals of pendimethalin from the outlet of the melt
crystallizer.

DETAILED DESCRIPTION OF THE INVENTION
The present invention relates to melt crystallization method of crystallization of pendimethalin which yiedrity.
In an embodiment of the present invention crude pendimethalin is converted into crystals of pendimethalin having high purity by method of melt crystallization employing melt crystallizer.
In another embodiment of the present invention crude pendimethalin is melted into flowable mass and then it is charge (220 kg) in the melt crystallizer which is followed by fast heating of the pendimethalin mass by applying hot water circulation through plates of the crystallizer (Hot water temperature should be 90°C-95°C). Heat the pendimethalin mass in the crystallizer to attain the temperature in the range of 80°C-85°C.
After pendimethalin mass has attained the temperature of 80°C-85°C, remove hot water from the whole heating system of the crystallizer followed by fast cooling of the pendimethalin mass by circulation of cold water in plates of the crystallizer. Cold water temperature should be kept at 30°C.
After the pendimethalin mass has attained the temperature of 65°C, start controlled cooling at the rate of 0.5qC to 1.0°C per hour to attain the temperature in the range of 37°C-38°C. After pendimethalin mass attains the temperature of 37°C-38°C, stop controlled cooling and remove the water from plates of the crystallizer and start controlled heating at a rate of 1°C per hour by applying hot water.
After reaching the temperature 44°C start removing pendimethalin crystal from drain point till temperature reaches to 51°C. This will be a First cut having purity 82%. Material output will be 12% to 13% of the input quantity. Yield is 28.3 kg.

Continue heating at a rate of 1°C per hour and remove second cut of pendimethalin crystal from drain point till the temperature reaches 57°C. Second cut purity will be around 95% pure based on GC (Gas chromatography). Material output will be around 38% to 39% of input quantity. Yield is 83.8 kg.
Continue heating at a rate of 1°C per hour and remove the third cut of pendimethalin crystal from drain point till the temperature reaches to 70°C. This will be third cut of pendimethalin crystal from 57°C to 70°C. Third cut Purity will be around 98% to 99%. Material output will be around 48% to 49% of the input quantity. Yield is 107 kg.
In an embodiment of the present invention, crude product is cooled in scraped surface crystallizers. These may be exchanger type or vessel type crystallizers depending on the specific application. Melt crystallizer is equipment which is similar to a rectangular tank. It consists of various plates installed at a fixed distance between itself. The molten liquid is added to this tank and undergoes a cycle of initial heating and then a specific cycle of cooling and chilling of the mass. It is at this stage that the product undergoes crystallization and the crystals which are in its purest form stick to the edges of these plates which are having a jacket through which the utilities flow through.
The crystallizer produces pure product crystals and thus concentrates the impurities in the remaining liquid mother liquor. The crystals are then separated from the impurity rich mother liquor producing a pure product stream and a reject stream. The reject contains the concentrated impurities but also valuable product which may be recovered depending on the specific application.
In an embodiment of the present invention the crystallization process of the present invention is carried out at safe operating temperatures below 90°C. The advantage of the above approach is that there is no alteration of the chemical structure of Pendimethalin by any thermal decomposition.

Heating and cooling cycles of crystallization and gradual chilling of the solution is essential to crystallize the crude product of Pendimethalin by the process of the present invention based on the higher purity to lower purity factor.
The process of crystallization of pendimethalin results in a crystals product with purity 98%-99% and yield 99.55 %.
Experimental data demonstrating the yield and purity obtained by the process of the present invention:

Input Input Quantity Purity
Pendimethalin (Technical grade) of 94% purity: 220 Kgs 94%

Output Recovered Quantity Purity
Pendimethalin crystals (First cut) 25-30 kgs 82%-85 %
Pendimethalin crystals (Second cut) 80 - 85 kgs 95%
Pendimethalin crystals (Third cut) 105-110 kgs 98%-99%
Product output:

Product Output Product output (weight) Product out put (percentage)
Cut-1 28.3 12.9 %
Cut-2 83.8 38.2 %
Cut-3 107 48.8%
Product output showing percentage purity and yield on weight basis.

Product Output Product output (weight) Percentage purity
Cut-1 28.3 82%
Cut-2 83.8 95%
Cut-3 107 98%-99%

Yield on weight basis 219.1 99.55 %

Examples 1:
1) Take 220 Kg of crude pendimethalin Technical in crystallizer. (Material should be uniformly melted. If material is not melted then first melt the material into flowable mass and then charge the same in Crystallizer).
2) Start fast heating of the pendimethalin mass by applying hot water circulation through plates.(Hot water temperature should be in the range of 90°C-95°C)
3) Heat the pendimethalin mass till it attains the temperature in the range of 80°C-85°C temperature of material.
4) After attending temperature in the range of 80°C-85°C, start fast cooling by circulating cold water in plates (Before this remove hot water from the whole heating system). Cooling water temperature should be kept at 30°C.
5) After the pendimethalin mass has attained the temperature of 65°C, start controlled cooling at the rate of 0.5°C to 1.0CC per hour.
6) After attaining the temperature in the range 37°C-38°C temperature of material stop cooling and remove water from plates of the crystallizer.
7) Start controlled heating at a rate of 1 °C per hour by applying hot water.
8) After attaining the temperature 44°C, start removing pendimethalin crystals from drain point till temperature reaches 51°C. This will be a First cut of pendimethalin crystal which will be of 82% purity. Material output will be 12% to 13% of the input quantity.
9) Continue heating at a rate of 1°C per hour and remove second cut of pendimethalin crystal from drain point till the temperature reaches 57°C. Second cut purity will be around 95% pure based on GC. Material output will be around 38% to 39% of input quantity.
10) Continue heating at a rate of 1°C per hour and remove third cut of pendimethalin crystal from drain point till temperature reaches to 70°C. This will be third cut of pendimethalin crystal from 57°C to 70°C. Purity of this material will be in the range 98% to 99%. Material output will be around 48% to 49% of the input quantity.

Experimental data:

Initial Final Time, Hrs Actual Time
Heating Cycle 09:15:00 AM 11:30:00 AM 2.15 2.15

Cooling Cycle 11:30:00 AM 01:30:00 PM 2 2

Control Cooling 1 01:30:00 PM 08:15:00 PM 30.45 30.45

Control
Cooling 2

Heating Cycle 08:15:00 AM 10:15:00 AM 26 26

Time Pump outlet PLC, data Utility Remarks
With Time Actual
9.15 40 90 46.1 40 START FAST HEATING
10.00 65 90 67.1 65
10.30 75 90 73.1 73
11.00 94.00 90.00 84.10 120.00
11.30 97.00 90.00 94.10 121.00 STOP FAST HEATING
11.30 97.00 65.00 94.10 70.00 START FAST COOLING
12.00 73 66.00 83.20 69.00
12.30 67.00 66.00 75.10 70.00
13.00 65.20 66.00 69.10 68.00
13.30 66.00 66.00 66.40 67.00 STOP FAST COOLING
13.30 66.00 65.00 65.00 65.00 START CONTROL COOLING
15.30 65.00 64.00 64.10 64.00
16.30 64.00 63.00 62.90 64.00
17.30 63.00 62.00 61.90 63.00
18.30 62.00 61.00 61.10 63.00
19.30 61.00 60.00 60.10 62.00
20.30 60.00 59.00 59.20 62.00
21.30 59.00 58.00 58.10 61.00
22.30 58.00 57.00 57.20 61.00
23.30 57.00 56.00 56.10 61.00
24.30 56.00 55.00 55.30 60.00
1.30 55.00 54.00 54.10 60.00
2.30 54.00 53.00 53.20 59.00
3.00 54.00 53.00 53.10 58.00 HOLD FOR 30 MIN

4.00 53.00 52.00 52.30 57.00
5.00 52 51 51.2 56
6.00 51 50 50.2 55
7.00 50 49 49.1 54
8.00 49 48 48 53
9.00 47 47 47 51
10.00 45 46 46 49
11.00 44 45 45 48
12.00 42 44 44.1 46
13.00 42 43 43.1 45
14.00 42 42 41.9 45
15.00 42 41 41.1 42
16.00 41 40 40.1 41
17.00 40 39 39.1 39
18.00 39 38 38.1 39
19.00 38 37 37.2 38
20.15 38 37 37.3 38 STOP CONTROL COOLING
20.15 38 37 37.3 50 START CONTROL HEATING
1.15 36 38 38.2 40
22.15 40 39 39.1 40
23.15 41 40 40.1 41
24.15 42 41 41.1 42
1.15 43 42 42.1 43
2.15 44 43 43.2 44
3.15 45 44 44.1 45
4.15 46 45 45 46
5.15 46 46 46.1 47
6.15 47 47 47.2 48
7.15 48 48 48.1 49
8.15 51 49 49 50
9.15 51 50 50 52
10.15 52 51 51.5 55
11.15 53 52 52 60
12.15 55 53 53 62
13.15 56 54 54 64
14.30 53 55 55.1 64
15.30 56 56 56 65
16.30 57 57 57.1 65
17.30 57 58 58 65
18.30 58 59 59.1 66
19.30 58 60 60.1 66
20.30 60 61 61 66
21.30 62 62 62.1 67
22.30 64 63 63 68
23.30 65 64 64.1 68
24.30 67 65 65.1 69

1.30
68 66 66.2 70
2.30 69 67 67 71
3.30 70 68 68.2 73
4.30 71 69 69 74
5.30 72 70 70.1 75
6.30 74 71 71.5 76
7.30 76 72 72.6 76
8.30 78 73 73.5 77
9.30 79 74 74.3 77
10.30 91 95 90.1 121
Draining Data:

Mat temp Draini
ng Weigh
t Total Weight Bucket
No Colour ANALYSIS
Purity by HPLC
BY RALLIS
42- 46.20 13.6 13.6 1 DARK BLACK 82.2 %
53.30 14.2 27.8 2 DARK BLACK 85.8
53.50 12.8 40.6 3 DARK BLACK 90.35
53.60 13 53.6 4 DARK BLACK 96.64
54.50 13 66.6 5 DARK BROWN 95.24
55.00 12.8 79.4 6 DARK BROWN 96.15
55.60 12.8 92.2 7 DARK BROWN 96.7
56.10 14.8 107 8 DARK BROWN 95.98
56.60 13.2 120.2 9 DARK BROWN 97.39
57.10 14.2 134.4 10 DARK BROWN 96.87
57.30 14.4 148.8 11 DARK BROWN 98
57.50 14.2 163 12 YELLOW 98.13
57.70 13.2 176.2 13 YELLOW 98.53
58.20 14 190.2 14 YELLOW 97.67
60.20 14.4 204.6 15 YELLOW 98.08
72.10 12 216.8 16 YELLOW 97.47

We claim:
1. An improved process for crystallizing Pendimethalin in a melt crystallizer
comprising the steps of:
i. Introducing uniformly melted crude pendimethalin mass into the melt
crystallizer; ii. heating the pendimethalin mass to attain the temperature in the range
of 80°Cto85°C; iii. cooling the pendimethalin mass until the compound attains the
temperature of 65°C; iv. start controlled cooling of the pendimethalin mass at the rate of 0.5°C
to 1°C per hour until compound attains the temperature in the range of
37°C to 38°C; v. stop controlled cooling and start controlled heating at the rate of 1°C
per hour until the material attains the temperature 44°C; vi. remove the crystals of pendimethalin from the outlet of the melt
crystallizer.
2. An improved process for crystallizing Pendimethalin as claimed in claim 1 wherein the crystals of pendimethalin are removed in three cuts at different temperature ranges during the controlled heating at the rate of 1°C.
3. An improved process for crystallizing Pendimethalin as claimed in claim 2 wherein the first cut of crystals of pendimethalin is removed in the temperature ranges of 44°C -51CC, wherein the purity of the pendimethalin crystal is 82%.
4. An improved process for crystallizing Pendimethalin as claimed in claim 2 wherein the second cut of crystals of pendimethalin in removed in the temperature ranges of 51°C-57°C, wherein the purity of the pendimethalin crystal is 95%.

5. An improved process for crystallizing Pendimethalin as claimed in claim 2 wherein the third cut of crystals of pendimethalin in removed in the temperature ranges of 57°C-70°C, wherein the purity of the pendimethalin crystal is in the range of 98% to 99%.