FORM 2
THE PATENTS ACT 1970
As amended by the Patents (Amendment) Act, 2002
COMPLETE SPECIFICATION (See Section 10; Rule 13)
TITLE
A process for the preparation of the insecticide imidacloprid
APPLICANTS
Excel Crop Care Limited,
184-87, Swami Vivekanand Road, Jogeshwari, Mumbai 400 102, Maharashtra, India, an Indian Company
INVENTORS
Shroff Dipesh Kantisen, Jain Ashok Kundanmal,
Chaudhari Rajendra Pralhad, Jadeja Raghuvirsmh Bharatsinh
and Gohil Mahendrasingh Sabalsinh, all Indian Nationals
and all of Excel Crop Care Limited,
184-87, Swami Vivekanand Road, Jogeshwari,
Mumbai 400 102, Maharashtra, India
The following specification particularly describes the nature of this invention and the manner in which it is to be performed :
13-8-2004 13 AUG 2004

FIELD OF INVENTION
This invention relates to a process for the preparation of the insecticide imidacloprid.
PRIOR ART
Imidacloprid namely 1-(6-chloro-3-pyridylmethyl)-N-nitroimidazolidin-2-ylideneamine is a systemic, chloro-nicotiny insecticide with soil, seed and foliar uses for the control of sucking insects including rice hoppers, aphids, thrips, whiteflies, termites, turf insects, soil insects and beetles. It is most commonly used on rice, cereals, maize, potatoes, vegetables, sugar beets, fruits, cotton, hops or turfs, and is especially systemic when used as a seed or soil treatment.
US Patent No 6307053 describes a process for the preparation of imidacloprid comprising reacting 2-nitroimidazolidine with 2-chloro-5-chloromethyl pyridine in stoichiometric amounts in the presence of an alkali metal carbonate in an organic solvent under reflux condition. The alkali metal carbonate may be lithium, potassium or sodium carbonate. The organic solvent may be alcohols, ketones, acetonitrile or dimethyl formamide. Due to the alkali carbonates being not very soluble in the

organic solvents, the solutions of the alkali carbonates are not easily flowable and pumpable and the reaction mixture is not very homogenous so as to be easily stirred. Therefore, the above process is difficult to carry out. Besides the filtrate containing imidacloprid obtained by the above process is concentrated by vacuum distillation. Due to the presence of unreacted alkali metal carbonates and their related salts in the filtrate resulting from use of alkali carbonates, there is bumping (flashing) turbulence during vacuum distillation of the filtrate thereby rendering the process further difficult to carry out. Also alkali metal carbonates have low basisity thereby increasing the reaction time. The above process is described to be an improvement over the process employing sodium hydride (NaH) in the place of alkali metal carbonate. Sodium hydride is a very hazardous reagent. Therefore, handling of the sodium hydride based reaction is very difficult and cumbersome.
Indian Patent No 181755 describes a process for the preparation of imidacloprid comprising among other steps, condensation of 3-chloromethyl-6-chloropyridine with 2-nitroimino-l,3-dihydro imidazole in the presence of inorganic bases and ketonic solvents. The inorganic bases used may be carbonates or bicarbonates of sodium or potassium. The

solvents may be acetone, methyl butyl ketone, methyl-t-butylketone or acetonitrile. The problems associated with the use of alkali carbonates in the above US Patent are encountered in this process also.
OBJECTS OF INVENTION
An object of the invention is to provide a process for the preparation
of the insecticide imidacloprid which is very easy to carry out.
Another object of the invention is to provide a process for the preparation of the insecticide imidacloprid which gives good yield and is economical.
Another object of the invention is to provide a process for the preparation of the insecticide imidacloprid which reduces the reaction time.
Another object of the invention is to provide a process for the preparation of the insecticide imidacloprid which eliminates hazardous reagents and is safe to carry out.

DETAILED DESCRIPTION OF INVENTION
According to the invention there is provided a process for the preparation of the insecticide imidacloprid comprising reacting 2-nitroimidazolidine with 2-chloro-5-chloromethyl pyridine in the molar ratio 1 : 1 to 1 :1.2 in the presence of an alkali metal hydroxide in a high boiling aprotic solvent at 45 to 60 °C under stirring.
It has been surprisingly found that the yield of imidacloprid is improved if the molar ratio of the 2-nitroimidazolidine is marginally higher than that of 2-chloro-5-chloromethyl pyridine. Preferably the reaction of 2-
nitroimidazolidine with 2-chloro-5-chloromethyl pyridine is carried out
in the molar ratio 1 :1.12 so as to improve the yield of imidacloprid.
The alkali metal hydroxide may be potassium hydroxide or sodium hydroxide, preferably sodium hydroxide
The high boiling aprotic solvent may be dimethyl formamide or N,N-methyl acetamide, preferably dimethylformamide.

Preferably the reaction of 2-nitroimidazolidine with 2-chloro-5-chloromethyl pyridine is carried out at 50 ° C so as to obtain good yields of imidacloprid.
It has also been surprisingly found that the yield of imidacloprid is improved if the alkali hydroxide is added in two lots one after the other.
According to the invention alkali metal hydroxide are employed in the reaction thereof, which have got improved dissolution in the high boiling aprotic solvents. Therefore, flowability and pumpability of the solutions of the alkali hydroxides is improved. Also homogeneity of the reaction mixture is improved so as to be easily stirred. Therefore, it is easy to carry out the process of the invention. According to the invention alkali carbonates in the reaction and resulting unreacted alkali metal carbonates and their related salts in the filtrate are eliminated. The alkali metal hydroxides have improved reactivity and basicitybecause of which reaction time is reduced and formation of unreacted alkali metal hydroxides in the filtrate is eliminated. Therefore, bumping (flashing) turbulence during vacuum distillation of the filtrate is avoided thereby rendering the

process further easy to be carried out. The invention eliminates the hazardous reagent sodium hydride and is, therefore, safe to carry out. According to the invention yield of imidacloprid is good thereby rendering the process economical.
The following experimental examples are illustrative of the invention but not limitative of the scope thereof.
Example 1 Sodium hydroxide (6gm) was added to 2-nitroiminoimidazolidine (16 gm, 0.123 moles) in dimethyl formamide (50 ml). The temperature of the reaction was brought down to 50 °C in a water bath. A solution of 2-chloro-5-chloromethyl pyridine (20 gm, 0.123 moles) in dimethyl formamide (100 ml) was added to the reaction in 4 hours. The reaction mixture was cooked for another 4 hours at the same temperature. The reaction was stirred throughout. On completion, the reaction was filtered. The residue contained sodium chloride (7 gm). The filtrate was concentrated by vacuum distillation and poured into demineralised water (100 ml). pH of the solution was adjusted to 4 using dilute hydrochloric acid to precipitate out imidacloprid which was filtered out

and washed with methanol (90 ml). Yield 23 gm, 76.6% with 94.16% purity.
Example 2
Sodium hydroxide (6 gm) was added to 2-nitroiminoimidazolidine (18 gm, 0.138 moles) in dimethyl formamide (50 ml). The temperature of the reaction was brought down to 50 °C in a water bath. A solution of 2-chloro-5-chloromethyl pyridine (20 gm, 0.123 moles) in dimethyl formamide (100 ml) was added to the reaction in 4 hours. The reaction mixture was cooked for another 4 hours at the same temperature. The reaction was stirred throughout. On completion, the reaction was filtered. The residue contained sodium chloride (6.45 gm). The filtrate was concentrated by vacuum distillation and poured into demineralised water (100 ml). pH of the solution was adjusted to 4 using dilute hydrochloric acid to precipitate out imidacloprid which was filtered out and washed with methanol (90 ml). Yield 20 gm, 66.6% with 95.18% purity.

Example 3 Sodium hydroxide (3 gm) was added to 2-nitroiminoimidazolidine (18 gm, 0.138 moles) in dimethyl formamide (50 ml). The temperature of the reaction was brought down to 50 °C in a water bath. A solution of 2-chloro-5-chloromethyl pyridine (20 gm, 0.123 moles) in dimethyl formamide (100 ml) was added to the reaction in 4 hours. Sodium hydroxide (3 gm) was also added to the reaction after half the solution of 2-chloro-5-chloromethyl pyridine was added to it. The reaction mixture was cooked for another 4 hours at the same temperature The reaction was stirred throughout. On completion, the reaction was filtered. The residue contained sodium chloride (7.4 gm). The filtrate was concentrated by vacuum distillation and poured into demineralised water (100 ml). pH of the solution was adjusted to 4 using dilute hydrochloric acid to precipitate out imidacloprid which was filtered out and washed with methanol (90 ml). Yield 23.5 gm, 78.3% with 96.2% purity.

We claim:
1. A process for the preparation of the insecticide imidacloprid comprising reacting 2-nitroimidazolidine with 2-chloro-5-chloromethyl pyridine in the molar ratio 1 : 1 to 1:1.2 in the presence of an alkali metal hydroxide in a high boiling aprotic solvent at 45 to 60 °C under stirring.
2. A process as claimed in claim 1, wherein the reaction of 2-nitroimidazolidine with 2-chloro-5-chloromethyl pyridine is carried out in the molar ratio 1 : 1.12.
3. A process as claimed in claim 1 or 2, wherein the alkali metal hydroxide is sodium hydroxide.
4. A process as claimed in anyone of claims 1 to 3, wherein the high boiling protic solvent is dimethyl formamide.
5. A process as claimed in any one of claims 1 to 4, wherein the reaction of 2-nitroimidazolidine with 2-chloro-5-chloromethyl pyridine is carried out at 50 °C.

6. A process as claimed in any one of claims 1 to 5, wherein the alkali hydroxide is added in two lots one after the other.
7. A process for the preparation of the insecticide imidacloprid substantially as herein described particularly with reference to anyone of Examples 1 to 3.
Dated this 12th day of August 2004
(Jose M A)
of Khaitan & Co
Agent for the Applicants