Field of Invention:
This invention relates to an improved method of preparation of Imidacloprid in presence of alkali in an organic solvent.
Background of Invention:
Imidacloprid (l-[(6-Chloro-3-pyridinyl) methyl]-4,5-dihydro-N-nitro-lH-imidozol-2-amine) is a known as an insecticide and is a neonicotinoid compound.
It was first disclosed in the US patent No. 4,742,060. The neonicotinoid compounds can be synthesized by reacting a heterocyclic compound with an amine compound in the presence of an alkali base in an organic solvent.
The aforesaid alkali base can be NaH or an alkali carbonate when the amine compound employed in the reaction is a uni-amine compound. However, it is preferable to employ NaH when the amine compound employed in the reaction is a di-amine compound. The alkali carbonate is not suitable for the reaction involving the di-amine compound due to a relatively poor yield.
Imidacloprid can be prepared by reacting 2-nitroiminoimidazolidine (a diamine compound) with 2-chloro-5-chloromethyl pyridine (CCMP) in the presence of 60% NaH in an organic solvent, such as DMF (diemthyl formamide), at a temperature ranging from room temperature to about 80°C. However, the use of NaH would give rise to safety concerns and transport problems. Moreover, the reaction has a poor yield. It is found that when NaH is replaced by alkali carbonate in the aforementioned reaction, a relatively large amount of by product is produced.
US patent 6,307,053, JP patent 2002 212178 and DE 10151695 teach a process for preparing imidacloprid comprising reacting 2-nitroiminoimidazolidine with 2-chloro-5-chloromethyl pyridine in the presence of an alkali carbonate. However, this method of the use of several chemical compounds which are poisonous and require careful handling and use. Furthermore, this method is complex and costly.
Thus the object of the present invention is to provide a process for preparing imidacloprid that is capable of overcoming the aforesaid drawbacks and that significantly improves the yield of the aforesaid reaction.

Summary of the Invention:
The present invention relates to a process for preparing imidacloprid comprising:
- reacting 2-chloro-5-cloromethyl pyridine with alkaline hyroxide in presence of an organic solvent such as herein described to form an intermediate,
- adding the said intermediate into a mixture of N-nitroiminoimidazolidine and an organic solvent such as herein described and refluxing the reaction mixture at the 50-60°C for 3-5 hours so as to obtain the product.
The alkaline hydroxide used for preparing the intermediate is sodium hydroxide.
The organic solvent used for carrying out the reaction is ketone.
The organic solvent used for carrying out the reaction is acetone.
Detailed Description of the Invention:
Preparation of imidacloprid according to the process of this invention is described in detail as follows.
The process for preparing imidacloprid comprises reacting N-nitroiminoimidazolidine with 2-chloro-5-chloromethyl pyridine in the presence of an alkaline hydroxide in an organic solvent, wherein a stoichiometric amount of the 2-chloro-5-chloromethyl pyridine is gradually added into mixture of a corresponding stoichiometric amount of the N-nitroiminoimidazolidine and the organic solvent under reflux condition.
Preferably, a mixture of 2-chloro-5-chloromethyl pyridine in organic solvent and alkali is heated to reflux at 50-60°C with continuous stirring. A solution of N-nitroiminoimidazolidine in organic solvent is added. Then the mixture is continuously stirred and refluxed at 50-60°C for 3-5 hours. The reaction mass is checked for completion. On the completion of the reaction, acetone is distilled off and the solid mass is cooled. This slid mass is washed with

water to separate the inorgani6 impurities from imidacloprid. The crude product is dried at 50-60°C.
The crude imidacloprid can be purified by various chromatography techniques, more preferably by HPLC.
The yield of the reaction is about 85-90%, which is quite high in comparison to the previously known methods.
The present invention will now be explained with examples however; the scope of the invention should not be limited to it.
Example 1:
A mixture of 2-chloro-5-chloromethyl pyridine (17.1 gm) in acetone and sodium hydroxidde is heated to reflux at 50-60°C with continuous stirring. A solution of N-nitroiminoimidazolidine in acetone is added. Then the mixture is continuously stirred and refluxed at 50-60°C for 3-5 hours. The reaction mass is checked for completion. On the completion of the reaction, acetone is distilled off and the solid mass is cooled. This slid mass is washed with water to separate the inorganic impurities from imidacloprid. The crude product is dried at 50-60°C. Yield =22.9 gm (89.8%); purity=96.13%.

We claim:
1. A process for preparing imidacloprid, comprising:
- reacting 2-chloro-5-chloromethyl pyridine with alkaline hyroxide in presence of an organic solvent such as herein described to form an intermediate,
- adding the said intermediate into a mixture of N-nitroiminoimidazolidine and an organic solvent such as herein described and refluxing the reaction mixture at the 50-60°C for 3-5 hours so as to obtain the product.

2. The process as claimed in claim 1 wherein the alkaline hydroxide is sodium hydroxide.
3. The process as claimed in claim 1 wherein the organic solvent is ketone.
4. The process as claimed in claim 3 wherein the organic solvent is acetone.