Process for preparing imidacloprid

Details Process for preparing imidacloprid Process for preparing imidacloprid

2000-12-29

2001-10-23

Morris, Patricia L. (Department: 1625)

Organic compounds -- part of the class 532-570 series

Organic compounds

Heterocyclic carbon compounds containing a hetero ring...

Reexamination Certificate

active

06307053

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a process for preparing imidacloprid in the presence of an alkali carbonate in an organic solvent.
2. Description of the Related Art
Imidacloprid (1-[(6-Chloro-3-pyridinyl) methyl]-4,5-dihydro-N-nitro-1H-imidazol-2-amine) is known as an insecticide, and is a neonicotinoid compound, which has been disclosed in U.S. Pat. No. 4,742,060, and which has a formula as shown below:
Wherein n=0 or 1; X=S, O, —N—R7 or —CH—R8; Y=N or =C—R9; R7, R8, R9=hydrogen or specifical organic radicals; Z=5- or 6-membered nitrogen-containing heterocyclic ring; R1, R2, R5, R6=hydrogen or alkyl group; R3, R4=hydrogen, hydroxy group or alkyl group. The neonicotinoid compound can be synthesized by reacting a hetercyclic 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. The aforementioned reactions can be represented by the following two examples:
Imidacloprid can be prepared by reacting 2-nitroiminoimidazolidine (a di-amine 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. The reaction can be represented as follows:
Due to the aforementioned drawbacks, a two-step reaction process for preparing Imidacloprid has been proposed heretofore, which can be represented as follows:
While the aforesaid yield can be improved and the aforesaid safety concerns and transport problems can be overcome by using the two-step reaction, the two-step reaction process is complex and costly.
SUMMARY OF THE INVENTION
Therefore, it is an object of the present invention 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.
Accordingly, a process for preparing imidacloprid according to the present invention, comprises reacting 2-nitroiminoimidazolidine with 2-chloro-5-chloromethyl pyridine in the presence of an alkali carbonate 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 2-nitroiminoimidazolidine and the organic solvent under reflux condition.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Preparation of imidacloprid according to the process of this invention is described in detail as follows.
The process for preparing imidacloprid comprises reacting 2-nitroiminoimidazolidine with 2-chloro-5-chloromethyl pyridine in the presence of an alkali carbonate 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 2-nitroiminoimidazolidine and the organic solvent under reflux condition.
Preferably, the stoichiometric amount of the 2-chloro-5-chloromethyl pyridine is dropwisely and continuously added into the mixture of the corresponding stoichiometric amount of the 2-nitroiminoimidazolidine and the organic solvent, and more preferably, the stoichiometric amount of the 2-chloro-5-chloromethyl pyridine is gradually and continuously added into the mixture of the corresponding stoichiometric amount of the 2-nitroiminoimidazolidine and the organic solvent at a rate of less than 0.03 equivalent of the 2-chloro-5-chloromethyl pyridine per minute.
Preferably, the alkali carbonate contains an alkali element that is selected from a group consisting of lithium, sodium, and potassium, and more preferably contains potassium.
Preferably, the organic solvent is selected from a group consisting of alcohols, ketones, DMF, and acetonitrile, and is more preferably acetonitrile.


REFERENCES:
patent: 5310920 (1994-05-01), Kodaka et al.

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