PROCESS FOR THE PREPARATION OF TRICHLORO METHYLPYRIDINE
Field of the invention
The present invention provides a process for the preparation of 3-trichloromethyl pyridine of Formula I.
Background of the invention Trichloromethyl aromatic compounds are useful as agricultural intermediates. Trichloromethyl N-heteroaromatic compounds, such as 3-trichloromethyl pyridine, are useful intermediates for the production of agricultural chemicals, including both insecticides and pesticides. The US patent no. 4,634,771 provides a method for the conversion of carboxylic acid groups on an aromatic or N-heteroaromatic ring compound to trichloromethyl groups using phenylphosphonous dichloride, chlorine, and phosphorus trichloride. The process uses phenylphosphonous chlorides which are highly reactive, complicated to prepare and difficult to handle. Hence, this process is not industrially feasible. The J. Chem. Soc., Perkin Trans. 1, 1989, 283-287 provides a process for the preparation of 3-trichloromethyl pyridine by reacting nicotinic acid with phosphorous pentachloride followed by heating at 115°C for 72 hours. The process suffers from the drawback that the reaction of nicotinic acid and phosphorous pentachloride results in highly exothermic reaction, lump formation due to stirring of reactants in solid form, thereby making the process industrially not feasible. The present inventors have observed that none of the prior art documents are enlightened to the beneficial use of phosphorous oxychloride along with phosphorous pentachloride for chlorination. The phosphorous oxychloride so used in the chlorination reaction is easily recycled back to make the chlorination reaction a continuous process, which is economically viable and industrially doable. Additionally, the handling difficulty is overcome and the reaction proceeds in a smooth manner making the process industrially feasible.
3
Object of the invention
The object of the present invention is to provide a process for the preparation of 3-trichloromethyl pyridine of Formula I
NCCl3
Formula I
Summary of the invention
The present invention provides a continuous process for the preparation of
3-trichloromethyl pyridine of Formula I, comprising; a) contacting nicotinic acid of Formula II with a mixture of phosphorous oxychloride and phosphorous pentachloride to obtain a first mixture of 3-trichloromethyl pyridine of Formula I and phosphorous oxychloride, b) separating the compound of Formula I and phosphorous oxychloride from the first mixture, and c) recycling phosphorous oxychloride obtained in step b) into step a).
NCOOH
N
CCl 3
Formula II Formula I
Detailed description of the invention
4
The present invention provides a continuous process for the preparation of 3-trichloromethyl pyridine of Formula I, comprising; a) contacting nicotinic acid of Formula II with a mixture of phosphorous oxychloride and phosphorous pentachloride to obtain a first mixture of 3-trichloromethyl pyridine of Formula I and phosphorous oxychloride, b) separating the compound of Formula I and phosphorous oxychloride from the first mixture, and c) recycling phosphorous oxychloride obtained in step b) into step a). N
COOH
N
CCl 3
Formula II Formula I
The nicotinic acid is contacted with a mixture of phosphorous pentachloride and phosphorous oxychloride at a temperature from about 80°C to 130°C and for a time period from about 20 hours to 80 hours.
In an aspect, the compound of Formula I is converted to 2-chloro-3-trifluoromethyl pyridine of Formula III by any method known in the art or as disclosed in the present application. In another aspect, the compound of Formula I is converted to 2-hydroxy-3-trifluoromethyl pyridine of Formula IV by any method known in the art or as disclosed in the present application.
NCF3Cl
NCF3OH
Formula III Formula IV
5
The compound of Formula II can be obtained commercially or can be prepared by any method known in the art, for example, as disclosed in US 2,295,870.
The phosphorous oxychloride separated in step b) is recycled back and the process is made continuous. The compound of Formula I separated in step b) may be purified by basifying with alkali hydroxide, for example, sodium hydroxide, and potassium hydroxide or mixtures thereof.
The compound of Formula I is isolated by any of the methods known in the art, for example, distillation, evaporation and layer separation or mixture thereof.
The compound of Formula I as obtained by the process of the present invention has a purity greater than 96%, preferably greater 98% by gas chromatography.
The term ‘about’ refers to a variation of 10% on the higher and lower side of specified parameter.
While the present invention has been described in terms of its specific embodiments, certain modifications and equivalents will be apparent to those skilled in the art and are intended to be included within the scope of the present invention.
Examples
Example 1: Preparation of 3-trichloromethylpyridine
Phosphorus oxychloride (50.0g, 0.32 mole) and phosphorus pentachloride (66.4 g, 0.31 mole) were taken in a reaction vessel. Nicotinic acid (20.0 g, 0.16 mole) was added to it portion-wise. Reaction mass was mixed thoroughly and heated at 115°C for 72 hours. Phosphorus oxychloride was distilled off under reduced pressure and the remaining oily reaction mass was slowly added to ice (200 g).
The phosphorus oxychloride (78.6 g), which was distilled off, was recycled back to the reaction vessel.
6
The oily mass was basified with 2% sodium hydroxide. The mixture was extracted with dichloromethane (3 x 100 ml). The combined extracts were dried and the solvent was evaporated. The residual oil was distilled to give the title compound.
Yield (%): 50.8
Purity (%): 98.98 (by gas chromatography)

We claim:
1. A continuous process for the preparation of 3-trichloromethyl pyridine of Formula I, comprising; a) contacting nicotinic acid of Formula II with a mixture of phosphorous oxychloride and phosphorous pentachloride to obtain a first mixture of 3-trichloromethyl pyridine of Formula I and phosphorous oxychloride, b) separating the compound of Formula I and phosphorous oxychloride from the first mixture, and c) recycling phosphorous oxychloride obtained in step b) into step a). N
COOH
N
CCl 3
Formula II Formula I
2. The process as claimed in claim 1, wherein the phosphorous oxychloride separated in step b) is recycled back.
3. The process as claimed in claim 1, wherein the compound of Formula I is purified by basifying with alkali hydroxide.
4. The process as claimed in claim 3, wherein alkali hydroxide is selected from the group consisting of sodium hydroxide and potassium hydroxide or mixture thereof.
5. The process as claimed in claim 1, wherein the compound of Formula I is isolated by distillation, evaporation and layer separation or mixture thereof.