Process for the Preparation of Meperfluthrin

Background of the invention

A pyrethroid is an organic compound similar to natural pyrethrin. Pyrethroid compounds constitute majority of the commercial household insecticides. Mosquito repellent products used on regular basis in household contain mostly pyrethroid derived compounds. Transfluthrin, Metofluthrin, Dimefluthrin, D-trans allethrin are amongst few known in the art.

Indian Patent application No. 8431/DELNP/2011 discloses insecticidal incense of Meperfluthrin i.e. 2,3,5,6-tetrafluro-4-(methoxymethyl)benzyl (lR,3S)-3-(2,2-dichlorovinyl)-2,2-dimethylcyclopropanecarboxylate, having (1R,3S) trans single optically active isomer.

The process for the preparation of Meperfluthrin reported in CN101580471 involves reaction of lR-trans Cypermethric acid chloride with 4-methoxymethyl-2,3,5,6-tetrafluorobenzyl alcohol in a suitable solvent and in the presence of acid scavenger to yield 4-methoxymethyl-2,3,5,6-tetrafluorobenzyl-(IR-trans)-3-(2,2-dichlorovinyl)-2,2-dimethyl cyclo propane carboxylate.

Yet another process reported in CN104628570 involves esterification of 4-methoxymethyl-2,3,5,6-tetrafluorobenzyl alcohol with High trans cypermethric acid or lR-cypermethric acid (HTCMA) at a temperature of 150-165°C and under pressure of 0.25-0.35MPa in an autoclave. Moreover, in this process, the product is obtained in 95% purity only.

Detailed description of the invention

The process of the present invention involves a clean esterification reaction between HTCMA and 4-methoxymethyl-2,3,5,6-tetrafluorobenzyl alcohol with simultaneous azeotropic removal of water. The reaction temperature is maintained from 90 - 120°C and at normal pressure. At an industrial scale, this difference in temperature and pressure would amount to a much convenient and easier to handle process. Meperfluthrin obtained by this process is having purity greater than 97%. Moreover hazardous pressure reaction (autoclave) is also avoided.

The reaction is performed in water immiscible organic solvents selected from aromatic, aliphatic and alicyclic hydrocarbons and halogenated hydrocarbons like benzene, toluene, xylene, mesitylene, tetralin, chlorobenzene, dichlorobenzene, bromobenzene, nitrobenzene, hexane, cyclohexane, trichloromethane, tetrachloromethane, dichlororethane, trichloroethane, tetrachloroethane, esters such as ethyl acetate, methyl acetate, dimethyl carbonate, diethyl carbonate, ethoxyethyl acetate, methoxyethyl acetate, ethers such as diisopropyl ether, dibutyl ether or the like and in the presence of esterification catalyst like PTSA, Sulfuric acid, Phosphoric acid, Nitric acid or the like. The reaction is performed at temperatures ranging from 90 - 120 °C for reaction period ranging from 2 - 10 hours by continuously removing water azeotropically.

The following example further illustrates the present invention, but should not be construed in anyway as to limit its scope.

Example - 1: Preparation of4-methoxymethyl-2,3,5,6'tetrafluorobenzyl-(lR-trans)-3-(2,2-dichlorovinyI)~2,2-dimethylcyclopropanecarboxylate 500 ml of toluene was charged to a 2 liter capacity 4-necked RB flask fitted with a mechanical stirrer, thermometer pocket with thermometer, a reflux condenser circulated with cold water fitted over a Dean-Stark apparatus. 224 grams (lmole) of 4-methoxymethyl-2,3,5,6-tetrafluorobenzyl alcohol, 215.3 grams [1.03 moles) of lR-trans cypermethric acid and 1.9 grams of concentrated sulfuric acid were charged to the reactor under stirring. The mass was gradually heated to 105 - 110°C, wherein water was removed azeotropically. After complete recovery of moisture, the mass was cooled to 45 - 50°C. The reaction mass was washed with 100 ml of water, 100 ml of 5% sodium carbonate solution, 100 ml of 2% sodium hypochlorite solution and finally twice with 100 ml of water.

The organic solution was distilled at 65 - 70°C under vacuum of 15 -25 mmHg to recover solvent toluene. The remaining residue was cooled and vacuum released under nitrogen atmosphere to yield 390 grams (94% yields) of ^methoxymethyl-Z^^^-tetrafluorobenzyl-flR-transJ-S-Z^-dichlorovinylJ-Z^-dimethyl cyclopropane carboxylate in greater than 97% purity.

Claims

1. A process for the preparation of Meperfluthrin comprising an esterification reaction between HTCMA (high trans cypermethric acid) and 4-methoxymethyl-2,3,5,6-tetrafluorobenzyl alcohol to generate Meperfluthrin in greater than 97% purity, wherein the reaction temperature is maintained between 90 - 120°C under atmospheric pressure.

2. The process of claim 1 wherein the reaction is performed in water immiscible organic solvent.

3.The process of claim 1 wherein the reaction is performed in the presence of esterification catalyst like PTSA or sulfuric acid or phosphoric acid or nitric acid or the like.

5. Meperfluthrin obtained by the process of claim 1.