Method for the preparation of 3-fluoroalkyl-1-methylpyrazol-4-carboxylic acid

1. A method for the preparation of a pesticide, the method comprising preparing a 3-fluoroalkyl-1-methylpyrazol-4-carboxylic acid by the following steps:

step 1, fluoroacetyl fluoride derivative shown in Formula I undergoes condensation with dimethyl amino vinyl methyl ketone, as a result, 3-dimethylamino methylene-1,1-difluoro-2,4-pentanedione derivative shown in Formula II is formed:

wherein, R 1 is hydrogen, fluorine or chlorine atom; R 2 is fluorine or chlorine atom;

step 2, ring closing reaction takes place between said 3-dimethylamino methylene-1,1-difluoro-2,4-pentanedione shown in Formula II and methylhydrazine, in this way, 3-fluoroalkyl-1-methyl-4-acetyl pyrazol derivative shown in Formula III is obtained;

step 3, the said 3-fluoroalkyl-1-methyl-4-acetyl pyrazol derivative shown in Formula III is oxidized in the presence of alkali, and then acidified, in this way, 3-fluoroalkyl-1-methylpyrazol-4-carboxylic acid shown in Formula IV is formed,

and transforming the 3-fluoroalkyl-1-methylpyrazol-4-carboxylic acid into an activated 3-fluoroalkyl-1-methylpyrazol-4-carboxylic acid and reacting the activated 3-fluoroalkyl-1-methylpyrazol-4-carboxylic acid with an amine to obtain the pesticide.

2. The method according to claim 1 , wherein in step 1, a gas of the said fluoro acetyl derivative of Formula I is directly introduced to a dichloromethane solution containing dimethyl amino vinyl methyl ketone, and the reaction temperature is −5˜0° C.

3. The method according to claim 1 , wherein in step 2, the reaction temperature is −40˜0° C., the reaction time is 1˜8 h, and the molar ratio between said methylhydrazine and 3-dimethylamino methylene-fluoro-2,4-pentanedione of Formula II is 1.1:1˜1.5:1.

4. The method of claim 3 , wherein the said reaction temperature of said step 2 is −25˜20° C., and the reaction time is 1˜2 h.

5. The method according to claim 1 , wherein in step 3, sodium hypochlorite solution or sodium hypobromite solution is used in the oxidation in the presence of alkali, the said sodium hypochlorite solution is prepared by introducing chlorine gas to sodium hydroxide water solution, and the said sodium hypobromite solution is prepared by introducing liquid bromine to sodium hydroxide water solution.

6. The method according to claim 1 , wherein in step 3, the reaction temperature is 0˜50° C., and the reaction time is 1˜5 h.

7. The method of claim 6 , wherein in step 3, the reaction temperature is 10˜20° C., and the reaction time is 2˜3 h.

8. The method of claim 6 , wherein HCl solution is used in said acidification, and the final pH value of said solution is adjusted to 1˜2.

9. The method according to claim 1 , wherein said fluoroacetyl fluoride derivative of Formula I is difluoroacetyl fluorine, said 3-fluoroalkyl-1-methylpyrazol-4-carboxylic acid of Formula IV is 3-(difluoromethyl)-1-methyl-1H-pyrazol-4-carboxylic acid.

10. The method according to claim 1 , wherein the pesticide is a fungicide amide.

11. The method according to claim 10 , wherein the pesticide is Bixafen, Fluxapyroxad, Isopyrazam or Sedaxane.

12. The method according to claim 1 , wherein the activated 3-fluoroalkyl-1-methylpyrazol-4-carboxylic acid is a carboxylic acid halide.

13. The method according to claim 1 , wherein the amine is aniline.