Method for the synthesis of 5-amino-1-phenyl-3-cyano-4-trifluoromethyl sulfinyl

Abstract

The present invention relates to a method for the preparation of the 5-amino-1-phenyl-3-cyano-4-trifluoromethyl sulfinyl pyrazole having the described general formula (I), particularly preferred for the synthesis of Fipronil I, through oxidation of a compound having the general formula (II) as follows: wherein R 1 and R 2 are independently hydrogen or halogen, and wherein the oxidizing agent is dichloroperacetic acid.

The invention claimed is: 
     
      
       1. A method for the preparation of the compound having the following general formula (I): 
       
         
           
           
               
               
           
         
       
       wherein R 1  and R 2  are independently hydrogen or halogen; through oxidation of a compound having the general formula (II) in the presence of dichloroacetic acid and of an oxidising agent: 
       
         
           
           
               
               
           
         
       
       wherein R 1  and R 2  are defined as above, where the oxidising agent is selected from the group comprising benzoyl peroxides, sodium peroxides, t-butyl peroxides and/or hydrogen peroxide, and wherein the oxidation is conducted in the absence of trichloroacetic and/or trichloroperacetic acid. 
      
     
     
      
       2. The method according to  claim 1 , wherein R 1  and R 2  are chlorine or bromine. 
      
     
     
      
       3. The method according to  claim 1 , wherein the compound having the general formula (I) is 5-amino-1-(2,6-dichloro-4-trifluoromethyl-phenyl)-4-trifluorometansulfinyl-1H-pyrazole-3-carbonitrile. 
      
     
     
      
       4. The method according to  claim 1 , wherein the dichloroacetic acid is oxidised to dichloroperacetic acid through the oxidising agent. 
      
     
     
      
       5. The method according to  claim 4 , wherein oxidation of the dichloroacetic acid takes place in situ. 
      
     
     
      
       6. The method according to  claim 1 , wherein, for each mole of compound having the general formula (I), 1.0-5.0 moles of oxidising agent are used. 
      
     
     
      
       7. The method according to  claim 1 , wherein, for each mole of compound having the general formula (I), 1.1-2.0 equivalents of oxidising agent are used. 
      
     
     
      
       8. The method according to  claim 1 , wherein, for each mole of compound having the general formula (II), 1.5 kg to 5 kg of dichloroacetic acid are used. 
      
     
     
      
       9. The method according to  claim 1 , wherein the temperature at which oxidation takes place is between 0° C. and 35° C. 
      
     
     
      
       10. The method according  claim 1 , wherein the temperature at which oxidation takes place is between 0° C.-20° C. and, preferably is 5° C. 
      
     
     
      
       11. The method according to  claim 1 , further comprising a step of recovering the non-oxidised compound having the general formula (II). 
      
     
     
      
       12. The method according to  claim 11 , wherein the step of recovering comprises a step of dissolving and subsequently recrystallising the compound having the general formula (I) with one or more of the solvents selected from the group comprising toluene, xylene, chlorobenzene, chlorinated aliphatic solvents and isopropanol. 
      
     
     
      
       13. The method according to  claim 1 , wherein the oxidation of the compound having the general formula (II) occurs in the presence of an acid catalyst. 
      
     
     
      
       14. The method according to  claim 13 , wherein the acid catalyst is a strong mineral acid selected from the group consisting in sulphuric acid, methanesulphonic acid, hydrochloric acid, nitric acid and their mixtures. 
      
     
     
      
       15. The method according to  claim 13 , wherein the ratio in moles between the compound of general formula (II) and the acid catalyst is 0.3 to 1.5, and is preferably substantially equal to 0.7. 
      
     
     
       16. A method for the preparation of the compound having the following general formula (I): 
       
         
           
           
               
               
           
         
         wherein R 1  and R 2  are independently hydrogen or halogen; 
         through oxidation of a compound having the general formula (II) in a reaction mixture of dichloroacetic acid and hydrogen peroxide: 
       
       
         
           
           
               
               
           
         
         wherein R 1  and R 2  are defined as above, and 
         wherein the oxidation is conducted in the absence of trichloroacetic and trichloroperacetic acid, and 
         wherein dichloroacetic acid is oxidized to dichloroperacetic acid in situ through the hydrogen peroxide, and dichloroperacetic acid oxidizes the compound of general formula (II) to the compound of general formula (I).  
       
     
     
       17. The method according to claim 16, wherein R 1  and R 2  are chlorine or bromine.  
     
     
       18. The method according to claim 16, wherein the compound having the general formula (I) is 5-amino-1-[2,6-dichloro-4-(trifluoromethyl)phenyl]-4-(trifluoromethylsulfinyl)pyrazole-3-carbonitrile.  
     
     
       19. The method according to claim 16, wherein the temperature at which oxidation takes place is between 0° C. and 35° C.  
     
     
       20. The method according to claim 16, wherein the temperature at which oxidation takes place is between 0° C. and 20° C.  
     
     
       21. The method according to claim 16, wherein the temperature at which the oxidation takes place is about 5° C.  
     
     
       22. The method according to claim 16, wherein, for each mole of compound having the general formula (I), 1.0-5.0 moles of hydrogen peroxide are used.  
     
     
       23. The method according to claim 16, wherein, for each mole of compound having the general formula (I), 1.1-2.0 equivalents of hydrogen peroxide are used.  
     
     
       24. The method according to claim 16, wherein, for each mole of compound having the general formula (II), 1.5-5 kg of dichloroacetic acid are used.  
     
     
       25. The method according to claim 16, wherein, the oxidation is conducted at a temperature between 0° C. and 20° C., for each mole of compound having the general formula (I), 1.0-5.0 moles of hydrogen peroxide and 1.5-5 kg of dichloroacetic acid are used.  
     
     
       26. The method according to claim 16, wherein, 80%-98% of the compound having the general formula (II) is converted to the compound having the general formula (I).