Studies Towards The Green Synthesis Of Fipronil As A Super-Effective And Safe Pesticide

In the 21^stcentury,the human population problem,food problem,energy problem and environment problem are the most outstanding problems to the human beings.Food production in agriculture is the most fundamental and important aspect of human beings.Pesticides and chemical fertilizers,which are used to make agriculture capable of producing stable and high yields,need to be further understood by the whole society.In addition,it is significant to protect the current fragile ecological environment as well as developing the eco-agriculture of China,by enhancing the use of green chemical technology in the process of the development of agriculture chemicals.Fipronil(â… )as a super-effective,wide-spectral and safe pesticide is known as the new generation of super-effective pesticide.In this thesis,an economically inexpensive,operationally simple and environmentally friendly synthetic process is developed,basing on analyzing and improving the literature synthetic methods and creating new synthetic methods of the product(â… )and its intermediates.Fipronil is prepared by two methods:in method 1,(â… )is synthesized by reacting 5-amino-3-cyano-1-(2,6-dichloro-4-trifluoromethylphenyl)-pyrazole(â…¥)with sodium trifluorornethanesulfinate in the presence of catalyst.However,sodium trifluorornethanesulfinate is hardly prepared with low yield.In method 2,(â… )is prepared in a new method,using 5-amino-3-cyano-1-(2,6-dichloro-4-trifluoromethyl -phenyl)-pyrazole(â…¥)as the starting material,comprising 3 steps such as electrophilic substitution by sulfur monochloride,radical reaction by trifluoromethyl bromide,oxidation by hydrogen peroxide.In comparison with the literature methods, the method has such advantages as operationally safe,high yield and environmentally friendly by using sulfur monochloride to prepare the disulphide.The intermediate 5-amino-3-cyano-1-(2,6-dichloro-4-trifluoromethylphenyl)pyrazole(â…¥) is synthesized by using 2,6-dichloro-4-trifluoromethylaniline(â…¤)as the starting material.The method comprises 2 steps such as diazotization and cyclization by ethyl 2,3-dicyanopropionate.The process is more easily prepared in high purity by reducing the amount of acetate acid and replacing chloroform by toluene.Compound(â…¤)is synthesized by chlorinating 4-trifluoromethylaniline(â…£), using H₂O₂/HCl as chlorinating agent.In comparison with the literature methods,the process is more easily treating,high yield and operationally safe.The intermediate(â…£)is prepared by reacting 4-trichloromethylphenyl isocyanate(â…¢)with hydrofluoric acid.The method has advantages such as convenient operating and easily treating.Compound(â…¢)is synthesized from 4-methylphenyl isocyanate,involving the chlorination reaction in the presence of initiator and ultraviolet alternatively.Nevertheless,the process has disadvantages such as high reaction temperature and high demands on equipments when using initiator as catalyst.Comparatively,the process has advantages such as mild conditions, convenient handling,high yield and environmentally friendly when using ultraviolet.In conclusion,the super-effective and wide-spectral pesticide Fipronil is successfully synthesized from 4-methylphenyl isocyanate by seven reacting steps.The process is operationally simple and safe,high yield,environmentally friendly and complying with the requirements of green chemistry.The work has built a firm base for the future industrial manufacturing of Fipronil.