Study On Synthesis And Thermal Decomposition Mechanism Of Perfluoro-2-methyl-3-pentanone

Researchers have been working to develop a new generation of environmentally friendly and efficient fire extinguishers to address issues related to traditional halon-based extinguishers.One alternative,perfluoro-2-methyl-3-pentanone,which has low ozone dissipation potential(ODP)and global warming potential(GWP),has been commercialized by 3M Company in the United States as Novec 1230.In recent years,scientific research institutes and related enterprises in China have begun to invest in research and development of this product.However,industrial scale production has yet to be realized.In this paper,the synthesis and thermal decomposition mechanisms of perfluoro-2-methyl-3-pentanone are studied.These results lay the foundation for industrialization of this fire extinguishing material.A synthesis route to perfluoro-2-methyl-3-pentanone from hexafluoropropylene by oligomerization,oxidation,and isomerization was designed and demonstrated on the basis of a literature review and analysis.Catalysts,such as potassium cyanide,alkali metal fluoride,cuprous bromide/bipyridyl,and biphenyl chromium,catalyze the oligomerization of hexafluoropropylene.The effects of temperature,solvent,catalyst loading,and stirring speed on the oligomerization of hexafluoropropylene catalyzed by potassium hexafluoride were investigated.The highest yield of the reaction was 85%.An alkali metal fluoride potassium fluoride and tetrabutylphosphonium chloride system gave a yield of 79%.The reaction based on cesium fluoride and crown ether was better than that of other catalysts and the y:ield of hexafluoropropylene dimer was 96%.The cupridinium bromide dipyridyl system can also catalyze the reaction well,and the yield of hexafluoropropylene dimer is 89%.The best catalyst in the diphenyl chromium system was ?-bis(1,3,5-trimethylphenyl)chromium.A mechanism for the oligomerization of hexafluoropropylene under coordination catalysis is proposed.Furthermore,both sodium hypochlorite and tertiary amine nitrogen oxide systems oxidized the hexafluoropropylene dimer.Epoxidation of perfluoro-2-methyl-2-pentene by sodium hypochlorite in diethylene glycol dimethyl ether solution required 3-5 h,achieving a yield of 79%.A new phase transfer-based catalytic oxidation method for the perfluoro-olefins is proposed.The yield of epoxide was 96%,based on addition of a tetrabutylammonium hydrogen sulfate phase transfer catalyst to the sodium hypochlorite solution system.Mechanistic aspects of the catalytic oxidation reaction of the perfluoro-olefin are discussed.In addition to solvent,temperature,and catalyst,the structure of substituents on the double bond,electronic effects,and stability of the carbanion intermediates are all important factors affecting the reactivity of the perfluoro-olefin.A new class of tertiary amine/peroxyacid or super acid catalytic oxidation is developed.The reaction,performed at room temperature for 1-2 h,yielded 95%of the epoxide.This catalytic oxidation system is more active towards tri-substituted or tetra-substituted perfluoro-olefins but has no oxidation activity towards disubstituted perfluoro-alkenes.The optimal reaction conditions for rearrangement of the perfluoro-epoxides to perfluoro-2-methyl-3-pentanone under organic base catalysis are determined.The thermal decomposition mechanism of perfluoro-2-methyl-3-pentanone was studied by density functional theory(DFT).These results showed that perfluoro-2-methyl-3-pentanone is a very thermodynamically stable compound and a radical cracking reaction is the main decomposition pathway.The formation processes and reaction energy barrier of the thermal decomposition products were calculated.Additionally,the formation pathway of carbon skeleton isomers based on addition of ?-cracking-free radicals to perfluoro-olefins was clarified.The multimolecular decomposition mechanism of perfluoro-2-methyl-3-pentanone at high temperature was studied by Reax FF force field molecular dynamics(ReaxFF MD).The effects of temperature on the decomposition mechanism,decomposition rate,and intermediate and product concentrations are discussed.At high temperatures,the thermal decomposition of perfluoro-2-methyl-3-pentanone gradually increased together with the variety and quantities of free radicals formed.The reaction mechanism showed that the initial decomposition pathways of perfluoro-2-methyl-3-pentanone occurs at the 2-position through C-CF3 bond breaking,the 2-3-position by C-C bond breaking,and the 2-4-position by C-F bond breaking.At 2000 K,radicals generated by the initial decomposition pathways undergo subsequent step-wise thermal decomposition.The final products of the reaction are mainly small free radical fragments and molecules.Thermal decomposition of perfluoro-2-methyl-3-pentanone was examined on the basis of theoretical research.These results showed that perfluoro-2-methyl-3-pentanone decomposes at temperatures over 550 0C.The main products of the thermal decomposition were consistent with the theoretical results.