Study On Baeyer-Villiger Oxidation Of Cyclic Ketones Catalyzed By Amino Acid Ionic Liquids

Lactones are the important organic synthetic intermediates and polymer monomers,which have been explored for practical applications in a wide range including the synthesis of spices,dyes and biomedical materials.Baeyer-Villiger oxidation is the most promising approach for the rapid synthesis of lactones.Traditionally,various organic peroxyacids are used as oxidants for this reaction,but the use of peroxyacid involves a lot of disadvantages such as high cost,poor stability and environmental unfriendly.To avoid these problems,pollution-free hydrogen peroxide was chosen as oxidant in this paper,and three kinds of amino acid ionic liquids as catalysts were used to catalyze the Baeyer-Villiger oxidation of cyclic ketones.The structures and thermal stabilities of these amino acid ionic liquids were characterized and tested by 1H NMR,13 C NMR,FT-IR and TG,respectively.The three kinds of catalytic systems in this paper were shown as follows:(1)Baeyer-Villiger oxidation system of cyclic ketones catalyzed by amino acid ionic liquids: A series of amino acid ionic liquids were prepared via protonation reaction with a variety of amino acids(such as L-proline,L-aspartic acid,L-alanine)and many other proton acids(such as sulfuric acid,trifluoroacetic acid or trifluoromethanesulfonic acid)as raw materials.These amino acid ionic liquids were used to catalyze the Baeyer-Villiger oxidation of cyclic ketones,and the best catalyst[Pro]CF3SO3 was screened out in the reaction of cyclopentane as template substrate.After this,the reaction conditions were optimized and the optimum process conditions were obtained: benzonitrile as solvent,n(cyclopentone): n(catalyst): n(H2O2)= 1 :0.06 : 4,T = 60? and t = 6 h.Under the above conditions,the conversion ofcyclopentanone could reach 96.57%,the yield of ?-valerolactone was 70.51%,and the selectivity of the reaction was 73.01%.After simple treatment,the ionic liquid[Pro]CF3SO3 could be recycled three times without obvious change under the optimum conditions.At last,the substrate adaptability of [Pro]CF3SO3 to other cyclic ketones was investigated,the results showed that [Pro]CF3SO3 has good catalytic effect on various cyclic ketones.(2)Baeyer-Villiger oxidation system of cyclic ketones catalyzed by amino acid ester-based ionic liquids: A series of amino acid ester-based ionic liquids were prepared via metathetical reaction with a variety of amino acid methyl ester hydrochlorides(such as L-proline methyl ester hydrochloride,L-aspartic acid dimethyl ester hydrochloride,L-alanine methyl ester hydrochloride)and many other metal acid salts(such as bis(trifluoromethane)sulfonimide lithium salt,potassium trifluoromethanesulfonate,or potassium hexafluorophosphate)as raw materials.These amino acid ester-based ionic liquids were used to catalyze the Baeyer-Villiger oxidation of cyclic ketones,and the best catalyst [Pro C1]NTf2 was screened out in the reaction of cyclopentane as template substrate.After this,the reaction conditions were optimized and the optimum process conditions were obtained: benzonitrile as solvent,n(cyclopentone): n(catalyst): n(H2O2)= 1 : 0.10 : 4,T = 50? and t = 5 h.Under the above conditions,the conversion of cyclopentanone could reach 95.89%,the yield of?-valerolactone was 73.70%,and the selectivity of the reaction was 76.86%.The substrate adaptability of [Pro C1]NTf2 to other cyclic ketones was investigated,and the results showed that various cyclic ketones could be well converted to the corresponding lactones under the catalysis of [Pro C1]NTf2.(3)Baeyer-Villiger oxidation system of cyclic ketones catalyzed by amino acid functionalized heteropolyacid ionic liquids: A series of amino acid functionalized heteropolyacid ionic liquids were prepared with different kinds of amino acids(such as L-proline,L-aspartic acid,L-alanine)and varieties of heteropoly acids(such as phosphotungstic acid,phosphomolybdic acid hydrate or tungstosilicic acid hydrate)as raw materials in different proportions.These amino acid functionalized heteropolyacid ionic liquids were used to catalyze the Baeyer-Villiger oxidation of cyclic ketones,and the best catalyst [Pro]H2PW12O40 was screened out in the reaction of cyclopentane as template substrate.After this,the reaction conditions were optimized and the optimumprocess conditions were obtained: benzonitrile as solvent,n(cyclopentone):n(catalyst): n(H2O2)= 1 : 0.04 : 3.5,T = 50? and t = 6 h.Under the above conditions,the conversion of cyclopentanone could reach 94.21%,the yield of ?-valerolactone was 80.38%,and the selectivity of the reaction was 85.32%.After simple treatment,the catalyst [Pro]H2PW12O40 could be recycled four times without obvious change under the optimum conditions.The catalytic effect of [Pro]H2PW12O40 on other cyclic ketones was also investigated,and the results showed that [Pro]H2PW12O40 also exhibited good substrate adaptability for other cyclic ketones.In this paper,three kinds of Baeyer-Villiger oxidation catalytic systems catalyzed by amino acid ionic liquids have been established,which have exhibited good catalytic effect on various cyclic ketones.Moreover,the amino acid ionic liquids also have many other advantages,such as low preparation cost,simple preparation process,easy separation and recycle.This paper widens the application scope of amino acid functionalized ionic liquids,and provides a new scientific basis for the study of Baeyer-Villiger oxidation catalyzed by acid catalysts.