Baeyer-villiger Oxidation Of Cyclic Ketones Catalyzed By Acid-functional Amino Alcohol Ionic Catalysts

Lactone compounds are important intermediates for the synthesis of drugs,dyes and pesticides,and have a wide range of application values.Cyclolactones can be obtained from cyclic ketone compounds by Baeyer-Villiger oxidation reaction.Therefore,exploring new and efficient Baeyer-Villiger oxidation reaction system of cyclic ketones has become a research focus in recent years.The traditional oxidant of Baeyer-Villiger oxidation reaction is mainly peroxyacid,but peroxyacid has the disadvantages of heavy by-product pollution,low atom utilization,high explosiveness,etc.In terms of green chemistry and atomic economy,H₂O₂ is green and low toxicity,and its by-product is water.Therefore,H₂O₂ can replace peroxyacid.The types of catalysts currently used in Baeyer-Villiger oxidation reactions mainly include acid catalysts,ligand compounds,hydrotalcites,transition metal complexes,and biological enzymes.However,the raw materials of most these catalysts are expensive,the synthesis process is complicated,the process conditions for cyclic ketones are demanding,and the conversion rate of cyclic ketones is generally not high.Biological enzyme catalysts have high catalytic activity,but to maintain the high activity of biological enzymes,the operating conditions are very strict,and industrial production cannot be achieved.Therefore,it is the primary task to explore green,environmentally friendly and low-cost high-efficiency catalysts for catalyzing the cyclic ketone Baeyer-Villiger oxidation reaction under mild reaction conditions.In this paper,three types of acid-functionalized amino alcohol ionic catalysts were designed and synthesized for the Baeyer-Villiger oxidation of cyclic ketones.The structural analysis and thermal stability test of the catalysts were performed by means of ¹H NMR,¹³C NMR,FT-IR,and TG.The three kinds of catalytic systems in this paper were shown as follows:（1）Baeyer-Villiger oxidation system of cyclic ketone catalyzed by acid-functionalized amino alcohol ionic liquids:L-prolinol,L-leucine,L-valinol,L-phenylalanin and other L-configuration amino alcohols respectively reacted with protonic acids such as,trifluoromethanesulfonic acid,trifluoroacetic acid,phosphotungstic acid,and phosphomolybdic acid to synthesize a series of acid-functional amino alcohol ionic liquids catalysts by one step of protonation,and these catalysts were applied to the Baeyer-Villiger oxidation reaction of cyclic ketones.Using2-heptylcyclopentanone as a template substrate,the catalyst with the best catalytic effect was[Pro-H]H₂PW₁₂O₄₀.After controlling only the variables,the reaction conditions were optimized one by one to obtain the best process conditions:n（2-heptane cyclopentanone）:n（catalyst）:n（hydrogen peroxide）=1:0.03:3,50℃,6 h,no solvent,the conversion rate of 2-heptylcyclopentanone could reach 95.37%,and the selectivity ofδ-dodecyllactone was 76.04%.After the catalyst[Pro-H]H₂PW₁₂O₄₀ was continuously used for 6 times,its weight was slightly reduced,which was related to the separation loss of the catalyst during the post-treatment.The conversion rate of 2-heptylcyclopentanone was still above 90%,and the selectivity ofδ-dodecyllactone could still maintain the level of about 70%.Under the optimal process conditions,the reactivity of[Pro-H]H₂PW₁₂O₄₀ to catalyze other cyclic ketones was investigated.The results proved that[Pro-H]H₂PW₁₂O₄₀ had good substrate universality in the Baeyer-Villiger oxidation reaction of cyclic ketones.（2）Baeyer-Villiger oxidation reaction system of cyclic ketone catalyzed by sulfonated amino alcohol ionic catalysts:First,L-proline,L-leucine,L-valinol,L-phenylalanin and other L-configuration amino alcohols reacted,with 1,3-propanesultone to synthesize sulfonated amino alcohol intermediates.Second,the intermediates reacted with a series of protonic acids by protonation reaction to generate sulfonated amino alcohol ionic catalysts,and these catalysts were used in the Baeyer-Villiger oxidation reaction of cyclic ketone.[Pro-ps]H₂PW₁₂O₄₀ was selected as the best catalyst with 2-heptylcyclopentanone as the template substrate.After the control variables are unique,the reaction conditions were optimized one by one,and the best process conditions were obtained:n（2-heptylcyclopentanone）:n（catalyst）:n（hydrogen peroxide）=1:0.03:4,40℃,8 h,no solvent,the conversion of 2-heptylcyclopentanone could reach 98.19%,and the selectivity ofδ-dodecyllactone was 82.84%.After the catalyst[Pro-ps]H₂PW₁₂O₄₀ was used continuously for 5 times,its weight was reduced from 0.4650 g to 0.4482 g,and the lost mass fraction was 3.61%.The conversion rate of 2-heptylcyclopentanone was still above 90%,and the selectivity ofδ-dodecyllactone could still maintain about 80%.It can be seen that the catalyst has good reusability and catalytic stability.Under the optimal process conditions,the catalytic effect of the catalyst[Pro-ps]H₂PW₁₂O₄₀ on other cyclic ketones was investigated,and the results proved that it had higher activity in catalyzing cyclic ketones of other structures.（3）Baeyer-Villiger oxidation reaction system of cyclic ketones catalyzed by metal-doped amino alcohol heteropoly acid salt ionic catalysts:The Lewis acidic metal ions(Co²⁺,Ni²⁺,Hf⁴⁺,Zr⁴⁺),and sulfonated amino alcohol cations（Pro-ps,Leu-ps,Val-ps,Phe-ps）were used as the counterions of phosphotungstate,so a series of Br?nsted-Lewis double acidic amino alcohol ionic catalysts were prepared,and used in the Baeyer-Villiger oxidation reaction of cyclic ketone.Ni[Pro-ps]PW₁₂O₄₀ was selected as the best catalyst with 2-heptylcyclopentanone as the template substrate.After the control variables were unique,the reaction conditions were optimized one by one,and the best process conditions were obtained:n（2-heptylcyclopentanone）:n（catalyst）:n（hydrogen peroxide）=1:0.1:4,50℃,5 h,no solvent,the conversion of 2-heptylcyclopentanone could reach 96.31%,and the selectivity ofδ-dodecyllactone was80.84%.After the catalyst Ni[Pro-ps]PW₁₂O₄₀ was used continuously for 7 times,the conversion rate of 2-heptylcyclopentanone was still above 90%,and the selectivity ofδ-dodecyllactone was still maintained at about 80%.The catalyst Ni[Pro-ps]PW₁₂O₄₀also showed excellent catalytic effect in catalyzing other cyclic ketones,and had good substrate universality.In the three types of chiral ionic catalysts for the Baeyer-Villiger oxidation reaction system of cyclic ketones,the amino alcohol-based ionic catalysts show the best catalytic activity and universality of substrates because of their moderate acidity and oxidization.This thesis lays a certain foundation for the subsequent research on asymmetric Baeyer-Villiger catalytic oxidation reaction.