Study On Direct Synthesis Of Low-carbon Esters From Low-carbon Aldehydes By Tishchenko Reaction

Low-carbon esters,simple structure organic substances,can not only be used as solvents and extractants in organic reactions and chemical production,but also be acted as significant intermediates in the synthesis of pesticides,drugs,and plasticizers.Low-carbon aldehydes Tishchenko reactions are regarded as a kind of efficient,economical,and green routes to synthesize low-carbon esters with the advantages of mild reaction conditions,less side reactions,and high quality of products.In this paper,a series of aluminium alcohols catalysts,such as aluminium isobutanol,aluminium propoxide,and aluminium n-butanol were prepared,and the preparation methods and technological conditions of aluminium alcohols catalysts were investigated and optimized,respectively.Physicochemical properties of the prepared catalysts were characterized via FT-IR and TG-DTA,etc.The results indicated that aluminium isobutanol was efficiently synthesized under the optimized conditions(n(Al):n(isobutanol)was 1:5,n(MCl):n(Al)was 1:10,reaction temperature was 110?).Tishchenko reactions of isobutyraldehyde,propionaldehyde,and n-butyraldehyde catalyzed over aluminium isobutanol,aluminium propoxide,and aluminium n-butanol,were investigated,respectively,and FT-IR,GC-MS,and ~1H NMR techniques were employed to analyze the products.Tishchenko reaction of isobutyraldehyde to isobutyl isobutyrate catalyzed by aluminium isobutanol was studied by single factor and multi-factor experiments and the optimum reaction conditions were obtained.The yield of isobutyl isobutyrate reached 96.00%.Under the same reaction conditions(m(aluminium isobutanol):m(isobutyraldehyde)was 1:10,m(MCl):m(aluminium isobutanol)was 1:10,reaction temperature was 10?,reaction time was 3.5 h),propyl propionate yield was 70.20% in Tishchenko reaction of propionaldehyde catalyzed via aluminium propoxide,and the yield of butyl butyrate was 78.50% in Tishchenko reaction of n-butyraldehyde catalyzed over aluminium n-butanol.Alcohol-aluminium catalyst exhibited excellent catalytic performance in Tishchenko reactions of low-carbon aldehydes,but it was easily inactivated.Therefore,acetylacetone metal salts and ionic liquids were used as the catalysts of low-carbon aldehydes Tishchenko reactions for the first time to explore their catalytic activities and recyclability,respectively.A series of homogeneous catalysts magnesium acetylacetonate,aluminum acetylacetonate,zinc acetylacetonate,and zirconium acetylacetonate were used to catalyze Tishchenko reaction of isobutyraldehyde,and optimum reaction conditions were obtained by single factor experiments.The results suggested that zirconium acetylacetonate shows excellent catalytic performance in this reaction.Under the optimal reaction conditions(m(zirconium acetylacetonate)was 5% of m(isobutyraldehyde),isobutyl alcohol was solvent,reaction temperature was 160?,reaction pressure was 0.75MPa,and reaction time was 6.0 h),isobutyl isobutyrate yield was 77.90%.The heterogeneous catalyst zirconium acetylacetonate/silica was prepared by immobilizing zirconium acetylacetonate on silica to realize the recycling of zirconium acetylacetonate.Physicochemical properties of zirconium acetylacetonate/silica were characterized by FT-IR,BET,and TG-DTA.Under the optimal reaction conditions(m(zirconium acetylacetonate/silica)was 10% of m(isobutyraldehyde),isobutyl alcohol was solvent,reaction temperature was 160?,reaction pressure was 0.75 MPa,and reaction time was 6.0 h),isobutyl isobutyrate yield was 73.30%,and zirconium acetylacetonate/silica could be recycled 3 times without any reduction in catalytic activity.To explore the substrates universality of zirconium acetylacetonate/silica catalyst,Tishchenko reactions of propionaldehyde,and n-butyraldehyde were also investigated under the same conditions,and the results showed that the yields of propyl propionate and butyl butyrate were 52.30% and 67.70%,respectively.Four basic ionic liquids of[ODBU]OH,[ODBU]Im,[BDBU]OH,and[BDBU]Im were synthesized and used in Tishchenko reaction of isobutyraldehyde.[ODBU]OH ionic liquid with relative weak alkaline showed good catalytic performance in isobutyraldehyde Tishchenko reaction,and the selectivity of isobutyl isobutyrate was 48.40%.Furthermore,[ODBU]OH ionic liquid could be reused 4 times and the yield of isobutyl isobutyrate remained almost unchanged,indicating that[ODBU]OH had good stability in isobutyraldehyde Tishchenko reaction.