Green And Quantitative Synthesis Of Esters On Water

The first principle of the 12 principles of green chemistry states that it is better to prevent waste than to treat or clean up waste after it is formed.However,one of the characteristics of synthetic organic reactions is product complexity.This dissertation is aimed at solving the problem by developing quantitative organic synthetic reactions on water,where no purification is required.First,the reactions between ?-glycosyl chloride and carboxylic acid in the presence of tetrabutylammomium bromide?TBAB?,water,Cs₂CO₃ and granular polytetrafluoroethylene?PTFE?were optimized to quantitative by varying the amount of TBAB,water,Cs₂CO₃ and temperature.Sole product ?-glycosyl ester was stereospecifically obtained.In this way,28 ?-glycosyl esters were synthesized,among which,8 were quantitative and 20 above 95%.This result compares favorable to the literature methods?yield in the literature: 12-95%,?:?=1:0.24-4.5?.Encouraged by these results,we expanded the scope of this synthetic method by using ?-halocarbonyl compounds,allyl bromide,iodide and methanesulfonate as alkyl donor to react with carboxylic acid.The reactions were optimized by varying the amount of phase transfer catalysts?PTCs?and temperature.Altogether,50 esters have been prepared.Among them,46 were quantitative and 30 products were obtained simply by filtration without any organic solvents involved in the entire process.In the literature,secondary alkyl esters were synthesized in low yileds?65-83%?.Using our method,all 10 such esters were prepared quantitatively.We have realized the selective esterification of a diiodide with p-toluic acid and palmitic acid.Furthermore,an ester was transformed into substituted oxazole and imidazole.It is the first time to utilize granular PTFE in aqueous esterification.Indispensable effects of PTFE and water were demonstrated by performing a series of control experiments.This method has the following advantanges over organic solvent mediated reactions: short reaction times,quantitive reaction yields in most of case,stereospecificity,tolerance of a broad scope of functional groups,simple workup and easiness to scale up?in 5-12 g scales,no organic solvents or chromatography used?.