Synthesis Of Unsaturated Carboxylic Acids?Esters? From CO₂ And Unsaturated Hydrocarbons

The reduction of CO₂ emission is one of highly concerning issue in society and scientific community.Chemically converting CO₂ to fine chemicals might be one of feasible method for CO₂ emission reduction,which will also lower down human beings' reliance on petroleum based materials.Among various transformations,the carboxylative coupling of CO₂ with unsaturated hydrocarbons to product carboxylic acids or esters are regarded as one of very promising routes.Since the first work about CO₂ based acrylic acid by Hoberg,chemical community has devoted continuous effort on it.In particular,pioneering work have been done by the US and European countries in the past years.Despite this fact,such kind of transformations are still in a laboratory study stage.Therefore,it is desirable to develop more rapid,efficient,low energy consuming and economic routes to approach carboxylic acids or esters from CO₂.In this thesis,three synthesis routes were studied,including ester acrylate synthesis from CO₂ and ethylene,ester acrylate synthesis from acetylene and CO₂,and substituted propiolic acid or ester synthesis from CO₂ and terminal alkyne.Firstly,based the current research background,the reaction behavior for the coupling of CO₂ with ethylene via a one-pot reaction process was studied.CO₂ and ethylene are coupled on nickel complex to form a mediate-nickelalactone.Subsequently propionic ester is formed by ring-opening agent.Ni?cod?2 bearing dppm ligand proved to be able to promote the coupling of CO₂ and ethylene on the metal complex.It was recognized that the metalliclactone plays an important role in the formation of acrylates.The introduction of nickelalactone directly to the CO₂,ethylene and alkyl iodide three-component reaction system,the desired propionic ester could be obtained.The addition of ancillary ligand could promote the formation of ester acrylate.Alkyl iodide helped to release the ester propionate or further release the ester acrylate.Weak polar solvent and sodium carbonate were efficient reagent.Subsequently,the two-step process was carefully studied.Both nickel complex and molybdenum complex can promote the caroxylative coupling of CO₂ and ethylene to acrylate.The nickelalactone was synthesized by CO₂ and ethylene,which was characterized by different technologies.Nickelalactone with high purity was made by ligand exchange,and was further used to release acrylate via ring-opening reaction by alkyl iodide.Among the four candidates,ethyle iodide showed the best ring-opening performance.In the case of metal promoted carboxylative coupling of CO₂ with ethylene,the ?-H elimination was regarded as the rate-determining step.However,the ?-H elimination has been proved to be extremely difficult.Considering that acetylene might be more reactive than ethylene.The caroxylative coupling of acetylene with CO₂ was further investigated.It was supposed that acrylate can be released from metal complex by hydrogenation.However,in fact hydrogenation by hydrogen was not feasible due to the high energy barrier.Using formic acid instead of H2 was therefore conducted.The formic acid reductive carboxylation of CO₂ and acetylene to produce acrylic acid was carefully studied.The results indicate that the bidentate ligand with weak steric hindrance can form the desired intermediate.However,the excessive hydrogenation of acrylic acid to propionic acid could not be avoided in this transformation.In addition,the reaction was also conducted by the introduction of anhydride to the system.It is assume that the produced CO through anhydride decarbonylation may be able to promote the catalytic reaction.Solvent played an important role in reaction.Porlar solvent resulted in comparatively high conversion.Temperature also had a significant effect on the reaction,while pressure has little effect on the reaction.Comparing to alkenes,owing to the weak acidity of terminal alkynes,it would be easier to be activated.Accordingly,the carboxylative coulping of CO₂ with terminal alkynes was studied in details.A type of N-heterocyclic carbene silver?I?complex or AgI was applied as the catalyst in this part of study,in which the carboxylative coupling of CO₂ with terminal alkynes to product various aryl/alkyl substituted propiolic acids,the three component coupling of CO₂,terminal alkynes and butyl iodide to aryl/alkyl substituted 2-alkynoates,the three component coupling of CO₂,terminal alkynes and benzyl iodide to benzyl alkynoates were successfully facilitated.In the case of carboxylative coupling of CO₂ with terminal alkynes,21 kinds of aryl/alkyl substituted propiolic acids were obtained under the condition of 1 mol%of Ag-NHC in the presence of Cs₂CO₃ in DMF at room temperature and atmospheric pressure.For the three component coupling of CO₂,terminal alkynes and butyl iodide,12 kinds of aryl/alkyl substituted 2-alkynoates were obtained under the condition of 2 mol%of Ag-NHC in the presence of Cs₂CO₃ in DMF at 40? and atmospheric pressure.Finally,under ligand free conditions,31 kinds of benzyl alkynoates were achieved when using 2 mol%AgI as catalystin the presence of Cs₂CO₃ in CH₃CN solvent at 40? and atmospheric pressure.