Research On Metal-free Direct Carboxylation Of Terminal Alkynes With Co2

With the accelerated industrialization of mankind,the large amount of carbon dioxide(CO2)emissions caused global warming and a series of climate anomalies,endangering human survival and development.But at the same time,carbon dioxide is also a very good C1 resource.Over the past few decades,researchers have reported a lot of chemical fixation of carbon dioxide,making a breakthrough in the progress of carbon dioxide as raw materials to synthesize different types of high value-added chemical products.The use of carbon dioxide and terminal alkyne synthesis of propiol acid compounds have a good industrial application prospect.Researchers now mainly use transition metals(such as silver,copper),rare earth metals etc.to catalyze carboxylation of carbon dioxide with alkynes.But these method suffer from the high cost of catalysts and complex ligands.There are also some researchers using base such as cesium carbonate,TBD to promote the reaction.But these reaction system face the same problem: the using of high cost base and high boiling point solvent which is hard to deal with.Therefore,the development of using a low price base,low boiling point solvent witch is easy to handle to promote the carboxylation of alkyne and carbon dioxide is of great significance.With these thoughts in mind,in this paper we have carried out a series of research on the catalysis of carboxylation of carbon dioxide with terminal alkynes.The main contents are as follows:1.A metal-free reaction system was developed using cheap base(potassium carbonate)as the base,acetonitrile which has low boiling point as the solvent.The carboxylation of phenylacetylene with carbon dioxide was selected as a model reaction.The effect of factors such as additive and temperature was investigated and the optimum reaction conditions are as follow: K2CO3(4 equivalents),n-tetrabutyl acetate(1.5 equivalents),carbon dioxide(10 atm),and acetonitrile(5 mL).90? for 20 h.And the carboxylation reaction of other types of terminal alkynes and carbon dioxide was studied under the optimum conditions.The yield was 53% ~ 92%.2.The results show that the reaction system has good effect on the carboxylation of different kind of terminal alkynes with carbon dioxide.Benzene ring bearing electron-donating groups or weak electron-withdrawing groups have good yields.But the reaction yield decreases when benzene ring bears strong electron-withdrawing group such as-CF3.In addition,good yield was obtained when terminal alkynes of heterocyclic,aliphatic were used.The preliminary mechanism studies show that the cation and anion composition of the additive have a great influence on the reaction.With the help of quaternary ammonium salt,the potassium carbonate removes the protonated hydrogen proton.Compared with the previous reports,the reaction system which is metal-free,using cheap and easy to obtain potassium carbonate as the base,significantly reduce the cost of the carboxylation reaction of terminal alkynes with CO2.This reaction system has a good application prospects...