Study On The Catalytic Performance Of Acidic Zeolite Hbeta In The Preparation Of Various Olefin Isomers

The polysubstituted alkenes is an important class of synthetic chemical intermediates,which is also the key structure units of advanced functional molecules,widely used in medicine,fargrances,dyes and other fields.Compared with traditional methods for the synthesis of alkenes,the direct functionalization of alkynes does not require pretreatment of the substrate,while avoiding the use of halogenated reagents,and thereby has been regarded as an efficient scheme for the synthesis of polysubstituted alkenes.The functionalization of alkynes has been successfully achieved by using catalysts such as transition metal complexes,Lewis acid metals,and ionic liquids.However,in these catalytic protocols,the addition of complex ligands,bases,oxidants or strong acids results in complex system,metal pollution,high cost and limited substrate scope.Therefore,the development of a clean and efficient catalytic system to synthesize polysubstituted alkenes remains great challenges.Beta zeolite possesses a three-dimensional twelve-membered ring pore structure,and there presents a large number of acidic sites on its surface,which can adsorb and activate substrates,widely using in various catalytic reactions.In this text,the synthesis of a variety of olefin isomers was systematically studied using proton-exchanged BEA zeolite HBeta as a catalyst.The main contents are as listed:1.HBeta-catalyzed hydroarylation of alkynes to 1,1-disubstituted alkenes.HBeta as the sole catalyst successfully realizes the hydroarylation reaction between various alkynes and aromatics without transition metals and sacrificial agents.By controlling the addition order of the reaction substrates,the elementary reaction steps were studied in depth.Combining with the characteristics of the alkyne that can be activated by the acid sites on the surface of the HBeta catalyst and the experimental results of isotope labeling,the possible reaction mechanism of hydroarylation reaction the HBeta-catalyzed alkyne was preliminarily proposed: The reaction undergoes an alkenyl cation intermediate process and a bimolecular adsorption reaction pathway.2.HBeta-catalyzed methylalkylation of alkynes to produce polysubstituted alkenes.Compared with the preparation of 1,1-disubstituted alkene isomers,the synthesis of polysubstituted alkenes is more challenging.We have attempted to use acidic zeolite HBeta as the sole catalyst and readily available ketone derivatives as methyl-and aryl-substituent donors to first realize the methylalkylation of alkynes,and successfully synthesized a variety of regioselective and stereoselective polysubstituted olefin isomers.It is found that the accessible acidic sites on HBeta are not only the activation sites for alkynes,but also the main reaction centers for in situ generation of alkene substituents of ketones.3.HBeta-catalyzed preparation of E-1-propenylbenzene with high selectivity from phenylpropanol.The phenylpropanol,a hydroxy compound widely present in natural products,was first used as raw material and HBeta as catalyst to synthesize trans-1-propenebenzene(E-1-propenylbenzene)with high selectivity under mild conditions.Through the study of the elementary reaction steps,two parallel reaction paths for the preparation of E-1-propenylbenzene from phenylpropanol catalyzed by HBeta are proposed,path I: the phenylpropanol first undergoes α-OH transfer on the acidic site to generate 1-phenyl-2-propanol,followed by dehydration of the isomeric hydroxyl group under the protonation of the acidic site to generate E-1-propenylbenzene with high selectivity;Path II:phenylpropanol is successively reacted on the acidic site of the catalyst to generate E-1-propenylbenzene(E/Z > 98%)by two steps sequential reactions of dehydration and double bond transfer.