Catalytic Performance Of Zeolite In The Synthesis Of Disulfide,Ketone And 1,1-disubstituted Alkene Chemicals

A variety of fine organic chemicals with different properties are prepared through organic synthesis,which provides an endless material basis for the rapid development of modern society.However,under the background of the increasingly serious global environmental pollution and energy crisis,the characteristics of homogeneous organic synthetic chemistry,such as high pollution,high energy consumption and complex system,cannot meet the essential requirements of green chemistry.Therefore,it is urgent to seek an alternative synthesis method for fine chemicals.The use of clean and green heterogeneous system to synthesize fine chemicals not only avoids the use of homogeneous catalysts,ligands and various additives,but also the heterogeneous catalyst can be easy to recycle and reuse,which is of great significance for the"eradicating pollution from the source"for the sustainable development strategy in green chemistry.Recently,scientists have developed a variety of heterogeneous catalysts to achieve the goal for the green synthesis of different fine chemicals.Among them,the zeolite is one kind of ideal heterogeneous catalysts,as its unique crystal structure,adjustable acid-base properties and good thermal and chemical stability.In this paper,we employ zeolite as heterogeneous catalyst,under mild reaction conditions,realizing the green preparation of disulfides,ketones and 1,1-disubstituted olefin and other chemicals,the specific contents are as follows:The electrophilic H of the thiols interacts with the electron-rich O in the-Ti-O-Ti-unit of ETS-10,leading to the formation of a colinear S-H-O bonded complex.Electron transfer occurs from O to S,resulting in homolysis of the S-H bond to generate sulfur radical and hydrogen radical followed by dimerization to afford the disulfides and hydrogen.In addition,through changing the compensating cations of ETS-10,the electron-donating ability of electron-rich oxygen in the-Ti-O-Ti-chain can be enhanced,thus improving the ability to catalyze S-H bond homolysis to generate free radicals,avoiding the use of oxidants and any additives.Based on the strong coordination ability of metal Co and electron-rich oxygen in ETS-10-Ti-O-Ti-chain,Co was introduced into ETS-10 and coordinated with electron-rich oxygen to construct a bifunctional active center for the homolysis of S-H bond in thiols.In this manner,the Co site and the electron-rich oxygen site in the bifunctional center can respectively coordinate with the S atom and the H atom in the S-H bond to synergistically catalyze the homolysis reaction of S-H,resulting in the initial reaction rate of the reaction has been improved to double.The ketone has been synthesized with high stereoselectivity using HBeta zeolite as catalyst in the hydration of alkynes with water.It has been found that the Br?nsted acid sites in the pore of HBeta acts as an acceptor for the alkynylπ-electron and thereby can adsorb and activate alkyne to form an alkenyl radical cationic intermediate.The nucleophile attack of water to the carbocation of the radical cation can form an enol intermediate,followed by a rapid tautomerisomerization reaction to afford the product ketone.The IR,Py-IR,UV-Vis,EPR and ¹³C NMR technologies have been employed to explore the adsorption sites and evolution of alkynes on HBeta zeolites,and the photoelectrical properties of the radical cation and the effect of its open-shell structure on the nuclear magnetic displacement of alkynyl carbons have also been studied.The mechanism of the alkynyl radical cation catalyzed by acid zeolites has been proposed for the first time.The mechanism of HBeta-catalyzed hydroarylation of alkynes with aromatics has been proposed for the first time,taking the formation of alkynes at the Br?nsted acid site of HBeta zeolite as the starting point.The Lewis acid site in HBeta zeolite can preactivate the aromatics and make them exhibit higher nucleophilic properties when they attack the carbocation in the free radical cations,resulting in the higher catalytic activity on HBeta than that of the water-soluble protic acids.Using HBeta zeolite as catalyst,the H-D exchange reaction between theα-H of ketone and deuterium water was achived in the clean system without metal and additives.By introducing the P to partially neutralizing strong acid sites of HBeta zeolite,got that the active site for the H-D exchange reaction of ketone and deuterium water is the strong Br?nsted acid site on HBeta zeolite.At the same time,the pore cavity of HBeta zeolite provides a limited reaction environment for the H-D exchange reaction,and it can stabilize the intermediate state of ketone in the reaction process,so as to promote the reaction.