Visible-light Photocatalytic C-C Bond Coupling To Value-added Chemicals

Carbon-carbon(C-C)coupling is widely used for the synthesis of many organic chemicals.The development of one-step method for the preparation of value-added chemicals with high atomic economy under mild reaction conditions has attracted more and more attention from both academia and industry.Visible-light photocatalytic C-C coupling plays an important role in the green chemistry for sustainable chemical synthesis.In this thesis,a series of value-added chemicals including higher aliphatic alcohols,higher aliphatic nitriles,higher aliphatic ketones,and ethylene glycol,are prepared via visible-light photocatalytic C-C coupling with high selectivity under mild reaction conditions.During such visible-light catalyzed process for C-H activation and C-C coupling,the functional groups in the small molecule are retained.The research contents and results are as follows:1.Hydrofunctionalization of olefins to higher aliphatic alcohols via visible-light photocatalytic coupling(1)A green scheme for high atomic economy was developed.Using methanol and olefin as raw materials,hydrofunctionalization of olefins was achieved by visible-light photocatalytic C-C coupling,and a series of higher aliphatic alcohol products with 100%anti-Markovnikov regioselectivity were successfully prepared.This method has general applicability for hydrofunctionalization of olefins to other value-added chemicals such as higher aliphatic nitriles and higher aliphatic ketones.(2)The visible-light photocatalytic C-C coupling of methanol and 1-decene was used as a model reaction to investigate the effects of various factors on the photocatalytic performance.The effect of different photocatalysts were firstly investigated.It was found that cadmium sulfide(CdS)with hexagonal/cubic bi-phase exhibited better catalytic performance than the CdS sample with single phase.In addition,the effects of reaction temperature,water content and olefin substrate concentration were also investigated.It was found that the increased reaction temperature increased the yield of target product.The increase of olefin substrate concentration within a certain range also exhibited a promoting effect.However,the addition of water hindered the formation of higher alcohols.(3)A possible reaction mechanism for the visible-light photocatalytic hydrofunctionalization of olefins to produce higher alcohols on CdS was proposed.Under visible-light irradiation,the CdS photocatalyst is excited by photons to generate photo-generated carriers.The holes directly oxidize the adsorbed methanol to the corresponding·CH2OH,which is immediately captured by the terminal carbon of the olefin.And the new carbon radical further combines with photogenerated electron and protonated by H~+to form the corresponding higher aliphatic alcohol.In this synergistic photooxidation reaction,the methanol oxidation reaction consumed one hole and produced one proton,while the olefin reduction process depleted one electron and one proton.Therefore,this method establishes a cyclic reaction pathway with high atomic economy.2.Visible-light photocatalytic coupling of methanol and formaldehyde into ethylene glycol(1)A mild method for the visible-light photocatalytic synthesis of ethylene glycol with high atomic efficiency was developed.Using cheap and abundant methanol as a feedstock,ethylene glycol was produced by C-C coupling reaction with formaldehyde over carbon nitride(g-C3N4)via visible-light catalysis.Control studies indicated that ethylene glycol can be obtained only when both methanol and formaldehyde were present simultaneously.However,no ethylene glycol was formed when only methanol or formaldehyde was added in the reaction system.(2)A possible reaction mechanism for the preparation of ethylene glycol by visible-light photocatalytic coupling of methanol and formaldehyde was proposed.Under visible-light irradiation,the g-C3N4 photocatalyst is excited by photons to generate photo-generated carriers.The holes directly oxidize the adsorbed methanol to the corresponding·CH2OH,which is immediately captured by the formaldehyde.And the formed·OCH2CH2OH radical further combines with photogenerated electron and protonated by H~+to generate the ethylene glycol.