Visible Light-Catalyzed Chlorination And Iodination Of Cyclohexane

Halogenated cyclohexane has numerous industrial applications.Chlorocyclohexane has been used in the preparation of the pharmaceutical benzhexol hydrochloride and the pesticide tricyclic tin,and iodocyclohexane can be applied as a raw material for the preparation of cyclohexanol and cyclohexanone.However,the direct chlorination and iodination of cyclohexane under mild conditions is restricted because the bond energy of cyclohexane is too high.In addition,the photosensitivity of C-I bond within iodocyclohexane,which is particularly prone to break easily under thermal and light conditions,the photocatalytic cyclohexane iodonation is somewhat limited.In halogenation reactions,a hydrogen atom transfer is the key step,and light-mediated hydrogen atom transfer is a powerful tool for functionalization of aliphatic C-H.Among the relevant catalysts reported,the decatungstate anion W₁₀O₃₂^4-has gained widespread attention,which differs from conventional polar reagents in that it does not require prefunctionalization,providing the opportunity to exploit reactivity with the advantage of being cheap and stable.Photocatalytic hydrogen atom transfer has become one of the most convenient and sustainable methods for the generation of carbon radicals.In this paper,the decatungstate was used as a photocatalyst to break the C（sp~3）-H bond of cyclohexane by a hydrogen atom transfer process under visible light irradiation and to react with different iodine reagents to achieve chlorination and iodination of cyclohexane.In this thesis,two decatungstats,Na₄(W₁₀O₃₂)（Na DT）（Bu₄N）₄[W₁₀O₃₂]（TBADT）,were prepared and characterized using IR,UV.The hypervalent iodine reagent,1-chloro-2,3-phenyliodoyl-3-one was also prepared（as the chlorine source）and characterized by NMR and mass spectrometry.Subsequently,the catalytic performance of the catalysts in cyclohexane chlorination was investigated.The results showed that only 1-chloro-2,3-phenyliodinyl-3-one was efficient compared to other chlorine sources in the TBADT catalytic cyclohexane chlorination.The optimal reaction conditions were obtained with 1-chloro-2,3-phenyliodonium-3-one as the chlorine source:nitrogen atmosphere under visible light irradiation,reaction time 11 h,catalyst amount 1 mol%,water volume of 0.5 m L,and the yield of chlorocyclohexane was50.17%.Then,the iodination of cyclohexane with elemental iodine under visible light was investigated using TBADT as the catalyst.The results showed that the iodination of cyclohexane under visible light was achieved by the addition of anthraquinone as a co-catalyst,since the effective iodination of iodine could not be achieved by TBADT alone.The effects of catalyst amount,co-catalyst amount,water amount and reaction time on iodination were also investigated.The optimal conditions were obtained:visible light irradiation,0.7 m L of water,3 mol%of TBADT and 25 mol%of anthraquinone,room temperature,reaction time 4 h,and the yield of iodocyclohexane was 77.93%.Acid was inhibited the iodine substitution reaction.