Coup Ling Reaction Of Aromatic Halides Catalyzed By N-Heterocyclic Carbene

The coupling reaction of aromatic halides is one of the important reactions for increasing carbon chain. The coupling reaction of aromatic halides with aldehyde catalyzed by N-heterocyclic carbene (NHC) can directly introduce acyl group to the electron deficient position of the benzene ring. The study has provided a new environmentally friendly method for the direct introduction of the acyl group to the electron-deficient aromatic ring to synthesize the aromatic ketones with electron-withdrawing group.According to the designability of ionic liquids in the structures,5 kinds of imidazolium ionic liquids have been synthesized by using 1-methylimidazole, 1-chlorobutane,1-chlorooctane,1-chlorododecane,1-chlorohexadecane and benzyl chloride as raw materials. The structures of the ionic liquids are characterized by JR.The prepared imidazolium ionic liquid as the catalyst precursor of NHC has been applied for the coupling reaction of aromatic halides with aldehyde. Effect factors are fully investigated. The best catalyst and the best reaction conditions are selected. The recycling of the ionic liquid is also investigated.The nucleophilic acylation of 4-fluoronitrobenzene and benzaldehyde is studied by using the prepared imidazolium ionic liquid as the catalyst precursor of NHC to synthesize 4-nitrobenzophenone. The selected optimal conditions are as follows: DMSO as the solvent, the ionic liquid (K-n-C12H25) as the catalyst precursor, potassium tert-butoxide as the alkali, the amount of the ionic liquid to the 4-fluoronitrobenzene 1:3, the mole ratio of the ionic liquid to the alkali 1:4, reaction temperature 30 ℃ and reaction time 6 h. Under the above optimal conditions, the conversion of 4-fluoronitrobenzene is 93.0%, and the yield of 4-nitrobenzophenone is 88.6%. The recycling efficiency of the ionic liquid is investigated. The result has showed that the yield of 4-nitrobenzophenone still can reach above 75% after 4 recycles of the ionic liquid.The nucleophilic acylation of 4-fluoronitrobenzene and p-tolualdehyde is studied by using the prepared imidazolium ionic liquid. The selected optimal conditions are as follows:DMSO as the solvent, the ionic liquid (R=n-C12H25) as the catalyst precursor, potassium tert-butoxide as the alkali, the amount of the ionic liquid to the 4-fluoronitrobenzene 1:3, the mole ratio of the ionic liquid to the alkali 1:4.5, reaction temperature 30 ℃ and reaction time 4 h. Under the above optimal conditions, the conversion of 4-fluoronitrobenzene is 94.3%, and the yield of 4-nitro-4’-methyl benzophenone is 86.6%. The recycling efficiency of the ionic liquid is investigated. The result has showed that the yield of 4-nitro-4’-methyl benzophenone still can reach above 60% after 5 recycles of the ionic liquid.The nucleophilic acylation of arylfluorides and aromatic aldehyde is studied by using the prepared imidazolium ionic liquid. The result has showed that the aromatic aldehyde with electron-donating group conducive to the reaction, and it almost no reacted when it has electron-withdrawing group on aromatic aldehyde.The nucleophilic acylation of 4-fluoronitrobenzene and butyraldehyde is studied by using the prepared imidazolium ionic liquid as the catalyst precursor of NHC to synthesize 4-nitro butyrophenone. The structure of the 4-nitro butyrophenone is characterized by 1H-NMR. Under the conditions of DMSO as the solvent, potassium tert-butoxide as the alkali, reaction temperature 30 ℃, the reaction has the better conversion and the yield which are 94.1% and 46.9%, respectively.The reaction of 4-fluoronitrobenzene and DMF is studied using the prepared imidazolium ionic liquid as the catalyst precursor of NHC. N,N-dimethyl-4-nitroaniline and N,N-dirnethyl-4-nitrobenzamide are synthesized with the presence of ionic liquid, and only N,N-dimethyl-4-nitroaniline is synthesized without the presence of ionic liquid. The best catalyst is 1-methyl-3-n-dodecyl imidazolium chlorine and the best base is NaH. Under the condition of 50 ℃, the conversion and the yield of N,N-dimethyl-4-nitroaniline are respectively 62.27% and 37.1% in the reaction of 4-fluoro nitrobenzene and DMF.