| Fluorine is a special element with extremely strong polarity that can bring exceptional behaviors to many fluorinated organic compounds.Halogen exchange fluorination is one of the most important methods to prepare fluorine compounds.Considering the alkaline metal fluorides have lower solubility in organic phase,halogen exchange fluorination needs to be carried out in the presence of phase transfer catalyst?PTC?which can lead to increase the concentration of the free fluoride ions in the organic phase.Therefore,the catalyst with the high efficiency is the key factor to synthesize fluorine compounds.The conventional preparation methods,although widely used,encounter serious problems to be resolved including complicated preparation process,long reaction time and low efficiency.Therefore,it is urgent to develop a efficient synthetic process to realize the efficient production of fluorides.In this dissertation,the conductance method was firstly used to study the system of fluorination catalyzed in the process of PTC.The solubility of fluorinating agents in organic solvents and the behavior of solvated of fluorinating agents in the water-organic solvent mixture were studied by the conductance method.Meanwhile,the halogen exchange fluoridation catalyzed by calixarene derivative and quaternary phosphonium salts were investigated.The catalytic mechanism of PTC was discussed based on the variation of conductivity.Finally the effects of water on the fluorination reaction were investigated by the conductance method,which provided a necessary technical approach for the efficient synthesis of fluorides.The results of this research can provide experimental evidence and theoretical basis for the synthesis of fluorinated compounds with high yield.The main conclusions of this dissertation are shown as follows:First of all,based on the conductance method,the solvents of halogen exchange fluorination were studied because the solvents were very important to the fluorination reaction.The conductance behavior of fluoride salts in organic solvent had been investigated,and the solubilities of KF and CsF in the different polar solvents DMSO,DMAc,DMF had been determined at 298.15K.The solubility of KF at 298.15K in DMF,DMSO,DMAc was 0.112mmol·L-1,0.168mmol·L-1,0.144mmol·L-1,respectively;and the solubility of CsF at 298.15K in DMF,DMSO,DMAc was0.699mmol·L-1,1.248 mmol·L-1,0.929mmol·L-1,respectively.The results indicate that the higher dielectric constant of the solvents,the stronger interionic repulsive force and the more free ions,which show that the higher the solubility of fluoride salts the greater the conductivity.The higher concentration of the free fluoride ions in the reaction system and the faster process of the fluorination reaction,the yields are improved.Based on conductance method of fluoride salt fluoridation behavior in different solvents,it shows that the conductance technology can be used to measure the free fluoride ions in fluorine reaction,direct fluorination process and improve the reaction yield.Secondly,the preparations of calix arene derivatives as PTCs for the fluorination reactions were studied.On the basis of synthesis of calix arene derivatives under conventional heating,calix arene derivatives under microwave irradiation were synthesized.Compared with conventional heating,the synthesis of the calix arene derivatives under microwave irradiation could be finished in 2-4h,and the product yield could increase by 13.1%to 32.9%.The calix[4]arene derivatives with different functions were designed,which had better catalytic activity in halogen exchange fluorination.The catalyst N?11?in which crown ether and onium salt connect with calix[4]arene was designed and synthesized.It showed that N?11?not only had complexing capacities with potassium,but also had the ability to extract fluorine ions into the organic phase.Under the synergistic catalysis of N?11?,the fluorination was obtained from 1-chloro-4-nitrobenzene in 3h,and the yield of products was 91.4%.Comparing with the usual catalyst,the yield increased by 10.2%,and the reaction time was shortened to 2h.The results indicated that N?11?was a PTC in halogen exchange fluorination with excellent performance and high efficiency.Then the fluorination reactions under the bicipital quaternary phosphonium salt were studied.Since most of nucleophilic catalytic fluorination research is still on the stage of increasing the concentration of fluoride ions and few study on the leaving group is carried out,while the leaving group is also an important factor to influence the reaction.Therefore,the double-phosphor quaternary salt catalysts were synthesized for activating the reaction substrate and their applications in fluorination reactions.In the process of catalytic fluorination under the bicipital quaternary phosphonium salt,the enhanced activity of the catalyst could be explained by synergistic effects between the neighbouring phosphonium cations,polarisation of the C-Cl bond of the substrate by one phosphonium centre was accompanied by simultaneous attack by the F-supplied by the neighbouring cation.The fluorination catalyzed by the bicipital quaternary phosphonium salt was obtained from 1-chloro-4-nitrobenzene in 3h,the yield of products was 89.7%.Compared with the non-catalysed process,the yield increased by27.0%.Therefore,in the fluorination reaction,the bicipital quaternary phosphonium salt is a kind of catalyst with dual catalytic activity and high efficiency.Finally,the effects of water on fluorination were studied.In the fluorine reaction,water is another special key factor affecting the fluorination reaction.Therefore,the conductivity behaviour of fluoride salts in H2O-DMF mixture was studied.The conductivity data were analysed by Kraus-Bray and Shedlovsky models.The limiting equivalent conductance values,the association constants and the dissociation constant for KF,CsF and TBAF were calculated.The results indicated that the limiting equivalent conductance values could increase and the dissociation constant could decrease with increasing H2O composition.Due to the solvation of fluoride ions in the presence of water in the fluorination reactions,which would lead to reduce the nucleophilicity of fluoride ions,the reaction rate would decline.On the contrary,the ion pairs are not completely dissociate in the absence of water due to the ion association of KF in organic solvents.The low concentration of the fluoride ions results in a drop in the reaction rate and consequently the conversion declines.Trace water is necessary which could lead to the low association constant,the high concentration of the free fluoride ions,and increase the conversion of fluorination.Therefore,the presence of trace water is favoring for the smooth process of fluorination. |
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