Alkylation Of 2,4-dichlorofluorobenzene With Carbon Tetrachloride Catalyzed By Chloroaluminic Acid Ionic Liquids

In this paper,the alkylation of 2,4-dichlorofluorobenzene and carbon tetrachloride was studied under catalysis of chloroaluminate ionic liquid.The reaction was carried out in a three-necked flask,and the reaction product was analyzed by HPLC.First,the catalytic performance of AlCl₃was evaluated as a reference for this reaction.Gas chromatography-mass spectrometry（GC-MS）,H NMR and C NMR analysis showed that only 2,4-dichloro-5-fluorotrichlorotoluene and dichloro-bis（2,4-dichloro-5-fluorophenyl）methane were produced in the products.Taking the conversion ratio of2,4-dichlorofluorobenzene and the yield of 2,4-dichloro-5-fluorotrichlorotoluene as indicators,the ionic liquid catalysts were first screened.The results showed that only aluminate ILs are appropriate,while those with Fe Cl₃,Zn Cl₂and Cu Cl are not suitable.Further,the effect of ionic liquid cation species and alkyl chain length on the reaction was studied.It was found that the cation of[Et₃NH]⁺is suitable,and the overly long alkyl chain will shield the catalytic activity of the anion due to the steric hinderance.Al F₃has no catalytic effect for this reaction.Al F_mCl_nand Na Cl-2AlCl₃can be recycled four times,with18.07%and 16.13%of yield of 2,4-dichloro-5-fluorotrichlorotoluene,respectively.Using Et₃NHCl-2AlCl₃as catalyst,the effects of influcing factors were studied by orthogonal experiments,including the raw material ratio,dropwise approach,reaction time and temperature.The results show that increasing the amount of carbon tetrachloride is beneficial to the increased yield of 2,4-dichloro-5-fluorotrichlorotoluene;the dropwise approach has little effect on the product distribution;increasing the amount of catalyst,the conversionrateof2,4-dichlorofluorobenzene,theyieldof2,4-dichloro-5-fluorotrichlorotolueneand dichloro-bis（2,4-dichloro-5-fluorophenyl）methane were all increased,but the dimer was increased more significantly.The optimized reaction conditions were determined as follows:75°C,rawmaterialmolarratio2,4-dichlorofluorobenzene:2,4-dichloro-5-fluorotrichlorotoluene:Et₃NHCl-2AlCl₃=1:1.5:1.5,and mixed feeding.As such,the conversion rate reached 95.2%,the yield of2,4-dichloro-5-fluorotrichlorotoluenewas5.97%,andtheyieldof dichloro-bis（2,4-dichloro-5-fluorophenyl）methane was 89.2%.In addition,the influence of the aluminum trichloride amount in the ionic liquid was also investigated.Et₃NHCl-1.75AlCl₃was a suitable catalyst,whereby 24.81%of yield of2,4-dichloro-5-fluorotrichlorotoluene was obtained.The extraction experiments showed that the partition coefficients of2,4-dichlorofluorobenzene and 2,4-dichloro-5-fluorotrichlorotoluene between ionic liquid and carbon tetrachloride are K_N1=0.59 and K_N2=2.81,respectively,which favors the production of bisubstitution product.Finally,the reusability performance of the catalyst was investigated.It was found that the conversion ratio of 2,4-dichlorofluorobenzene was kept at about 70%after 5 times reusing Et₃NHCl-2AlCl₃,with 3%of yield of2,4-dichloro-5-fluorotrichlorotolueneandover65%ofyieldof dichloro-bis（2,4-dichloro-5-fluorophenyl）methane.