Technical Study On Preparation Of 4-fluorobenzaldehyde By Halogen-exchange Fluorination

Halogen-exchange fluorination was applied to synthesis fluorobenzaldehyde, fluorination of 4-chlorobenzaldehyde was studied in PTC using spray-dried KF as fluorinating agent.Factors influencing the yield were discussed on solvents and catalytic selecting, KF drying technology, waste management and by-reaction contral. Synergism catalytic and solvent. reaction temperature, reaction time, reagent mole ratio and stirring speed was studied in halogen-exchange fluorination of PCAD with spray-dried. As the dosage of KF and catalyst, reaction time, different stirring speed and the dosage of the solvent respectively increased, the yield of product firstly uprised and then leveled off. As reaction temperature increased, the yield of product firstly uprised and then lowered. When the mole ratio(KF : PCAD)was 4:1, the dosage of the catalyst was 0.05mol~0.15mol, reaction time was 2h~10h, stirring speed 100r/min~500r/min, the dosage of the solvent was 10mL~20mL, the reaction temperature was 180℃~220℃, the yield of 4-Fluorobenzaldehyde was 21%~93%. The optimum reaction conditions were found as follows: n(PCAD):n(KF):n(Cat1):n(Cat2)=1:4:0.15:0.05, reaction temperature 210℃, reaction time 8h and synergism nitrobenzene and TMSO2 as solvent. Under these conditions, 4-Fluorobenzaldehyde was obtained with 93.0%yield, 95.4%conversion, 97.4% selectivity. The process for the production of low cost, small industrial pollution, will have broad market prospects. The structure was validated by the information provided from FTIR and GC. The results show that the end product is 4-Fluorobenzaldehyde.Many by-products were detected in the reaction mixture and considered to be formed deriving form water, solvent and the reaction themselves. Conducted waste management, include gas absorption, catalyst and solvent recycling.