Synthesis Of4-fluorobenzaldehyde By F-Cl Exchange Fluorination In Supercritical Carbon Dioxide

Preparation of4-fluorobenzaldehyde by halogen-exchange fluorination of4-chlorobenzaldehyde (PCAD) with tetrabutylammonium fluoride was studied in thisarticle. Methanol was used as co-solvent and Ph4PBr was used as catalyst insupercritical carbon dioxide.The effects of factors such as different co-solvents, reaction time, material molarratios, reaction temperature, reaction pressure on the yield of4-fluorobenzaldehydewere discussed in detail. In10mL methanol and2.00g Ph4PBr,4-fluorobenzaldehydecould be satisfactorily obtained in supercritical carbon dioxide under kinds ofconditions, yielding of4-fluorobenzaldehyde was15.9%to48.1%when reaction timewas2h to6h, the mole ratio (TBAF：PCAD) was1.0to3.0, reaction temperature was100℃to140℃, reaction pressure was7.5MPa to9.5MPa. The yield of4-fluorobenzaldehyde firstly uprised and then lowered as reaction time, reactiontemperature, reaction pressure increased. The yield of4-fluorobenzaldehyde firstlyuprised and then leveled off as the mole ratio (TBAF：PCAD) increased. The optimalreaction conditions were found as follows, n(TBAF)：n(PCAD)：n(Ph4PBr)=1.5：1：0.1, CH3OH10mL, reaction temperature120℃, reaction time4h and reactionpressure9MPa. Under these conditions,4-fluorobenzaldehyde was obtained with47.2%yield.Kinetics research proved that this reaction was a first order reaction. The reactionrate constant was0.214h-1,0.244h-1,0.303h-1,0.342h-1respectively when thetemperature was363K,373K,383K,393K. The activation energy was20168.151J·mol-1, pre-exponential was166.834.