Halex reaction of benzyl chloride with potassium fluoride to benzyl fluoride using ionic liquid as catalyst and potassium iodide as co-catalyst: Insight into mechanism and kinetics of solid-liquid phase transfer catalysis

Organic fluorides are of interest owing to their very high chemical and thermal stability. Most of the commercial applications include refrigerants in air conditioning systems, fluoropolymers synthesis such as polytetrafluoroethylene (PTFE), and in synthesis of pharmaceutical compounds, surfactants and agrochemicals. In the current work, the synthesis of benzyl fluoride was accomplished by reacting benzyl chloride with solid potassium fluoride using tetrabutylphosphonium bromide as catalyst and solid potassium iodide as co-catalyst under solidliquid phase transfer catalysis at 80 oC. Benzyl fluoride finds use in treatment of Asthama and as an intermediate compound in synthesis of herbicides and dyes. The mechanism was based on homogeneous solubilization of solid KF and KI. Tetrabutylphosphonium bromide forms complex with inorganic solid and dissolves in the organic phase where halogen exchange reaction occurs. The reaction is intrinsically kinetically controlled. A mathematical model was developed to study the kinetics of reaction and used to extract the rate constant and activation energy.