In-situ characterization of RF field induced reactions by Raman spectroscopy - I. Urethane formation kinetics and mechanisms

The effects Of radiofrequency (RF) electromagnetic field on the kinetics an d mechanism of a series of secondary alcohol and phenylisocyanate reactions were studied by in-situ Raman spectroscopy. The urethane reaction rates un der intense RF fields increased significantly. A 2-propnnol and phenylisocy anate reaction under an RF field of 6.3 kV/cm could reach 90 percent conver sion in less than 150 seconds, yet it took more than 30 min without the exp osure to an RF field. The maximum reaction rate of such a reaction system i ncreased from 0.4 to 1.6 percent per second when the RF field intensity inc reased from 1.6 to 6.3 kV/cm. Reaction kinetics simulation based on a simpl e kinetic model was employed to analyze the mechanisms of these reactions. The simulation results suggest that an intense RF field has no direct influ ence on urethane reaction mechanism and kinetic parameters. The main effect of an RF field on pure urethane reactions is the dielectric heating effect . Although the heat generated during the reaction due to the systems' diele ctric loss is small, an intense RF field creates high initial heating rates , which induces high heat generation of these exothermic reaction (urethane ) systems, and results in high reaction temperatures (from 20 degreesC to 1 60 degreesC in about 45 seconds for a 2-propanol and phenylisocyanate react ion under an RF field of 6.3 kV/cm).