Experimental and theoretical study of the kinetic of proton transfer reaction by ion mobility spectrometry

Abstract

Rate constants of the proton transfer reactions RH++DMP→R+DMP·H+, where R was acetone (Ac), trimethyl amine (TMA) or H2O and DMP was 2,4-dimethyl pyridine have been measured by ion mobility spectrometry (IMS). The Reactant R was injected into the ionization region of IMS to produce RH+ while DMP was continuously delivered to the drift region to react with the RH+ pulsed into the drift tube by a shutter grid. Since DMP.H+ was generated along the drift tube, a tail appeared in the IMS spectrum that contained kinetic information. To prevent proton-bound dimer formation, the reactions were carried out at elevated temperatures (170–230°C). We measured rate constants of 1.17×10−9, 0.90×10−9 and 0.68×10−9cm3s−1 for proton transfer from H3O+, Ac·H+ and TMA·H+ to DMP, respectively. The experimental rate constants were almost temperature independent, indicating that no activation energy was involved in those proton transfer reactions. The rate constants were also calculated by using average dipole orientation (ADO) theory at B3LYP and MP2 levels. The calculated values revealed acceptable agreement between the experimental and theoretical trends.