Intrinsic (gas-phase) acidity and basicity of paracetamol

Abstract

Gas phase protonation enthalpy (proton affinity) and deprotonation enthalpy of paracetamol, PA = 909.4 ± 8.4 kJmol -1 and ∆acidH 0 = 1430.3 ± 8.8 kJmol -1 , have been experimentally determined by the extended kinetic method (EKM) using ESI-triple-quadrupole mass spectrometry. Gas phase basicity and acidity deduced from these experiments, GB = 869.9 ± 8.4 kJmol -1 and GA = 1404.7 ± 8.8 kJmol -1 are in good agreement with calculations performed at the B3LYP level of theory with 6-311++G(3df,2p) and 6-311++G(d,p) basis sets. We also have derived the enthalpy of formation of deprotonated (ΔfH 0 (g) = -386.4 ± 9.0 kJ·mol -1 ) and protonated (ΔfH 0 (g) = 346.3 ± 8.6 kJ·mol -1 ) paracetamol ions.