Kinetic Parameter Estimation of Solvent Free ReactionsMonitored by 13C NMR Spectroscopy. A Case Study: Mono andDi-(hydroxy)ethylation of Aniline with EthyleneCarbonate

The kinetics of solvent-free reactions can be followed in situ by 13C NMR spectroscopy, provided that the reaction mixture can be maintained liquid at the monitoring temperature. The pros and cons of the technique and the correct translation of the signal intensities into concentrations are discussed. A good model for this investigation is the reaction of ethylene carbonate (1) with aniline (2): at 140 °C, two alkylation products of N-mono- and N,N-bis-(2-hydroxy)ethylation of aniline form (compounds 3 and 4, respectively). The overall reaction occurs with heavy volume shrinking, so that the physical as well as the chemical features evolve during the course of the process. The chemical evolution is described by the kinetic constants k1 and k2 of the two N-alkylation steps, the physical evolution by the time dependent activity coefficients α(t). Two complementary procedures are utilized for the determination of these parameters.