13C‑NMR Spectroscopic Study of the Kinetics of Formaldehyde Oligomerization Reactions in the System (Formaldehyde + Water + Isoprenol)

Isoprenol (3-methyl-3-buten-1-ol) is an important intermediate in the chemical industry, which is used, for example, in the production of citral. It is produced from aqueous formaldehyde and isobutene and has to be separated from mixtures containing formaldehyde and water in the purification process, which is complicated, as formaldehyde is highly reactive and forms oligomers with both water and isoprenol. These oligomerization reactions are slow under conditions relevant for the isoprenol process so that reliable information on the kinetics of the formaldehyde oligomerization reactions is needed for understanding and modeling the process. While this information is already available for the oligomerization reactions of formaldehyde and water, there is no information yet on the kinetics of the oligomerization reactions of formaldehyde and isoprenol. Therefore, reaction kinetic experiments in the systems (formaldehyde + isoprenol) and (formaldehyde + water + isoprenol) were performed in the present work using quantitative 13C-NMR spectroscopy at temperatures ranging from 282 to 333 K and at pH values ranging from 0.6 to 6.8. Based on the new experimental data and information taken from the literature, a reaction kinetic model was developed, which describes the reaction kinetics in the system (formaldehyde + water + isoprenol) and its binary formaldehyde-containing subsystems. A first application of the model to a thin-film evaporation process is presented.