NMR Spectroscopic Investigation of the Cannizzaro Reaction as Side Reaction in Aqueous Formaldehyde Solutions

The formation of formic acid in aqueous formaldehyde solutions via the Cannizzaro reaction poses significant technological challenges, particularly with respect to corrosion. Although the Cannizzaro reaction has been studied extensively in the literature, it remains poorly quantified under typical industrial process conditions. In this work, we present the first systematic kinetic study of this reaction as a side reaction in aqueous formaldehyde solutions. Using 1H NMR spectroscopy, we simultaneously quantified monomeric formaldehyde, methanol, formic acid, and poly(oxymethylene) hemiformals at overall formaldehyde mass fractions of 0.3–0.5 g g–1, temperatures of 353–393 K, and pH values of 2–9. Reaction monitoring over several days revealed a linear increase in formic acid concentration, confirming kinetic control. Rate constants of the Cannizzaro reaction were determined from the experimental data and correlated as a function of temperature and pH value. The results allow reliable prediction of formic acid accumulation in technical aqueous formaldehyde solutions, thereby supporting corrosion mitigation and the maintenance of quality standards in formaldehyde technology.