Quantification of Monomeric Formaldehyde in Aqueous Solutions by NMR Spectroscopy and Determination of the Chemical Equilibrium Constant of Methylene Glycol Formation

Formaldehyde is an important intermediate in the chemical industry. It is highly reactive and usually handled in aqueous solutions, where it is mainly bound in the oligomeric reaction products methylene glycol and poly(oxymethylene) glycols. Quantitative information on the very low concentration of monomeric formaldehyde in these solutions is difficult to obtain, but crucial for many applications in which this highly reactive species plays a key role. Rivlin et al. (J. Phys. Chem. B 2015, 119, 4479–4487) have shown that NMR spectroscopy can be applied successfully for determining the concentration of monomeric formaldehyde, but they have used either 13C enriched formaldehyde (for 13C NMR) or deuterated water (for 1H NMR) and have studied only dilute formaldehyde solutions at temperatures below 333 K. We show here that the amount of monomeric formaldehyde in aqueous solutions can be determined without the use of deuterated water by 1H NMR spectroscopy and apply the method for studies at temperatures between 293 and 393 K at overall formaldehyde concentrations up to 0.5 g g–1. New data were used to determine the chemical equilibrium constant of methylene glycol formation, for which only strongly scattering data were previously available in the literature.