NMR.-Investigation of the Formaldehyde Addition and Oligomerisation Equilibria in the System Formaldehyde/Water/Acetic Acid/Hydrochloric Acid

An NMR. investigation of the state of formaldehyde in acidic solutions has been carried out. Solutions of DCl/D2O/CD3COOD containing two sources of formaldehyde, i.e. paraformaldehyde (I) and trioxane (II), were used for this purpose. In systems I and II the effect of various D2O/CD3COOD ratios, at a constant DCl concentration, was studied, while for II the effect of changing DCl concentration was also investigated. The results show that in aqueous solution, formaldehyde exists primarily as the monomeric and linear oligomeric forms of methylene glycol. Reducing the amount of D2O (at constant DCl concentration), while increasing the CD3COOD content, results in an increase in the polymeric species and in trioxane. In addition, substitution of water by acetic acid results in systems that are catalytically more active than aqueous solutions of the same hydrochloric acid concentration. Along with the usual polymer‐monomer equilibria which exist in such solutions, side reactions of methylene glycol with the hydrochloric acid present also occur to a small extent, e.g. acetylation, substitution of OH by Cl and the Cannizzaro reaction. It is suggested that these findings will result in a better understanding of the formaldehyde crosslinking reactions in cotton cellulose.