~(13)C-NMR, ~(13)C-~(13)C gCOSY, and ESI-MS Characterization of Ether-Bridged Condensation Products in N,N0-Dimethylurea-Formaldehyde Systems

摘要

The reaction of urea with formaldehyde is the basis for the production of urea-formaldehyde (UF) resins which are widely applied in the wood industry. The presence of ether-bridged condensation products in the UF resin reaction system is an open question in the literature. It is addressed in the present work. The N,N0-dimethylurea-formaldehyde model system was studied since it is chemically similar to the UF resin reaction system but allows for a simple elucidation of all reaction products. It was analyzed by ~(13)C-NMR spectroscopy and ESI-MS. In corresponding NMR and MS spectra, peaks due to methoxymethylenebis(dimethyl)urea and its hemiformal were observed. ~(13)C-~(13)C gCOSY analysis was conducted using labeled ~(13)C-formaldehyde. The correlation spectra showed evidence for an ether-bridged compound and mass spectra exhibited peaks agreeing with labeled methoxymethylenebis(dimethyl)urea and its hemiformal. Methoxymethylenebis(dimethyl)urea was characterized in N,N0-dimethylurea-formaldehyde systems in acidic and slightly basic media. As urea is very similar to N,N0-dimethylurea, the results of this work strengthen the assumption that etherbridged condensation products are likely to form in UF resins.