Quantitative on-line NMR spectroscopy is used to study the kinetics of the reaction of aqueous formaldehyde and urea. The investigation focuses on the formation of low molecular mass compounds during the methylolation step. The experiments were carried out at overall formaldehyde to urea molar ratios between 1:1 and 4:1, pH values between 6 and 8, and temperatures between 313 and 353 K. The experimental data were used to develop a kinetic model based on the true species concentrations. The model describes the experimental data well and can be used to predict the composition of the reacting mixture of aqueous formaldehyde and urea during the methylolation step as a function of time.

Urea-formaldehyde resins are bulk products of the chemical industry. Their synthesis involves a complex reaction network. The present work contributes to its elucidation by presenting results from detailed NMR spectroscopic studies with different methods. Besides (1)H NMR and (13)C NMR, (15)N NMR spectroscopy is also applied. (15)N-enriched urea was used for the investigations. A detailed NMR signal assignment and a model of the reaction network of the hydroxymethylation step of the synthesis are presented. Because of its higher spectral dispersion and the fact that all key reactions directly involve the nitrogen centers, (15)N NMR provides a much larger amount of detail than do (1)H and (13)C NMR spectroscopy. Symmetric and asymmetric dimethylol urea can be clearly distinguished and separated from monomethylol urea, trimethylol urea, and methylene-bridged urea. The existence of hemiformals of methylol urea is confirmed. 1,3,5-Oxadiazinan-4-on (uron) and its derivatives were not found in the reaction mixtures investigated here but were prepared via alternative routes. The molar ratios of formaldehyde to urea were 1, 2, and 4, the pH values 7.5 and 8.5, and the reaction temperature 60 °C.

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,N′‐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 13C‐NMR spectroscopy and ESI‐MS. In corresponding NMR and MS spectra, peaks due to methoxymethylenebis(dimethyl)urea and its hemiformal were observed. 13C‐13C gCOSY analysis was conducted using labeled 13C‐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,N′‐dimethylurea‐formaldehyde systems in acidic and slightly basic media. As urea is very similar to N,N′‐dimethylurea, the results of this work strengthen the assumption that ether‐bridged condensation products are likely to form in UF resins. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

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Urea-formaldehyde resins are bulk products of the chemical industry. Their synthesis involves a complex reaction network. The present work contributes to its elucidation by presenting results from detailed NMR spectroscopic studies with different methods. Besides 1H NMR and 13C NMR also 15N NMR spectroscopy is applied. 15N-enriched urea was used for the investigations. A detailed NMR signal assignment and a model of the reaction network of the hydroxymethylation step of the synthesis are presented. Due to its higher spectral dispersion and the fact, that all key reactions directly involve the nitrogen centers, 15N NMR provides a much larger amount of detail than 1H and 13C NMR spectroscopy. Symmetric and asymmetric dimethylol urea can be clearly distinguished and separated from monomethylol urea, trimethylol urea and methylene bridged urea. The existence of hemiformals of methylol ureas is confirmed. 1,3,5-oxadiazinan-4-on (uron) and its derivatives were not found in the reaction mixtures investigated here, but were prepared via alternative routes. The molar ratios of formaldehyde to urea were 1, 2 and 4, the pH-values 7.5 and 8.5 and the reaction temperature 60° C.