Formation of methylolureas under alkaline condition: A theoretical study

Abstract

The base-catalytic reactions between urea and formaldehyde were investigated by using theoretical methods of B3LYP and MP2 with solvent effects included. The urea anion H2NCONH- produced by the reaction of urea with OH- can react with two forms of formaldehyde, CH 2O and CH2(OH)2, via nucleophilic addition and SN2 2 mechanisms, respectively. The addition mechanism is energetically more favourable. The calculated potential energy barriers for the formations of mono-methylolureas (MMU), di-methylolureas (DMU) and tri-methylolureas (TMU) are close, suggesting that the -NH2 and -HN- groups have close reactivity toward formaldehyde or substitutions of methylol groups on urea do not significantly decrease the reactivity of the left reactive positions. Statistical factor may explain the observed lower reactivity of methylolureas than free urea. The steric hindrance is the main factor that rationalizes the absence of tetra-methylolurea in experiment.