Comprehensive thermodynamic and kinetic studies on N-methylation and N-formylation during methacrolein synthesis via aldol reaction

Two types of N -methylation and N -formylation during MAL synthesis was revealed. • Comprehensive thermodynamic and kinetic studies were systematically conducted. • The formate species was identified as the key intermediates for these reactions. • Reaction networks for N -methylation and N -formylation were proposed. Synthesis of methacrolein (MAL) from propionaldehyde and formaldehyde (FA) via mild Mannich reaction catalyzed by sec-amine is a crucial step for methyl methacrylate (MMA) production. However, the undesired N -methylation and N -formylation of catalytically active sec -amine centers by FA leads to catalyst consumption. In this work, comprehensive thermodynamic and kinetic investigations were conducted for these two types of crucial side reactions on the basis of reaction networks understanding. It was identified by in situ ATR FTIR that the generated formic acid/formate species are responsible for the formation of N -methyldiethanolamine and N, N -bis (2-hydroxyethyl) formamide byproducts. Thermodynamic analyses confirmed required parameters and demonstrated that these reactions are both exothermic and product-favored under standard condition, with N -methylation exhibiting much stronger driving force than N -formylation. Kinetic assessments further revealed reaction rate constants, reaction orders and activation energies, with deviation within 5%, and lower reaction barrier of N -formylation than N -methylation. These findings suggest practical strategies for reaction process optimization and catalyst stability improvement.