The aza-Michael reaction is the addition of an amine to an electron deficient C=C double bond. This reaction is also used in the synthesis of precursors of polymeric networks. In this study, we paid attention to the kinetics and mechanism of the aza-Michael addition of cyclohexylamine (CHXA) to diethyl maleate (DEM) performed as a solvent-free, catalyst-free reaction and to concurrent reactions. In situ Raman spectroscopy, NMR spectroscopy and gas chromatography/mass spectrometry have shown the occurrence of three simultaneous reactions: (i) the aza-Michael addition of CHXA to DEM leading to diethyl 2-(cyclohexylamino)succinate, (ii) isomerization of DEM to diethyl fumarate (DEF), and (iii) the aza-Michael addition of CHXA to DEF formed by the reaction (ii). All of these reactions proceed with third order kinetics, first order in DEM or DEF and second order in CHXA. We propose a kinetic model that allows kinetic constants to be estimated. Furthermore, a numerical solution of the set of differential equations confirms the expected kinetic equations of reactions (i) and (ii) and gives values of rate constants comparable to the estimated ones. A DFT mechanistic study illustrates the structure of the reaction intermediates and transition states of all reactions and explains the contribution of the second amine molecule in the reaction mechanism.

氮杂-迈克尔反应是将胺加成至电子缺陷的C = C双键。该反应也用于聚合网络前体的合成。在这项研究中，我们关注环己胺（CHXA）在马来酸二乙酯（DEM）中的氮杂-迈克尔加成反应的动力学和机理，这是无溶剂，无催化剂的反应和同时发生的反应。原位拉曼光谱法，NMR光谱法和气相色谱/质谱法显示了三个同时发生的反应：（i）CHXA的氮杂-迈克尔加成反应生成DEM，导致2-（环己基氨基）琥珀酸二乙酯，（ii）异构化DEM到富马酸二乙酯（DEF），和（iii）将CHXA的氮杂-迈克尔加成至由反应（ii）形成的DEF中。所有这些反应均以三级动力学进行，一级在DEM或DEF中进行，而二级在CHXA中进行。我们提出了一个动力学模型，可以估算动力学常数。此外，一组微分方程的数值解确定了反应（i）和（ii）的预期动力学方程，并给出了与估算值可比的速率常数值。DFT机理研究说明了反应中间体的结构和所有反应的过渡态，并解释了第二胺分子在反应机理中的作用。