Department of Organic Chemistry and Technology, Budapest University of Technology and Economics, 1521 Budapest, Hungary.
Medicinal Chemistry Research Group, Research Centre for Natural Sciences, 1117 Budapest, Hungary.
Molecules. 2021 Aug 31;26(17):5303. doi: 10.3390/molecules26175303.
It is well-known that the P-acids including phosphonic acids resist undergoing direct esterification. However, it was found that a series of alkylphoshonic acids could be involved in monoesterification with C-C alcohols under microwave (MW) irradiation in the presence of [bmim][BF] as an additive. The selectivity amounted to 80-98%, while the isolated yields fell in the range of 61-79%. The method developed is a green method for P-acid esterification. DFT calculations at the M062X/6-311+G (d,p) level of theory (performed considering the solvent effect of the corresponding alcohol) explored the three-step mechanism, and justified a higher enthalpy of activation (160.6-194.1 kJ·mol) that may be overcome only by MW irradiation. The major role of the [bmim][BF] additive is to increase the absorption of MW energy. The specific chemical role of the [BF] anion of the ionic liquid in an alternative mechanism was also raised by the computations.
众所周知，膦酸包括膦酸酯不易发生直接酯化反应。然而，人们发现，在微波（MW）辐照下，在[bmim][BF]作为添加剂的存在下，一系列烷基膦酸可以与 C-C 醇进行单酯化反应。选择性高达 80-98%，而分离收率在 61-79%之间。所开发的方法是一种绿色的 P 酸酯化方法。在 M062X/6-311+G（d，p）理论水平（考虑相应醇的溶剂效应）进行的 DFT 计算探索了三步机制，并证明了更高的活化焓（160.6-194.1 kJ·mol），这可能只有通过 MW 辐射才能克服。[bmim][BF]添加剂的主要作用是增加 MW 能量的吸收。计算还提出了离子液体中[BF]阴离子在替代机制中的特殊化学作用。
