Department of Organic Chemistry and Technology, Budapest University of Technology and Economics, 1521 Budapest, Hungary.
Org Biomol Chem. 2012 Mar 14;10(10):2011-8. doi: 10.1039/c2ob06972e. Epub 2012 Feb 1.
It is well-known that phosphinic acids do not undergo direct esterifications with alcohols under thermal conditions. However, the esterifications take place under microwave (MW) irradiation due to the beneficial effect of MW. As a comparison, maximum 12-15% conversions were observed on traditional heating. It was proved experimentally that the MW-assisted esterifications are not reversible under the conditions applied that may be the consequence of the hydrophobic medium established by the long chain alcohol/phosphinic ester. Neither the thermodynamic, nor the kinetic data obtained by high level quantum chemical calculations justify the direct esterification of phosphinic acids under thermal conditions. The thermodynamic data show that there is no driving force for the reactions under discussion. As a consequence of the relatively high values of activation enthalpy (102-161 kJ mol(-1)), these esterifications are controlled kinetically. Comparing the energetics of the esterification of phosphinic acids and the preparative results obtained under MW conditions, one can see the potential of the MW technique in the synthesis of phosphinates. During our study, a series of new cyclic phosphinates with lipophilic alkyl groups was synthesized.
众所周知，膦酸在热条件下不会与醇直接酯化。然而，由于微波（MW）的有益影响，酯化反应在微波辐射下发生。相比之下，在传统加热下观察到最大 12-15%的转化率。实验证明，在应用条件下，MW 辅助酯化是不可逆的，这可能是长链醇/膦酸酯所建立的疏水介质的结果。通过高水平量子化学计算获得的热力学和动力学数据都不能证明膦酸在热条件下可以直接酯化。热力学数据表明，讨论中的反应没有驱动力。由于活化焓（102-161 kJ mol(-1))值较高，这些酯化反应受动力学控制。比较膦酸酯化的能量学和在 MW 条件下获得的制备结果，可以看出 MW 技术在膦酸盐合成中的潜力。在我们的研究中，合成了一系列带有亲脂性烷基的新型环状膦酸盐。
