Kua Jeremy, Rodriguez Alyssa A, Marucci Lily A, Galloway Melissa M, De Haan David O
Department of Chemistry and Biochemistry, University of San Diego , 5998 Alcala Park, San Diego, California 92110, United States.
J Phys Chem A. 2015 Mar 12;119(10):2122-31. doi: 10.1021/jp512396d. Epub 2015 Feb 27.
Density functional theory calculations, including Poisson-Boltzmann implicit solvent and free energy corrections, are applied to construct a free energy map of formaldehyde and ammonia co-oligomerization in aqueous solution at pH 7. The stepwise route to forming hexamethylenetetramine (HMTA), the one clearly identified major product in a complex mixture, involves a series of addition reactions of formaldehyde and ammonia coupled with dehydration and cyclization reactions at key steps in the pathway. The free energy map also allows us to propose the possible identity of some major peaks observed by mass spectroscopy in the reaction mixture being the result of stable species not along the pathway to HMTA, in particular those formed by intramolecular condensation of hydroxyl groups to form six-membered rings with ether linkages. Our study complements a baseline free energy map previously worked out for the self-oligomerization of formaldehyde in solution at pH 7 using the same computational protocol and published in this journal (J. Phys. Chem. A 2013, 117, 12658).
密度泛函理论计算，包括泊松-玻尔兹曼隐式溶剂模型和自由能校正，被用于构建pH = 7的水溶液中甲醛和氨共低聚反应的自由能图。逐步形成六亚甲基四胺（HMTA）的途径，HMTA是在复杂混合物中明确鉴定出的主要产物，该途径涉及甲醛和氨的一系列加成反应，以及在该途径关键步骤中的脱水和环化反应。自由能图还使我们能够推测出反应混合物中通过质谱观察到的一些主要峰可能对应的物质，这些物质并非沿着生成HMTA的途径产生，特别是那些由羟基分子内缩合形成带有醚键的六元环而产生的物质。我们的研究补充了之前使用相同计算方法得出的、发表在本期刊（《物理化学杂志A》2013年，第117卷，第12658页）上的关于pH = 7的溶液中甲醛自低聚反应的基线自由能图。
