Thermodynamics for complex formation of boric acid and borate with hydroxy acids and diols
Thermodynamics for complex formation of boric acid and borate with hydroxy acids and diols
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DOI：
10.1016/j.molliq.2021.117343
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发表时间：
2021-09-08
影响因子：
6
通讯作者：
Takamuku, Toshiyuki
中科院分区：
文献类型：
--
作者：
Maseda, Mikio;Miyazaki, Yoshinobu;Takamuku, Toshiyuki
用B-11 NMR和质谱研究了硼酸（B（OH）（3））和硼酸盐（B（OH）（4）（-））与乙醇酸、乳酸、2-羟基丁酸、3-羟基丁酸、苹果酸和（s）-1，2-丙二醇在水溶液中的配合物形成。本文比较了羟基酸（B-HA）体系与多元醇（B-OL）体系和（S）-1，2-丙二醇多元醇体系的1：1和1：2硼酸络合物的形成常数和热力学参数Δ H度和Δ S度。在B-HA和B-OL系统中，1：1复合物的形成是由化学驱动的。前者是由于硼酸的结构发生变化，并伴随着硼酸与羟基酸的脱水缩合而引起的。在后者中，硼酸盐增益仅来自硼酸盐与多元醇的脱水缩合。B-HA和B-OL系统的Δ H度值彼此相当，尽管水分子的脱水数量不同，即，一个和两个水分子。B-HA体系中1：2复合物的形成是由熵驱动的，而B-OL体系中1：2复合物的形成是由熵驱动的。这两个系统之间的差异归因于分离的配体分子的灵活性。由于分离的羟基酸形成分子内氢键，当羟基酸由于分子内氢键的断裂而与1：1复合物结合时，产生羟基酸的熵增益。因此，B-HA体系中配合物的稳定性主要取决于配体自由度的增加。(C)2021爱思唯尔有限公司版权所有。
The complex formation of boric acid (B(OH)(3)) and borate (B(OH)(4)(-)) with glycolic acid, lactic acid, 2-hydroxybutyric acid, 3-hydroxybutyric acid, malic acid, and (s)-1,2-propanediol in aqueous solutions has been investigated using B-11 NMR and mass spectroscopy. The formation constants and the thermodynamic parameters, Delta H degrees and Delta S degrees, of the 1:1 and 1:2 complexes of boric acid for the hydroxy acid (B-HA) systems were compared with those for the polyol (B-OL) systems previously reported, together with those for a polyol of (s)-1,2-propanediol presently examined. The 1:1 complex formation was enthalpically driven in both B-HA and B-OL systems. In the former, the enthalpic gain is caused by the structural change of boric acid, accompanied by the dehydration condensation of boric acid with hydroxy acid. In the latter, the enthalpic gain only arises from the dehydration condensation of borate with polyol. The Delta H degrees values for the B-HA and B-OL systems are comparable with each other, despite the different numbers of dehydration of water molecules, i.e., one and two water molecules, respectively. The formation of 1:2 complex was entropically driven in the B-HA systems, while that in the B-OL systems was enthalpically progressed. This difference between the two systems is attributed to the flexibility of isolated ligand molecules. Since the isolated hydroxy acids form the intramolecular hydrogen bond, the entropic gain of the hydroxy acids is generated as the hydroxy acid is bound to 1:1 complex due to the breaking of the intramolecular hydrogen bond. Thus, the stabilities of the complexes in the B-HA systems mainly depend on the gain for the freedom of ligand. (C) 2021 Elsevier B.V. All rights reserved.