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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Theoretical Study of Decomposition of Methanediol in Aqueous Solution
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Theoretical Study of Decomposition of Methanediol in Aqueous Solution

机译：水溶液中甲烷分解的理论研究

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摘要

Methanediol is a product of the hydration of formaldehyde and is more abundant than formaldehyde in aqueous solution. We carried out a number of quantum chemical simulations to study the decomposition of methanediol in aqueous solution. The decomposition of a methanediol proceeds by transferring a proton from a hydroxyl to an oxygen atom of the other hydroxyl in the methanediol. The decomposition of the methanediol completes after the cleavage of the bond between the formaldehyde and the water molecule. The probability of the proton transfer increases by the quantum mechanical tunneling at the low temperature because the width of the potential barrier for the decomposition becomes similar to the de Broglie wavelength of the proton. We consider the catalytic effect of water molecules in aqueous solution. The structure of the methanediol is not required to change significantly when undergoing decomposition due to the active role of water molecules to transfer a proton. We consider three types of arrangement for water molecules with respect to a methanediol: (1) a ring structure formed by a methanediol and water molecules; (2) a water cluster attracted to a methanediol by hydrogen bonds; and (3) a water cluster and additional water molecules, both of which are attracted to a methanediol by hydrogen bonds. The activation energy for the decomposition is reduced by a water cluster more efficiently than water molecules in a ring structure. However, the activation energy reduced by a water cluster is still larger than that obtained from laboratory experiments. We include water molecules that are attracted to a methanediol by hydrogen bonds during the water-cluster-catalyzed decomposition of a methanediol. The hydrogen bonds with the water molecules permit little change in the structure of the methanediol during the decomposition and play a significant role to reduce the activation energy for the decomposition. The rate constant obtained from the theoretical simulation agrees well with that determined by the laboratory experiment.
机译：甲烷二醇是甲醛水合的产物，在水溶液中比甲醛更丰富。我们进行了许多量子化学模拟，以研究甲烷二醇在水溶液中的分解。甲烷二醇的分解通过将质子从羟基转移至甲烷二醇中另一个羟基的氧原子而进行。甲醛与水分子之间的键断裂后，甲烷二醇的分解完成。质子转移的可能性通过低温下的量子机械隧穿而增加，因为分解势垒的宽度变得与质子的德布罗意波长相似。我们考虑水溶液中水分子的催化作用。由于水分子传递质子的积极作用，分解时不需要甲烷二醇的结构发生显着变化。我们考虑相对于甲二醇的水分子的三种排列方式：（1）由丙二醇和水分子形成的环结构; （2）通过氢键吸引到甲烷二醇的水团; （3）水簇和另外的水分子，两者均通过氢键被吸引至甲烷二醇。水团簇比环状结构中的水分子更有效地降低了分解的活化能。但是，水簇降低的活化能仍然比实验室实验获得的活化能大。我们包括了水分子催化的甲烷二醇分解过程中通过氢键被甲烷二醇吸引的水分子。与水分子的氢键在分解过程中几乎不会改变甲烷二醇的结构，并在降低分解的活化能方面起着重要作用。从理论模拟获得的速率常数与实验室实验确定的速率常数非常吻合。

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