每周分子Molecule of the Week

Original ACS美国化学会 ACS美国化学会 2022-07-01

Molecule of the Week: Deuterium oxide

每周分子：重水

氧化氘(D₂O)，又称“重水”，是水的一种形式，含有两个²H或D。重水这个词也用来指一些¹H原子被²H原子取代的水。在这种情况下，两种同位素之间的快速交换形成的半重HDO分子是D₂O分子的两倍。

1934年诺贝尔化学奖得主Harold Urey是氘化学的先驱。1931年，他和他在哥伦比亚大学（纽约市）的同事们仔细地蒸馏了5升液态氢，生成了1毫升的氘分子。不久之后，他们通过长时间的电解从普通水中生成了D₂O。

几十年来，D₂O在许多化学应用中都非常有用。D₂O溶剂中反应速率与H₂O中反应速率的差异常常为反应机理提供线索（如果水是反应物之一，这一点尤为重要）。

在一些核反应堆中，D₂O用来减慢中子的速度，使它们与可裂变的²³⁵U而不是不裂变的²³⁸U发生反应，从而消除了铀浓缩的需要。在这个应用中，D₂O优于H₂O，因为其热中子俘获截面比水大约6倍。

重水信息速览

CAS 登记号	7789-20-0
分子式	D₂O
摩尔质量	20.03 g/mol
外观	Colorless liquid
熔点	3.8 ºC
沸点	101.4 ºC
水溶性	互溶

重水危害信息

GHS 分类*: 非危害物质或混合物

【关于每周分子】

自2001年以来，“每周分子”已成为广受欢迎的栏目。多数分子由读者推荐。每个结构都经由科学家审查，并以3-D和平面图像的形式显示，同时附有该分子简介。可以通过美国化学文摘社（CAS）提供的SciFinder中的CAS REGISTRY获取每周分子的更多信息。CAS REGISTRY中的每条物质信息都展示了物质的CAS登记号、索引名、通用名、商品名、书目信息等其他更多信息。发送邮件至motw@acs.org推荐您感兴趣的分子。

Deuterium oxide (D₂O), aka “heavy water”, is the form of water that contains two atoms of the ²H, or D, isotope. The term heavy water is also used for water in which ²H atoms replace only some of the ¹H atoms. In this case, rapid exchange between the two isotopes forms twice as many “semiheavy” HDO molecules as D₂O.

Harold Urey, the 1934 Nobel Prize laureate in chemistry, pioneered deuterium chemistry. In 1931, he and his colleagues at Columbia University (New York City) carefully distilled 5 L of liquid hydrogen to produce 1 mL of molecular deuterium. Shortly afterward, they produced D₂O from ordinary water by using prolonged electrolysis.

For decades, D₂O has been extremely useful in many chemical applications. The difference between a reaction rate in D₂O solvent versus that in H₂O often provides clues as to the reaction’s mechanism. This is especially important if water is one of the reactants.

In some nuclear reactors, D₂O is used to slow down neutrons so that they react with fissionable ²³⁵U rather than nonfissioning ²³⁸U, thus eliminating the need for uranium enrichment. D₂O is superior to H₂O for this use because of its ≈6 times greater thermal neutron capture cross section.

Deuterium oxide fast facts

CAS Reg. No.	7789-20-0
Empirical formula	D₂O
Molar mass	20.03 g/mol
Appearance	无色液体
Melting point	3.8 ºC
Boiling point	101.4 ºC
Water solubility	Miscible

Deuterium oxide hazard information

GHS classification*: not a hazardous substance or mixture

*Globally Harmonized System of Classification and Labeling of Chemicals. Explanation of pictograms.

About Molecule of the Week

MOTW has been a popular feature on ACS website since 2001. Many molecules are suggested by our website visitors. Every structure is reviewed by a scientist and displayed in 3-D and flat images with a brief description. Each week’s molecule also links to a sample record from the CAS REGISTRY, which is searched using SciFinder. Each record displays the registry number, index name and synonyms, bibliographic information, and more. Send us a molecule suggestion at motw@acs.org.

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