每周分子 | Molecule of the Week

Original ACS 美国化学会 ACS美国化学会 2022-07-01

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每周分子：八甲基环四硅氧烷

Molecule of the Week:

Octamethylcyclotetrasiloxane

八甲基环四硅氧烷是环硅氧烷或环聚二甲基硅氧烷家族成员。它因具有4个二甲基硅氧烷单元，被简称为D4。D4以油性液体或低熔点固体的形式存在。

1946年，通用电气公司(位于美国纽约州斯克内塔迪)的Winton Patnode和Donald F. Wilcock，在利用甲基氯硅烷水解制备甲基聚硅氧烷的广泛研究中，制备了D4。他们报道的众多反应之一是：将二甲基二氯硅烷(Me₂SiCl₂)与大量水混合生成了一种无色的油，该油中有一种成分的经验分子式与Me₂SiO相近。

分析结果表明，该油主要为分子式为(Me₂SiO)_x的环状低聚物混合物，分离得到的化合物范围为x = 3 到x = 10。每种环硅氧烷的相对含量随水解条件(如Me₂SiCl₂/H₂O的比例以及共溶剂、酸或碱的存在)而变化。总的来说，D4 (x = 4)是含量最丰富的产物。

如今，D4的商业生产仍是借助同样的通用方法。产品混合物通过蒸馏，分离成各种成分。D4和其他低聚物被用于制备聚(二甲基硅氧烷) [(Me₂SiO)_n]，俗称硅油。D4本身被用作塑料和橡胶制品、油漆、粘合剂、化妆品、食品包装等许多其他产品领域的添加剂。其全球产量达数十万吨。

由于其广泛的生产和使用，D4因其对环境和健康的不利影响而受到审查。去年9月，美国环境保护署宣布对D4工业用途的环境风险进行评估。美国FDA将决定是否对其食品、医疗保健和个人护理用途进行评估。

八甲基环四硅氧烷信息速览

CAS 登记号	556-67-2
CAS SciFinder命名	Cyclotetrasiloxane, 2,2,4,4,6,6,8,8-octamethyl-
分子式	C₈H₂₄O₄Si₄
摩尔质量	296.62 g/mol
外观	无色油状液体或白色固体
熔点	17–18°C
沸点	175–176°C
水溶性	56 µg/L

八甲基环四硅氧烷危害信息

GHS分类：易燃液体，分类1
H224-极易燃液体和蒸汽
GHS分类：急性毒性，口服，分类4
H302-吞食有害
GHS分类：急性毒性，皮肤，分类3
H311-皮肤接触毒性
GHS分类：生殖毒性，分类2
H361-疑似损害生育能力或未出生的孩子
GHS分类：长期(慢性)水生危，分类3
H413-可能对水生生物造成长期有害影响

【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CAS SciFinderⁿ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吧。

Octamethylcyclotetrasiloxane is a member of the cyclic siloxane, or cyclomethicone, family. It is often called simply D4 because of its four dimethylsiloxane units. It exists as an oily liquid or low-melting solid.

In 1946, Winton Patnode and Donald F. Wilcock at General Electric (Schenectady, NY) prepared D4 as part of an extensive study of methylpolysiloxanes made by hydrolyzing methylchlorosilanes. In one the many reactions they reported, they mixed dimethyldichlorosilane (Me₂SiCl₂) with large volumes of water to produce a colorless oil with a composition that had an empirical formula close to that of Me₂SiO.

Analysis of the oil showed that it was primarily a mixture of cyclic oligomers of the formula (Me₂SiO)_x, with isolated compounds ranging from x = 3 to x = 10. The relative amounts of each of the cyclosiloxanes varied with hydrolysis conditions such as the Me₂SiCl₂/H₂O ratio and the presence of cosolvents, acids, or bases. In general, D4 (x = 4) was the most abundant product.

Today, D4 is commercially produced by the same general method. The product mixture is separated into its components via distillation. D4 and the other oligomers are used to prepare poly(dimethylsiloxane) [(Me₂SiO)_n], familiarly known as silicone oil. D4 itself is used as an additive to plastic and rubber products, paints, adhesives, cosmetics, food packaging, and many other product areas. Its worldwide production is in the hundreds of thousands of tonnes.

Because of its widespread production and use, D4 has come under scrutiny for its adverse environmental and health effects. Last September, the US Environmental Protection Agency announced an evaluation of the environmental risks of its industrial uses. It will be up to the Food and Drug Administration to determine whether its food, health care, and personal care uses are evaluated.

Octamethylcyclotetrasiloxanefast facts

CAS Reg. No.	556-67-2
SciFinder nomenclature	Cyclotetrasiloxane, 2,2,4,4,6,6,8,8-octamethyl-
Empirical formula	C₈H₂₄O₄Si₄
Molar mass	296.62 g/mol
Appearance	Colorless oily liquid or white solid
Melting point	17–18°C
Boiling point	175–176°C
Water solubility	56 µg/L

Octamethylcyclotetrasiloxanehazard information

Flammable liquids, category 1
H224-Extremely flammable liquid and vapor
Acute toxicity, oral, category 4
H302-Harmful if swallowed
Acute toxicity, dermal, category 3
H311-Toxic in contact with skin
Reproductive toxicity, category 2
H361-Suspected of damaging fertility or the unborn child
Long-term (chronic) aquatic hazard, category 3
H413-May cause long-lasting harmful effects to aquatic life

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 CAS SciFinderⁿ. 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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