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Names | |
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Preferred IUPAC name Octamethyl-1,3,5,7,2,4,6,8-tetroxatetrasilocane | |
Other names
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Identifiers | |
3D model (JSmol) | |
ChEBI | |
ChemSpider | |
ECHA InfoCard | 100.008.307 |
EC Number |
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PubChem CID | |
UNII | |
CompTox Dashboard (EPA) | |
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Properties | |
[(CH3)2SiO]4 | |
Molar mass | 296.616 g·mol−1 |
Density | 0.956 g/mL |
Melting point | 17–18 °C (63–64 °F; 290–291 K) |
Boiling point | 175–176 °C (347–349 °F; 448–449 K) |
56.2±2.5 ppb (23 °C) [1] | |
log P | 6.98±0.13 [2] |
Vapor pressure | 124.5±6.2 Pa (25 °C) [3] |
Hazards | |
GHS labelling: | |
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Warning | |
H361f, H410 M=10 [4] | |
Related compounds | |
Related compounds | |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). |
Octamethylcyclotetrasiloxane, also called D4, is an organosilicon compound and one of a number of cyclic siloxanes (cyclomethicones). It is a colorless viscous liquid with a high boiling point. It has historically been used on a large scale in personal care products including cosmetics, hair conditioners and emollients (moisturising creams), [5] Global production in 1993 was 136,000 tons, [6] however it is now facing significant pressure from regulators. It is a substance of very high concern In the EU, where it was classified as a PBT and effectively banned in personal care products in 2018. The US EPA began reevaluating its risks in 2020. [7] Replacements include branched-chain alkanes (isoparaffins).
Commercially D4 is produced from dimethyldichlorosilane. Hydrolysis of the dichloride produces a mixture of cyclic dimethylsiloxanes and polydimethylsiloxane. From this mixture, the cyclic siloxanes including D4 can be removed by distillation. In the presence of a strong base such as KOH, the polymer/ring mixture is equilibrated, allowing complete conversion to the more volatile cyclic siloxanes: [5]
D4 and D5 are also precursors to the polymer. The catalyst is again KOH.
![]() | This article may be too technical for most readers to understand.(September 2022) |
D4 is of low acute toxicity. The LC50 for a single four hour inhalation exposure in rats is 36 mg/L. The oral LD50 in rats is above 4800 mg/kg and the dermal LD50in rats is above 2400 mg/kg. [8]
As the smallest cyclic dimethylsiloxane that does not experience considerable ring strain, [9] D4 is one of the most abundant siloxanes in the environment, e.g. in landfill gases. [10] D4 and D5 have attracted attention because they are pervasive. Cyclic siloxanes can be detected in some species of aquatic life. [11] An independent, peer-reviewed study in the US found "negligible risk from D4 to organisms" [12] while a scientific assessment by the Australian government stated, "the direct risks to aquatic life from exposure to these chemicals at expected surface water concentrations are not likely to be significant." [13]
In the European Union, D4 was characterized as a substance of very high concern (SVHC) due to its PBT and vPvB properties and was thus included in the candidate list for authorisation. [14] [ clarification needed ] D4 shall not be placed on the market in wash-off cosmetic products in a concentration equal to or greater than 0.1% by weight of either substance, after 31 January 2020. [15] Conversely, a detailed review and analysis of the science by the State of Washington in 2017 led to the removal of D4 from their CHCC listing. [16] [ clarification needed ] That decision prompted the State of Oregon to follow suit in 2018. [17]
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