Octamethylcyclotetrasiloxane

Last updated
Octamethylcyclotetrasiloxane
Octamethylcyclotetrasiloxane Structural Formula V.1.svg
Octamethylcyclotetrasiloxane-3D-balls.png
Names
Preferred IUPAC name
Octamethyl-1,3,5,7,2,4,6,8-tetroxatetrasilocane
Other names
  • D4
  • D4
  • OMCTS
Identifiers
3D model (JSmol)
ChEBI
ChemSpider
ECHA InfoCard 100.008.307 OOjs UI icon edit-ltr-progressive.svg
EC Number
  • 209-136-7
PubChem CID
UNII
  • InChI=1S/C8H24O4Si4/c1-13(2)9-14(3,4)11-16(7,8)12-15(5,6)10-13/h1-8H3
    Key: HMMGMWAXVFQUOA-UHFFFAOYSA-N
  • C[Si]1(O[Si](O[Si](O[Si](O1)(C)C)(C)C)(C)C)C
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:
GHS-pictogram-silhouette.svg [4]
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 with the formula [(CH3)2SiO]4. It is a colorless viscous liquid. It is a common cyclomethicone. It is widely used in cosmetics. [5]

Contents

Production and polymerization

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]

[(CH3)2SiO]4nn[(CH3)2SiO]4

D4 and D5 are also precursors to the polymer. The catalyst is again KOH.

Occurrence

It is among the most important of all the cyclic siloxanes, with a global production volume of 136 million kilograms in 1993. [6] 100,000–1,000,000 tonnes per year of D4 is manufactured and/or imported in the European Economic Area. [7]

Safety and environmental considerations

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]

See also

Related Research Articles

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References

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