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Skeletal formula of decamethylcyclopentasiloxane
Space-filling model of the decamethylcyclopentasiloxane molecule
IUPAC name
Other names

Cyclic dimethylsiloxane pentamer

3D model (JSmol)
ECHA InfoCard 100.007.969
EC Number
  • 208-764-9
MeSH Decamethylcyclopentasiloxane
RTECS number
  • GY5945200
Molar mass 370.770 g·mol−1
Appearance Colourless liquid
Density 0.958 g cm−3
Melting point −47 °C; −53 °F; 226 K
Boiling point 210 °C (410 °F; 483 K)
17.03±0.72 ppb (23 °C) [1]
log P 8.07[2]
Vapor pressure 20.4±1.1 Pa (25 °C) [3]
Viscosity 3.74 cP
Safety data sheet External MSDS
GHS pictograms GHS02: FlammableGHS08: Health hazard
GHS Signal word Warning
H226, H361, H412, H413
P201, P202, P210, P233, P240, P241, P242, P243, P273, P280, P281, P303+361+353, P308+313, P370+378, P403+235, P405, P501
NFPA 704 (fire diamond)
Flammability code 2: Must be moderately heated or exposed to relatively high ambient temperature before ignition can occur. Flash point between 38 and 93 °C (100 and 200 °F). E.g. diesel fuelHealth code 1: Exposure would cause irritation but only minor residual injury. E.g. turpentineReactivity code 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g. liquid nitrogenSpecial hazards (white): no codeNFPA 704 four-colored diamond
Flash point 73 °C (163 °F; 346 K)
Related compounds
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Decamethylcyclopentasiloxane (D5) is an organosilicon compound with the formula [(CH3)2SiO]5. It is a colorless and odorless liquid that is slightly volatile.[4]


The compound is classified as a cyclomethicone. Such fluids are commonly used in cosmetics, such as deodorants, sunblocks, hair sprays and skin care products. It is becoming more common in hair conditioners, as it makes the hair easier to brush without breakage. It is also used as part of silicone-based personal lubricants. D5 is considered an emollient. In Canada, among the volume used in consumer products approximately 70% were for antiperspirants and 20% for hair care products.[5] 10,000–100,000 tonnes per year of D5 is manufactured and/or imported in the European Economic Area.[6] Atmospheric emissions of D5 in the Northern Hemisphere were estimated to 30,000 tonnes per year.[7]

Production and polymerization[edit]

Commercially D5 is produced from dimethyldichlorosilane. Hydrolysis of the dichloride produces a mixture of cyclic dimethylsiloxanes and polydimethylsiloxane. From this mixture, the cyclic siloxanes including D5 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:[8]

n5 [(CH3)2SiO]nn [(CH3)2SiO]5

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

Safety and environmental considerations[edit]

The LD50 for D5 in rats is >50 g/kg.[8]

The environmental impacts of D5 and D4 have attracted attention because these compounds are pervasive. Cyclic siloxanes have been detected in some species of aquatic life.[9] A scientific review in Canada has determined that “Siloxane D5 does not pose a danger to the environment”[10] and a scientific assessment of D5 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."[11] However, in the European Union, D5 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.[12] Since 31 January 2020, D5 cannot be placed on the market in the European Union in wash-off cosmetic products in a concentration equal to or greater than 0.1 % by weight.[13]


  1. ^ Sudarsanan Varaprath; Cecil L. Frye; Jerry Hamelink (1996). "Aqueous solubility of permethylsiloxanes (silicones)". Environmental Toxicology and Chemistry. 15 (8): 1263–1265. doi:10.1002/etc.5620150803.
  2. ^ Shihe Xu, Bruce Kropscott (2012). "Method for Simultaneous Determination of Partition Coefficients for Cyclic Volatile Methylsiloxanes and Dimethylsilanediol". Analytical Chemistry. 84 (4): 1948–1955. doi:10.1021/ac202953t. PMID 22304371.
  3. ^ Ying Duan Lei; Frank Wania; Dan Mathers (2010). "Temperature-Dependent Vapor Pressure of Selected Cyclic and Linear Polydimethylsiloxane Oligomers". Journal of Chemical & Engineering Data. 55 (12): 5868–5873. doi:10.1021/je100835n.
  4. ^ Record of Decamethylcyclopentasiloxan in the GESTIS Substance Database of the Institute for Occupational Safety and Health, accessed on 25. September 2015.
  5. ^ Donald Mackay, Christina E. Cowan-Ellsberry, David E. Powell, Kent B. Woodburn, Shihe Xu, Gary E. Kozerski, Jaeshin Kim (2015). "Decamethylcyclopentasiloxane (D5) environmental sources, fate, transport, and routes of exposure". Environmental Toxicology and Chemistry. 34 (12): 2689–2702. doi:10.1002/etc.2941.CS1 maint: multiple names: authors list (link)
  6. ^ "InfoCard – Decamethylcyclopentasiloxane". ECHA. Retrieved 2018-07-18.
  7. ^ Michael S. McLachlan, Amelie Kierkegaard, Kaj M. Hansen, Roger van Egmond, Jesper H. Christensen, Carsten A. Skjøth (2010). "Concentrations and Fate of Decamethylcyclopentasiloxane (D5) in the Atmosphere". Environmental Science & Technology. 44 (14): 5365. doi:10.1021/es100411w.CS1 maint: multiple names: authors list (link)
  8. ^ a b Moretto, Hans-Heinrich; Schulze, Manfred; Wagner, Gebhard (2005). "Silicones". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a24_057.
  9. ^ Wang, De-Gao; Norwood, Warren; Alaee, Mehran; Byer, Jonathan D.; Brimble, Samantha: Review of recent advances in research on the toxicity, detection, occurrence and fate of cyclic volatile methyl siloxanes in the environment, Chemosphere 2013, volume 93, pages 711–725. doi:10.1016/j.chemosphere.2012.10.041
  10. ^ Report of the Board of Review for Decamethylcyclopentasiloxane (Siloxane D5) established under Section 333(1) of the Canadian Environmental Protection Act of 1999, October 20, 2011
  11. ^ "Cyclic volatile methyl siloxanes: Environment tier II assessment" Australian Department of Health. Retrieved 2018-12-04.
  12. ^ "Candidate List of substances of very high concern for Authorisation – Decamethylcyclopentasiloxane". ECHA. Retrieved 2018-07-18.
  13. ^ "Commission Regulation (EU) 2018/35 of 10 January 2018 amending Annex XVII to Regulation (EC) No 1907/2006 of the European Parliament and of the Council concerning the Registration, Evaluation, Authorisation and Restriction of Chemicals (REACH) as regards octamethylcyclotetrasiloxane ('D4') and decamethylcyclopentasiloxane ('D5')". Retrieved 2018-07-18.

External links[edit]