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

Skeletal formula of decamethylcyclopentasiloxane
Ball-and-stick model of the decamethylcyclopentasiloxane molecule
Ball-and-stick model of the molecule as found in the crystal structure determined by single-crystal X-ray diffraction[1]
Preferred IUPAC name
Other names
  • Cyclopentamethicone
  • Cyclic dimethylsiloxane pentamer
  • D5
  • D5
  • 2,2,4,4,6,6,8,8,10,10-Decamethylcyclopentasiloxane
3D model (JSmol)
ECHA InfoCard 100.007.969 Edit this at Wikidata
EC Number
  • 208-764-9
MeSH Decamethylcyclopentasiloxane
RTECS number
  • GY5945200
  • InChI=1S/C10H30O5Si5/c1-16(2)11-17(3,4)13-19(7,8)15-20(9,10)14-18(5,6)12-16/h1-10H3 checkY
  • InChI=1/C10H30O5Si5/c1-16(2)11-17(3,4)13-19(7,8)15-20(9,10)14-18(5,6)12-16/h1-10H3
  • C[Si]1(C)O[Si](C)(C)O[Si](C)(C)O[Si](C)(C)O[Si](C)(C)O1
  • O1[Si](O[Si](O[Si](O[Si](O[Si]1(C)C)(C)C)(C)C)(C)C)(C)C
Molar mass 370.770 g·mol−1
Appearance Colourless liquid
Density 0.958 g/cm3
Melting point −47 °C; −53 °F; 226 K
Boiling point 210 °C (410 °F; 483 K)
17.03±0.72 ppb (23 °C) [2]
log P 8.07[3]
Vapor pressure 20.4±1.1 Pa (25 °C) [4]
Viscosity 3.74 cP
GHS labelling:
GHS02: FlammableGHS08: Health hazard
H226, H361, H412, H413
P201, P202, P210, P233, P240, P241, P242, P243, P273, P280, P281, P303+P361+P353, P308+P313, P370+P378, P403+P235, P405, P501
NFPA 704 (fire diamond)
Flash point 73 °C (163 °F; 346 K)
Safety data sheet (SDS) External MSDS
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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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.[6] 10,000–100,000 tonnes per year of D5 is manufactured and/or imported in the European Economic Area.[7] Atmospheric emissions of D5 in the Northern Hemisphere were estimated to 30,000 tonnes per year.[8]

Production and polymerizationEdit

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:[9]

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

where n is a positive integer. D4 and D5 are also precursors to the polymer. The catalyst is again KOH.

Safety and environmental considerationsEdit

The LD50 for D5 in rats is >50 g/kg.[9]

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.[10] A scientific review in Canada has determined that “Siloxane D5 does not pose a danger to the environment”[11] 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."[12] 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.[13] 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.[14]

See alsoEdit


  1. ^ S. Parsons, D. Rankin, P. A. Wood (2004). "CSD Communication YAGTOQ: decamethylpentasilsesquioxane". Cambridge Structural Database: Access Structures. Cambridge Crystallographic Data Centre. doi:10.5517/cc89wzd. Retrieved 2021-08-18.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  2. ^ 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.
  3. ^ 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.
  4. ^ 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.
  5. ^ Record of Decamethylcyclopentasiloxan in the GESTIS Substance Database of the Institute for Occupational Safety and Health, accessed on 25. September 2015.
  6. ^ 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. PMID 26213270.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  7. ^ "InfoCard – Decamethylcyclopentasiloxane". ECHA. Retrieved 2018-07-18.
  8. ^ 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): 5365–5370. Bibcode:2010EnST...44.5365M. doi:10.1021/es100411w. PMID 20568739.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  9. ^ 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. ISBN 3527306730.
  10. ^ 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
  11. ^ 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
  12. ^ "Cyclic volatile methyl siloxanes: Environment tier II assessment" Australian Department of Health. Retrieved 2018-12-04.
  13. ^ "Candidate List of substances of very high concern for Authorisation – Decamethylcyclopentasiloxane". ECHA. Retrieved 2018-07-18.
  14. ^ "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 linksEdit