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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]

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 370.77 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
Irritant Xi
R-phrases (outdated) R36/37/38
S-phrases (outdated) S23, S24/25
NFPA 704
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



Commercially D5, is produced by cracking polysiloxanes. The silicone polymer equilibrated in the presence of strong base to give the pentamer:

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

The tetramer octamethylcyclotetrasiloxane is also generated. These two cyclic species are separated from the polymer by distillation.[6]


D5 and D4 have attracted attention because they are pervasive. Although never reported as being toxic, one report suggests cyclic siloxanes can be detected in some species of aquatic life.[7] However, other scientific reviews have determined that "Siloxane D5 does not pose a danger to the environment."[8]


  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. 
  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. 
  6. ^ Moretto, Hans-Heinrich; Schulze, Manfred; Wagner, Gebhard (2005). "Silicones". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a24_057. 
  7. ^ 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
  8. ^ 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

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