Cyclopentasiloxane

Decamethylcyclopentasiloxane

Names
IUPAC name Decamethyl-1,3,5,7,9,2,4,6,8,10-pentaoxapentasilecane
Other names Cyclopentamethicone Cyclic dimethylsiloxane pentamer D5 2,2,4,4,6,6,8,8,10,10-Decamethylcyclopentasiloxane
Identifiers
CAS Number	541-02-6 Y
3D model (Jmol)	Interactive image Interactive image
Beilstein Reference	1800166
ChemSpider	10451 Y
ECHA InfoCard	100.007.969
EC Number	208-764-9
MeSH	Decamethylcyclopentasiloxane
PubChem CID	10913
RTECS number	GY5945200
UNII	0THT5PCI0R Y
InChI 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 Y Key: XMSXQFUHVRWGNA-UHFFFAOYSA-N Y 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 Key: XMSXQFUHVRWGNA-UHFFFAOYAC
SMILES 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
Properties
Chemical formula	C10H30O5Si5
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)
Solubility in water	17.03±0.72 ppb (23 °C)
Vapor pressure	20.4±1.1 Pa (25 °C)
Viscosity	3.74 cP
Hazards
Safety data sheet	External MSDS
EU classification (DSD)	Xi
R-phrases	R36/37/38
S-phrases	S23, S24/25
NFPA 704	2 1 0
Flash point	73 °C (163 °F; 346 K)
Related compounds
Related Organosilicon compounds	Octamethylcyclotetrasiloxane
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Y  (what is YN ?)
Infobox references

Cyclic dimethylsiloxane pentamer
D₅

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

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

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

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. However, other scientific reviews have determined that "Siloxane D5 does not pose a danger to the environment."