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Decamethylcyclopentasiloxane, also known as D5 and D5, is an
organosilicon compound Organosilicon compounds are organometallic compounds containing carbon–silicon bonds. Organosilicon chemistry is the corresponding science of their preparation and properties. Most organosilicon compounds are similar to the ordinary organic co ...
with the formula . It is a colorless and odorless liquid that is slightly volatile.


Use

The compound is classified as a cyclomethicone. Such fluids are commonly used in cosmetics, such as
deodorant A deodorant is a substance applied to the body to prevent or mask body odor due to bacterial breakdown of perspiration or vaginal secretions, for example in the armpits, groin, or feet. A subclass of deodorants, called antiperspirants, preven ...
s, sunblocks,
hair spray Hair spray (also hair lacquer or spritz) is a common cosmetic hairstyling product that is sprayed onto hair to protect against humidity and wind. Hair sprays typically consist of several components for the hair as well as a propellant. Ingr ...
s and
skin care Skin care is a range of practices that support skin integrity, enhance its appearance, and relieve skin conditions. They can include nutrition, avoidance of excessive sun exposure, and appropriate use of emollients. Practices that enhance appea ...
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 lubricant Personal lubricants (colloquially termed lube) are specialized lubricants used during sexual acts, such as intercourse and masturbation, to reduce friction to or between the penis and vagina, anus or other body parts or applied to sex toys to re ...
s. D5 is considered an
emollient A moisturizer, or emollient, is a cosmetic preparation used for protecting, moisturizing, and lubricating the skin. These functions are normally performed by sebum produced by healthy skin. The word "emollient" is derived from the Latin verb ''m ...
. In Canada, among the volume used in consumer products approximately 70% were for
antiperspirant A deodorant is a substance applied to the body to prevent or mask body odor due to bacterial breakdown of perspiration or vaginal secretions, for example in the armpits, groin, or feet. A subclass of deodorants, called antiperspirants, prev ...
s and 20% for hair care products. 10,000–100,000 tonnes per year of D5 is manufactured and/or imported in the
European Economic Area The European Economic Area (EEA) was established via the ''Agreement on the European Economic Area'', an international agreement which enables the extension of the European Union's single market to member states of the European Free Trade Ass ...
. Atmospheric emissions of D5 in the Northern Hemisphere were estimated to 30,000 tonnes per year.


Production and polymerization

Commercially D5 is produced from
dimethyldichlorosilane Dimethyldichlorosilane is a tetrahedral, organosilicon compound with the formula Si(CH3)2Cl2. At room temperature it is a colorless liquid that readily reacts with water to form both linear and cyclic Si-O chains. Dimethyldichlorosilane is made ...
.
Hydrolysis Hydrolysis (; ) is any chemical reaction in which a molecule of water breaks one or more chemical bonds. The term is used broadly for substitution, elimination, and solvation reactions in which water is the nucleophile. Biological 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: : where ''n'' is a positive
integer An integer is the number zero (), a positive natural number (, , , etc.) or a negative integer with a minus sign ( −1, −2, −3, etc.). The negative numbers are the additive inverses of the corresponding positive numbers. In the language ...
. D4 and D5 are also precursors to the polymer. The catalyst is again KOH.


Safety and environmental considerations

The LD50 for D5 in rats is >50 g/kg. 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.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 The Chemosphere is a modernist house in Los Angeles, California, designed by John Lautner in 1960. The building, which the ''Encyclopædia Britannica'' once called "the most modern home built in the world", is admired both for the ingenuity of ...
2013, volume 93, pages 711–725. A scientific review in Canada has determined that “Siloxane D5 does not pose a danger to the environment” 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." However, in the
European Union The European Union (EU) is a supranational political and economic union of member states that are located primarily in Europe. The union has a total area of and an estimated total population of about 447million. The EU has often been ...
, 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. 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.


See also

* Hexamethylcyclotrisiloxane (D3) * Octamethylcyclotetrasiloxane (D4)


References


External links

* * {{cite journal, doi=10.1016/j.yrtph.2015.06.011, title=Toxicology of decamethylcyclopentasiloxane (D5), last1=Dekant, first1=Wolfgang, last2=Klaunig, first2=James E., journal=
Regulatory Toxicology and Pharmacology ''Regulatory Toxicology and Pharmacology'' is a monthly peer-reviewed scientific journal which covers legal aspects of toxicological and pharmacological regulations. It is published by Elsevier on behalf of the International Society of Regulatory ...
, date=2016, volume=74, pages=S67–S76, pmid=26111607 , doi-access=free Cosmetics chemicals Organosilicon compounds PBT substances Personal lubricants Siloxanes