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 c ...

with the formula . It is a colorless and odorless liquid that is slightly volatile.

Use

The compound is classified as a

cyclomethicone A siloxane is a functional group in organosilicon chemistry with the Si−O−Si linkage. The parent siloxanes include the oligomeric and polymeric hydrides with the formulae H(OSiH2)''n''OH and (OSiH2)n. Siloxanes also include branched compound ...

. 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, prevents ...

sunblock Sunscreen, also known as sunblock or sun cream, is a photoprotective topical product for the skin that mainly absorbs, or to a much lesser extent reflects, some of the sun's ultraviolet (UV) radiation and thus helps protect against sunburn and ...

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 red ...

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, preven ...

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 As ...

. 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 hydrolys ...

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 languag ...

. 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 A siloxane is a functional group in organosilicon chemistry with the Si−O−Si linkage. The parent siloxanes include the oligomeric and polymeric hydrides with the formulae H(OSiH2)''n''OH and (OSiH2)n. Siloxanes also include branched compou ...

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 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 de ...

, D₅ was characterized as a

substance of very high concern A substance of very high concern (SVHC) is a chemical substance (or part of a group of chemical substances) concerning which it has been proposed that use within the European Union be subject to authorisation under the REACH Regulation. Indeed, l ...

(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.

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

Use

Production and polymerization

Safety and environmental considerations

See also

References

External links