Decamethylcyclopentasiloxane
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Decamethylcyclopentasiloxane, also known as D5 and D5, is an
organosilicon compound Organosilicon chemistry is the study of organometallic compounds containing carbon–silicon bonds, to which they are called organosilicon compounds. Most organosilicon compounds are similar to the ordinary organic compounds, being colourless, f ...
with the formula . It is a colorless and odorless liquid that is slightly volatile. It is used in various cosmetic products. It also is used as a
dry cleaning Dry cleaning is any cleaning process for clothing and textiles using a solvent other than water. Clothes are instead soaked in a water-free liquid solvent (usually non-polar, as opposed to water which is a Solvent#Solvent classifications, polar ...
solvent and has been marketed as an "eco-friendly" and "green" alternative to perchloroethylene in the 2000s, under the tradename GreenEarth. Decamethylcyclopentasiloxane is persistent in nature and possibly
bioaccumulative Bioaccumulation is the gradual accumulation of substances, such as pesticides or other chemicals, in an organism. Bioaccumulation occurs when an organism absorbs a substance faster than it can be lost or eliminated by catabolism and excretion. ...
. Decamethylcyclopentasiloxane is considered non-toxic but its long-term health effects are unknown.


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 caused by bacterial breakdown of perspiration, for example in the armpits, groin, or feet. A subclass of deodorants, called antiperspirants, prevents sweating itself, t ...
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 and have it stay in a desired shape. Hair sprays typically consist of several components for the ...
s and
skin care Skin care or skincare is the practice of maintaining and improving the health and appearance of the skin. It includes washing, moisturizing, protecting from the sun, and treating skin problems like acne and dryness. Skin care can help prevent i ...
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 In Organosilicon chemistry, organosilicon and polymer chemistry, a silicone or polysiloxane is a polymer composed of repeating units of siloxane (, where R = Organyl group, organic group). They are typically colorless oils or elastomer, rubber ...
-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 ...
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 ''mo ...
. 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 caused by bacterial breakdown of perspiration, for example in the armpits, groin, or feet. A subclass of deodorants, called antiperspirants, prevents sweating itself, t ...
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 Asso ...
. Atmospheric emissions of D5 in the
Northern Hemisphere The Northern Hemisphere is the half of Earth that is north of the equator. For other planets in the Solar System, north is defined by humans as being in the same celestial sphere, celestial hemisphere relative to the invariable plane of the Solar ...
were estimated to 30,000 tonnes per year. Decamethylcyclopentasiloxane has also been tried as a dry-cleaning solvent in the early 2000s. It was marketed as a more environmentally friendly solvent than
tetrachloroethylene Tetrachloroethylene, also known as perchloroethylene or under the systematic name tetrachloroethene, and abbreviations such as perc (or PERC), and PCE, is a chlorocarbon with the formula . It is a non-flammable, stable, colorless and heavy liqu ...
(the most common dry-cleaning solvent worldwide) despite being controlled in the EU for to its
persistent, bioaccumulative and toxic Persistent, bioaccumulative and toxic substances (PBTs) are a class of compounds that have high resistance to degradation from abiotic and biotic factors, high mobility in the environment and high toxicity. Because of these factors PBTs have been ...
characteristics.


Production and polymerization

Commercially D5 is produced from
dimethyldichlorosilane Dimethyldichlorosilane is a tetrahedral organosilicon compound with the formula . 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 on an indust ...
.
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 reaction, substitution, elimination reaction, elimination, and solvation reactions in which water ...
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 (0), a positive natural number (1, 2, 3, ...), or the negation of a positive natural number (−1, −2, −3, ...). The negations or additive inverses of the positive natural numbers are referred to as negative in ...
. D4 and D5 are also precursors to the polymer. The catalyst is again KOH.


Safety and environmental considerations

D5 is nontoxic with an LD50 of >50 g/kg for rats. The environmental impacts of D5 and D4 have attracted attention because these compounds are pervasive. Cyclic
siloxanes In organosilicon chemistry, a siloxane is an organic compound containing a functional group of two silicon atoms bound to an oxygen atom: . The parent siloxanes include the oligomeric and polymeric hydrides with the formulae and . 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 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 union, supranational political union, political and economic union of Member state of the European Union, member states that are Geography of the European Union, located primarily in Europe. The u ...
, 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) which has been proposed as a candidate for inclusion on the Authorization or Restriction list (seeECHA Lists of REACH. The addition of a ...
(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 Dry cleaning Organosilicon compounds PBT substances Personal lubricants Siloxanes