Decamethylcyclopentasiloxane

Use

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. 10,000–100,000 tonnes per year of D5 is manufactured and/or imported in the European Economic Area. Atmospheric emissions of D5 in the Northern Hemisphere were estimated to 30,000 tonnes per year.

Decamethylcyclopentasiloxane is also used as a dry-cleaning solvent. It was first marketed by GreenEarth Cleaning in the 1990s and was claimed to be eco-friendlier than tetrachloroethylene (the most common dry-cleaning solvent worldwide since the 1950s) despite being controlled in the EU for to its persistent, bioaccumulative and toxic characteristics. Decamethylcyclopentasiloxane is more bioaccumulative than tetrachloroethylene and it does not break down in nature. Its use in dry cleaning will be prohibited in the European Union after June 2026 due to its environmental effect.

Production and polymerization

Commercially D5 is produced from dimethyldichlorosilane. 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. D4 and D5 are also precursors to the polymer. The catalyst is again KOH.

Safety and environmental considerations

D5 is acutely nontoxic with an LD50 of 50 g/kg for rats. Possible negative long-term effects of D5 were not investigated.

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. 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, 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.

References

References

1. S. Parsons, D. Rankin, P. A. Wood. (2004). "CSD Communication YAGTOQ: decamethylpentasilsesquioxane". [[Cambridge Crystallographic Data Centre]].
2. (1996). "Aqueous solubility of permethylsiloxanes (silicones)". [[Environmental Toxicology and Chemistry]].
3. (2010). "Temperature-Dependent Vapor Pressure of Selected Cyclic and Linear Polydimethylsiloxane Oligomers". [[Journal of Chemical & Engineering Data]].
4. Shihe Xu, Bruce Kropscott. (2012). "Method for Simultaneous Determination of Partition Coefficients for Cyclic Volatile Methylsiloxanes and Dimethylsilanediol". Analytical Chemistry.
5. {{GESTIS
6. [[Donald Mackay (scientist). (2015). "Decamethylcyclopentasiloxane (D5) environmental sources, fate, transport, and routes of exposure". Environmental Toxicology and Chemistry.
7. "InfoCard – Decamethylcyclopentasiloxane". [[ECHA]].
8. Michael S. McLachlan, Amelie Kierkegaard, Kaj M. Hansen, Roger van Egmond, Jesper H. Christensen, Carsten A. Skjøth. (2010). "Concentrations and Fate of Decamethylcyclopentasiloxane (D₅) in the Atmosphere". [[Environmental Science & Technology]].
9. (2018-01-10). "Commission Regulation (EU) 2018/35 of 10 January 2018 amending Annex XVII to Regulation (EC) No 1907/2006 of the European Parliament and of the Council concerning the Registration, Evaluation, Authorisation and Restriction of Chemicals (REACH) as regards octamethylcyclotetrasiloxane ('D4') and decamethylcyclopentasiloxane ('D5') (Text with EEA relevance. )".
10. [https://www.cirs-group.com/en/chemicals/eu-commission-announces-new-restrictions-on-d4-d5-and-d6 EU Commission Announces New Restrictions on D4, D5, and D6]
11. (2005). "Silicones". Wiley-VCH.
12. It has caused tumours in female rats but it was not evaluated further for possible carcinogenicity. It may affect the liver and the immune system in long term.[https://web.archive.org/web/20220119014216/https://www.turi.org/content/download/7399/134622/file/2012%20M%26P%20Report%2027%20Assessment%20of%20Safer%20Alternatives%20to%20Perchloroethylene.pdf "Assessment of Alternatives to Perchloroethylene for the Dry Cleaning Industry"] (PDF). TURI: Toxics Use Reduction Institute. UMass Lowell. June 2012.
13. 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 (journal). Chemosphere]] 2013, volume 93, pages 711–725. {{doi. 10.1016/j.chemosphere.2012.10.041
14. [http://www.ec.gc.ca/lcpe-cepa/515887B7-AF58-45B7-ADA9-B4ADF8F204DB/CdR-BoR-D5_eng.pdf 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]
15. [https://www.nicnas.gov.au/chemical-information/imap-assessments/imap-assessments/tier-ii-environment-assessments/cvms "Cyclic volatile methyl siloxanes: Environment tier II assessment"] {{Webarchive. link. (2020-05-27 Australian Department of Health. Retrieved 2018-12-04.)
16. "Candidate List of substances of very high concern for Authorisation – Decamethylcyclopentasiloxane". [[ECHA]].
17. "Commission Regulation (EU) 2018/35 of 10 January 2018 amending Annex XVII to Regulation (EC) No 1907/2006 of the European Parliament and of the Council concerning the Registration, Evaluation, Authorisation and Restriction of Chemicals (REACH) as regards octamethylcyclotetrasiloxane ('D4') and decamethylcyclopentasiloxane ('D5')".