Talk:Decamethylcyclopentasiloxane

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Not sure if this should really be a chemistry stub, ostensibly since I'm not a chemist! This is what I get for reading the back of my deoderant can and looking up the ingredients on wikipedia! :) Njan | ^talk 17:24, 06 Aug 2006 (GMT+1)

I am a chemist and this stuff doesn't stay in your body for 5 years! —Preceding unsigned comment added by 67.184.125.235 (talk) 01:51, 1 February 2008 (UTC)

hi —Preceding unsigned comment added by 24.127.123.128 (talk) 22:27, 21 April 2008 (UTC)

Like a crown-ether

Angew. Chem. Int. Ed. (2006) 45, 2773-2777

Ben (talk) 14:48, 17 March 2009 (UTC)

More detail needed

It would be nice to know why this chemical would be included in deodorants, etc. I also noticed that in at least one brand that includes this ingredient, the "sensitive skin" version of the same omits this ingredient. Therefore some allergy/irritability information would be useful in this article.

— Spel-Punc-Gram (talk) 22:05, 26 July 2013 (UTC)

Environmental concerns

I opened the report cited by the text, and the report summary does not specifically support the text (and I was not willing to purchase the full report). I also added another source and balanced the text. Comments welcome. Journalist1983 (talk) 01:58, 18 November 2015 (UTC)

Thanks. There is still a lot of information missing in the article. Freely accessible reports include the UK Environmental Risk Assessment Report, the PBT/vPvB Evaluation by the ECHA and this editorial cited in de:Decamethylcyclopentasiloxan#Risikobewertung. --Leyo 09:38, 18 November 2015 (UTC)

I agree. Thank you. Will look at cited source and add additional content when I get time.Journalist1983 (talk) 01:27, 23 November 2015 (UTC)

Misleading information on production

In the article, it says that “commercially D₅, is produced by cracking polysiloxanes”. By skipping important production steps, this information is highly misleading. It is true that cyclic dimethylsiloxanes may be produced from polydimethylsiloxanes. However, in practice, it works the other way round, i.e. cyclic dimethylsiloxanes are the intermediates used to produce silicones e.g. using ring-opening polymerization (see e.g. chapter 2.1, silicones.eu, cyclosiloxanes.org, Basic Silicone Chemistry).
Even Ullmann's Encyclopedia of Industrial Chemistry that is cited in the article, does not support the content of the article. In section 2.1.3, it says “Octamethylcyclotetrasiloxane and decamethylcyclopentasiloxane are major industrial products, which are either marketed as such or used for the production of polydimethylsiloxanes. Cyclization is performed by heating the hydrolysis or methanolysis mixture with potassium hydroxide. Potassium hydroxide catalyzes an equilibration reaction in which the Si–O–Si bonds are cleaved and reformed. During the reaction, the lower-boiling octamethylcyclotetrasiloxane and decamethylcyclopentasiloxane are distilled continuously from the reaction mixture.” In addition, the following reactions are given in section 2.1.2 on the methanolysis:

Rochow synthesis:

${\ce {n*Si + 2n*CH3Cl -> n*(CH3)2SiCl2}}$

Methanolysis:

${\ce {n*(CH3)2SiCl2 + 2n*CH3OH -> [(CH3)2SiO]n + 2n*CH3Cl + n*H2O}}$

Overall:

${\ce {n*Si + 2n*CH3OH -> [(CH3)2SiO]n + n*H2O}}$

The product of the overall reaction is actually a mixture of cyclic dimethylsiloxanes including D₅.
Especially, I would like to ask Smokefoot who added the disputed section, to rewrite it in an appropriate manner. Unfortunately, myself I am a layperson when it comes to chemical syntheses. --Leyo 21:06, 16 July 2018 (UTC) PS. Octamethylcyclotetrasiloxane#Production may then be adapted accordingly.

OK, I will look over the material and revise it.

• It seems that D5 is produced from the polysiloxane, maybe not by thermal cracking (although that would work) but by base-catalyzed re-equilibration.
• The initial "Rochow synthesis" ${\ce {n*Si + 2n*CH3Cl -> n*(CH3)2SiCl2}}$, the Direct process) is not so relevant because the action is after the Si-O bonds are formed.
• he main thing here is manipulation of n for (Me₂SiO)_n, for n = 5,6 vs ∞.

At least that is my initial reading of your (very helpful) advice given above. --Smokefoot (talk) 22:33, 16 July 2018 (UTC)

I looked the article this morning. The chemistry is fine. Not sure why one might describe the contents as "misleading" but if you see opportunities to improve it, please say so.--Smokefoot (talk) 13:33, 17 July 2018 (UTC)

I might also call it selective truth. Well, what about using the simple, but more comprehensive description of the production from the James A. Kent's Handbook of Industrial Chemistry and Biotechnology?

The preparation of cyclic materials starts with the production of pure silicon via the reduction of quartz with coke in an electric furnace. The silicon metal then reacts with methyl chloride to give a mixture of silicones, from which dimethyldichlorosilane is removed by distillation. Subsequent hydrolysis gives the cyclic dimethylsiloxane.

IMHO with a few tweaks and small additions (e.g. distillation of D₅), this description may be used in the article. --Leyo 20:41, 17 July 2018 (UTC)

Oh. Yes, one needs starting materials for chemical synthesis, and these starting materials are prepared from other starting materials. Its a question of how far back one wants to go. For LSD, its preparation could in principle start with the isolation of benzene from petroleum and then go from there, I guess. This morning I created the article on C(PPh3)2. The prep does not describe how one makes PPh3. Last weekend I created rhenium(VI) chloride. That article does not describe the isolation of Re metal from its ores. Similarly the companion article on vanadium(V) chloride does not even discuss how one obtains the precursor VF₅. I hope that this explanation helps. --Smokefoot (talk) 21:47, 17 July 2018 (UTC)

Your examples are not comparable to this case here. Yes, we may skip the production of of silicon, but starting with “polysiloxanes” is inappropriate. No company buys polysiloxanes to produce D₅. --Leyo 22:36, 17 July 2018 (UTC)

Not really odourless.

D5 has a very mild and weak sweet odour. ⲔⲖⲞⲢⲠⲒⲔⲢⲒⲚ (talk) 18:23, 30 December 2023 (UTC)