556-67-2

Colorless clear liquid

ChEBI: A cyclosiloxane that is the octamethyl derivative of cyclotetrasiloxane.

Commercially Octamethylcyclotetrasiloxane is produced from dimethyldichlorosilane. Dimethyldichlorosilane is added dropwise to water, the temperature is maintained at 30-40°C, stratified, the acid water is released, the oily material is hydrolyzed with sodium hydroxide solution, the hydrolysate and 0.5%-2% potassium hydroxide are added to the cracking kettle and cracked at 120-140°C and 99.8 kPa vacuum. The cracked material is fractionated and the fraction is collected at 173-176°C to obtain octamethylcyclotetraoxysilane.

Octamethylcyclotetrasiloxane (D4) can interfere with the body’s hormones. In animals, it can affect the reproductive system.
D4 is classified as a category 1 endocrine disruptor by the European Commission. A 2018 study commissioned by the Danish EPA identified D4 as an endocrine disruptor. The Global Harmonized System Label Requirements classified D4 as suspected to produce reproductive toxicity. D4 was added to the Toxic Substances Control Act work plan due to reproductive toxicity, moderate environmental persistence, and high bioaccumulation potential.
Adverse reproductive effects including estrogenic effects have been observed in rodents. The European Chemicals Agency characterized D4 as a persistent, bioaccumulative, and toxic chemical, and designated D4 as a Substance of Very High Concern.

Flammable

A skin irritant. When heated todecomposition it emits acrid smoke and irritating vapors.

The solid exists in two forms, m 16.30o and 17.65o. Dry it over CaH2 and distil it. Further fractionation can be effected by repeated partial freezing and discarding the liquid phase. [Osthoff & Grubb J Am Chem Soc 76 399 1954, Hoffman J Am Chem Soc 75 6313 1953, Beilstein 4 IV 4125.]