Octamethylcyclotetrasiloxane (D4): Silane Hydrolysate Cracked with Potash in Diphenyl Ether (Asahi 1980)

Dimethyldichlorosilane dropped into cold strong hydrochloric acid hydrolyses to a silicone oil: rings and chains of dimethylsiloxane, just over half of it the four-ring D4. Heated with a little potash in diphenyl ether under vacuum, the chains crack back into volatile rings that distil off. Asahi's chemists fractionated the distillate, sent the smaller three-ring D3 back round, and took off D4 of 99.4 % purity. Source: K. Hirakawa and M. Honda (Asahi Kasei), US 4,197,251 (1980), Comparative Example 1 and Example 1. The tools and the step layout are ours. Picture drawn by Youblob.