Question

How silicon fluids prepare...is dimethyl dichloro silicon is used?​

Answer 1

The Silicon–Carbon Bond

Silicone polymers are expensive compared with organic polymers because of the cost of reducing silicon dioxide to silicon. In the Rochow process, this is then heated with appropriate catalysts to 300–400 °C and reacted with methyl chloride to give a range of methyl-substituted chlorosilanes. These are then hydrolysed to give the silicones. Any method of preparing soluble derivatives from silica under relatively ambient conditions would be of considerable commerical importance, particularly if they react readily with organic nucleophiles.

As long ago as 1931, six-coordinate catechol salts were prepared from silica gel in water under basic conditions (Equation (1)).54 The reaction also works for silica gel and finely divided quartz and for (MeO)4Si. Rice hull ash (92% silica) loaded with 5 wt.% potassium hydroxide reacts with dimethyl carbonate at 625 K to give tetramethoxysilane quantitatively, and with diethyl carbonate at 725 K to give tetraethoxysilane in 80% yield (Equation (2)).55 Refluxing mixtures of silica with barium oxide in excess glycol for several hours gives a clear solution from which crystals of the hexaalkoxysilicate Ba2+[Si(OCH2CH2O)3]2− were obtained and showed strong cation–anion interactions and hydrogen bonding with glycol in the lattice.56

(1)

(2)

While doubly charged cations appear to encourage six-coordination, five-coordination results with alkali metal cations. Thus, heating silica gel, fused silica, or sand with an alkali metal hydroxide, MOH, in an excess of glycol, and allowing the excess glycol to slowly distil off with the water generated, led to dissolution of silica gel in 1–2 h, fused silica in 3–6 h, or sand in more than 200 h. Cooling led to the isolation of the five-coordinate derivative K+[Si(OCH2CH2O)2OCH2CH2OH]− and the bridged dimeric species M2[Si2(OCH2CH2O)5] with one glycol unit bridging two silicon sites. These compounds readily undergo alcohol exchange and give the six-coordinate derivative with catechol.