Silicomes-oxalic Acid, H₄Si₃O₆

Silicomes-oxalic Acid, H₄Si₃O₆, which is the silicon analogue of mesoxalic acid:



is formed by the action of moist air on octachlorosilicopropane, Si₃Cl₈, at 0° C. It is a white unstable powder, which is insoluble in water, but reacts with alkali forming silicate and hydrogen:

H₄Si₃O₆ + 6NaOH = 3Na₂SiO₃ + 3H₂O + 2H₂.

It possesses reducing properties, indicated thus:

H₄Si₃O₆ + 2O = 2H₂O + 3SiO₂.

Silico-oxalic acid and silicomes-oxalic acid yield identical forms of silica when treated with ammonia, and Martin 1 accounts for this fact by the following scheme, in which the polymerised and cyclic constitution of these two acids is set forth:

Si2(OEt)6 Ethyl ortho-silico-oxalate	Si3Cl8 Octachlorosilicopropane
↓ H2O	↓ H2O
Si2(OH)6 ortho-silico-oxalic acid (unstable); 3 mols. condense	Si3(OH)8 ortho-silicomes-oxalic acid (unstable); 2 mols. condense
↓	↓
Silico-oxalic acid	Silicomes-oxalic acid
↓ NH3 aq.	↓ NH3 aq.

When ethyl ortho-silico-oxalate (hexa-ethoxysilico-ethane) is treated with sodium or potassium hydroxide solution, hydrogen is evolved, and a silicate formed by the interpolation of an oxygen atom between the two silicon atoms thus:

+ 2KOH + H₂O = + 2ROH + H₂.