Chemical elements
    Physical Properties
    Chemical Properties
      Silicon Tetrahydride
      Silicon Tetrafluoride
      Hydrofluosilicic Acid
      Silicon Subfluoride
      Silicon Tetrachloride
      Silicon Tetrabromide
      Silicon Tetra-iodide
      Mixed Halides of Silicon
      Halogen Derivatives of Silico-ethane
      Halogen Derivatives of Silicopropane
      Halogen Derivatives of Silicobutane
      Halogen Derivatives of Silicopentane and Silicohexane
      Silicon Oxychlorides
      Silicon Dioxide
      Silicoformic Anhydride
      Silico-oxalic Acid
      Silicomes-oxalic Acid
      Silicon Disulphide
      Silicon Monosulphide
      Silicon Oxysulphide
      Silicon Thiochloride
      Silicon Thiobromide
      Silicon Chloroitydrosulphide
      Silicon Selenide
      Silicon Tetramide
      Silicon Di-imide
      Silicon Nitrimide
      Siliconitrogen Hydride
      Silicon Nitrides
      Crystalline Silicon Monocarbide
      Silicon Dicarbide
      Silicon Carboxide
      Borides of Silicon
    PDB 1fuq-4ehr

Silico-oxalic Acid, (H2Si2O4)n

This compound, the silicon analogue of oxalic acid, is formed by the hydrolysis of hexachlorosilico-ethane, Si2Cl6, or hexa-iodosilico-ethane, Si2I6, by means of ice-cold water:

(SiCl3)2 + 4H2O = (SiOOH)2 + 6HCl.

Hexa-iodosilico-ethane also reacts with absolute alcohol thus:

Si2I6 + 6C2H5OH = (SiOOH)2 + 6C2H5I + 2H2O.

Silico-oxalic acid is conveniently prepared by allowing moist air to act slowly upon hexachlorosilico-ethane contained in a platinum capsule cooled by ice, and then washing the product with cold water till it is free from chloride, and drying it in a vacuum. It is a white insoluble powder which explodes feebly when heated or rubbed. It dissolves in alkalis, forming silicates with evolution of hydrogen, thus:

H2Si2O4 + 4NaOH = 2Na2SiO3 + 2H2O + H2;

consequently it is a reducing agent; it reduces permanganic acid quickly, and chromic acid slowly, but does not precipitate gold from cold solution. That silico-oxalic acid possesses but half the reducing power of silicoformic anhydride is indicated by the equations:

H2Si2O3 + 2O = H2O + 2SiO2
H2Si2O4 + O = H2O + 2SiO2.

The name silico-oxalic acid is hardly justifiable since this substance forms no salts.

As regards the constitution of this compound, the formula (SiOOH)2 postulates reducing properties allied to those of (COOH)2; nevertheless it has been proposed to formulate this substance thus:

Now the formula is derivable directly from , whilst the above formula involves an intramolecular change, for which some analogy appears to be provided, for instance by phosphorous acid:


The cases, however, are not parallel, for in the latter example the valency of the phosphorus atom is increased. Moreover, there is serious objection to assuming an oxygen chain to be present in the molecule of silico-oxalic acid, and no objection to retaining the formula analogous to that of oxalic acid.

Further, it has been shown by Martin that silico-oxalic acid is produced, in a yield of 99-100 per cent., by the reaction:

Si2(OEt)6 + 4H2O = Si2O4H2 + 6EtOH;

and since the series of reactions:

Cl3Si.SiCl3 -(EtOH)→ (EtO)3Si.Si(OEt)3 -(H2))→ (HO)3Si.Si(OH)3 -(-2H2O)→ HO.SiO.SiO.OH,

proceeds quantitatively, this fact affords additional evidence that the constitution of silico-oxalic acid is analogous to that of oxalic acid. The compound is, however, probably a polymer with a cyclic constitution, as appears below.

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