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Physico-Chemical Properties

Dimethoxymethylsilaneis a liquid at standard temperature and pressure, with a predicted melting point of <-20°C and a predicted boiling point of 80°C at 1013 hPa. It has a predicted density of 0.92 g/cm3at 25°C, a predicted viscosity of 0.5 mm2/s at 20°C and a predicted vapour pressure of 7100 Pa at 25°C.

Dimethoxymethylsilane is classified as a highly flammable liquid on the basis of a measured flash point of <-20°C and a predicted boiling point of 80°C. The substance has a measured auto-ignition temperature of <awaiting data>, and it is not explosive and not oxidising on the basis of chemical structure.

In contact with water, dimethoxymethylsilane reacts rapidly to produce methylsilanediol,methylsilanetriol,methanol and hydrogen according to the following equation:

CH3Si(OCH3)2H + 2 H2O → CH3Si(OH)2H + 2 CH3(OH)

CH3Si(OH)2H + H2O → CH3Si(OH)3 + H2

Therefore, requirements for testing of water-based physicochemical properties for the substance are waived on the basis of instability in water. The properties of the silanol hydrolysis products, methylsilanediol and methylsilanetriol are assessed instead.

Methylsilanediol and methylsilanetriolare predicted to be very soluble in water (> 10000 mg/l) with predicted low log Kowvalues of -1 and -2.4 respectively. Methylsilanediol and methylsilanetriol are not surface active and do not undergo significant dissociation within the environmentally-relevant range. The hydrolysis products are much less volatile than the parent substance with predicted vapour pressures of 6.5 Pa at 25°Cand 0.05 Pa at 25°C respectively.

Silanediols and silanetriols may undergo condensation reactions to give siloxane dimers, oligomers and polymers, according to the scheme:

 

R2Si(OH)2    R2Si(OH)OSi(OH)R2    R2Si(OH)O[Si(R2)O]nSi(OH)R2

RSi(OH)3    RSi(OH)2OSi(OH)2R    RSi(OH)2O[Si(R)(OH)O]nSi(OH)2R

 

(where R is an alkyl or aryl side-chain)

 

A highly cross-linked gel may form. The degree of condensation that will occur may vary with:

  • Concentration of the silanol; the greater the initial concentration, the greater the degree of condensation. Significant condensation is not expected at concentrations less than approximately 100 mg/l, but is dependent on specific conditions.
  • pH; the condensation reaction may be either acid or base catalysed.
  • Temperature.
  • Other species present.