Registration Dossier
Registration Dossier
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EC number: 229-929-1 | CAS number: 6843-66-9
Endpoint summary
Administrative data
Description of key information
Additional information
- 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.
- Timescale
- The nature of the R group
Physico-chemical properties
Dimethoxydiphenylsilane is a liquid at standard temperature and pressure, with a measured melting point of <-180°C and a predicted boiling point of 300°C. It has a predicted density of 1 g/cm3 at 25°C, a predicted viscosity of 5.7 mm2/s at 20°C and a predicted vapour pressure of 0.03 Pa at 25°C.
The substance is not classified for flammability on the basis of a measured flash point of 151°C (closed cup). It has a measured auto-ignition temperature of 430°C, and is not explosive and not oxidising on the basis of chemical structure. On the basis of structure it is not expected to be surface active.
In contact with water, dimethoxydiphenylsilane reacts rapidly (half-life 0.6 hours at pH 7 and 20°C) to produce diphenylsilanediol and methanol according to the following equation:
(C6H5)2Si(OCH3)2 + 2 H2O → (C6H5)2Si(OH)2 + 2 CH3OH
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, diphenylsilanediol and methanol, are assessed instead.
Methanol is miscible with water, has a low log Kow (-0.82 to -0.64) and high vapour pressure (12790 Pa at 20°C).
Diphenylsilanediol is predicted to be slightly soluble in water (508 mg/l) with a predicted log Kow value of 2.0. It is not surface active and does not undergo significant dissociation within the environmentally-relevant range. It is much less volatile than the parent substance (vapour pressure = 9.9E-06 Pa at 25°C, predicted).
Silanediols may undergo condensation reactions to give siloxane dimers, oligomers (including cyclosiloxanes) and polymers, according to the scheme:
R2Si(OH)2 ⇄ R2Si(OH)OSi(OH)R2 ⇄ R2Si(OH)O[Si(R2)O]nSi(OH)R2
(where R is an alkyl or aryl side-chain)
The degree of condensation that will occur may vary with:
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