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Physical & Chemical properties

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Physico-chemical properties

(3-chloropropyl)diethoxymethylsilane is a liquid at standard temperature and pressure, with an estimated melting point of <20°C, and a measured boiling point of 206°C. It has a measured relative density of 0.987 at 20°C, a measured viscosity of 1.4 mPasat 25°Cand a predicted vapour pressure of 6.8 Pa at 20°C.

 

The substance is not classified as flammable on the basis of a measured flash point of 74°C and the boiling point of 206°C. It has a measured auto-ignition temperature of 210°C, and is not explosive and not oxidising on the basis of chemical structure.

In contact with water, (3-chloropropyl)diethoxymethylsilane is predicted to react very rapidly (half-life 9.5 hours at 20 - 25°C and pH7) to produce (3-chloropropyl)methylsilanediol and ethanol according to the following equation:

(ClCH2CH2CH2)Si(CH3)(OCH2CH3)2 + 2 H2O →

(ClCH2CH2CH2)Si(CH3)(OH)2 + 2 CH3CH2OH

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 product, (3-chloropropyl)methylsilanediol,are assessed instead. The hydrolysis product is predicted to be soluble in water (6000 mg/l), with low log Kow (0.8). It is not surface active. The first dissociation constant of a structurally analogous silanediol (dimethylsilandiol) has been reported to be around pKa= 11.9. The hydrolysis product is less volatile than the parent substance (predicted vapour pressure = 0.021 Pa at 25°C).

Ethanol is miscible with water, has low log Kow (-0.3) and high vapour pressure (7910 Pa at 25°C).

Silanediols 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

 

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

 

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.
  • Timescale
  • The nature of the R group