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Physico-chemical Properties

                 

N-[3-(trimethoxysilyl)propyl]butylamine is a liquid at standard temperature and pressure. It has a measured melting point of -119 °C, a measured the boiling point of 248°C and a measured density of 0.95 g/cm3 at 20 °C. The static viscosity of the substance is predicted to be 2.8 mm2/s at 20 °C and the vapour pressure of the substance is predicted to be 0.76 Pa at 25°C.

 

The substance is classified as a non-flammable liquid on the basis of the boiling point and a measured flash point of 85.5 °C. It is not pyrophoric or flammable in contact with water. It has a measured self-ignition temperature of 250 °C, and is not explosive and not oxidising on the basis of chemical structure. It is not surface active. A first pKa’s of 10.65 has been reported for the amine group (parent substance).

In contact with water N-[3-(trimethoxysilyl)propyl]butylamine reacts rapidly (half-life 3.6 hours at pH 7 and 20 - 25°C) to produce 3-(N-butylamino)propylsilanetriol and methanol according to the following equation:

          

(CH3O)3SiCH2CH2CH2NHCH2CH2CH2CH3 + 3H2O   →  (HO)3SiCH2CH2CH2NHCH2CH2CH2CH3  + 3CH3OH

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

The silanol hydrolysis product, 3-(N-butylamino)propylsilanetriol, is predicted to be very soluble in water 20 °C (1E+06 mg/l) and has a log Kow of 0.9 (predicted). It is less volatile than the parent substance with a vapour pressure of 1.2E-05 at 25 °C (predicted). The first dissociation constant (hydroxyl groups) of a structurally analogous silanetriol (phenylsilanetriol) has been reported to be around pKa10.

Methanol is miscible with water, has low log Kow(-0.82 to -0.64) and high vapour pressure (12790 Pa at 20 °C) (OECD, 2004).

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

 

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.  
  • The nature of the R group
  • The number of Si-OH groups; silanetriols condense more rapidly than silanediols.