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Physical & Chemical properties

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Physico-chemical properties

N-[3-(dimethoxymethylsilyl)-2-methylpropyl]ethylenediamine is a clear, colourless to pale yellow liquid at standard temperature and pressure. The melting point was predicted to be well below -20°C and the boiling point was predicted to be 247°C. It has a predicted density of 0.95 g/cm3 at 25°C, a predicted static viscosity of 3.2 mm2/s at 20°C and a predicted vapour pressure of 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 96°C. It is not pyrophoric or flammable in contact with water. It has a measured self-ignition temperature of 295°C, and is not explosive and not oxidising on the basis of chemical structure. It is not surface active. First and second pKa’s of 7.15 and 10.09 have been reported for the amine groups (parent substance).

For the hydrolysis half-life time, read-across data from the analogue substance, N-[3 -(dimethoxymethylsilyl)propyl]ethylenediamine has been used since there are no hydrolysis data available for N-[3-(dimethoxymethylsilyl)-2-methylpropyl]ethylenediamine. The hydrolysis half-life time of N-[3-(dimethoxymethylsilyl)propyl]ethylenediamine is <3 minutes at pH 4 and 9, and 15 minutes at pH 7.

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.

N-[3-(dimethoxymethylsilyl)-2-methylpropyl]ethylenediamine produces a silanol hydrolysis product N-[3 -(dihydroxymethylsilyl)-2 -methylpropyl]ethylenediamine and methanol according to the following equation:

(CH3O)2Si(CH3)CH2CH(CH3)CH2NHCH2CH2NH2 + 2H2O   →  (HO)2Si(CH3)CH2CH(CH3)CH2NHCH2CH2NH2 + 2CH3OH

The silanol hydrolysis product is predicted to be very soluble in water 20oC (1E+06 mg/l) and has a log Kowof -1.0 at 20°C (predicted). It is less volatile than the parent substance with a vapour pressure of 2.4E-04 at 25°C (predicted). The first dissociation constant (hydroxyl groups) of a structurally analogous silanediol (dimethylsilanediol) has been reported to be around pKa 12.

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).

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