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Diss Factsheets

Physical & Chemical properties

Endpoint summary

Administrative data

Description of key information

The substance, N,N',N''-tricyclohexyl-1-methylsilanetriamine is not stable in water, which affects the approach to the determination of physicochemical properties.

N,N',N''-Tricyclohexyl-1-methylsilanetriamine is a liquid at standard temperature and pressure, with a measured freezing point of -24°C, and a measured boiling point of 315°C. It has a measured relative density of 0.96 at 20°C, a kinematic viscosity value of 98.2 mm2/s at 20°C. It is not expected to be surface active. The substance has a measured vapour pressure of 0.19 Pa at 20°C and 1.1 Pa at 50°C.

The substance is not classified for flammability according to Regulation (EC) No. 1272/2008 on the basis of a flash point of 97.5± 0.5°C at 1013 hPa and a measured boiling point of 315°C. It has a measured auto-ignition temperature of 251°C at 967-969 hPa, and is not explosive and not oxidising on the basis of structural examination.

In contact with water, N,N',N''-tricyclohexyl-1-methylsilanetriamine hydrolyses very rapidly (half-life <3 minutes at pH 4, <2 minutes at pH 7 and 5.1 minutes at pH 9 and 25°C) to produce methylsilanetriol (1 mole, CAS No. 2445-53-6) and cyclohexylamine (3 moles, CAS No. 108-91-8) according to the following equation:

CH3Si(NHC6H11)3 + 3H2O → CH3Si(OH)3 + 3C6H11NH2

Therefore, the 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, methylsilanetriol and cyclohexylamine are assessed instead.

Cyclohexylamine is reported to be miscible with water (Budavari 1996), has low log Kow of 1.49 (Hansch et al. 1995) and a vapour pressure of approximately 1350 Pa at 25°C (Daubert and Danner 1989). The reported pKa of 10.63 (Perrin 1972) indicates that it has the potential to protonate when in the environment and will exist almost entirely in cationic form while in the environment. Therefore, the log Kow has been corrected for ionisation, log Kow values of -4, -4, -2 and -0.1 at pH 2, pH 4, pH 7 and pH 9 respectively was obtained for cyclohexylamine.

The silanol hydrolysis product, methylsilanetriol, may undergo condensation reactions in aqueous solution to give siloxane dimers, linear and cyclic oligomers and highly cross-linked polymeric particles (a colloidal suspension of small solid particles known as a sol) that may over time form an insoluble gel and a dynamic equilibrium is established. The overall rate and extent of condensation is dependent on nominal loading, temperature, and pH of the system, as well as what else is present in the solution.

The condensation reactions of silanetriols may be modelled as an equilibrium between monomer, dimer, trimer and tetramer, with the linear tetramer cyclising to the thermodynamically stable cyclic tetramer. At higher loadings, cross-linking reactions between the cyclic tetramers may occur. The reactions are reversible unless the cyclic tetramer concentration exceeds its solubility; in this case, the cyclic tetramer forms a separate phase, driving the equilibrium towards the tetramer. At loadings below 500 mg/l of methylsilanetriol, the soluble monomer is expected to predominate in solution (>99%), with small amounts of dimer and oligomers. Condensation reactions are expected to become important at loadings above about 1000 mg/l causing the formation of insoluble polymeric particles and gels over time. Further information is given in a supporting report (PFA 2016am) attached in Section 13.

The saturation concentration in water of the silanol hydrolysis product methylsilanetriol is therefore limited by condensation reactions to approximately 1000 mg/l. However, it is very hydrophilic (calculated solubility is 1E+06 mg/l at 20°C using a QSAR method) with a predicted low log Kow of -2.4. It is not surface active. The silanol hydrolysis product is much less volatile than the parent substance (predicted vapour pressure = 5.3E-02 Pa at 25°C).


Budavari, S. (ed.). The Merck Index - An Encyclopedia of Chemicals, Drugs, and Biologicals. Whitehouse Station, NJ: Merck and Co., Inc., 1996., p. 460

Daubert, T.E., R.P. Danner (1989). Physical and Thermodynamic Properties of Pure Chemicals Data Compilation. Washington, D.C.: Taylor and Francis

Hansch, C., Leo, A., D. Hoekman (1995). Exploring QSAR - Hydrophobic, Electronic, and Steric Constants. Washington, DC: American Chemical Society., 1995., p. 10

Perrin D D (1972). Dissociation constants of organic bases in aqueous solution. IUPAC Chem Data Ser, Suppl 1972. Buttersworth, London.

PFA (2016am). Silanols and aquatic systems. Reference 404.105.003

Additional information