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EC number: 221-336-6 | CAS number: 3069-29-2
Endpoint summary
Administrative data
Description of key information
The substance, N-[3-(dimethoxymethylsilyl)propyl]ethylenediamine, is not stable in water, which affects the approach to the determination of physicochemical properties. The significance of this for read-across is discussed in the relevant sections.
N-[3-(Dimethoxymethylsilyl)propyl]ethylenediamine is a liquid at ambient temperature and pressure, with a melting point of <-20°C and a predicted boiling point of 240°C at 1013 hPa. It has a predicted density of 0.96 g/cm3 at 20°C and a predicted kinematic viscosity of 3.0 mm2/s at 20°C. The substance has a predicted vapour pressure of 1.1 Pa at 25°C.
The substance is not classified for flammability according to Regulation (EC) No 1272/2008 on the basis of a measured flash point of 91.0 ± 1.0°C at 1013 hPa and a predicted boiling point of 240°C at 1013 hPa. It has a measured auto-ignition temperature of 294°C at 98.4 kPa and is not explosive and not oxidising on the basis of chemical structure.
In contact with water, N-[3-(dimethoxymethylsilyl)propyl]ethylenediamine reacts very rapidly (half-life of <3 minutes at pH 4, 15 minutes at pH 7 and <3 minutes at pH 9 and 20-25°C) to produce N-[3-(dihydroxymethylsilyl)propyl]ethylenediamine and methanol according to the following equation:
(NH2C2H4NHC3H6)(CH3)Si(OCH3)2 + 2H2O ¿ (HO)2Si(CH3)(C3H6NHC2H4NH2) + 2CH3OH
Therefore, requirements for testing of water-based physicochemical properties for the submission substance are waived on the basis of instability in water. The properties of the silanol hydrolysis product, N-[3-(dihydroxymethylsilyl)propyl]ethylenediamine, and methanol are assessed instead. However, the properties of the parent substance have been predicted using validated QSARs.
The unionised form of the parent substance has a predicted log Kow of 1.0. In solution, the amine group will protonate; therefore, the estimated log Kow for the unionised form was corrected for ionisation using the equation CORR = 1/1 +10A(pH-pKa) [where A = 1 for acids, -1 for bases; pH = pH-value of the environment; pKa = acid/base dissociation constant]. Log Kow values of -4 at pH 2, -4 at pH 4, -2.0 at pH 7 and -0.1 at pH 9 were determined for the substance. N-[3-(Dimethoxymethylsilyl)propyl]ethylenediamine has a predicted water solubility value of 8.6E+05 mg/L at 20°C. On the basis of structural examination, it is not surface-active and the acid dissociation constants (pKa) of the diamine group were estimated to be approximately 7 and approximately 10. This means that the substance is present as a mixture of the singly and doubly ionised (cationic) forms at environmentally relevant pH.
Methanol is miscible with water, has low log Kow (-0.82 to -0.64) and high vapour pressure (12790 Pa at 20°C) (OECD 2004a).
The silanol hydrolysis product, N-[3-(dihydroxymethylsilyl)propyl]ethylenediamine, may undergo condensation reactions in solution to give siloxane dimers, linear and cyclic oligomers. 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 silanediols may be modelled as an equilibrium between monomer, dimer, trimer and tetramer, with the linear tetramer cyclising to the thermodynamically stable cyclic tetramer. 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 above about 1000 mg/L the concentration of the cyclic tetramer of the silanol hydrolysis product is predicted to exceed its solubility, resulting in formation of a separate phase. Further information is given in a supporting report (PFA 2016am) attached in Section 13.
The saturation concentration in water of the silanol hydrolysis product, N-[3-(dihydroxymethylsilyl)propyl]ethylenediamine, is therefore limited by condensation reactions to approximately 1000 mg/L. However, it is very hydrophilic (calculated solubility is 1.0E+06 mg/L using a QSAR method) and the silanol hydrolysis product has a predicted log Kow of -4 at pH 2, pH 4 and pH 7; at pH 9, it is -2.5.
N-[3-(Dihydroxymethylsilyl)propyl]ethylenediamine is not surface active and is much less volatile than the parent substance with a predicted vapour pressure of 3.5E-04 Pa at 25°C. The first dissociation constant of a structurally analogous silanediol (dimethylsilanediol) has been reported to be around pKa of 12.
References:
OECD (2004a): SIDS Initial Assessment Report for SIAM 19, Berlin, Germany, 18 - 20 October 2004, Methanol, CAS 67-56-1).
PFA (2016am). Peter Fisk Associates, Analogue Report - Silanols and aquatic systems. Reference:404.105.003
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