Bis(trimethoxysilylpropyl)amine

Adsorption / desorption

Link to relevant study record(s)

Reference

Endpoint:

adsorption / desorption: screening

Data waiving:

study scientifically not necessary / other information available

Justification for data waiving:

other:

Key value for chemical safety assessment

Koc at 20 °C:

2.78

Additional information

Bis(trimethoxysilylpropyl)amine (CAS 82985-35-1) decomposes fast in the environment, due to rapid hydrolysis in contact with water forming the corresponding hydrolysis products bis(trihydroxysilylpropyl)amine and methanol (half-life < 1 h at neutral pH and room temperature). The silanol hydrolysis product has a very low octanol–water partition coefficient (log Kow = -4 based on QSAR) and thus low potential for adsorption. The other hydrolysis product, methanol has also negligible adsorptive properties (OECD, 2004). Thus in accordance with Column 2 of REACH Annex VIII, the adsorption/desorption screening test does not need to be conducted.

For the purposes of the chemical safety assessment further information on the adsorption behavior of the silanol hydrolysis product bis(trihydroxysilylpropyl)amine (since the parent compound is not stable in the environment), was collected using an appropriate calculation method.

Considering the ionizing properties of the compound, the adsorption potential has been calculated using Franco and Trapp ‘s expressions (2008) on estimation of the organic carbon-water partitioning coefficient of ionisable organic substances. The log Kow, the pH as well as the pKa values were used as input parameters. The pka values were determined using the software SPARC v4.6 (pKa calculator). Three macro pKa values were calculated i.e 10.77, 11.98, 12.8. The pKa value closest to environmental relevant conditions (10.77) was used for the calculation of the Koc coefficient. 

The following equation was used for Koc calculation as suggested by the authors:

 

Koc =Fn x 10^{0.37xlogPn+1.70}+Fion x 10^{pKa^0.65xf^0.14}

Where:

 

Fn = 1/(1+10^(pH-pKa))

Pn: Kow of the neutral molecule (EpiWin)

pKa: 10.77 (calculated with SPARC)

Fion = 1- Fn

f: Ratio of concentration in octanol to total concentration: Kow (overall)/(Kow (overall) + 1)

The log Koc of the hydrolysis product was calculated to be 0.42 at pH 4; 0.44 at pH 7 and 0.73 at pH 9. These values indicate the low adsorption potential of the substance to organic carbons in soil. According to the Guidance on Information Requirements and Chemical Safety Assessment, Chapter R.7.1.8.5 the log D value for the ionized molecule determined around the default pH of 7 is considered more relevant for chemical safety assessment. On this basis the calculated log Koc of 0.44 (Koc = 2.78 at pH 7) has been used for the chemical safety assessment.

 

Reference:

Franco A. & Trapp S., 2008: Estimation of the soil-water partition coefficient normalized to organic carbon for ionizable organic chemicals. Environmental Toxicology and Chemistry, Vol. 27, No. 10, pp. 1995–2004.