N-[3-(trimethoxysilyl)propyl-1,3-Benzenedimethanamine

Partition coefficient

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

partition coefficient

Data waiving:

study technically not feasible

Justification for data waiving:

the study does not need to be conducted because the substance decomposes

Reference 2

Endpoint:

partition coefficient

Type of information:

(Q)SAR

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

results derived from a valid (Q)SAR model and falling into its applicability domain, with adequate and reliable documentation / justification

Justification for type of information:

See attached QMRF/QPRF

Principles of method if other than guideline:

The result was obtained using an appropriate QSAR method (see attached QMRF and QPRF for details).

The model is the publicly available KOWWIN v1.68 program (USEPA 2011). KOWWIN is part of EPI Suite v4.1 and may be downloaded from http://www.epa.gov/oppt/exposure/pubs/episuite.htm. The model is based on fragment values. That is, the chemical structure is broken down into its constituent functional groups, and the contribution of each group toward the overall partition coefficient is calculated. The constants used within KOWWIN have been derived by SRC from a wide range of organic chemicals. The authors of this QMRF have carried out additional validation and found the method to be applicable organosilicon compounds, excluding di- and tri-alkoxysilanes.

USEPA 2011. KOWWIN v. 1.68, US EPA. 2011. Estimation Programs Interface Suite™ for Microsoft® Windows, v 4.10. United States Environmental Protection Agency, Washington, DC, USA. Available at http://www.epa.gov/oppt/exposure/pubs/episuite.htm.

Partition coefficient type:

octanol-water

Type:

log Pow

Partition coefficient:

-1.6

Temp.:

20 °C

Remarks on result:

other: value for unionised form

Type:

log Pow

Partition coefficient:

-4

Temp.:

20 °C

pH:

7

Remarks on result:

other: corrected for ionisation

Type:

log Pow

Partition coefficient:

-4

Temp.:

20 °C

pH:

2

Remarks on result:

other: corrected for ionisation

Type:

log Pow

Partition coefficient:

-4

Temp.:

20 °C

pH:

4

Remarks on result:

other: corrected for ionisation

Type:

log Pow

Partition coefficient:

-2.6

Temp.:

20 °C

pH:

9

Remarks on result:

other: corrected for ionisation

Details on results:

The two amine groups in the substance will protonate in solution; 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] and the pKa for the first amine group.

Conclusions:

Partition coefficient values of -4, -4, -4 and -2.6 at pH 2, pH 4, pH 7 and pH 9 respectively were obtained for the hydrolysis product of the registered substance, using an accepted calculation method. The result is considered to be reliable.

Description of key information

Log K_ow [Constituent 1; N-[3-(trimethoxysilyl)propyl]-1,3-benzenedimethanamine]: -1.5 at pH 7 (QSAR)

Log K_ow [Constituent 2; -[(2,2-dimethoxy-1,2-azasilolidin-1-yl)benzenedimethanamine]: not relevant, very rapid hydrolysis

Log K_ow [N-[3-(trihydroxysilyl)propyl]-1,3-benzenedimethanamine]: -4 at pH 7 (QSAR)

Log K_ow [methanol]: -0.82 to -0.64

Additional information

The requirement to conduct an n-octanol/water partition coefficient study for the substance is waived because all the constituents of the substance undergo either rapid or very rapid hydrolysis in contact with water with half-lives of <12 hours. The final hydrolysis products in this care are N-[3-(trihydroxysilyl)propyl]-1,3-benzenedimethanamine and methanol.

In addition, the determination of the log K_ow of the substance as a whole substance is not scientifically meaningful for the purpose of assessment of exposure or risk. The needs associated with a sound understanding of partition coefficient of the substance is adequately met by the available data on the constituents. The partition coefficient data for constituents of the substance were determined using a validated QSAR estimation method.

A predicted log K_ow value of 1.5 was determined for N-[3-(trimethoxysilyl)propyl]-1,3-benzenedimethanamine (Constituent 1) using a validated QSAR estimation method. Constituent 1 is doubly protonated at neutral and acid pH. At pH 9, mixture of singly and doubly ionised molecules is expected to be present. The log K_ow prediction refers to the unionised form of Constituent 1. The two amine groups will protonate in solution (pKa1 = 8.6 and pKa2 = 9.8); therefore, the estimated log K_ow for the unionised form was corrected for ionisation based on the second pKa (which will generate the unionised form) using the equation CORR = 1/1 +10^A(pH-pKa) [where A = 1 for acids, -1 for bases; pH = pH-value of the environment; pKa = acid/base dissociation constant]. The corrected log K_owvalues are:-4 at pH 2, -4 at pH 4, -1.3 at pH 7 and 0.63 at pH 9. Log K_ow is not predicted for Constituent 2 due to its very rapid hydrolysis in contact with water.

The relevant corrected log K_ow values are used for assessment purposes.

Similarly, the unionised form of the silanol hydrolysis product of Constituent 1 and Constituent 2; N-[3-(trihydroxysilyl)propyl]-1,3-benzenedimethanamine has a predicted log K_ow value of -1.6 using a validated QSAR estimation method. The corrected log K_ow value are: -4 at pH 2, -4 at pH 4, -4 at pH 7 and -3 at pH 9

Methanol has a reported log K_ow of -0.82 to -0.64 (OECD 2004).

Reference:

OECD (2004): SIDS Initial Assessment Report for SIAM 19, Berlin, Germany, 18-20 October 2004, Methanol, CAS 67-56-1.