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Adsorption / desorption

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Description of key information

The potential of the structural analogue aspartic acid, N,N’-[methylenebis(2-methyl-4,1-cyclohexanediyl) ]bis-,1,1',4,4'-tetraethyl ester to sorb or sediment was determined according to EU-Method C.19 (HPLC-Method) yielding a logKoc between 4.2 and 5.1. The sorption coefficient was determined at pH 6 and pH 8 showing that the sorption behaviour does not depend on the prevailing pH. For environmental assessment a mean log Koc value of  4.7 (Koc 44668) was used (Bayer, 2003).
According to the classification of Swann et al. (1983), the structural analogue aspartic acid, N,N’-[methylenebis(2 -methyl-4,1-cyclohexanediyl) ]bis-,1,1',4,4'-tetraethyl ester has a high potential to sorb on soil.

Key value for chemical safety assessment

Koc at 20 °C:
44 668

Additional information

The applied HPLC method as stipulated in the EU-method C.19 method is suitable to determine sorption coefficients for mixtures having logKoc values up to a value of 5. As the test substance is a mixture of stereoisomeric components, only an unresolved elution band was obtained. Consequently, a logKoc range was reported rather than a single value.

In the underlying method, the calibration was based on standards with a maximal logKoc of 4. Thus, the logKoc of the test substance could solely be evaluated by linear extrapolation beyond the prescribed calibration range.

To comply with the requirements of the EU-guideline C.19 for the measurement of ionisable substances, the sorption coefficient was determined at pH 6 and pH 8.Aspartic acid, N,N'-[methylenebis(2 -methyl-4,1 -cyclohexanediyl)]bis-, 1,1',4,4'-tetraethyl ester as an organic base, is partly ionized at pH 6 and non-ionised at pH 8. The pKa of the test substance was estimated prior to the experiment by the means of the software ACD/pKa v 6.0 to select the required pH values.

The determined sorption coefficient (logKoc) at pH 6 (ionised form) covers the range between 4.3 and 5.1, whereas the logKoc of the non-ionised form of this organic base ranges between 4.2 and 5.1. Based on theses results it can be seen, that the sorption behaviour does not depend on the prevailing pH.

Study was performed with aspartic acid, N,N'-[methylenebis(2-methyl-4,1-cyclohexanediyl)]bis-, 1,1',4,4'-tetraethyl ester which is a structural analogue to aspartic acid, N,N'-(methylenedi-4,1-cyclohexanediyl)bis-, 1,1',4,4'-tetraethyl ester. Both substances are diethyl esters of aspartic acid linked to a dicyclohexylmethyldiamine moiety. The difference between these two substances is merely the presence of two methyl groups connected to the cyclohexane rings. This structural analogy was confirmed by the Member State responsible for the notification of both substances under the NONS regulation. The Member State decided that test results obtained for one substance can be transferred to the other substance and that testing of both substances is usually not required. This decision is in accordance with the grouping of substances and read-across approach in Annex XI, 1.5 of the REACH Regulation.

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