Sebacic acid, compound with hexane-1,6-diamine (1:1)

Partition coefficient

Description of key information

Depending on pH:
HMD: range of log kow varied from -4.04 to 0.44
Sebacic acid: range of log kow from -6.897 to 2.19
Based on its two components, the substance sebacic acid, compound with hexane-1,6-hexanediamine (1:1) is considered to have a low potential of bioaccumulation.

Additional information

According to ECHA guidance R7a, the relative extent to which ionisable substances (as salts) are likely to be dissociated in the environment (with pH usually in the range 5 - 9) can have a marked effect on physico-chemical properties such as n-octanol/water partition coefficient (Kow). For substances which dissociate, values for Kow shall be derived for the forms (i.e. neutral and/or dissociated) which are relevant at environnementally relevant pH range.

When dealing with salts of organic compounds, as it is the case here for sebacic acid compound with hexane-1,6-diamine (1:1), ECHA guidance R7a also indicates that QSAR methods will be valuable in assessing the properties of each half of an organic salt. Therefore, a weight-of evidence approach was used here based on QSAR data for each half of the salt:

- Hexamethylenediamine (HMD, CAS 124-09-4): Four data are available and were used in a weight-of-evidence approach. Two data were scored as Klimisch 2. Among them, that obtained through the recommended SPARC model provides results in function of pH. The calculated log D varies from -4.04 to 0.44 at 25°C over the whole pH range, due to ionisation of the substance. At environmentally relevant pH (i.e .from 5 to 9), the calculated log D varies from -4.04 to -2.04. The other Klimisch 2 data from Meylan (1995) used a QSAR method to calculate a Log P equal to 0.35; keeping in mind that the model does not take into account temperature and pH (fragments are considered unionised). The two Klimisch 4 data report Log Kow of 0.28 and 0.35. Considering the previous data, it is thus suspected these values are for the unionised form. On the basis of all these data, in particular those at environmentally relevant pH, the substance hexamethylenediamine (or hexane-1,6-diamine, HMD) should have low potential for bioaccumulation.

- Sebacid acid (CAS 111-20-6): Two data are available and were quoted as Klimisch 2. Both data were used in a weight-of evidence approach. One of them was obtained through the recommended SPARC model which provides results in function of pH. The calculated log D varies from -6.897 to 1.846 at 25°C over the whole pH range, due to ionisation of the substance. At environmentally relevant pH (i.e. from 5 to 9), the calculated log D varies from -6.161 to 0.954. At 25 °C and pH = 7, log Kow is equal to -2.65. The other data was obtained through the recommended KOWWIN (EPISuite) model which calculates a Log P equal to 2.19.