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Physical & Chemical properties

Partition coefficient

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Description of key information

The partition coefficient of 1,3 Diphenylguanidine was first determined according to the OECD guideline 117, but this method may not applied to ionisable substance. Thus, a second study was performed in accordance with OECD testing guideline 107 and GLP requirements and at pH 11 ( i.e. one unit higher than the pKa). 
The partition coefficient of 1,3 Diphenylguanidine was 2.42 at pH 11

Key value for chemical safety assessment

Log Kow (Log Pow):
2.42
at the temperature of:
21.1 °C

Additional information

The partition coefficient of DPG (1,3-diphenylguanidine) was evaluated in 2 studies.

The first one was performed in accordance with OECD testing guideline 117 and GLP requirements. The partition coefficient of 1,3-diphenylguanidine was > 6.2 at pH = 9.3 and of 4.4 at pH = 7.01. This result is different from the other log Kow values that have been determined with other methods:

  • the log Kow of DPG was evaluated at 1.69 in another study, but no pH was reported then the state of ionization of DPG during the experiment is unknown.
  • the calculated log Kow value with EPISUITE software is 2.89.

 

The difference of results between these data suggest that the OECD 117 method may not be the most appropriate for DPG. Indeed, as indicated in the Chapter R.7A of the REACH guidance (Section R.7.1.8.3), the HPLC method is to be applied to acids and bases in their non-ionised forms, although the pH should be kept in the range to 2 to 9. But according to several publications, the dissociation constant of DPG is about 10.13. That means that a pH of at least 11.13 should be used during the log Kow measurement of DPG in order to be in the presence of the non-ionized form.

Therefore, a more reliable method for such substances is the shake-flask method (OECD 107) using an appropriate buffer with a pH of at least one unit below (free acid) or above (free base) the pKa. This is why a second study according to OECD 107 guideline and GLP requirements was performed for the determination of the Log Kow of DPG: the partition coefficient was evaluated at pH 11 ( i.e. one unit higher than the pK): Log Kow = 2.42.