Registration Dossier
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EC number: 241-749-5 | CAS number: 17766-26-6
Partition coefficient
Administrative data
Link to relevant study record(s)
Description of key information
log D = 0.73 at 25 °C, pH4
log D = 0.01 at 25 °C, pH7
log D = -1.55 at 25 °C, pH9
Key value for chemical safety assessment
- Log Kow (Log Pow):
- 0.01
- at the temperature of:
- 25 °C
Additional information
For the substance TMT the partition coefficient was estimated with ACD/LogD Suite Program for different pH values. Calculations were carried out for the keto and enolic forms of the undissociated organic acid and the anionic and cationic organic components. Prior to this calculation the pKa values for all dissociation/ionization steps were calculated. The real partition coefficient Log D depends on the ratio between the concentrations of the different ionic species. Log D was determined as 0.73, 0.01 and -1.55 for pH 4, 7 and 9 respectively.
The Log Powvalue for the neutral, undissociated keto form (1,3,5-triazine-2,4,6-trithione) is calculated as 0.73. The neutral form is only existent below pH = 5. With increasing pH values the partition coefficients (Log D) decreases sharply to a value below -2 in the strong alkaline region as consequence of the stepwise dissociation/depronotation of the substance. Also in the strong acid range below pH = 1 the partition coefficient is decreasing as consequence of beginning protonation of the amino groups.
The Log Pow value of the neutral, undissociated enolic form (1,3,5-triazine-2,4,6-trithiol), which is considered as less relevant, is calculated as 2. But in contrast to the keto form, the neutral enolic form does not exist in the whole pH range from 0 to 14. At all pH values the (hypothetical) enolic form exists in the ionic form with significantly negative Log D values. For this reason, it seems reasonable, to use the values of the keto form for exposure assessments to gain a reliable “worst case” scenario.
In another QSAR study (KOWWIN) the log Pow of the triply charged form was determined to be -4.4 at 25 °C. This is in agreement with the results of the first study but is environmentally not relevant because this forms exists only for pH > 10 (pKa = 10.4).
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