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Physical & Chemical properties

Partition coefficient

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Description of key information

The n-octanol/water partitioning coefficient is not relevant for inorganic substances such as sulphamidic acid. Given the very high solubility in water, a logKow of 0 is proposed to enable the interface to Chesar (in secondary literature an experimental log Kow of 0.1 is reported referenced as Bell EB (1983), but this reference could not be found in public libraries). Nevertheless, this value is cited in the EPI Suite model referenced to “E. B. Bell in Kirk-Othmer Encyclopedia of Chemical Technology vol. 21 (Wiley-Interscience, New York, 3rd ed., 1983) pp 949-960”, but therein experimental details are also very limited.

The EPI Suite (US EPA) Version 4.1 model KOWWIN v1.68 (September 2010) estimated the log Kow to be -4.3438. However, it must be considered that inorganic substances such as sulphamidic acid are not within the training data set and also outside the applicability domain of the model. Nevertheless, it should be noted that for phenyl sulfamide (exp. log Kow 0.40 and Kowwin estimate 0.47) and phenethyl sulfamide (exp. log Kow 0.81 and Kowwin estimate 0.87), the correlation is good, although these are sulfamides.

Considering however, that Benzenesulfonic acid, 4-amino- (exp. log Kow -2.16, Okamoto, H. et al. 1991 and Kowwin estimate -2.08) and Benzenesulfonic acid, 3-NH2, Na salt (exp. log Kow -3.40, Sangster et al. 1994 and Kowwin estimate -3.87) were part of the model validation set, the estimated value for sulphamidic acid does get some weight.

Further support for a negative log Kow value is also provided by solubility data, reported in Kirk-Othmer Encyclopedia of Chemical Technology. 3rd ed., Volumes 1-26. New York, NY: John Wiley and Sons, 1978-1984, reporting a water solubility of sulphamidic acid being 17.57 wt% in water at 20 °C (consistent with 181.4 g/L at 20 °C exp. determined, Muckove 2010, see this dossier), but only 0.0412 wt% in methanol and 0.0167 wt% in ethanol (at 25 °C). As polarity with incresing chain length of alcohols does decrease the solubility in n-octanol is expected being much lower than 0.01 wt%. As a result following a worst case estimate the log Kow is log 0.01/17.57 = -3.25, supporting the estimate derived by Kowwin QSAR method.

However, the conclusion is clear that sulphamidic acid is not having the potential to bioaccumulate, and although a strongly negative log Kow value appears appropriate, for hazard and risk assessment a log Kow value of 0 is used as very conservative approach.

Key value for chemical safety assessment

Log Kow (Log Pow):
0
at the temperature of:
20 °C

Additional information