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Physical & Chemical properties

Vapour pressure

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Description of key information

The vapour pressure of a commercial sample of Benzenesulfonic acid, C10-13-alkyl derivs., compds. with triethanolamine is <5 Pa at 20°C and 50 °C.All available data support the hypothesis that the vapour pressure of the LAS-TEA salt would be much lower than this measured value.   Based on a weight of evidence a value of 0.0011Pa is used for the CSR.

Key value for chemical safety assessment

Vapour pressure:
0.001 Pa
at the temperature of:
20 °C

Additional information

The vapour pressure of <5 Pa at 20°C was determined in a reliable study. However, this result is not representative of the vapour pressure of the substance. The result is considered to be much higher than expected because the tested product contains residual water or TEA (difficult to remove). 

Since LAS-TEA is a dissociating salt, as a first order approximation, the vapour pressure of LAS-TEA could be extrapolated from the vapour pressures of the  constituent 'ions', which would provide an upper limit for the vapour pressure of the LAS-TEA salt. In the theoretical worst case that LAS-TEA fully dissociates to LAS- and TEA+ and that LAS- and TEA+ are subsequently wholly converted to neutral LAS and TEA, the vapour pressure would be that of either LAS or TEA, whichever has the highest vapour pressure. On the basis that salts are usually less volatile than their non-ionic precursors and that LAS-TEA is heavier and would therefore have a lower vapour pressure than LAS-Na, the vapour pressure of LAS-TEA is likely to be lower than these values.


The vapour pressure of LAS-Na, as given in the LAS-Na dossier, is 3.13E-13 Pa. 
EPISuite provides an estimate for the vapour pressure of LAS as 6.8e-8 Pa (LAS represented as neutral 4-decyl benzene sulfonic acid.

 

The vapour pressure of TEA, as given in the TEA dossier, is <0.03Pa. EPISuite provides an experimental value for TEA at 0.00048 Pa (3.59E-6 mm Hg; Daubert & Danner 1989). For 2, 2,2-Nitrilotriethanol hydrochloride (TEA hydrochloride), an estimated value of 8.38E-06mmHg (0.0011Pa) at 25oC is predicted (CSID:91990, http://www.chemspider.com/Chemical-Structure.91990.html (accessed 17:22, Mar 19, 2013)).

The highest available value is 0.0011 Pa for TEA-HCl This of course is a conservative surrogate value, since LAS-TEA is heavier and would therefore have a lower vapour pressure than TEA-HCl, LAS-TEA consists of only part TEA, and it is extremely unlikely that all TEA would be available for evaporation, even under conditions where LAS-TEA dissociates. All available data support the hypothesis that the vapour pressure of the LAS-TEA salt would be much lower than the measured value. 

 

Taking this information together, a worst case vapour pressure of 0.0011 Pa is proposed, based on the estimated vapour pressure of the lighter TEA-HCl salt. LAS-TEA can be expected to be less volatile than any of its constituent 'salts.