Benzenesulfonic acid, 4-C10-13-sec-alkyl derivs., compds. with isopropanolamine

Vapour pressure

Description of key information

The vapour pressure of a commercial sample of Benzenesulfonic acid, 2(or 4)-C10-14-alkyl derivs., compds. with isopropanolamine is <5 Pa at 20°C and 50 °C.  All available evidence support the hypothesis that the vapour pressure of the LAS-MIPA salt would be much lower than this measured value.  Based on a weight of evidence a value of 0.01 Pa at 25oC is used for the CSR.

Key value for chemical safety assessment

Vapour pressure:

0.01 Pa

at the temperature of:

25 °C

Additional information

The vapour pressure of <5 Pa at 20°C was determined in a reliable study. The vapour pressure of chemical substances is a thermodynamic property. At the boiling point of a liquid substance, the vapour pressure is equal to the (atmospheric) pressure over the liquid. The vapour pressure at different temperatures can be calculated using the Clausius-Clapeyron equation, where the natural log of the vapour pressure is directly proportional to the heat of vaporization of the substance.

The heat of vaporization of the substance can be determined by measuring vapour pressure at (at least) two different temperatures. Since the energy needed for boiling directly determines the boiling point of a substance, the heat of vaporization, at the boiling point, can be estimated from the absolute temperature at the boiling point. Lyman (1982) describes a number of estimation models for predicting the heat of vaporization. With such a model, the vapour pressure at any temperature can be estimated directly from the boiling point, since the vapour pressure at the boiling point is by definition known (i.e. equal to atmospheric pressure). Grain, in Lyman (1982), recommends the Fishtine-Klein method.

The heat of vaporization is not a constant, but varies with temperature. This means that although this approach suffices for estimating vapour pressure at temperatures close to the boiling point (in temperature ranges where the heat of vaporizationcan be assumed to be constant), and therefore for estimating vapour pressure at ambient temperature for low-boiling substances, for substances with a much higher boiling point, the temperature-dependence of the heat of vaporization has to be taken into account. Grain recommends the (modified) Watson approach.

Based on this approach, Grain proposed a method for estimating vapour pressure at temperatureTof organic substances from (measured) boiling point data at atmospheric pressure

With this approach, the vapour pressure of LAS-MIPA at atmospheric pressure and ambient temperature can be estimated, if its boiling point at atmospheric pressure is known. LAS-MIPA decomposes (long) before it reaches boiling point. Reliable studies record decomposition at temperatures > 290°C. Boiling point (BP) is therefore > 290°C.

The boiling point of linear dodecylbenzene, as reported in its SIDS report, is around 280°C; several other sources are available, notably a Wikipedia entry giving 290°C. The BP of linear dodecyl benzene sulfonate, according to supplier Fisher Scientific, is >300–315°C. For linear dodecyl benzene sulfonate, sodium salt, the relevant SIDS report reports decomposition > 444°C. Finally, for linear dodecyl benzene sulfonate, ammonium salt, LookChem reports a BP of 511°C. Although these data are not equally reliable, they collectively support the notion that the BP of LAS-MIPA will be higher than that of LAS or LAS-Na, and that therefore LAS-MIPA BP will be > 444°C.

Using a BP of 444°C to estimate the vapour pressure of LAS-MIPA, the Grain equation results in a value of 4.45E10^-9Pa. When using a very conservative value of 315^oC, a vapour pressure of 6.94E10^-4is obtained. It can therefore be stated that the vapor pressure of LAS-MIPA is very likely lower than 0.01 Pa.