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Physical & Chemical properties

Vapour pressure

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Description of key information

<1 Pa at 25 °C

Key value for chemical safety assessment

Additional information

The value for vapour pressure of UVCB substance CAS 61788-89-4 (Fatty acids, C18-unsaturated, dimers) is based on a weight of evidence using experimental and QSAR data for the monomer and dimer linear and branched, unsaturated and saturated C18 fatty acids.

According to the Raoult’s law, the vapour pressure of ideal mixture is equal to the mole-fraction-weighted sum of the components' vapour pressures and the vapour pressure of mixture should be lower than the vapour pressure of the component which has the highest vapour pressure in its pure form. In case of CAS 61788-89-4 the negative deviations from the Raoult’s law are expected because the viscosity of the mixture is significantly higher than the viscosity of components of a mixture. Therefore, the negative deviations from ideal mixture are expected and vapour pressure of the mixture is expected to be lower than estimated by Raoult’s law and in consequence lower than the vapour pressure of the most volatile component.

The vapour pressure of mixture (and UVCB substance) is expected to be lower than the vapour pressure of the component which has the highest vapour pressure in its pure form. The highest vapour pressure was estimated by QSAR MPBPWIN v1.43 model for the saturated branched monomer of C18 fatty acid and it is 2.72·10-2 Pa at 25 °C.


The conservative vapour pressure value <1Pa at 25 °C is taken as a key value for the chemical safety assessment of the substance 61788-89-4 (Fatty acids, C18-unsaturated, dimers, “Dimer”).