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Vapour pressure

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Description of key information

The calculated vapour pressure of octadecyl isocyanate, the main ingredient of the 'Reaction mass of hexadecyl isocyanate and octadecyl isocyanate', was 0.26 Pa. 

Key value for chemical safety assessment

Vapour pressure:
0.26 Pa
at the temperature of:
25 °C

Additional information

There is no reliable data available for the test substance itself. But as results are present for both main constituents of the reaction mass (65% and 35%), this data is taken into account for further assessment as read-across approach. It is assumed that due to the similarity of the chemical structures of both main constituents the ecotoxicological hazards of the reaction mass can be described with data of one or both main components as a realistic approach.

Isocyanates are known to rapidly hydrolyse under the formation of the corresponding amine as well as solid polyurea compounds *. However, the insoluble inert polyurea is not assumed to cause environmental hazards due to the reduced uptake of high molecular mass compounds, whereas the amine is assumed to be the ecotoxicological relevant species. Concluding, tests performed using the corresponding amine can equally be used to assess the ecotoxicological hazards of isocyanates assuming the complete transfer of the isocyanate into the corresponding amine while neglecting the formation of a certain fraction ecotoxicological not active polyurea compounds. An underestimation of environmental hazards is thus avoided supporting a conservative and thus protective hazard assessment.

* Bayer Industry Services (2004). 4-chlorophenyl-isocyanate: Investigation on Stability in Aqueous Test Solutions. Project No: 200300181. Leverkusen, Germany.

* Bayer Industry Services (2003). Isopropylisocyante: Investigation on Stability in Aqueous Test Solutions. Project No: 200300095. Leverkusen, Germany.

The reaction mass of hexadecyl isocyanate and octadecyl isocyanate, as defined in section 1, consists of 35 % of hexadecyl isocyanate and 65 % of octadecyl isocyanate. The calculated vapour pressures of hexadecyl isocyanate and octadecyl isocyanate were 0.047 and 0.26 Pa, respectively. As a worst case scenario the vapour pressure of 0.26 Pa was chosen to assess the fugacity of the substance.

Isocyanates are known to rapidly hydrolyse under the formation of the corresponding amine as well as solid polyurea compounds. Therefore the calculated value for the vapour pressure of isocyanates is of theoretical interest only. The calculated vapour pressure of hexadecylamine, the corresponding amine of hexadecyl isocyanate, is 0.049 Pa at 25°C and of octadecylamine, the corresponding amine of octadecyl isocyanate, 0.0116 Pa at 25°C. But as a worst case the calculated vapour pressure of octadecyl isocyanate was taken into account for further assessment.

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