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Physical & Chemical properties

Vapour pressure

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Description of key information

The vapour pressure of butenes was determined to be 484-1160 kPa at 25°C, depending on the isomer. The endpoint value was extrapolated from lower temperatures for the different butene structures.

Key value for chemical safety assessment

Vapour pressure:
837.25 kPa
at the temperature of:
25 °C

Additional information

In accordance with REACH Annex XI, this study does not need to be conducted as it is technically not possible. These substances have a vapour pressure above the limit of detection of the guideline methods. In accordance with ECHA (2008) Guidance on information requirements and chemical safety assessment chapter R.7a, the vapour pressure study is not required for a substance with a boiling point <30°C as these substances will have a vapour pressure above the limit of measurement (i.e. 10^5 Pa). As the boiling point of butenes ranges from -6.26°C to 3.71°C, this endpoint can be waived.

The waiver is supported by data from the CRC Handbook (Lide 2008) and Zwolinski and Wilhoit (1971). No information on the methods used is available. However, the information is taken from reliable peer reviewed handbooks and is considered reliable and suitable for use for this endpoint. According to the CRC Handbook, the vapour pressure of butenes was determined to be 484 kPa - 1160 kPa at 25°C. The endpoint value was extrapolated from values at lower temperatures for the different butene structures. Vapour pressure values are available for 2-methylpropene (1160 kPa at 25°C), but-1-ene (1100 kPa at 25°C) and 2-butene (484 kPa - 605 kPa at 25°C). The mean of the vapour pressure values for the butenes is 837.25 kPa at 25°C and this has been used to complete the 'key value for chemical safety assessment'.

According to Zwolinski and Wilhoit (1971), the vapour pressure of butenes was determined to be 141 kPa - 206 kPa at 12.8°C. The endpoint was determined by extrapolation using the Antonine equation. The vapour pressure at 12.8°C was determined to be 206.2 kPa for 2-methylpropene, 201.3 kPa for but-1-ene and141.3 kPa – 156.1 kPa for 2-butene.