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Physical & Chemical properties

Vapour pressure

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vapour pressure
Type of information:
experimental study
Adequacy of study:
key study
Study period:
2008-10-21 - 2009-01-23
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
according to guideline
OECD Guideline 104 (Vapour Pressure Curve)
GLP compliance:
yes (incl. QA statement)
Type of method:
static method
Key result
Test no.:
20 °C
Vapour pressure:
182 Pa
Key result
Test no.:
25 °C
Vapour pressure:
243 Pa
Key result
Transition / decomposition:
Using the static method, vapour pressure at 20 °C was estimated with 182 Pa. Vapour pressure at 25 °C was estimated with 243 Pa. These values were derived from the regression equation of two individual experiments with five resp. seven pairs vapour pressure / temperature.

From the regression, a boiling point of 189.9 °C (463.1 K) at standard pressure was estimated.
Executive summary:

The vapour pressure of the test item 3-Methylpyrazol was calculated as 182 Pa at 20 °C and 243 Pa at 25°C. The values recorded at increasing and decreasing temperature were significantly different. This could be due to the fact that the purity of the test item is lower than 100%. An other explanation could be that during the heating process, the substance could have been decomposed. An additional experiment was made: after recording the pressure at room temperature, the vessel containing test item was heated to 52.5 °C and cooled down to 20.2 °C again. The pressure in the head space was recorded after cooling, too. A difference of approx. 500 Pa was found. After turning on the vacuum pump once more and waiting for equilibrium afterwards, the value changed to the value which had been found before heating. To ensure the apparatus was tight and no air streamed into the vessel during the experiment we did the same experiment with an emptied vessel. It was shown that the vessel during one week being vacuumed was tight and even a period of heating could not change pressure. The values recorded at the increasing phase of experiment 1 and 2 correlate very well. For the calculation of the vapour pressure, the values of the heating phase of both experiments were used.

Description of key information

The vapour pressure of 3-Methylpyrazol at 20 °C was estimated with 182 Pa. Vapour pressure at 25 °C was estimated with 243 Pa.

Key value for chemical safety assessment

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

Additional information

The reported study is GLP compliant and has Klimisch score 1. The vapour pressure of 3-Methylpyrazol at 20 °C was estimated with 182 Pa. Vapour pressure at 25 °C was estimated with 243 Pa.