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Vapour pressure

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Reference
Endpoint:
vapour pressure
Type of information:
experimental study
Adequacy of study:
key study
Study period:
1996-09-23
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
comparable to guideline study with acceptable restrictions
Remarks:
The study is regarded as reliable with restrictions because it was not conducted in compliance with GLP regulation but data are comprehensive and scientifically acceptable. The test item is classified as organic peroxide Type C. In accordance with ECHA guidance IR/CSA chapter R.7a (version 4.1, October 2015) the testing with OECD standard method was not conducted. These studies were considered to be technically not possible as the substance will decompose during measurement and for safety reasons due to its explosive properties. To generate data in order to perform a risk assessment an alternative method using fast measurements under reduced pressure were conducted. These data were considered more reliable as compared to the alternative approach using QSAR estimation. In conclusion these data were regarded as reliable with restrictions.
Qualifier:
equivalent or similar to
Guideline:
other: ASTM E1782 - 14 Standard Test Method for Determining Vapor Pressure by Thermal Analysis
Deviations:
not applicable
Remarks:
study was conducted before implementation of guideline
Principles of method if other than guideline:
In hermetic sealed containers with pinholes in the lid at a given temperature an equilibrium will be established between test item in the gas phase and in the condensed phase. As the test item is heated, the pressure exerted by the volatile component the vapour pressure increases. The material in a DSC pan is held at a constant pressure, and then there will be an endothermic heat flow associated with the condensed material entering the vapour phase. When this vapour pressure equals the external pressure on the vapour space, the liquid boils isothermally at that temperature. The applied pressure will be changed and the temperature at which boiling occurs changes a corresponding amount. The temperature range of the method is limited. The lower pressure limit depends on the capacity of the vacuum pump, the lower temperature limit of the DSC-apparatus (25 °C) or by the melting point of the test item. The upper limit depends on the thermal stability of the test item. Using the measured boiling temperatures at given vapour pressure a plot will be constructed in which the vapour pressure is related to the temperature. Form the measured data points of the vapour pressure curve the constants A, B and C of the Antoine equation are derived and the vapour pressure of the test item is calculated by extrapolation of the measured vapour pressure curve for the temperatures 20, 25 and 50 °C. The DSC was checked using the measuring onset temperature of fusion and the heat of fusion of Indium.
GLP compliance:
not specified
Type of method:
other: Vacuum Differential scanning calorimetry
Temp.:
20 °C
Vapour pressure:
2 Pa
Remarks on result:
other: extrapolated value from the Antoine equation
Temp.:
25 °C
Vapour pressure:
3 Pa
Remarks on result:
other: extrapolated value from the Antoine equation
Temp.:
50 °C
Vapour pressure:
36 Pa
Remarks on result:
other: extrapolated value from the Antoine equation
Transition / decomposition:
yes
Remarks:
The Self-Accelerating Decomposition Temperature (SADT) of the substances was determined to be 40°C at 1013.25 hPa. For details please refer to IUCLID section 4.23
Transition temp.:
>= 40 °C

Table 1 Vacuum DSC results of test item

Measured

Calculated after fit

pressure (mbar)

T boiling point (°C)

pressure (mbar)

1.24

65.4

1.22

1.99

72.0

1.97

4.11

83.6

4.32

6.15

89.43

6.22

7.56

92.6

7.56

10.11

96.9

9.74

Please refer to the attached Illustration for a p,T-diagram

 

Two fits were done on the set data points.

 

Antoine :

 

Log(p) = A – B/(C+T) or p= 10 ^ {A-B/(C+T)} where

 

A,B and C : constants

p: pressure (mbar)

T: temperature in K

 

Table 2 Fit parameters for test item in temperature range: 65°C to 96°C.

fit model

constant A

constant B

constant C

Antoine

7.6411

1755.28

-106.20

 

Example (for T = 350 K): p= 10 ^{7.6411-1755.28/(350-106.20)} = 2.76 mbar

 

Table 3 pressure table 

Temperature (°C)

Pressure (mbar)

20

0.02

extrapolation

25

0.03

extrapolation

30

0.05

extrapolation

40

0.14

extrapolation

50

0.36

extrapolation

60

0.81

extrapolation

70

1.71

interpolation

80

3.41

interpolation

90

6.46

interpolation

100

11.6

extrapolation

 

Conclusions:
The vapour pressure of the test item tert.-Butylperoxy- 2-ethylhexanoat was determined to be 2 Pa at 20 °C, 3 Pa at 25 °C and 36 Pa at 50 °C respectively.
Executive summary:

A study was conducted using Vacuum DSC to determine the vapour pressure of the test item. Using the vacuum DSC test, it was possible to handle the test item at temperatures above the SADT (please refer to IUCLID section 4.23 for more details about SADT) because very low amounts were used; the measurements were very fast and under reduced pressure. Vacuum DSC experiments were carried out at various constant pressure levels. Therefore approximately 10 mg product was weight into a 70 microliter aluminium cup with a pierced lid. The pressure of the oven was set to the desired pressure and was controlled by a pressure controller. The scan was started after reaching a constant pressure using a heating rate of 5 °C/min. During this scan, the product reached the boiling point at the set pressure and evaporated. A sudden increase in the endothermic effect related to the boiling of the test item was then obtained. After 6 scans in the temperature range of 65°C up to 96°C at different pressures (124 Pa up to 1011 Pa) a plot was constructed in which the vapour pressure is related to the temperature. Form the measured data points of the vapour pressure curve the constants A, B and C of the Antoine equation were derived and the vapour pressure of the test item was calculated by extrapolation of the measured vapour pressure curve for the temperatures 20, 25 and 50 °C. The vapour pressure of the test item tert.-Butylperoxy- 2-ethylhexanoat was determined to be 2 Pa at 20 °C, 3 Pa at 25 °C and 36 Pa at 50 °C respectively. No observations were made which caused any doubt on the validity of the test data.

Description of key information

The vapour pressure of the test item tert.-Butylperoxy- 2-ethylhexanoat was determined to be 2 Pa at 20 °C, 3 Pa at 25 °C and 36 Pa at 50 °C respectively.

Key value for chemical safety assessment

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

Additional information

Waiving of the OECD / EU standard method

In accordance with ECHA guidance IR/CSA chapter R.7a (version 4.1, October 2015) the testing with OECD standard method was not conducted. Standard testing according to these guidelines was considered to be technically not feasible as the substance will decompose during measurement and for safety reasons due to its explosive properties. To generate data in order to perform a risk assessment an alternative method using fast measurements under reduced pressure was conducted. These data were considered more reliable as compared to the alternative approach using QSAR estimation. Thus, no vapour pressure data in accordance with OECD TG 104 is available.

 

Determination of the vapour pressure using vacuum DSC (Differential Scanning Calorimetry)

 

A study was conducted using Vacuum DSC to determine the vapour pressure of the test item. Using the vacuum DSC test, it was possible to handle the test item at temperatures above the SADT (please refer to IUCLID section 4.23 for more details about SADT) because very low amounts were used; the measurements were very fast and under reduced pressure. Vacuum DSC experiments were carried out at various constant pressure levels. Therefore approximately 10 mg product was weight into a 70 microliter aluminium cup with a pierced lid. The pressure of the oven was set to the desired pressure and was controlled by a pressure controller. The scan was started after reaching a constant pressure using a heating rate of 5 °C/min. During this scan, the product reached the boiling point at the set pressure and evaporated. A sudden increase in the endothermic effect related to the boiling of the test item was then obtained. After 6 scans in the temperature range of 65°C up to 96°C at different pressures (124 Pa up to 1011 Pa) a plot was constructed in which the vapour pressure is related to the temperature. Form the measured data points of the vapour pressure curve the constants A, B and C of the Antoine equation were derived and the vapour pressure of the test item was calculated by extrapolation of the measured vapour pressure curve for the temperatures 20, 25 and 50 °C. The vapour pressure of the test item tert.-Butylperoxy- 2-ethylhexanoat was determined to be 2 Pa at 20 °C, 3 Pa at 25 °C and 36 Pa at 50 °C respectively. No observations were made which caused any doubt on the validity of the test data.