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Physical & Chemical properties

Vapour pressure

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Reference
Endpoint:
vapour pressure
Type of information:
experimental study
Adequacy of study:
key study
Study period:
August 12, 2016 - August 14, 2016
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to
Guideline:
OECD Guideline 104 (Vapour Pressure Curve)
Deviations:
no
Qualifier:
according to
Guideline:
EU Method A.4 (Vapour Pressure)
Deviations:
no
GLP compliance:
no
Type of method:
effusion method: vapour pressure balance
Key result
Test no.:
#1
Temp.:
20 °C
Vapour pressure:
< 0 Pa
Key result
Test no.:
#2
Temp.:
25 °C
Vapour pressure:
< 0 Pa
Key result
Test no.:
#3
Temp.:
50 °C
Vapour pressure:
< 0 Pa

Individual results

Vapour pressure balance

The vapour pressure was measured in the temperature range of 50 °C to 80, °C. Above 80 °C melting of the test item was detected. The measured vapour pressures at the corresponding temperatures are listed inTable 1.

Table1: Measured vapour pressures and corresponding temperatures

Temperature / °C

Vapour pressure / hPa

50

1.3 × 10-6

60

2.7 × 10-6

70

3.3 × 10-6

80

6.0 × 10-6

All values were below the detection limit of 1 mPa.

Since the test did not yield vapour pressures sufficiently high to extrapolate to 20, 25 and 50 °C these values were estimated. According to the Antoine equation, the vapour pressure can be calculated. For an extrapolation to lower temperatures a conservative assumption of the Antoine constant C is 273.15. This results in a linear dependency of log(p) of the inverse Temperature 1/T (in K). Values for the resulting slope of the Antoine equation (constant B) for substances of high molecular weight, which can be derived from literature values (e.g. Handbook of Chemistry and Physics) are lower than -5000. Thus, for a conservative estimation of the vapour pressure of the test item at 20, 25 and 50 °C, a value of -5000 for constant B and a value of 273.15 for constant C, respectively, were used.

The detection limit (1 × 10-5 hPa) at the highest measurement point (80 °C) was used for the calculation as all measured vapour pressures were below the detection limit.

Based on this assumption, the constant A of the Antoine equation was calculated. Subsequently, the vapour pressure at 20, 25 and 50 °C can be calculated with the Antoine equation.

 

Table2: Calculated vapour pressure at 20, 25 and 50 °C

T / °C

p / hPa

p / Pa

20

< 1.3×10-8

< 1.3×10-6

25

< 2.4×10-8

< 2.4×10-6

50

< 4.9× 10-7

< 4.9× 10-5

This is a conservative estimation of the vapour pressure of the test item for the listed temperatures.

 

Conclusions:
As all measured values were below the detection limit of the method, the following uppper limit vapour pressure for the test item were calculated: <1.3x10^-6 Pa (20°C); <2.4x10^-6 Pa (25°C); <4.9x10^-5 Pa (50°C)
Executive summary:

The vapour pressure was determined according to OECD 104. The method is based on the estimation of the mass of test item flowing out per unit of time of a Knudsen cell in the form of vapour, through a micro-orifice under ultra-vacuum conditions. The test item is filled into the test cell and placed in a furnace in the vacuum chamber from which the sample evaporates while heating with asurrounding heater. The mass of effused vapour is obtained by determining the loss of mass of the cell. The vapour pressure is calculated by applying the Hertz-Knudsen relation with correction factors that depend on parameters of the apparatus.

The recommended range of the vapour pressure for this method is 10-5to 10-2 hPa and for the temperature between approximately 0 and 120 °C. As the test item started melting above 80°C, the vapour pressure was measured in the temperature range of 50 °C to 80, °C. All measured values were below the detection limit of 1 mPa, wherefore the values for 20, 25 and 50 °C were calculated according to the Antoine equation.

Table2: Calculated vapour pressure at 20, 25 and 50 °C

T / °C

p / hPa

p / Pa

20

< 1.3×10-8

< 1.3×10-6

25

< 2.4×10-8

< 2.4×10-6

50

< 4.9× 10-7

< 4.9× 10-5

This is a conservative estimation of the vapour pressure of the test item for the listed temperatures.

 

Description of key information

The vapour pressure was determined according to OECD 104 via vapour pressure balance. As all measured values were below the detection limit of the method (< 1 mPa), the following uppper limit vapour pressure for the test item were calculated according to the Antoine equation.

Table: Calculated vapour pressure at 20, 25 and 50 °C

T / °C

p / hPa

p / Pa

20

< 1.3×10-8

< 1.3×10-6

25

< 2.4×10-8

< 2.4×10-6

50

< 4.9× 10-7

< 4.9× 10-5

This is a conservative estimation of the vapour pressure of the test item for the listed temperatures.

 

Key value for chemical safety assessment

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

Additional information