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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:
May - September 2012
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: The study was not conducted following to GLP or following the OECD guideline. However, it was well conducted via accepted methodology.
Qualifier:
equivalent or similar to
Guideline:
OECD Guideline 104 (Vapour Pressure Curve)
Deviations:
yes
Remarks:
The OECD Guideline calls for a plate instead of a pan, which was used in this study.
GLP compliance:
no
Type of method:
effusion method: isothermal thermogravimetry
Specific details on test material used for the study:
CYANOX® 1790 Antioxidant
IUPAC nomenclature - Tris(4-tert-butyl-3-hydroxy-2,6-dimethylbenzyl) isocyanurate
Synonym - [tris(4-t-butyl-3-hydroxy-2,6-dimethyl-benzyl)-s-triazine-2,4,6-(1H,3H,5H) trione]
Lot WP1031901
Appearance - White powder, odorless
CAS No. 40601-76-1
Molecular Formula - C42H57N3O6
Molecular Weight - 699.92 g/mole
Purity > 99%
Temp.:
20 °C
Vapour pressure:
0 Pa
Temp.:
25 °C
Vapour pressure:
0 Pa

The estimated vapor pressure of the test substance at 20°C is: 0.000094226 Pa.

The estimated vapor pressure of the test substance at 25°C is: 0.000163485 Pa.

The vapor pressure equation in Pascal is: Y = -4183.2X + 10.244 - R² = 0.9986

where Y = log Pressure (Pa), and X = 1/K.

The equation was derived from the experimental evaporation rates of the test substance and standard reference material and the literature value of the standard reference material. The literature value vapor pressures of benzoic acid was plotted as log P vs. 1/K. This is in order to obtain the linear fit equation (Clausius-Clapeyron) to interpolate the vapor pressure at any temperature.

Benzoic acid was placed into 6 mm Al pans. The benzoic acid was added to the pan as a melt in order to obtain an even surface area throughout the pan and then allowed to resolidify. Afterwhich, several isothermic runs were made on the TGA. A plot of the evaporation rate of benzoic acid vs. vapor pressure is used to calibrate the instrument parameters.

Benzoic Acid Evaporation Rate Vs. Literature Value for Vapor Pressure

°C

1/K

Evaporation rate Benzoic Acid (wt%./min)

log evaporation rate (wt%./min)

Vapor pressure Pa

Log P PA

50

0.003095

0.00274

-2.562249437

1.8759531

0.273221977

60

0.003002

0.006225

-2.205860644

5.133205

0.710388609

70

0.002914

0.01665

-1.778585762

13.253002

1.122314264

80

0.002832

0.03513

-1.45432185

32.39919

1.510534153

90

0.002754

0.0707

-1.150580586

75.438114

1.877590822

100

0.00268

0.1609

-0.793443956

167.86247

2.224953609

130

0.00248

1.267

0.102776615

1236.715748

3.092269891

140

0.00242

2.004

0.301897717

2040.34899

3.309704457

160

0.002309

4.34

0.63748973

5181.457127

3.714451909

The equation generated from these data is used to calibrate the instrument. The log evaporation rates of the test substance was plugged into the equation Y = 1.0558X + 3.0261 in order to calculate the vapor pressure at the experimental temperature. Y = log pressure of benzoic acid (Pascal) and X = log evaporation rate of benzoic acid (wt.%/min). 

 

 Experimental Evaporation Rates on the Test Substance and Calculated Vapor

Sample Temperature

Evaporation Rate

Calculated Vapor Pressure

°C

1/K

Wt%/min

Log Wt%/min

Log P (Pa)

P (Pa)

80

0.002832

0.0000403

-4.3949

-1.6140

0.0243

90

0.002754

0.0000828

-4.0821

-1.2838

0.0520

100

0.002680

0.0001832

-3.7371

-0.9195

0.1204

120

0.002544

0.0005362

-3.2707

-0.4271

0.3740

150

0.002363

0.0030060

-2.5220

0.3634

2.3087

Calculated Vapor Pressure of Test Substance based on Calibration Curve and Evaporation Ratesplotted against Temperature

 

The method was validated by measuring the evaporation rates of substances of known vapor pressures. The vapor pressure was then calculated using the benzoic acid calibration curve. The differences in the experimental vapor pressure and the literature value are provided below followed by the plotted data. The literature values were calculated from the Antoine Equation provided in the Yaw’s handbook.

 

Antoine Equation: log P = A-B / (T+C)

 

Title: Yaws' Handbook of Antoine Coefficients for Vapor Pressure (2nd Electronic Edition) Table: Antoine Equation and Coefficients for Organic Compounds

material or substance name

CAS Registry No.

molecular formula

A

B

C

Tmin (°C)

Tmax (°C)

1-chlorooctane

111-85-3

C8H17Cl

7.1309

1638.28

201.999

-25

369.261

benzoic acid

65-85-0

C7H6O2

7.41844

1824.74

152.886

122.37

477.85

1-octanol

111-87-5

C8H18O

7.16033

1536.79

163.905

-15.5

379.35

Vapor pressure calculated is in mmHg

Experimental Vapor Pressures Vs. known values

Material

Temperature (°C)

log evaporation rate (wt%/min)

Log Vapor Pressure (mmHg)Experimental

Vapor Pressure (mmHg)Experimental

Vapor PressueLiterature Value

% Difference

Napthalene

60

-0.674074

0.125931

1.5471

1.3364

-15.77

Napthalene

80

-0.168578

0.637610

5.2871

4.3412

-21.79

Napthalene

100

0.213783

1.094439

13.3941

12.4291

-7.76

octanol

50

-0.898253

-0.024121

0.8971

0.9460

5.17

octanol

60

-0.661942

0.296749

1.5934

1.9804

19.54

octanol

90

0.176959

1.107712

12.2471

12.8148

4.43

1-chlorooctane

60

0.031004

0.879227

8.5888

7.5723

-13.42

1-chlorooctane

70

0.226084

1.105634

13.8007

12.7536

-8.21

1-chlorooctane

50

-0.160522

0.638807

5.3916

4.3532

-23.86

1-chlorooctane

80

0.387746

1.319220

20.4448

20.8555

1.97

Conclusions:
The vapor pressure of the test substance was determined by using an effusion method incorporating isothermal thermogravimetric analysis (TGA). The estimated vapor pressure of the test substance at 20°C and 25°C is 0.000094226 Pa and 0.000163485 Pa respectively. The linear fit equation is Y = -4183.2X + 10.244 where Y = log Pressure (Pa), and X = 1/K. The equation can be used to calculate the vapor pressure of the test substance at any temperature provided a phase change or decomposition does not occur.

Description of key information

The vapour pressure was determined by a method essentially equivalent to OECD guideline 104 and method ST-AN-25

Key value for chemical safety assessment

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

Additional information

The vapor pressure of the test substance was determined by using an effusion method incorporating isothermal thermogravimetric analysis (TGA). The estimated vapor pressure of the test substance at 20°C and 25°C is 0.000094226 Pa and 0.000163485 Pa respectively. The linear fit equation is Y = -4183.2X + 10.244 where Y = log Pressure (Pa), and X = 1/K. The equation can be used to calculate the vapor pressure of the test substance at any temperature provided a phase change or decomposition does not occur.