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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:
August, 2011
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: Well conducted study, according to EU and OECD guidelines, with Internal management system and certificate of analysis included in the report.
Qualifier:
according to
Guideline:
other: ASTM 1782-08, Standard test method for determining vapour pressure by Thermal Analysis, 2008
Deviations:
no
Principles of method if other than guideline:
This test method is not included into EC Regulation 761/2009, Guideline A.4 Vapour Pressure , nor into OECD Guideline 104 Vapour pressure . Nevertheless, this method was taken because for substances which are thermally unstable and contain impurities it is a more suitable method than the other listed in the above-mentioned guidelines. It is expected that this method will be included into EC Guideline A.4 in the near future. A request for inclusion was sent to the Dutch National Coördinator for EC Test Methods.
GLP compliance:
no
Type of method:
other: DSC (Differential Scanning Calorimeter)
Temp.:
25 °C
Vapour pressure:
< 0.01 Pa

Measurement results and evaluation

The Antoine curve of the test substance could not be constructed because no boiling point could be found below 8 Pa (Lower pressure limit of test apparatus). The decomposition temperature was already reached. In the following chapters, an extrapolation is done down from the p,T- pair at the decomposition temperature to 25°C. An extrapolation is done to determine the maximum expectable vapour pressure at 25°C. The slope, used for this extrapolation is derived from existing data. The real vapour pressure is expected to be lower than the extrapolated value.

Available data

Vapourpressure and heat of vaporization were calculated using Advanced Chemistry Development (ACD/Labs) Software V11.02.

Results of these calculations are:

 

-          Vapour pressure               6.27*10-7Pa at 25 °C      

-          Enthalpy of vaporization 73.38+/-3.0 kJ/mol at 760 Torr (is atmospheric pressure).

 

A vapour pressure measurement was carried out on the test substance. This was a DSC heating experiment carried out at an absolute pressure of 0.080 mBar (8 Pa).

No boiling effects were observed below 96°C.

A fast decomposition occurred above 96°C. Based on this test it can be concluded that the vapourpressure of test substance is below 0.080 mBar at 96°C.

 

Calculation of the vapourpressure at 25°C

The calculation of the vapourpressure of the test substance at 25°C is based on the measured value at 96°C; below 0.080 mBar, and on the enthalpy of vaporization; 73380 J/mol.

Relation between vapourpressure and temperature is given by the Clausius-Clapeyron equation:

Ln P/P0= (- dHvap/R) *(1/T – 1/T0)

In which:

P              is the pressure to be calculated at 25°C in mBar

P0             is the pressure at 96°C; in this case below 0.080 mBar or 8.0 Pa.

ΔHvap         is the heat of vaporization; 73380±3000 J/mol as calculated by ACD/Labs

R              is the gas constant; 8.314 J/mol.K

T              is 298.15K (or 25°C)

T0             is 369.15K (or 96°C)

The calculated vapourpressure of the test substance at 25°C, P is below 3.40·10-2Pa
(corrected for worst case error inΔHvap.   ΔHvap. = 73380 J/mole).

Based on DSC measurement, it cannot be concluded that the vapourpressure of the test substance is just or farbelow 0.034 Pa.

 

Relation between vapour pressure and mol weight applied to estimate the vapour pressure of the test substance.

It is a well known principle in the field of physical chemistry that substances with a high mol weight have a low vapour pressure. This relation is given in the chart below for different types of organic components.

 

Relation for linear, non polar organic substances.

Linear alkanes in the range of C5H12to C20H42are the non polar substances for this comparison. See the blue dots in the chart. Vapourpressure data is collected from the REACH document as given in reference [9.1]. All these data are given at 25°C, instead of 20°C.

 

Relation for linear, polar organic substances.

A high polar organic substance will have a lower vapourpressure than a non polar substance with the same mol weight. This is shown in the chart by comparing the non polar alkanes with the polar alcohols.

The linear alcohols, ethanol, 1-butanol, 1-hexanol, 1-decanol and 1-dodecanol, are the polar substances for this comparison. See the red dots in the chart. Data is collected from Handbook of the Thermodynamics of Organic Compounds, R.M. Stephenson, S. Malanowski, Elsevier Scientific Publishing Co. Inc, 1987

 

Relation for branched organic substances.

It is also a well known principle that branched substances with a certain mol weight have a higher vapourpressure than linear substances with a corresponding mol weight. Organic peroxides are the branched substances that are compared with the linear substances. The data of organic peroxides is shown as green triangles in the chart in the attachment

A table of the applied substances with the vapourpressure data is given in the attachment

The mol weight of the test substance is 430.62. Extrapolation of the dotted lines in the chart to the mol weight of the test substance will result in a vapourpressure in the range of1*10-6Pa to 1*10-9Pa. The calculated vapourpressure according to ACD/Labs is also given in the chart; the red dot in the lower right corner.

Discussion

  Three methods are applied to estimate the vapourpressure of the test substance:
 

The ACD/Labs calculation method: Pvap= 6.27*10-7Pa at 25 °C.

DSC method in combination with the calculated heat of evaporation: Pvap< 3.40·10-2Pa at 25 °C. 

From the relation between vapourpressure and mol weight: Pvapin the range of 1*10-6to 1*10-9Pa at 25 °C.

Based on these three results one can conclude that the vapourpressure of the test substance at 25°C will most likely be in the range of 1*10-7Pa to 1*10-9Pa. The value of 1*10-6Pa is based on the ACD/Labs calculation.

The vapourpressure of the test substance at 25°C will surely be below 0.01 Pa (or 0.1 µBar).




 

.

 
 
 



 

Conclusions:
The vapour pressure of 1,1,4,4-tetramethylbutane-1,4-diyl bis(2-ethylperoxyhexanoate) at 25°C is well below 0.01 Pa or 0.1 µBar.
Executive summary:

The vapourpressure of 1,1,4,4-tetramethylbutane-1,4-diyl-bis(2-ethylperoxyhexanoate was determined according to ASTM E1782-08 . This method is not included in EC Regulation No 761/2009, Guideline A.4 , but it is expected that this will occur in the near future. In 2010 a request for inclusion was sent to the Dutch National Coordinator for EC Test Methods.

The vapour pressure of test substance at 25°C is derived from calculated and experimental data.

The vapour pressure of the test substance at 25°C is well below 0.01 Pa or 0.1 µBar. 

(In the range of 10-6– 10-9Pa).

 

Description of key information

The vapour pressure of  1,1,4,4-tetramethylbutane-1,4-diyl bis(2-ethylperoxyhexanoate) at 25°C is well below 0.01 Pa.

Key value for chemical safety assessment

Vapour pressure:
0.01 Pa
at the temperature of:
25 °C

Additional information