Reaction mass of bisisopropyl peroxydicarbonate and bis-sec-butyl peroxydicarbonate and isopropyl-secbutylperoxydicarbonate

Vapour pressure

Link to relevant study record(s)

Reference

Endpoint:

vapour pressure

Type of information:

other: Safety detail report

Adequacy of study:

key study

Study period:

Experimental completion date: 21 January 2000

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

study well documented, meets generally accepted scientific principles, acceptable for assessment

Qualifier:

no guideline followed

Principles of method if other than guideline:

Various methods were used to measure the vapour pressure of multiple substances, including Trigonox ADC.

Method 1 Differential scanning calorimeter. The pressure is measured accurately with an electronic micro membrane manometer. The vacuum DSC experiments were carried out at various controlled pressure levels.
Approximately 15 mg is weighed into a 70 micro litre aluminium cup with a pierced lid.
After reaching a constant pressure, the DSC temperature scan is started. The heating rate is 5°C/min. During this scan, the product will evaporate. A sudden increase in the endothermic heat flow is then obtained. This represents the initial boiling point of the mixture at the pre-set pressure. A condenser, cooled by CO2 ice extrudates, captures the gases. After at least 4 DSC scans at different pressures, a plot is constructed with 10log p (p: mbara) versus T(K), the Antoine plot of the product. A turbo molecular vacuum pump as added to this method to allow lower pressures to be reached.

Method 2, a closed system. The headspace temperature of the system is set at the same value as the sample temperature. The system is equipped with a turbo molecular vacuum pump. This pump is additional to the 2-stage oil vacuum pump and is applied to give extra low initial pressure values. This pump is positioned in the line between the first pump and the flask.
Approximately 5 ml product is put into a clean, dry 500-ml flask. The flask is closed and the valve to the vacuum pumps is opened. The 2-stage vacuum pump is started. The dissolved gases are removed. When the substance gasses intensively, the boiling point is already reached. The temperature here, is lower then in the bath. The valve has to be closed and wait for constant temperature.
Again, the valve has to be opened. When the boiling point is reached again, immediately close the valve. If below 0.5 mbara still no boiling point is reached, the turbo molecular vacuum pump is started.
After reaching a constant value (boiling), the valve to the pumps is closed. The initial value p(initial), during the first few seconds, is close to the vapour pressure of the product. After closing the valve, the pressure rises slowly. This is partly the result of a small leakage. The leak-value determined is before, in an empty system and will be used later on for correction.
The decomposition products formed during the experiment will also contribute to the total pressure.
The method is validated with n-dodecane.
The measured values fo which correspond quite well with the literature values.
Theoretically, when the vapour/liquid equilibrium is reached, the pressure will give a stable value. This is only valid when no volatile products are formed by decomposition. This method is applied to unstable organic peroxides. These products have a quite low vapour pressure.
In practice, decomposition products contribute to the total pressure. In a closed system the pressure will increase continuously. Only the initial pressure value can be used as an indication of the vapour pressure, but the vapour/liquid equilibrium then, could not be fully reached yet.
To correct for this influence, a factor is introduced: 1½.
For calculation of the vapour pressure of organic peroxides, the maximum vapour pressure p(max) = p(initial) * 1½



Finally, the turbo molecular vacuum pump is also attached to the DSC-system to create a better vacuum, and some peroxides are measured here again.

GLP compliance:

no

Type of method:

other: DSC/ Closed system

Key result

Test no.:

#1

Temp.:

10 °C

Vapour pressure:

< 0.03 mBar

Remarks on result:

other: closed system

Key result

Test no.:

#2

Temp.:

40 °C

Vapour pressure:

< 0.1 mBar

Remarks on result:

other: DSC method with turbo molecular vacuum pump

Method 1

In the DSC method, the volatile components are evaporated completely, without influencing the pressure. The pressure is controlled. During the temperature scan, decomposition products, which are more volatile then the peroxide, evaporate and will not interfere below a certain pressure level. The total pressure then, can be considered as the vapour pressure of the organic peroxide.

Method 2

The maximum pressure values was calculated as follows: p(max) = p(initial) * 1½

Where the real vapour pressure p ≤ p(max).

p(initial) is the pressure at which the vacuum system is closed. The vacuum pump is disconnected from the system.

The system is validated with dodecane. A relatively small difference between measurement and literature values for n-dodecane was found. Therefore, the factor 1½ is sufficient to set the upper vapour pressure limit.

 

In the closed system, decomposition will immediately influence the total pressure, especially at low pressures. Only if the decomposition rate is very low, relatively stable values can be measured.

The rate of decomposition of Tx ADC at 10°C and <0.1 mbar is much higher than the calculated value from thermal data (DSC- SADT (self accelerating decomposition temperature)).

We know that the rate of decomposition of a peroxide will decrease at an increasing pressure. However, this effect is quite small.

DSC + turbo molecular pump

After the introduction of the turbo molecular vacuum pump in the DSC method, lower pressures could be reached.

The system was not able to control the pressure accurately. While the pressure rises during the temperature scan, the pressure increased a little. However lower pressures were achieved, again, no boiling effect of the peroxides was observed. Only maximum values at certain temperatures can be given.

Conclusions:

As already known, the measurement of the vapour pressure of thermally very unstable peroxides is difficult to perform, this meant that the vapour pressure for Trigonox ADC could only be determined as below a certain value. The vapour pressure for Trigonox ADC was determined to be <0.030 mbara at 10°C using the closed system method, and was <0.1 mbara at 40°C using the DSC with turbo molecular pump method.

Executive summary:

An experiment was undertaken to determine the vapour pressure of Trigonox ADC.

Two methods were chosen to look at this firstly via DSC (differential scanning calorimeter). The pressure is measured accurately with an electronic micro membrane manometer. The vacuum DSC experiments were carried out at various controlled pressure levels. This method was also carried out using the turbo molecular vacuum pump.

In the second method a closed system is created. The headspace temperature of the system is set at the same value as the sample temperature. The system is equipped with a turbo molecular vacuum pump. This pump is additional to the 2-stage oil vacuum pump and is applied to give extra low initial pressure values. This pump is positioned in the line between the first pump and the flask.

As already known, the measurement of the vapour pressure of thermally very unstable peroxides is difficult to perform, this meant that the vapour pressure for Trigonox ADC could only be determined as below a certain value. The vapour pressure for Trigonox ADC was determined to be <0.030 mbara at 10°C using the closed system method, and was <0.1 mbara at 40°C using the DSC with turbo molecular pump method.

Description of key information

As already known, the measurement of the vapour pressure of thermally very unstable peroxides is difficult to perform, this meant that the vapour pressure for Trigonox ADC could only be determined as below a certain value. The vapour pressure for Trigonox ADC was determined to be <0.030 mbara at 10°C using the closed system method, and was <0.1 mbara at 40°C using the DSC with turbo molecular pump method.

Key value for chemical safety assessment

Vapour pressure:

10 Pa

at the temperature of:

40 °C