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Vapour pressure

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Reference
Endpoint:
vapour pressure
Type of information:
(Q)SAR
Adequacy of study:
supporting study
Study period:
2018-02-26
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
results derived from a valid (Q)SAR model and falling into its applicability domain, with adequate and reliable documentation / justification
Justification for type of information:
1. SOFTWARE
EPIWIN software by US-EPA

2. MODEL (incl. version number)
MPBPVPWIN v1.43

3. SMILES OR OTHER IDENTIFIERS USED AS INPUT FOR THE MODEL
OC(C[n+]1ccccc1)CS(=O)(=O)[O-]

4. SCIENTIFIC VALIDITY OF THE (Q)SAR MODEL
- The complete test sets of experimental data for (melting point, boiling point and) vapour pressure can be downloaded via the Internet at: http://esc.syrres.com/interkow/EpiSuiteData.htm

5. APPLICABILITY DOMAIN
Estimation accuracy: The accuracy of MPBPWIN's "suggested" VP estimate was tested on a dataset of 3037 compounds with known, experimental VP values between 15 and 30 deg C (the vast majority at 25 or 20 deg C). The experimental values were taken from the PHYSPROP Database that is part of the EPI Suite. For this test, the CAS numbers were run through MPBPWIN as a standard batch-mode run (using the default VP estimation temperature of 25 deg C) and the batch estimates were compared to PHYSPROP's experimental VP. The plot clearly indicates that the estimation error increases as the vapour pressure (both experimental and estimated) decreases, especially when the vapour pressure decreases below 1x10-6 mm Hg (0.0001333 Pa).
The estimation methodology uses the normal boil point to estimate the liquid-phase vapour pressure. For solids, the melting point is required to convert the liquid-phase vapour pressure to the solid-phase vapour pressure. VP estimation error can be introduced by:
(1) poor Boiling Point estimates or values
(2) poor Melting Point estimates or values (for solids)

The 3037 compound test set contains 1642 compounds with available experimental Boiling points and Melting points. For this subset of compounds, the estimation accuracy statistics are (based on log VP):

number = 1642
r2 = 0.949
std deviation = 0.59
avg deviation = 0.32

These statistics clearly indicate that VP estimates are more accurate with experimental BP and MP data.

Estimation domain: The intended application domain is organic chemicals. Inorganic and organometallic chemicals generally are outside the domain.
Currently there is no universally accepted definition of model domain. However, users may wish to consider the possibility that property estimates are less accurate for compounds outside the Molecular Weight range of the training set compounds, and/or that have more instances of a given fragment than the maximum for all training set compounds. It is also possible that a compound may have a functional group(s) or other structural features not represented in the training set, and for which no fragment coefficient was developed. These points should be taken into consideration when interpreting model results.
The complete training sets for MPBPWIN's estimation methodology are not available. Therefore, describing a precise estimation domain for this methodology is not possible. The current applicability of the MPBPWIN methodology is best described by its accuracy in predicting vapour pressure as described above in the accuracy section.

6. ADEQUACY OF THE RESULT
The result calculated for the organic substance 2-hydroxy-3-pyridinium-1-ylpropane-1-sulfonate (PPSOH) seems reasonable. The beginning of melting (245.4°C) under decomposition has been used in addition to the estimated melting point to estimate the vapour pressure of the substance at 20 and 25°C. Further, due to the magnitude of the result it is considered as adequate.
Guideline:
other: REACH guidance on QSARs Chapter R.6
Version / remarks:
May 2008
Principles of method if other than guideline:
Vapour Pressure is estimated by three methods; all three methods use the boiling point. The first is the Antoine method (see Chapter 14 of W.J. Lyman's book "Handbook of Chemical Property Estimation Methods", Washington, DC: American Chemical Society, 1990). The second is the modified Grain method (see page 31 of Neely and Blau's Environmental Exposure from Chemicals, Volume I, CRC Press, 1985). The third is the Mackay method (see page 31-2 of Neely and Blau's Environmental Exposure from Chemicals, Volume I, CRC Press, 1985).
GLP compliance:
no
Remarks:
not applicable
Type of method:
other: QSAR estimation
Key result
Temp.:
25 °C
Vapour pressure:
0 Pa
Remarks on result:
other: Modified Grain Method (MPBPWIN v1.43) - most relevant for solids
Remarks:
based on experimentally determined melting point of 245.4°C
Temp.:
25 °C
Vapour pressure:
0 Pa
Remarks on result:
other: Antoine Method (MPBPWIN v1.43)
Remarks:
based on experimentally determined melting point of 245.4°C
Temp.:
25 °C
Vapour pressure:
0 Pa
Remarks on result:
other: Mackay Method (MPBPWIN v1.43)
Remarks:
based on experimentally determined melting point of 245.4°C
Temp.:
25 °C
Vapour pressure:
0 Pa
Remarks on result:
other: Modified Grain Method (MPBPWIN v1.43) - most relevant for solids
Remarks:
based on estimated Melting Point
Temp.:
25 °C
Vapour pressure:
0 Pa
Remarks on result:
other: Antoine Method (MPBPWIN v1.43)
Remarks:
based on estimated Melting Point
Temp.:
25 °C
Vapour pressure:
0 Pa
Remarks on result:
other: Mackay Method (MPBPWIN v1.43)
Remarks:
based on estimated Melting Point
Temp.:
20 °C
Vapour pressure:
0 Pa
Remarks on result:
other: Modified Grain Method (MPBPWIN v1.43) - most relevant for solids
Remarks:
based on experimentally determined melting point of 245.4°C
Temp.:
20 °C
Vapour pressure:
0
Remarks on result:
other: Modified Grain Method (MPBPWIN v1.43) - most relevant for solids
Remarks:
based on estimated Melting Point
Conclusions:
The study report describes a scientifically accepted calculation method for the vapour pressure using the US-EPA software MPBPWIN v1.43.No GLP criteria are applicable for the usage of this tool and the QSAR estimation is easily repeatable. The result is adequate for the regulatory purpose.
The calculation resulted in a value of 7.12E-08 Pa at 25 °C (Modified Grain Method).
Executive summary:

The vapour pressure of the substance 2-hydroxy-3-pyridinium-1-ylpropane-1-sulfonate (PPSOH) was determined by the computer program MPBPWIN v1.43 (EPIWIN software) by US-EPA (2012). The program calculates the vapour pressure according to three different methods: Antoine, Modified Grain and Mackay. The Modified Grain method is preferentially adopted and therefore the most important one [Lyman, W.J., 1985. In: Environmental Exposure From Chemicals. Volume I., Neely, W.B. and Blau, G.E. (eds), Boca Raton, FL: CRC Press, Inc., Chapter 2]. The beginning of melting (245.4°C) under decomposition has been used in addition to the estimated melting point to estimate the vapour pressure of the substance at 20 and 25°C. According to the Modified Grain Method the substance has a vapour pressure of 7.12E-08 Pa at 25°C (most relevant for solids) using a melting point of 245.4°C. The estimation error increases as the vapour pressure decreases, especially when the vapour pressure is below 0.000133Pa, but the calculated value can anyway viewed as indicative of a very low vapour pressure, which is sufficient considering the magnitude of the result.

Description of key information

Vapour pressure: 7.12E-08 Pa at 25°C (Modified Grain Method, MPBPWIN v1.43 (EPIWIN software) estimation)

Key value for chemical safety assessment

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

Additional information