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Vapour pressure

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vapour pressure
Type of information:
Adequacy of study:
weight of evidence
Study period:
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:
QSAR prediction:

1. SOFTWARE : EPI Suite, by the U.S. Envirnmental Protection Agency

2. MODEL (incl. version number): MPBPWIN v1.43


4. SCIENTIFIC VALIDITY OF THE (Q)SAR MODEL: The model is included in the EPI Suite to which the OECD QSAR toolbox makes reference.

The training set for mpbpvpwin model is available at:
The documentation shows molecular weights between 2 and 1356 g/mol and a large range of molecular fragments. The representative molecule falls within the molecular weight domain of the model and the molecular fragments include the ones characterising the molecule. It is therefore understood that the model is reliable for the prediction of the vapour pressure of sulfated oils.

The result of the prediction is considered adequate for the purpose of the risk assessment, even if the estimation error in the model increases as the vapor pressure (both experimental and estimated) decreases, especially when the vapor pressure decreases below 1x10-6 mm Hg (0.0001333 Pascals). Anyway, the accuracy of the model in the range of low vapour pressure values is not considered to negatively influence the conclusion, which is provided in a weight-of-evidence approach.
Note that no entry has been set for MP and BP, because these values (addressed in section 4.2 and 4.3) refer to a test item which includes water and other molecules (coming from the non-reacted raw material) and do not strictly refer to the representative molecule chosen for the QSAR model application.
other: EPI SUITE v.4.11 - On-line MPBPWIN User's Guide
other: ECHA Chapter R.06 - Guidance on QSARs and grouping of chemicals - May2008
Principles of method if other than guideline:
The MPBPWIN software estimates boiling point (at 760 mm Hg), melting point and vapour pressure of organic compounds. It requires only a chemical structure to make these predictions.

The estimation methodology for the boiling point has been adapted from the Stein and Brown method ("Estimation of Normal Boiling Points from Group Contributions", J. Chem. Inf. Comput. Sci. 34: 581-87, 1994). The Melting Point is estimated by two different methods; the first is the Joback Group Contribution Method, and the second is a Gold and Ogle method which simply uses the following formula: Tm = 0.5839 Tb where Tm is the melting point in Kelvin and Tb is the boiling point in Kelvin. Although Melting Point estimation can be inaccurate, averaging the results of these two methods can yield reasonable estimates for many structures.

Vapor 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). For solids, a melting point is required to adjust the vapor pressure from a subcooled (supercooled) liquid to a solid. Data entry allows measured BP and MP to be to used; when entered, the measured values are used instead of the estimated values. The preferred VP method for solids is the Modified Grain method, although the Antoine method in this program is nearly as good because it uses the exact same methodology to convert super-cooled VP to solid VP. For liquids, the mean of the Grain and Antoine methods is preferred. The Mackay method is not as applicable to as many chemical classes as the other methods, so it is generally not preferred.

The current version of MPBPWIN calculates and reports the subcooled liquid vapor pressure for solid compounds.
GLP compliance:
Type of method:
other: in silico
Specific details on test material used for the study:
Representative molecule of sulfated oils, for QSAR application.
Key result
25 °C
Vapour pressure:
0 Pa
Remarks on result:
other: MPBPWIN estimation: 3.3E-26 Pa (Mean of Antoine & Grain methods)



CHEM   : Oils, vegetable, sulfated, ammonium salts

MOL FOR: C57 H108 N1 O10 S1

MOL WT : 999.56

------------------------ SUMMARY MPBPWIN v1.43 --------------------

Boiling Point: 1088.95 deg C (Adapted Stein and Brown Method)

Melting Point:  349.84 deg C (Adapted Joback Method)

Melting Point:  349.84 deg C (Gold and Ogle Method)

Mean Melt Pt :  349.84 deg C (Joback; Gold,Ogle Methods)

 Selected MP:  349.84 deg C (Weighted Value)

Vapor Pressure Estimations (25 deg C):

 (Using BP: 1088.95 deg C (estimated))

 (Using MP: 349.84 deg C (estimated))

   VP:  9.13E-086 mm Hg (Antoine Method)

     :  0 Pa  (Antoine Method)

   VP:  4.95E-028 mm Hg (Modified Grain Method)

     :  6.59E-026 Pa  (Modified Grain Method)

   VP:  2.28E-027 mm Hg (Mackay Method)

     :  3.04E-025 Pa  (Mackay Method)

 Selected VP:  4.95E-028 mm Hg (Modified Grain Method)

            :  6.59E-026 Pa (Modified Grain Method)

 Subcooled liquid VP:  2.53E-024 mm Hg (25 deg C, Mod-Grain method)

                    :  3.38E-022 Pa  (25 deg C, Mod-Grain method)




Group |  3  |  -CH3              |   21.98  |   65.94

Group | 45  |  -CH2-             |   24.22  | 1089.90

Group |  2  |  >CH-              |   11.86  |   23.72

Group |  4  |  =CH-              |   27.95  |  111.80

Group |  2  |  -O- (nonring)     |   25.16  |   50.32

Group |  3  |  -COO- (ester)     |   78.85  |  236.55

Group |  1  |  >S(=O)(=O)        |  171.58  |  171.58

Group |  1  |  >N< (+5)          |  340.00  |  340.00

Corr   |  1  |  Diester-type      |  -35.00  |  -35.00

  *   |     |  Equation Constant |          |  198.18


RESULT-uncorr|  BOILING POINT in deg Kelvin  | 2252.99

RESULT- corr |  BOILING POINT in deg Kelvin  | 1362.11

            |  BOILING POINT in deg C       | 1088.95





Group |  3  |  -CH3              |   -5.10  |  -15.30

Group | 45  |  -CH2-             |   11.27  |  507.15

Group |  2  |  >CH-              |   12.64  |   25.28

Group |  4  |  =CH-              |    8.73  |   34.92

Group |  2  |  -O- (nonring)     |   22.23  |   44.46

Group |  3  |  -COO- (ester)     |   53.60  |  160.80

Group |  1  |  >S(=O)(=O)        |  150.00  |  150.00

Group |  1  |  >N< (+5)          |  340.00  |  340.00

Corr   |  1  |  Diester-type      | -130.00  | -130.00

  *   |     |  Equation Constant |          |  122.50


  RESULT    |  MELTING POINT in deg Kelvin  | 1239.81

RESULT-limit |  MELTING POINT in deg Kelvin  |  623.00

            |  MELTING POINT in deg C       |  349.84


Estimated vapour pressure of the substance at 25 deg C: 3.3E-26Pa.
Executive summary:

The vapour pressure of the representative molecule of the substance has been estimated with the U.S. Environmental Protection Agency software named MPBPWIN (v.1.43) from EPI Suite package (v.4.11). According to the rule applied for liquid substances, the selected estimation is the mean value found with Antoine and Grain methods.

The estimated vapour pressure of the substance at 25 deg C results to be 3.3E-26 Pa.

Description of key information

Estimated vapour pressure for oils, vegetable, sulfated, ammonium salts, at 25 deg C: 3.3E-26 Pa.

Value used for chemical safety assessment 1.0E-6 Pa (the lowest value considered by EUSES).

Key value for chemical safety assessment

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

Additional information

Sulfated oils are UVCB substances and a defined vapour pressure is therefore difficult to obtain. As stated in the document, the main experimental tests usually performed to determine the vapour pressure are not applicable for this kind of substances (Gas saturation method, Effusion method by vapour pressure balance, Estimation method have been cited). The water contained in the substance is considered the most volatile component (from literature data, the vapour pressure of water at 20 deg C is about 2 kPa); but a value cannot be experimentally determined for the characteristic molecules representative of sulfated oils. A lower value of vapour pressure is expected, as the sulfated oils are made up of large and ionic molecules. However, in order to provide an estimate, (Q)SAR methods have been applied and the US EPA's EPI Suite v.4.11 has been used, namely the module MPBPWIN v.1.43. The model and the predictions are considered reliable.

The vapour pressures at 25 deg C for sulfated oils representative structures have been predicted below 1.0E-6 Pa (value used for CSA, the lowest value considered by EUSES). The calculations have been run without using the boiling point values found for the test item, because not considered related to the representative molecules for QSAR applications.