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Vapour pressure

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Endpoint:
vapour pressure
Type of information:
(Q)SAR
Adequacy of study:
weight of evidence
Study period:
run on 2013-04-24
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
results derived from a (Q)SAR model, with limited documentation / justification, but validity of model and reliability of prediction considered adequate based on a generally acknowledged source
Remarks:
The value is not an experimental result, however the QSAR model is recommended by the ECHA guidance document on information requirements, and is well documented with regard to validation parameters according to OECD principles. Moreover, the substance investigated is fully characterised towards the applicability domain, and the result is supported by consistency of boiling point estimated by the model with available experimental result.
Justification for type of information:
1. SOFTWARE
Estimation Programs Interface Suite™ for Microsoft® Windows, v 4.10

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

3. SMILES OR OTHER IDENTIFIERS USED AS INPUT FOR THE MODEL
O(C(C(C(C(C(CC1)(C)C)C2)(C1)C)C3)(C2)C)C3

4. SCIENTIFIC VALIDITY OF THE (Q)SAR MODEL
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 (estimated vs experimental log VP in mm Hg):
n = 3037
r2 = 0.914
std dev = 1.057
avg dev = 0.644
The plot clearly indicates that the estimation error increases as the vapor pressure (both experimental and estimated) decreases, especially when the vapor pressure decreases below 1x10-6 mm Hg (0.0001333 Pascals).
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.

5. APPLICABILITY DOMAIN
Estimation 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 vapor pressure as described above in the Accuracy section.

Other information on the three VP methods are available from the "Help" menu of the model.
The complete test sets of experimental data for melting point, boiling point and vapor pressure can be downloaded via the Internet at:   http://esc.syrres.com/interkow/EpiSuiteData.htm

6. ADEQUACY OF THE RESULT
All fragments are within the list of descriptors and coefficients used by the MPBPWIN program.
Reason / purpose:
reference to other study
Reason / purpose:
reference to other study
Reason / purpose:
other:
Principles of method if other than guideline:
QSAR estimation
Temp.:
20 °C
Vapour pressure:
0.254 Pa
Remarks on result:
other: estimated value with known MP=80°C and default BP = 276.83°C estimated by the model
Temp.:
20 °C
Vapour pressure:
0.022 Pa
Remarks on result:
other: refined value with known MP=80°C and experimental BP = 324°C

Boiling point and vapour pressure are closely related, therefore comparison of estimated BP vs experimental when available can be used to confirm the predictibility of the model:

The model shows significant underestimation in the prediction of boiling point, compared to the available experimental value (please refer to point 4.3). However, the experimental value can be entered for refinement of the estimated VP.

The selected VP (by the model) was the modified Grain method.

Conclusions:
Low volatility (based on volatility bands criteria for occupational exposure (Chesar / ECETOC TRA), << 500 Pa).
Executive summary:

Vapour pressure of the test substance was estimated with the QSAR model MPBPWIN from Episuite, using known melting point as additional data input for refinement.

Default BP value calculated by the model for purpose of VP equation was found to be underestimated compared to the available experimental data, therefore the refined result, with measured BP as input, of 0.0222 Pa at 20°C is retained.

Endpoint:
vapour pressure
Type of information:
experimental study
Adequacy of study:
weight of evidence
Reliability:
4 (not assignable)
Rationale for reliability incl. deficiencies:
documentation insufficient for assessment
Remarks:
The method can be related to the current guideline, however insufficient experimental details are provided, and the result is out of the recommended range. Morerover, purity of the test substance is not stated. Therefore validation cannot be granted.
Qualifier:
equivalent or similar to
Guideline:
OECD Guideline 104 (Vapour Pressure Curve)
GLP compliance:
no
Type of method:
dynamic method
Key result
Temp.:
20 °C
Vapour pressure:
0.054 Pa
Remarks on result:
other: extrapolated

The report contains graphical results, but detailed values are not provided.

The coefficients of the Antoine's equation are as follows:

VP(T) = 10 exp(A-(B/(T+C)))

A = 7.0329

B = 2098.781

C = 181.360

T: temperature in °C

VP: vapour pressure in mm Hg

The boiling temperature was extrapolated to be 324°C (at 760 mm Hg).

Conclusions:
Low volatility (based on volatility bands criteria for occupational exposure (Chesar / ECETOC TRA), << 500 Pa).
Executive summary:

The vapour pressure of the test substance was measured with an ebulliometer, which can be related to a dynamic method, as cited in OECD104 guideline.

Eight measurements were recorded between 160 and 230°C. The coefficients of the non-linear Antoine's equation between log VP and 1/T were calculated. Vapour pressure at 20°C was extrapolated from this relashionship to be ca 0.054 Pa at 20°C.

Endpoint:
vapour pressure
Type of information:
(Q)SAR
Adequacy of study:
weight of evidence
Study period:
run on 2013-04-08
Reliability:
4 (not assignable)
Rationale for reliability incl. deficiencies:
results derived from a (Q)SAR model, with limited documentation / justification
Remarks:
The value is not an experimental result, however the QSAR model is recommended by the ECHA guidance document on information requirements. No documentation is available in the on-line calculator with regard to validation parameters according to OECD principles, therefore validity cannot be assigned. The result is nevertheless supported by consistency of boiling point estimated by the model with available experimental result.
Justification for type of information:
1. SOFTWARE
SPARC

2. MODEL (incl. version number)
v4.6

3. SMILES OR OTHER IDENTIFIERS USED AS INPUT FOR THE MODEL
O(C(C(C(C(C(CC1)(C)C)C2)(C1)C)C3)(C2)C)C3

4. SCIENTIFIC VALIDITY OF THE (Q)SAR MODEL
In SPARC, all the physical property estimations derive from a common set of core models describing intra/intermolecular interactions, and require as user inputs molecular structure (both solute and solvent(s)) and reaction conditions of interest (temperature, pressure, etc.).
The vapor pressure, vpoi of a pure solute, i, can be expressed as function of all the intermolecular interaction mechanisms, Δ Gii (interaction), as
log vpoi = (-Δ Gii (Interaction )/2.303.RT) + LogT + C
where log (T) + C describes the change in the entropy contribution associated with the volume change in going from the liquid to the gas phase. The crystal energy term, CE, must be added to the equation for molecules that are solids at 25°C; the CE contribution becomes important, especially for rigid structures such as aromatic or ethylenic molecules that have high melting points.

The SPARC self-interactions model can predict the vapor pressure at 25°C within experimental error over a wide range of molecular structures and measurements (over 8 log units). For simple structures, SPARC can calculate the vapor pressure to better than a factor of 2. For complex structures such as some of the pesticides and pharmaceutical drugs where dipole-dipole and/or hydrogen bond interactions are strong, SPARC calculates the vapor pressure within a factor of 3-4.
SPARC-calculated vs. observed (log atm) vapor pressure for 747 organic molecules at 25°C, including all the vapor pressure measurements (real not extrapolated) found in the literature, showed a RMS (Root Mean Square) deviation error of 0.15 log atm and R2 was 0.994.
Reason / purpose:
reference to other study
Reason / purpose:
reference to other study
Reason / purpose:
other:
Principles of method if other than guideline:
QSAR estimation
Temp.:
20 °C
Vapour pressure:
0.018 Pa
Remarks on result:
other: estimated value with known MP=80°C

Estimated Boiling Point = 299.5°C

Heat of vaporisation = 19.57 kcal/mol

Boiling point and vapour pressure are closely related, therefore comparison of estimated BP vs experimental when available can be used to confirm the predictibility of the model:

The model slightly underestimates the prediction for the boiling point, compared to the available experimental value (324°C; please refer to point 4.3). Therefore, the prediction for the vapour pressure is supposed to be slightly overestimated. However, no further refinement is possible with SPARC model.

Conclusions:
Low volatility (based on volatility bands criteria for occupational exposure (Chesar / ECETOC TRA), << 500 Pa).
Executive summary:

Vapour pressure of the test substance was estimated with the QSAR model SPARC, using known melting point as additional data input for refinement. Boiling Point was also calculated by the model for comparison with the available experimental data, and was found to be slightly underestimated. Therefore actual VP is expected to be slightly less than the estimated value of 0.0175 Pa at 20°C.

Description of key information

Low volatility.

Key value for chemical safety assessment

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

Additional information

An experimental study is available on the substance, however validity could not be assigned due to lack of information. It was therefore completed with estimations using two QSAR models. Results were found to be consistent, respectively 0.054, 0.0222 and 0.0175 Pa at 20°C, supporting the weight of evidence for low volatility. The experimental result was prefered as key value for purpose of CSA.