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Vapour pressure

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Endpoint:
vapour pressure
Type of information:
(Q)SAR
Adequacy of study:
key study
Study period:
run on 2011-11-23
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(OC(C1)CCCCCCC)C1

4. SCIENTIFIC VALIDITY OF THE (Q)SAR MODEL
This program (MPBPWIN) estimates the boiling point (at 760 mm Hg), melting point and vapor pressure of organic compounds.
Vapor Pressure is estimated by three separate methods: (1) the Antoine method, (2) the modified Grain method, and (3) the Mackay method. All three use the normal boiling point to estimate VP. Data entry allows measured BP and MP to be to used; when entered, the measured values are used instead of its values estimated from the adapted Stein and Brown method. 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.

All fragments are within the list of descriptors and coefficients used by the MPBPWIN program.

The model shows good prediction for the boiling point, compared to the available experimental value (please refer to point 4.3).
As both properties (BP and VP) are inter-related, no major error is anticipated for the vapour pressure.

5. APPLICABILITY DOMAIN
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.

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
The accuracy and margin of safety is considered sufficient to allocate the substance to a volatility band, according to Chesar / ECETOC TRA criteria for occupational exposure.
Reason / purpose:
reference to other study
Reason / purpose:
reference to other study
Principles of method if other than guideline:
QSAR estimation
GLP compliance:
no
Temp.:
25 °C
Vapour pressure:
0.545 Pa
Remarks on result:
other: estimated value with default BP = 286.00°C from the experimental database of the model
Temp.:
25 °C
Vapour pressure:
0.274 Pa
Remarks on result:
other: refined value with experimental BP = 299°C

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.

Default BP value from the model (experimental database) for purpose of VP equation was found to be very consistent with the available experimental data, therefore good prediction is anticipated.

The refined result of 0.274 Pa at 25°C is retained.

Endpoint:
vapour pressure
Type of information:
experimental study
Adequacy of study:
supporting study
Reliability:
4 (not assignable)
Rationale for reliability incl. deficiencies:
documentation insufficient for assessment
Remarks:
This publication provides no experimental data nor results on vapour pressure measurements performed to determine the enthalpy of vaporization. Therefore, thermodynamic values can only be used for reverse calculation, and validity cannot be assigned.
Principles of method if other than guideline:
The enthalpies of vaporization were determined by the transfer method.
Compound   delta Hm at 298.15 K (kJ/mol)
 gamma-pentanolactone 53.9
 gamma-hexanolactone 57.2
 gamma-heptanolactone (61.6)
 gamma-octanolactone (65.9)
 gamma-nonanolactone 70.3
 gamma-decanolactone (74.6)

The set of experimental data reported for the three lactones tested can be used to calculate the methylene group increment: ca 4.4 kJ/mol for the molar enthalpy of vaporization at 298.15 K. Values in parentheses in the above table were so calculated.

Executive summary:

This publication refers to measurement of thermodynamic properties of three lactones.

The enthalpy of vaporisation can be used to calculate the vapour pressure, according to the Clapeyron equation.

Endpoint:
vapour pressure
Type of information:
read-across based on grouping of substances (category approach)
Adequacy of study:
supporting study
Justification for type of information:
Data are available for three analogues with increasing carbon chain length.
Reason / purpose:
read-across source
Reason / purpose:
reference to other study
Temp.:
25 °C
Vapour pressure:
0.024 Pa
Compound   delta Hm at 298.15 K (kJ/mol)
 gamma-pentanolactone 53.9
 gamma-hexanolactone 57.2
 gamma-heptanolactone (61.6)
 gamma-octanolactone (65.9)
 gamma-nonanolactone 70.3
 gamma-decanolactone (74.6)

The set of experimental data reported for the three lactones tested can be used to calculate the methylene group increment: ca 4.4 kJ/mol for the molar enthalpy of vaporization at 298.15 K. Values in parentheses in the above table were so calculated.

Therefore, for the following gamma-undecalactone (target substance), the enthalpy can be extrapolated to 79.0 kJ/mol

The vapour pressure Psat can be calculated according to the Clapeyron equation:

ln (Psat/P0) = (M*Lv/R)*(1/T0 - 1/T)

where:

T0 : boiling temperature, in K, at P0 (default P0 = Patm = 101325 Pa)

M: molar weight, in kg/mol

Lv: Latent heat of vaporization, in J/kg

T: temperature of Psat, in K

Note: M*Lv = delta Hm, in J/mol

Psat of the substance was calculated considering Hm above, and the experimental boiling point of 299°C (please refer to IU point 4.3).

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

The enthalpy of vaporisation of the target substance was extrapolated, based on carbon number increment, from a publication on measurement of thermodynamic properties of three analogue lactones.

The vapour pressure was then calculated, according to the Clapeyron equation, as 0.024 Pa at 25°C .

Description of key information

Low volatility (from QSAR).

Key value for chemical safety assessment

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

Additional information

No experimental study is available on the substance. Therefore, the vapour pressure was assessed using a QSAR model on the parent, and extrapolation from a publication relating to enthalpy of vaporization of analogues. Results were considered consistent to support the weight of evidence for low volatility, but values were quite different respectively 0.274 and 0.024 Pa at 25°C. Considering the reliability of the publication could not be assigned, while the QSAR demonstrated good predictibility, and also gave the worst-case result, the calculated

value was retained as key value for purpose of CSA.