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Vapour pressure

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Reference
Endpoint:
vapour pressure
Type of information:
(Q)SAR
Adequacy of study:
weight of evidence
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Accepted calculation method.
Justification for type of information:
1. SOFTWARE
EPI Suite - MPBPWIN

2. MODEL (incl. version number)
MPBPWIN V1.44 estimates vapour pressure by three different methods. They basically require the normal boiling point of the substance for the calculation of the vapour pressure, however if the substance is a solid at 25 °C, the melting point is needed as an additional descriptor. If these values are not available from experiment, the program uses the values calculated by itself, on the basis of the molecular structure. The default temperature value is 25 °C.

3. SMILES OR OTHER IDENTIFIERS USED AS INPUT FOR THE MODEL
OC(C(C(C(O)CC1)CC2)C1)C2

4. SCIENTIFIC VALIDITY OF THE (Q)SAR MODEL
1. Defined endpoint:
Logarithmic vapour pressure (P), ln P, at 25 °C, where P is in atm (subsequently recalculated into mmHg and Pa)
2. Unambiguous algorithm:
The Antoine equation used to estimate P from the normal boiling point Tb is:
ln P = [ΔHb(Tb - C2)2][1/(Tb - C2) - 1/(T - C2)]/(ΔZbRTb2) where:
ΔHb – heat of vaporisation at boiling temperature
Tb (= TbKf(8.75 + Rln Tb); Kf - structural factor, available),
C2 – constant estimated via Thomson’s rule: C2 = -18 + 0.19Tb,
ΔZb = 0.97,
R – ideal gas constant (= 8.314 J/mol K),
T – temperature at which VP is measured (usually 25 °C = 298.15 K))

The Modified Grain equation uses the relative temperature t, which is defined by T/Tb:
ln P = Kfln (RTb)[1 - (3 - 2t)m/t - 2m(3 - 2t)(m-1)ln t]/ΔZb
where the notation used in the previous equation remains and m = 0.4133 - 0.2575t.

For solids, to both equations a term employing the relative temperature with respect to the melting point, t’, must be added (t’= T/Tm):
ln P(solid) = ln P(liquid) + lnΔP,
lnΔP = 0.6ln (Rt’) [1 - (3 - 2t’)m’/t' - 2m’(3 - 2t’)(m’-1)ln t’]
where m’ = 0.4133 - 0.2575t’.
The Mackay equation uses the reciprocal values of t and t’, u = 1/t and u’ = 1/t’:
ln P = -(4.4 + ln Tb)[1.803(u – 1) - 0.803 ln u] – 6.8(u’ - 1)
The melting point term with u’ is ignored for liquids.
MPBPWIN reports the pressure P estimate from all three methods. It then reports a "suggested" P.
For solids, the Modified Grain estimate is the suggested P. For liquids and gases, the suggested P is the average of the Antoine and the modified Grain estimates. The Mackay method is not used in the suggested P.

5. APPLICABILITY DOMAIN
Currently there is no universally accepted definition of model domain. The complete training set is not available. However, it should be considered that a compound may be characterised by structural features (e.g. functional groups) not represented in the training set. It is recommended that possibly precise experimental value of boiling point (for solids: also melting point) is known. One must be aware that in some cases the boiling point or the melting point cannot be determined due to decomposition.
Compounds with higher molecular weights are also to be treated with care as it is likely that the corresponding molecule size and type is not adequately represented in the model training set. These points should be taken into consideration when interpreting model results.

6. Appropriate measures of goodness of fit, robustness and predictivity:
Training set statistics is not available. However, the accuracy of the "suggested" MPBPWIN vapour pressure estimate was tested on a large dataset of 3037 compounds with known experimental P values between 15 and 30 °C (the vast majority at 25 or 20 °C). The experimental values were taken from the PHYSPROP Database. Of the 3037 compounds in total, for 1642 experimental reliable values of melting and boiling points were known. The statistic restricted to these compounds is given in brackets.

Test set statistics:
N = 3037 compounds (1642)
correlation coefficient R2 = 0.914 (0.949)
standard deviation = 1.057 log units (0.59); P in mmHg
average deviation = 0.644 log units (0.32); P in mmHg
The error increases significantly when the P decreases below 1E-6 mmHg.

Test set estimation error (all 3037 compounds):
within 0.10 log units – 34.1%
within 0.20 log units – 45.6%
within 0.40 log units – 60.0%
within 0.50 log units – 64.9%
within 0.60 log units – 69.0%
within 0.80 log units – 75.0%
within 1.00 log unit – 80.0%

7. Mechanistic interpretation, if possible:
The methods used for the estimation of the vapour pressure are based on thermodynamic considerations, concerning the relationship between the vapour pressure and the normal boiling point; for solids additionally the melting point.

More complete description of the Antoine method is provided in: Lyman, W.J. et al, 1990. Handbook of Chemical Property Estimation Methods. Washington, DC: American Chemical Society, Chapter 14.

More complete descriptions of the Modified Grain and Mackay
method are provided in: 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.

Guideline:
other: REACH Guidance on QSARs R.6
Principles of method if other than guideline:
Calculation based on MPBPWIN v1.43, Estimation Programs Interface Suite™ for Microsoft® Windows v4.10. US EPA, United States Environmental Protection Agency, Washington, DC, USA.
GLP compliance:
no
Type of method:
other: QSAR
Specific details on test material used for the study:
SMILES : OC(C(C(C(O)CC1)CC2)C1)C2
Temp.:
25 °C
Vapour pressure:
0 Pa

MPBPWIN v1.44 predicted that naphthalene-1,5 -diol has a vapour pressure of 1.61E-5 Pa @ 25°C.

Modified Grain method. QSAR result; transition/decomposition is not specified/reported. For detailed description of the model and its applicability, see "Justification for type of information"

Conclusions:
MPBPWIN v1.44 predicted that naphthalene-1,5 -diol has a vapour pressure of 1.61E-5 Pa @ 25°C

Description of key information

MPBPWIN v1.44 predicted that naphthalene-1,5 -diol has a vapour pressure of 1.61E-5 Pa @ 25°C

Key value for chemical safety assessment

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

Additional information