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Vapour pressure

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Reference
Endpoint:
vapour pressure
Type of information:
calculation (if not (Q)SAR)
Adequacy of study:
key study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
accepted calculation method
Justification for type of information:
1. SOFTWARE: EPIWEB 4.1

2. MODEL (incl. version number): MPBPVP

3. SMILES OR OTHER IDENTIFIERS USED AS INPUT FOR THE MODEL:
CuHEEDTA: C1(=O)CN(CC(=O)O[Na])CCN(CCO[Na])CC(=O)O[Cu]O1
CuDTPA: C(=O)(CN(CC(=O)O[Na])CCN1CC(=O)O[Cu]OC(=O)CN(CC(=O)O[Na])CC1)O[Na]

4. SCIENTIFIC VALIDITY OF THE (Q)SAR MODEL
[Explain how the model fulfils the OECD principles for (Q)SAR model validation. Consider attaching the QMRF or providing a link]
- Defined endpoint: Vapour Pressure

- Unambiguous algorithm:
MPBPWIN estimates vapor pressure (VP) 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. Unless the user enters a boiling point on the data entry screen,  MPBPWIN uses the estimated boiling point from the adapted Stein and Brown method as described in the Boiling Point section of this help file. For solids, the modified Grain method is used.
Chapter 2 of Lyman (1985) describes the modified Grain method used by MPBPWIN.  This method is a modification and significant improvement of the modified Watson method.  It is applicable to solids, liquids and gases. The modified Grain method equations are attached.


- Defined domain of applicability:

MPBPWIN reports the VP estimate from all three methods.  It then reports a "suggested" VP.  For solids, the modified Grain estimate is the suggested VP.  For liquids and gases, the suggested VP is the average of the Antoine and the modified Grain estimates.  The Mackay method is not used in the suggested VP because its application is currently limited to its derivation classes.

- Appropriate measures of goodness-of-fit and robustness and predictivity:
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 (R^2 = 0.914). 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
  r^2 = 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.

 
- Mechanistic interpretation:
See methodology

5. APPLICABILITY DOMAIN
[Explain how the substance falls within the applicability domain of the model]
- Descriptor domain:
CuEDTA, CuHEEDTA and CuDTPA are all solids.

- Structural and mechanistic domains:
not applicable

- Similarity with analogues in the training set:
not provided
- Other considerations (as appropriate):
none

6. ADEQUACY OF THE RESULT
[Explain how the prediction fits the purpose of classification and labelling and/or risk assessment]
For EDTA, HEEDTA and DTPA, it is known that these are substances with very low vapour pressures (<10^-12 Pa). The EpiSuite predictions are to support that the vapour pressure is still very low when metal ions are added.
Guideline:
other: REACH Guidance on QSARs R.6
Principles of method if other than guideline:
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.
Temp.:
25 °C
Vapour pressure:
0 mm Hg
Remarks on result:
other: Prediction for CuHEEDTA
Temp.:
25 °C
Vapour pressure:
0 mm Hg
Remarks on result:
other: Prediction for CuDTPA
Conclusions:
The estimated vapour pressure of the reaction mixture of CuHEEDTA and CuDTPA lies between 1.12E-21 and 2.44E-19 mm Hg.

Description of key information

The estimated vapour pressure of the reaction mixture of CuDTPA and CuHEEDTA lies between 1.12E-21 and 2.44E-19 mm Hg.

Key value for chemical safety assessment

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

Additional information