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Vapour pressure

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Reference
Endpoint:
vapour pressure
Type of information:
calculation (if not (Q)SAR)
Remarks:
Migrated phrase: estimated by calculation
Adequacy of study:
key study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: applicability of calculation demonstrated
Principles of method if other than guideline:
Antoine equation
GLP compliance:
no
Temp.:
ca. 20 °C
Vapour pressure:
ca. 0.29 Pa

1.   Equations Used

The Antoine equation is a three parameter equation relating vapour pressureto temperature.

Ln P = A – B/(T-C)
                    Equation 1

where Ln is the natural log
P is the vapour pressure
T is the corresponding temperature (K)

Methods are needed to evaluate the three parameters A, B & C

Constant C is evaluated by Thomson’s Rule

C = -18+0.19Tb.
                          Equation 2

Where Tbis the boiling point at 1 atmosphere. Using this equation, P is the vapour pressure in atmospheres.

From the Boiling Point Study in the dossier, Tb= 567.9K

Constant A is evaluated by using the value of the boiling point at atmospheric pressure.

A= B/(Tb-C)
                                 Equation 3

Constant B is evaluated by the integration of the Clausius-Clapeyron equation (seeHandbook of Chemical Property Estimation Methods for derivation) to produce

B = ΔHb/(ΔZRTb2) x [(Tb-C)2]    Equation 4

where ΔHbis the latent heat of vaporisation at the boiling point
ΔZ is the compressibility factor
R is the universal gas constant 1.987 cal/molK
ΔZ is taken as 0.97, see Miller

Lastly ΔHbneeds to be evaluated by the method of Fishtine

ΔHb/Tb= KF(8.75+RlnTb)
           Equation 5

KFis a factor dependant on the compound type & number of carbon atoms

From Handbook of Chemical Property Estimation Methods, Table 14-4, for an Aldehyde with 12-20 carbon atoms,

KF= 1.01


The calculation is shown in the embedded spreadsheet (section 6).
 The answer of 0.002 mmHg is within the range of applicability and so is a valid method.

Calculation of Vapour Pressure for Amyl Cinnamic Aldehyde
For derivation of Equations see Tennants Fine Chemicals report for IUCLID , section 4
A=B/(Tb-C)
B =dH/(dZRTb^2)x((Tb-C)^2)
C=-18+0.19xTb
dH= Kfx(8.75+RLnTb)xTb dZ= 0.97 R= 1.987
  TbK Kf LnTb dH T K C B A LnP P atm P mmHg P Pa
ACA 567.9 1.01 6.341945 12246.74 293 89.901 4501.54 9.417468 -12.7468 2.91E-06 0.002213 0.291163
This is within applicability of the method.
I M Bowdery
08/01/2013
Tennants Fine Chemicals



Conclusions:
Amyl Cinnamic Aldehyde had a calculated Vapour Pressure of 0.29Pa at 20°C
Executive summary:

Amyl Cinnamic Aldehyde had a calculated Vapour Pressure of 0.29Pa at 20°C

Description of key information

Amyl Cinnamic Aldehyde had a calculated Vapour Pressure of 0.29Pa at 20°C

Key value for chemical safety assessment

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

Additional information

1.   Reason for Carrying out Vapour Pressure Calculation & Choice of Equation

A search was carried out to identify any reliable studies that were available. Only one was identified but when approached the company did not have a reliable report for the study and so a study could not be used.

There were two calculated values reported, one was based on the modified Grain method but no company was identified; also the method is not recommended (see discussion below).
 The second one just quoted a value less than, so was not satisfactory.

So it was decided to carry out a calculation in-house and possible methods were identified by reference to the standard Handbook of Chemical Property Estimation Methods Chapter 14 Vapour Pressure.
 Two methods are recommended, the range of applicability are as below:-

Antoine equation has applicability of 10-3to 760mmHg
Modified Watson Correlation has applicability of
 10-7to 760mmHg

If the vapour pressure is greater than 10-3mmHg, then the Antoine equation is recommended.
 The data quoted in the databases and HPV report were around 10-3mmHg, so this equation was used initially.