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EC number: 203-825-6
CAS number: 111-01-3
A Quantitative Structure-Property Relationship (QSPR) model was used to
calculate the water solubility of the test item
2,6,10,15,19,23-hexamethyltetracosane. This QSPR model has been
validated as a QSAR model to be compliant with the OECD recommendations
for QSAR modeling (OECD, 2004) and predicts the endpoint value which
would be expected when testing the substance under experimental
conditions in a laboratory following the Guideline for Testing of
Chemicals No. 105, "Water Solubility". The criterion predicted was the
solubility in water in mg.L-1.
The purpose of the in silico study was to determine the water solubility
of test item in pure water at 25°C.
The determination was performed using a regression method in which
validated log KOW values are plotted against the log of sub-cooled
liquid water solubility from studies of high quality. These have been
carried out using one of the methods recommended in the OECD guideline
105 or an adaptation of these.
The result below is the anticipated water solubility value following a
study conducted according to OECD guideline 105 or acceptable
modifications thereof (e.g. using a slow-stir method instead of shake
flask). The water solubility is calculated as follows:
- water solubility at 25°C = 5.39.10-13 mg test item.L-1
- 95% confidence limits = 4.92.10-13 to 5.90.10-13 mg test item.L-1
The water solubility of the test substance has been first
determined by performing a shake flask assay according to the OECD
guideline n°105: “Water solubility”, adopted July, 27, 1995.
In fact, as initial considerations, the OCDE guideline mentioned
that shake flask method covers solubilities above 10-2g/L.
Therefore a preliminary test must be performed in order to ensure the
method is applicable to the test substance. As a result of the
preliminary test, the author concluded that 100 mL is still not enough
to completely dissolve the test substance in water after 24h. Therefore
the final test was carried out over 72 hours while the guideline
recommends to allow more time (up to 96 hours) to ascertain that the
flask method is a relevant test method for the substance. The water
solubility of the substance at 20 °C was determined as 0.002 +/- 0.001
g/L as the mean of the three values obtained at 24, 48 and 72 hours.
Nevertheless, there are significant differences between the individual
daily results (for example reduction from 7, 5 and 6 mg/L in three
replicates to 1, 2 and 1 mg/L of substance between 24 and 48 h
suggesting that the substance formed emulsions in the test solution
which led to inconsistencies). No indication is provided of the Limit of
detection or quantification so it is not clear if the results are above
or below the LOQ. Since the test substance is poorly soluble, the test
should have been performed up to 96 hours. A final result of 3 mg/L was
found at 72 hours. The study was repeated and a value of 1 mg/L was
determined. A statement was made that the accuracy of the study is
questionable due to the low solubility of the substance. This study
cannot be considered an accurate determination of the water solubility
and a qualitative value of <2 mg/L should be considered.
The result of the final test should not be considered as valid
since the equilibrium time might not been reached, results between days
are inconsistent and many details are not included in the report.
Moreover the flask method is not adapted for such low water solubility
and the likely emulsification of the substance during high energy mixing
appears to have led to misleadingly high results.
A standard OECD 105 study is inappropriate for the accurate
measurement of water solubility of such a large hydrophobic molecule.
Therefore is it assessed as a "disregarded study", and such
determination by calculation (QSAR) is currently the most appropriate
To conclude, the only valid results are the ones from the study intitled
"Determination of the water solubility of
2,6,10,15,19,23-hexamethyltetracosane - QSPR model adapted specifically
to OECD test guideline 105" performed by Kreatis, 2017.
The result below is the anticipated water solubility by QSAR
value following a study conducted according to OECD guideline 105 or
acceptable modifications thereof (e.g. using a slow-stir method instead
of shake flask). The water solubility is calculated as follows:
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