1,4-Benzenediamine, N,N'-mixed Ph and tolyl derivs.

Water solubility

Description of key information

Water solubilities for the 3 main constituents of 1,4-benzenediamine, N,N'-mixed Ph and tolyl derivatives are: 0.13, 0.11 and 0.045 mg/L.
N,N'-diphenyl-p-phenylenediamine;  R-59;  CAS: 74-31-7:  0.13 mg/L;
N-(2-methylphenyl)-N'-phenylbenzene-1,4-diamine; R-1679; CAS: 27173-16-6: 0.11 mg/L;
N,N'-bis(2-methylphenylbenzene)-1,4-diamine; R-898; CAS: 15017-02-4: 0.045 mg/L

Key value for chemical safety assessment

Water solubility:

0.095 mg/L

at the temperature of:

20 °C

Additional information

The water solubility for DAPD, 0.095 mg/L, was calculated as the average of water solubilities of the 3 main components.

The water solubility of 1,4-benzenediamine, N,N’-mixed phenyl and tolyl derivatives was tested using two different testing protocols. A first test used the Column Elution method as described in the OECD protocol n° 105 in combination with a GC analysis of the saturated solution. In the second test, a saturated solution of test substance was created via the flask method and analyzed by total carbon measurement, in accordance with EU protocol A6. Due to the difference in test setup and analytical technique used, the two test procedures lead to fundamentally different values for the water solubility of 1,4-benzenediamine, N,N’-mixed phenyl and tolyl derivatives.

Difference in the composition of the saturated test solution.

It should be noted that both techniques used to create a saturated test solution are specifically suitable for the examination of pure substances. However, as 1,4-benzenediamine, N,N’-mixed phenyl and tolyl derivatives is a multi-constituent substance, the application of both protocols leads to test solutions that are not identical in composition.

When using the flask method, in which a large amount of ground test substance (> 5 times than the estimated amount that would dissolve) is brought into contact with a certain amount of water and stirred for 24 hours, the watery solution will be enriched in the soluble constituents or impurities present in the multi-constituent substance.

The protocol for the column elution method describes that the first 5 bed volumes of water eluted from the column should be removed, in order to remove any highly soluble substances present in the test material. As a consequence, the watery solution will be depleted in the highly soluble impurities or constituents.

Difference in analytical technique used.

Both the total carbon measurement and GC analysis are considered to be valid and suitable methods for analyzing the amount of test substance dissolved in the saturated test solution. However, the total carbon measurement will lead to one value for the multi-constituent substance “1,4-benzenediamine, N,N’-mixed phenyl and tolyl derivatives” as such, whereas the GC analysis will differentiate between the substance’s main constituents and impurities.

As a consequence, by using the column elution technique in combination with GC analysis the total water solubility of DAPD is underestimated, as the soluble impurities that are part of the composition of DAPD are not taken into account. The technique does however give a reliable estimation of the water solubilities of the 3 main constituents of DAPD.

On the other hand, the flask elution method in combination with total carbon measurements clearly overestimates the water solubility of the testing substance, as the tested solution is enriched in highly soluble impurities and total carbon measurement does not differentiate between the impurities and the main constituents.

Adequacy for the purpose of chemical safety assessment.

It can be concluded that neither of both techniques described above would lead to a good estimation of this “overall” water solubility value.

Upon assessing the adequacy of the available test results for the purpose of the risk assessment it needs however to be taken into account that separate exposure scenarioʼs have been built for each of the main constituents of the multi-constituent substance. As a consequence, specific water solubility values for the 3 main constituents are to be taken into account in these exposure assessments. In a final stage of the risk assessment, the results of the 3 separate assessments are then combined to come to one overall conclusion. It is therefore relevant for the risk assessment process to have the 3 separate water solubility values for the main constituents of DAPD.

Based on the above reasoning the column elution test combined with GC analysis was assigned as key study.