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Environmental fate & pathways

Hydrolysis

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Description of key information

The hydrolysis of Santoflex 7PPD (N-(1,4-dimethylpentyl)-N'-phenylbenzene-1,4-diamine) was investigated for pH 4, pH 7 and pH 9 at 20 °C and 50 °C based on OECD TG 111. The half-life of 7PPD was determined to be 7 hours at 20 °C (pH 7) and 1 hour at 50 °C (pH 7).

The following hydrolysis products were determined: 4-Hydroxydiphenylamine, Aniline, p-Benzoquinone, p-Hydroquinone. During the study an additional hydrolysis product was detected in the hydrolysis test solutions at pH 7 and pH 9 only. The LC-MS spectrum of the component shows a molecular ion signal at m/z = 200.0712, which can be assigned to the protonated molecular ion [M+H]+ of C12H9NO2, M = 199 g/mol. The component therefore appears to have a molecular weight of 199 Dalton linked to a formula C12H9NO2. This would probably fit to “overoxidised 4-HDPA” (4-(phenylnitroso)benzen-1-olate or 4-(phenylnitroso)cyclohexa-2,5-dien-1-one) (short name: “N-Oxide”).

7PPD was found to be hydrolytically instable at pH 4, pH 7 and pH 9. Recoveries of the test item are near 100 % indicating a satisfying repeatability of the method applied to quantify the test item concentration.

The hydrolysis tests at 20 °C were prolonged up to 30 days monitoring 7PPD and in addition primary and secondary hydrolysis products. Identified primary hydrolysis products of Santoflex 7PPD are 4-Hydroxydiphenylamine (4-HDPA) and “N-Oxide”. 4-HDAP was built by release of 1,4-dimethylpentylamine. Oxidation of 4-HDAP resulted in “N-Oxide”. Due to subsequent hydrolysis of primary degradation products secondary hydrolysis products are Aniline, p-Benzoquinone, and p-Hydroquinone.

At pH 4 the degradation products 4-HDPA and N-Oxide could not be measured, while Aniline, p-Benzoquinone, and p-Hydroquinone were formed. Therefore, it was supposed that 4-HDPA and N-Oxide are highly instable at pH 4 and immediately degrade to Aniline and quinones (p-Benzoquinone, and p-Hydroquinone).

Therefore, it is assumed that the same reported hydrolysis mechanism occurs at hydrolysis of Santoflex 7PPD at all investigated pH values 4, 7, and 9.

Key value for chemical safety assessment

Half-life for hydrolysis:
7 h
at the temperature of:
20 °C

Additional information

Mass balance of Santoflex 7PPD including primary and secondary hydrolysis products was monitored over 30 days of hydrolysis. Comparison of the starting concentration of Santoflex 7PPD to the summarized concentration of measured degradation products after 30 days showed deviations at all investigated pH values:

 

pH 4:At the beginning of measurement the concentration of Santoflex 7 PPD was determined to be 3.2 µmol/L. After 30 days the sum of all measured degradation products was reported to be 4.38 µmol/L. It is assumed that deviation in mass balancing could be a result of measuring inaccuracy of the analytical method. Real starting concentration of Santoflex 7PPD in hydrolysis test was reported to be 3.58 µmol/L. Due to delayed starting of measurement (caused by preparation of the sample, like dilution, mixing) the concentration of 7PPD at t=0 hrs was measured to be 3.2 µmol /L instead of 3.58 µmol/L. This deviation could result in higher mass balance at the end of measurement. Additional, several reported concentrations of Aniline, p-Benzoquinone, and p-Hydroquinone were measured to be outside calibration range (below the lowest calibration level) but taken into account for the mass balance. This could also result in inaccuracy of reported values.

 

pH 7 and pH 9:At pH 7 a starting concentration of Santoflex 7PPD 3.0 µmol/L (at pH 9: 2.98 µmol/L) was measured at the beginning of hydrolysis. After 30 days the sum of all measured degradation products was reported to be 2.61 µmol/L (at pH 9: 2.35 µmol/L). It is assumed that deviations in mass balancing are caused by calibration inaccuracy of “N-Oxide”. This degradation product was quantified using the response factor of the parent compound 7PPD at 202 nm assuming similar UV absorption of their chemical structures. This calibration could influence the reported values of concentration and therefore has an influence on correct mass balane. Additionally deviation in mass balancing could be a result of measuring inaccuracy of the analytical method. Several reported concentrations of 7PPD, Aniline, and p-Benzoquinone were measured to be outside calibration range (below the lowest calibration level) but taken into account for the mass balance. This could result in inaccuracy of reported values. Additionally it is assumed that the concentration of p-Hydroquinone at pH 7 (p-Hydroquinone and p-Benzoquinone at pH 9) was below limit of detection and therefore could not be included into the sum of all degradation products (Currenta, 2016).