N,N'-bis(1,4-dimethylpentyl)-p-phenylenediamine

Endpoint summary

Additional information

77PD is a member of the paraphenylenediamine (PD) “family”, which further included 6PPD (N-1,3-dimethylbutyl-N'-phenyl-p-phenylenediamine), 7PPD (N-(1,4-dimethylpentyl)-N'-phenylbenzene-1,4-diamine), and 44PD (N,N'-di-sec-butyl-p-phenylenediamine), The justification for the read-across approach between these four substances is provided in a separate document (Currenta 2012i).

Conclusion on degradation:

According to available information on degradation, all PPDs in question including 77PD are not readily biodegradable and no significant biodegradation is observed but primary abiotic degradation takes place.

The pathway of hydrolysis occurs in the same manner for all PPDs: Half-lives for the primary degradation are in the range of 3.4 to 8 hours (77PD: 3.4 hours). Primary degradation products of 77PD are 44 -QDI (the oxidised form of 77PD), 1,4 -dimethylpentylamino-p-phenol and 1,4 -dimethylpentylamine.

There are some indications that secondary degradation is faster in case of 77PD/44PD than in case of 6PPD/7PPD. Common secondary hydrolysis products of all PPDs are p-benzoquinone and p-hydroquinone and an amine. In case of 77D the amine is 1,4 -dimethylpentylamine.

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The question arises why the PPDs are not readily biodegradable, some of their hydrolysis products (p-benzoquinone, p-hydroquinone and 1,4 -dimethylpentylamine) are known to biodegrade quite rapidly. Thus, limited biodegradation could have been expected. A possible explanation for this contradiction is the fact that p-hydroquinone is highly toxic against bacteria. Based on an EC50 of 71 mg/L and a NOEC of 1 mg/L the resulting PNEC(STP) is 0.71 mg/L. Biodegradation tests according to the OECD 30x series are typically performed with initial concentrations of 100 mg/L. Thus, even low concentrations of p-hydroquinone formed by hydrolysis may have a significant effect and kill bacteria or at least inhibit bacterial growth in the biodegradation tests on 77PD. In the atmosphere rapid photodegradation takes place by reaction with photochemically produced OH radicals. The half-life of 7PPD is calculated to be 1.7 hours in that test system. (Currenta, 2009)

In order to evaluate the behaviour of PPDs in the environment,mechanistic studies have been performed: The reaction of paraphenylenediamines with oxygene and ozone radicals was studied (Klemchuk 1985 Polymer Stabilization and Degradation (ACS Symosium Series 280), Ignatz-Hoover 2012 Rubber & Plastics News (March 19, 2012)):

• Reaction with oxygene: Formation of quinone-diimines followed by oxidation of the nitrogene forming N-oxides.
• Quninone-diimines may also react to mono-quinoneimines which might further react to p-benzoquinone
• Reaction with ozone: Addition of ozone to nitrogene with cleavage of the C-N structure forming N-oxides. Quinone-iminines and N-oxides are reactive species which might further react forming higher and more complex molecules.

In an aerobic soil simulation test performed with the analogous substance 7PPD (N-(1,4-dimethylpentyl)-N'-phenylbenzene-1,4-diamine, CAS No. 3081-01-4)according to OECD 307 with 4 different soil types with a pH range of 3.86 to 7.19, 7PPD showed a rapid degradation loss in all soil types by strong and irreversible adsorption or binding. The half-lives were in the range of 0.03 to 1.9 days at 12°C. No metabolites were formed. At day 56 (end of study) only 4.5 to 9.1% of AR could be extracted using repeated Soxhlet-extractions with different solvents. NERs at day 56 were in the range of 76.4 to 84.8%. Several attempts have been made in order to characterise the non-extractable residues (NERs). Acidic reflux extractions at 100 °C, following ambient extractions, released 10.8 to 12.8% AR on day 56. The acidic reflux conditions were found to be residue altering. The residue released by reflux extraction was considered as part of the NER type 1, defined as non extractable residue that is sorbed or entrapped within the soil organic matter. The residue remaining in the soil after refluxing was considered as bound residue, consisting of NER-type 2 (covalently bound) and NER-type 3 (biogenic NER).

The anaerobic soil simulation test according to OECD 307 yielded a rapid degradation loss of the parent substance mainly during the aerobic phase with a half-life of 1.5 days. One metabolite was identified (1-N-(5-methyl-hexan-2-yl)-4-N-phenylcyclohexa-2,5-dione-4,4-diimine) which degraded with a half-life of 66.9 days at 12°C.

Environmental data, monitoring data:

Waste water from 25 representative rubber manufacturing sites in Europe (France, Germany, Italy, Poland, Spain, UK), including tyre and general rubber goods manufacturing, were sampled and analysed for 6PPD and the hydrolysis product 4-hydroxydiphenylamine (4-HDPA). Additional information was collected from individual sites, mainly on tonnages, waste water flow and relevant production conditions.

The total emission of the test substance to waste water was measured reaching a value of 5.61 kg/year (90th percentile). Inserting this figure into the estimation program EUSES, the following result was determined:

Safe use can be demonstrated for a site with a waste water load of 6PPD of up to 3.5 kg/year, emitting to a standard sewage treatment plant (STP; 10.000 inhabitants) and to a standard river (20.000 m³/day). This amount is reduced to 1.5 kg/year if the sewage sludge generated in the sewage treatment plant is applied to agricultural soil. 

Statistical evaluation showed that with regard to local concentrations in receiving rivers and the concentration in agricultural soils, safe use is established using the 90^thpercentile of the rubber manufacturing sites.