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Description of key information

The test item is hydrolytically unstable. The results suggest that half-life is short, probably less than one hour at 5 °C. At environmentally relevant temperatures, the substance will undergo hydrolytical degradation significantly faster. With respect to REACH Annex VII the substance can be considered as unstable since the half-life is clearly below 12 h (criterion according to Annex VII, point 7.7).

Key value for chemical safety assessment

Half-life for hydrolysis:
1 h
at the temperature of:
5 °C

Additional information

A study was performed in accordance with OECD guideline 111 to determine the hydrolysis behaviour of the test item in dependence of the pH. Sterile aqueous buffer solutions of different pH values (pH 4 and 7) were spiked with the test item and incubated in the dark under controlled laboratory conditions (at 5 °C). After appropriate time intervals, buffer solutions were analysed for hydrolysis products. The following reaction products were detected:

- 2,4,4-trimethyl-1-pentanol (CAS No. 16325-63-6)

Six additional products were present in GC chromatograms but could not be identified unambiguously. The proportions of the reaction products are variable over the study period. Only the decomposition product 2,4,4-trimethyl-1-pentanol could be quantified against an external standard.

Hydrolytic degradation of di(3,5,5-trimethylhexanoyl)peroxide was thus followed indirectly by monitoring concentrations of the breakdown product 2,2,4-trimethyl-1-pentanol over 24 hours. Total dissolved test material concentrations were estimated from the AUC proportions of 2,2,4-trimethyl-1-pentanol at the respective sampling times. Approximate concentrations of the parent substance di(3,5,5-trimethylhexanoyl)peroxide in pH 7 test solution at 1 and 24 h were estimated using the fluorescein method, which is not substance-specific but is capable of detecting peroxide groups.

Total dissolved test material concentrations increased over time. Intact peroxide was verified at concentrations of approximately 1 mg/L after 1 hour and 10 mg/L after 24 hours. This corresponds to a peroxide proportion among dissolved test material of 3.26 and 18.6 % after 1 and 24 hours, respectively.

These test results demonstrate that:

- dissolution of the test substance progressively increases over time

- hydrolytical degradation starts immediately at dissolution, is not clearly distinguishable from the latter, and can be considered to be controlled predominantly by diffusion processes

- at any sampling time investigated the proportion of intact peroxide is low

- based on the low fraction of intact peroxide both at 1 h and 24 h the hydrolytical half-life is very short, probably less than one hour

- deceleration of the reaction rate after 8 hours is assumed to be the result of saturation of the aqueous solution with 2,4,4-trimethyl-1-pentanol or any other poorly soluble decomposition products.