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Environmental fate & pathways

Hydrolysis

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Description of key information

Reading across results from EPIKOTE 828 (CAS No. 25068-38-6), the registered substance is considered to be susceptible to hydrolysis at pH 4, 7 and 10, with a hydrolysis half-life of 117 hrs at 25°C (95% confidence range: 68–204 h). Products of hydrolysis are expected to be the mono-diol and the di-diol from ring-opening of the two epoxy groups.

Key value for chemical safety assessment

Half-life for hydrolysis:
117 h
at the temperature of:
25 °C

Additional information

The key study is a Klimisch-1, GLP-compliant, guideline study, sponsored by Hexion Specialty Chemicals Inc., and carried out on the read-across substance EPIKOTE 828 (CAS No. 25068-38-6) in 1993 by Shell Research Sittingbourne (Fisk PR) according to OECD 111 (EC A.6).

The registered substance and the read-across substance both belong to the class of terminal aliphatic epoxides, each possessing glycidyl ether (i.e., 1,2-epoxypropoxy) functional groups attached to a hydrocarbon moiety that is either devoid of other functionality, or that may possess an occasionally aliphatic hydroxyl group. In both cases, the only groups on the molecules that are expected to be susceptible to hydrolysis under environmental conditions are the epoxy groups, which would be expected to hydrolyse into the equivalent 1,2-diols under acidic, neutral or alkaline conditions. It is known in general that the hydrolysis of terminal epoxides proceeds primarily via neucleophilic displacement at the terminal carbon, and that the nature of the structure to which the terminal epoxides are attached has little effect on their hydrolysis rates under neutral or alkaline conditions. It is also known that the acid-catalysed hydrolysis rate is very sensitive to further substitution of the epoxy carbons that would affect the stability of the carbonium ion intermediate (Mabey and Mill, 1978). In this case, however, the registered and read-across substances both contain identical unsubstituted glycidyl ether groups, and would therefore not be expected to possess markedly different acid hydrolysis rates. On this basis, the read-across substance is considered to be an appropriate surrogate for the registered substance, and the hydrolysis rates of the glycidyl ether groups on the registered substance are expected to be similar to those experimentally determined for the read-across substance at pH 4, 7 and 10.

The hydrolysis of the read-across substance was investigated at 1.93 mg/l and 50°C in buffered solutions of pH 4, 7 and 9. Samples were taken over 24 hrs. Based on the experimental data and information on other epoxides the author suggest that hydrolysis is independent from pH and the values determined at pH 4, 7 and 9 can be combined to calculate a hydrolysis half-life of 117 hrs [~4.9 days] at 25°C (95% confidence range: 68–204 h). Products of hydrolysis were identified as mono-diol and the di-diol from reaction of the two epoxy groups.

Also, evidence of hydrolysis of the registered substance was observed during its water solubility test (Štreit, 2010). A review of “Fig. No. 1:LC/MS analysis of Grilonit 1/10 water solution” in the Annexes reveal that the primary peak (Retention Time = 10.2 mins) fell from ~3.5 to ~2.2 over the course of the 4-day experiment (3 days at 30°C + 1 at 20°C). This amounts to a 37% loss of the primary component over this 96-hour [4 day] period, which is most probably due to ring-opening hydrolysis of the epoxy groups, and compares well with the 50% loss seen for the read-across substance in 117 hrs [~4.9] days at 25°C, further supporting the read-across.

Reference
MabeyW, Mill T (1978). Critical review of hydrolysis of organic compounds in water under environmental conditions. J Phys Chem Ref Data 7(2):383-415.