Di-tert-pentyl peroxide

Hydrolysis

Description of key information

key studies, OECD Guideline 111, GLP, validity 2:
- Half-life (pH 4; 50°C) = 2310.5 hours;
- Half-life (pH 7; 50°C)=  1386.3 hours;
- Half-life (pH 9; 50°C) =  990.2 hours.

Key value for chemical safety assessment

Half-life for hydrolysis:

1 386.3 h

at the temperature of:

50 °C

Additional information

Two valid key studies are available to assess the hydrolysis potential of di-tert-amyl peroxide as a function of pH. These studies were performed according to the OECD Guideline 111 with GLP statement.

The same preliminary test was performed for the two studies. In this preliminary test, the test substance was added into each buffer (pH 1.2, 4, 7 and 9; de-oxygenated by bubbling nitrogen) as follow: 15 µL of test item were mixed with 750mL of each buffer during one night under stirring. The solutions were then separated by decantation and 250 mL of clear solution were diluted to 500 mL with the corresponding buffers. These solutions were transferred to 100 mL flasks, closed with butyl rubber caps. Two replicates were prepared for each buffer. All test vessels were incubated at 50 +/- 0.5 °C and kept protected from light during five days. The solutions were then analysed. The results showed a decrease of the test substance with all buffers. One can conclude that the results obtained in the preliminary test did not demonstrate actual hydrolysis but might reveal a loss of the test item due to its volatility.

The definitive tests were performed at pH 7 and 9 (corresponding to the first key study) and at pH 4 (corresponding to the second key study).

The test substance was added into each buffer (pH 4, 7 and 9; de-oxygenated by bubbling nitrogen) as follow: 20 µL (for pH 7 and 9) of 40 µL (for pH 4) of test item were mixed with 1 L (for pH 7 and 9) or 2L (for pH 4) of buffer during 30 min under stirring (Slow Stir flasks). The solutions were then separated by decantation and the convenient volume of clear solutions were then used for the preparation of the series of flasks. Series of 36 mL flasks were then prepared and incubated at 50, 37 and 15°C. Two replicates were prepared for each buffer. The solutions were then analysed along with time.

At pH 7 and 50 °C, after 32 days, hydrolysis was only 46.2 %. For the other temperatures, 21.2 % of the test item were hydrolyzed in 32 days at 37 °C and 9.6 % in 32 days at 15 °C. Pseudo-first order reaction kinetics can only be observed at 50 °C. Therefore, it was not possible to calculate half-times at 37 and 15 °C. At pH 9 and 50 °C, after 32 days, hydrolysis was 62.8 %. For the other temperatures, 32 % of the test item were hydrolyzed in 32 days at 37 °C and 14.1 % in 32 days at 15 °C. Pseudo-first order reaction kinetics can only be observed at 50 °C.Therefore, it was not possible to calculate half-times at 37 and 15 °C. At pH 4 and 50 °C, after 24 days, hydrolysis was only 21.2 %. For the other temperatures, 15 % of the test item were hydrolyzed in 24 days at 37 °C and no hydrolysis was clearly observed after 30 days at 15 °C. Pseudo-first order reaction kinetics can only be observed at 50 °C. Therefore, it was not possible to calculate half-times at 37 and 15 °C.

In conclusion, significant hydrolysis of the test substance is not observed. This substance is thus considered as stable.

The half-life time at 25°C cannot be extrapolated from the results obtained at the 3 temperatures tested, for each pH, using Arrhenius equation.

The half-life times for the test substance as a function of pH are presented below:

- Half-life (pH 4; 50°C) = 2310.5 hours;

- Half-life (pH 7; 50°C)= 1386.3 hours;

- Half-life (pH 9; 50°C) = 990.2 hours.