Bis(4-methylbenzoyl)peroxide

Hydrolysis

Link to relevant study record(s)

Reference

Endpoint:

hydrolysis

Type of information:

experimental study

Adequacy of study:

key study

Study period:

June - November 2014

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: GLP study according to protocol.

Qualifier:

according to guideline

Guideline:

OECD Guideline 111 (Hydrolysis as a Function of pH)

Deviations:

yes

Remarks:

• No Thymol was added to the buffer solutions. The addition of Thymol as a disinfectant is not necessary because the buffer solutions were sterilized also • No confidence limits were calculated for the half-life figures.

GLP compliance:

yes (incl. QA statement)

Radiolabelling:

no

Analytical monitoring:

yes

Buffers:

Sterile test buffer solutions of pH 4, 7 and 9 were prepared in glass bottles according to the description in Annex 3 of OECD 111 and purged with nitrogen for at least 5 minutes

Details on test conditions:

Hydrolysis of unstable substances (Tier 2)
A stock solution of the test substance was prepared in acetonitrile. From this a diluted stock with a test substance concentration of 2 mg/L was prepared in acetonitrile. An amount of the diluted stock solution was transferred to a volumetric flask of 100 mL and filled up with the buffer solution, resulting in an initial concentration of 20 µg/L. Subsequently about 10 mL of the spiked buffer solution was transferred to sterile glass test vials. The vials were closed tightly and placed in the dark in the thermostatically controlled water bath at three different temperatures of respectively 10.0 ± 0.5°C, 20.0 ± 0.5°C and 30.0 ± 0.5°C. At the moment the test vials were placed in the water bath, the first sample was taken and analyzed using the analytical method described in Annex 3. Sampling times were chosen based on the available results. For each sampling time duplicate sample bottles were prepared and both sample bottles were analyzed separately.
A separate glass vessel without test substance was placed in the water bath at the different test temperatures. After equilibration with the temperature of the water bath the pH was checked of this vessel. The temperature of the thermostatic water bath was checked at the start and end of the tests and at each sampling time.

Identification of hydrolysis products (Tier 3)
To confirm the hydrolysis of the test substance an analytical method was applied to show the presence of hydrolysis product. Based on information of the sponsor the main hydrolysis product is p-toluic acid. Because the applied analytical method was not suitable for detection of the hydrolysis product at a concentration lower than 50 µg/L it was not possible to include the identification of the hydrolysis product in Tier 2 of the study. A separate test was conducted by adding an excess of test substance to one of the buffer solutions, details are given below.
A sterile test buffer solution of pH 7 was prepared in a glass bottle according to the description in Annex 3 of OECD 111 and purged with nitrogen for at least 5 minutes.
A stock solution of the test substance was prepared in acetonitrile. An amount of the stock solution was transferred to a volumetric flask of 50 mL and filled up with the buffer solution, resulting in an initial concentration of 5 mg/L. Subsequently about 10 mL of the spiked buffer solution was transferred to sterile glass test vials. The vials were closed tightly and placed in the dark in the thermostatically controlled water bath at 30.0 ± 0.5°C. At the moment the test vials were placed in the water bath, the first sample was taken and analyzed using the analytical method described in Annex 4. One and two weeks after adding the test substance to the buffer solution, sample bottles were taken from the water bath and analyzed.
A separate glass vessel without test substance was placed in the water bath at the test temperature. After equilibration with the temperature of the water bath the pH was checked of this vessel. The temperature of the thermostatic water bath was checked at the start and end of the test and at each sampling time

Additional experiment
A sterile buffer solution of pH 1.2 was prepared in a glass bottle according to the description in Annex 3 of OECD 111 and purged with nitrogen for at least 5 minutes.
The same procedure for preparing the test vials as described in section of Tier 2 was applied. The test temperature was 37.0 ± 0.5°C. Sampling times were chosen within the first day and up to 6 hours.
A separate glass vessel without test substance was placed in the water bath at the test temperature. After equilibration with the temperature of the water bath the pH was checked of this vessel. The temperature of the thermostatic water bath was checked at the start and end of the test and at each sampling time.

Duration:

240 h

pH:

4

Temp.:

10 °C

Initial conc. measured:

13.2 - 13.6 µg/L

Duration:

3 240 min

pH:

4

Temp.:

20 °C

Initial conc. measured:

14.2 - 22.5 µg/L

Duration:

1 260 min

pH:

4

Temp.:

30 °C

Initial conc. measured:

15.4 - 17.2 µg/L

Duration:

95 h

pH:

7

Temp.:

10 °C

Initial conc. measured:

17.4 - 17.9 µg/L

Duration:

1 440 min

pH:

7

Temp.:

20 °C

Initial conc. measured:

14.4 - 14.6 µg/L

Duration:

360 min

pH:

7

Temp.:

30 °C

Initial conc. measured:

14.2 - 15.2 µg/L

Duration:

360 min

pH:

9

Temp.:

10 °C

Initial conc. measured:

9.8 - 11.8 µg/L

Duration:

125 min

pH:

9

Temp.:

20 °C

Initial conc. measured:

12.2 µg/L

Duration:

50 min

pH:

9

Temp.:

30 °C

Initial conc. measured:

10.2 - 13.4 µg/L

Number of replicates:

2

Preliminary study:

The test substance is known to hydrolyse at pH value 8 and therefore tier 1 of the guideline was left out.

Transformation products:

yes

No.:

#1

Details on hydrolysis and appearance of transformation product(s):

To confirm the hydrolysis of the test substance the main hydrolysis product p-toluic acid was identified at pH 7, 30 ºC. Based on sponsor information in combination with the determined retention time, p-toluic acid was confirmed to be the hydrolysis product. One and two weeks after starting the hydrolysis test increasing amounts of p-toluic acid were observed. Results are displayed in the table below.

Time Concentration
p-toluic acid
days µg/L
0 7 645
14 1174

pH:

4

Temp.:

10 °C

Hydrolysis rate constant:

0.009 - 0.01 h-1

DT50:

72 - 80 h

Type:

(pseudo-)first order (= half-life)

Remarks on result:

other: Mean half-life: 76h

pH:

4

Temp.:

20 °C

Hydrolysis rate constant:

0 - 0 min-1

DT50:

25 - 26 h

Type:

(pseudo-)first order (= half-life)

Remarks on result:

other: Mean half-life: 26h

pH:

4

Temp.:

30 °C

Hydrolysis rate constant:

0.001 - 0.001 min-1

DT50:

11 h

Type:

(pseudo-)first order (= half-life)

Remarks on result:

other: Mean half-life: 11h

pH:

7

Temp.:

10 °C

Hydrolysis rate constant:

0.016 - 0.017 h-1

DT50:

40 - 44 h

Type:

(pseudo-)first order (= half-life)

Remarks on result:

other: Mean half-life: 42h

pH:

7

Temp.:

20 °C

Hydrolysis rate constant:

0.001 - 0.001 min-1

DT50:

11 - 12 h

Type:

(pseudo-)first order (= half-life)

Remarks on result:

other: Mean half-life: 12h

pH:

7

Temp.:

30 °C

Hydrolysis rate constant:

0.002 - 0.003 min-1

DT50:

4 - 7 h

Type:

(pseudo-)first order (= half-life)

Remarks on result:

other: Mean half-life: 9h

pH:

9

Temp.:

10 °C

Hydrolysis rate constant:

0.006 - 0.007 min-1

DT50:

103 - 125 min

Type:

(pseudo-)first order (= half-life)

Remarks on result:

other: Mean half-life: 114min

pH:

9

Temp.:

20 °C

Hydrolysis rate constant:

0.019 - 0.019 min-1

DT50:

36 min

Type:

(pseudo-)first order (= half-life)

Remarks on result:

other: Mean half-life: 36min

pH:

9

Temp.:

30 °C

Hydrolysis rate constant:

0.051 - 0.058 min-1

DT50:

12 - 14 min

Type:

(pseudo-)first order (= half-life)

Remarks on result:

other: Mean half-life: 13min

Other kinetic parameters:

Results pH 1.2, 37°C
Time Conc. (Ct) Hydrolysis
hours µg/L %
0 14.3 0.0
0.5 15.6 -9.6
1 19.4 1) 1)
2 9.6 32.4
4 7.0 50.8
6 7.2 49.8
1) Measured concentration was >20% higher than initial
concentration and therefore considered to be an outlier

Using the determined half-lives at the different test temperatures, the half-life for pH 4 at a temperature of 25°C was interpolated to be 18 hours.

Using the determined half-lives at the different test temperatures, the half-life for pH 7 at a temperature of 25°C was interpolated to be 9 hours.

Using the determined half-lives at the different test temperatures, the half-life for pH 9 at a temperature of 25°C was interpolated to be 23 minutes.

Validity criteria fulfilled:

yes

Conclusions:

The purpose of this study was to determine if the test substance would hydrolyze at environmentally relevant pH values, complying with the OECD Guideline No. 111.

The test substance is known to hydrolyse at pH value 8 and therefore tier 1 of the guideline was left out.

An overview of the calculated half-lives for the test substance at the different pH values and tested temperatures are displayed in the table below. Also the interpolated half-lives for the temperature of 25°C are displayed.

pH Temperature Replicate t½
value °C hr
pH 4 10 I 80
II 72
Mean 76
20 I 25
II 26
Mean 26
30 I 11
II 11
Mean 11
25 interpolated 18
pH 7 10 I 40
II 44
Mean 42
20 I 11
II 12
Mean 12
30 I 7
II 4
Mean 6
25 interpolated 9
t½
min
pH 9 10 I 103
II 125
Mean 114
20 I 36
II 36
Mean 36
30 I 12
II 14
Mean 13
25 interpolated 23


To confirm the hydrolysis of the test substance the main hydrolysis product p-toluic acid was identified at pH 7, 30 ºC. Based on sponsor information in combination with the determined retention time, p-toluic acid was confirmed to be the hydrolysis product. One and two weeks after starting the hydrolysis test increasing amounts of p-toluic acid were observed. Results are displayed in the table below.

Time Concentration
p-toluic acid
days µg/L
0 7 645
14 1174

An additional hydrolysis experiment was carried out for pH value 1.2 at 37°C. Hydrolysis results are displayed in the table below.

Time Concentration (Ct) Hydrolysis
hours µg/L %
0 14.3 0.0
0.5 15.6 -9.6
1 19.4 1) 1)
2 9.6 32.4
4 7.0 50.8
6 7.2 49.8
1) Measured concentration was >20% higher than initial measured
concentration and therefore considered to be an outlier

Executive summary:

Test substance was observed to hydrolyse at each tested pH values and test temperature. Interpolated half-lives at 25°C are also determined for the tested pH value.

Description of key information

Half life at pH 9 is 360 min @ 10 oC, 125 min @ 20 oC and 50 min @ 30 oC

Half life at pH 7 is 95 h @ 10 oC, 1440 min @ 20 oC and 360 min @ 30 oC

Half life at pH 4 is 240 h @ 10 oC, 3240 min @ 20 oC and 1260 min @ 30 oC

Key value for chemical safety assessment

Half-life for hydrolysis:

9 h

at the temperature of:

25 °C