tert-pentyl 2-ethylperoxyhexanoate

Hydrolysis

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

hydrolysis

Type of information:

experimental study

Adequacy of study:

key study

Study period:

From 15/05/2013 to 08/07/2013

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: see 'Remark'

Remarks:

This study was performed according to OECD Guideline 111 with GLP statement. This study report is composed of the preliminary test and the definitive test at pH 4. This study is considered reliable with restrictions as one deviation was observed. The hydrolysis test at 15°C was stopped at 24 days and 70% hydrolysis instead of 30 days or 90% hydrolysis.

Reason / purpose for cross-reference:

reference to other study

Qualifier:

according to guideline

Guideline:

OECD Guideline 111 (Hydrolysis as a Function of pH)

Deviations:

no

Principles of method if other than guideline:

Not applicable

GLP compliance:

yes (incl. QA statement)

Remarks:

2012-07-18

Specific details on test material used for the study:

Details on properties of test surrogate or analogue material (migrated information):
None

Radiolabelling:

no

Analytical monitoring:

yes

Details on sampling:

- Processing of samples: dilution with acetonitrile and pH 4.0 medium (final composition 50/50). Dilution factor x2 or 2.5.

Buffers:

For pH 1.2, 4, 7 and 9 of preliminary test, see "cross-reference to other study".
The definitive test was carried out at pH 4. The corresponding buffer solution was prepared using reagent grade chemicals and ultra-pure water. One litre of solution was prepared with ultra-pure water and used as follow:
- C8H5KO4: Potassium phtalate monobasic for 0.1 M solution (Merck Ref: 1.04874.0250, batch: A0332774 204): 500 mL
- NaOH 0.1M (Merck Titrisol Ref. 1.09959.0001, batch: HC36315): 4 mL

Estimation method (if used):

Not applicable

Details on test conditions:

PRELIMINARY TEST:
Premilinary test conditions were already reported in pH 7 and 9 report (see "cross-reference to other study").

DEFINITIVE TEST:
The test substance was addedd into the buffer (de-oxygenated by bubbling nitrogen) as follow: 10 µL of test item were mixed with 1L of buffer during 45 min under stirring (slow stir flask). The solution was then separated by decantation and 3 samples of 100 mL were prepared. These solutions were transferred to 100 mL flasks, closed with butyl rubber caps (head space should be avoided). Two replicates were prepared for pH 4 buffer. All test vessels were incubated at 50, 37 and 15°C. The solutions were then analysed along with time.

Duration:

581.5 h

pH:

4

Temp.:

15

Initial conc. measured:

8 mg/L

Duration:

149.5 h

pH:

4

Temp.:

37

Initial conc. measured:

8 mg/L

Duration:

28.5 h

pH:

4

Temp.:

50

Initial conc. measured:

8 mg/L

Number of replicates:

2

Positive controls:

not specified

Negative controls:

not specified

Statistical methods:

None

Preliminary study:

see "cross-reference to other study"

Test performance:

The definitive test was performed at pH 4.

Transformation products:

not measured

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

Not applicable

pH:

4

Temp.:

50 °C

Hydrolysis rate constant:

0.117 h-1

DT50:

5.9 h

Type:

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

pH:

4

Temp.:

37 °C

Hydrolysis rate constant:

0.02 h-1

DT50:

35.2 h

Type:

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

pH:

4

Temp.:

25 °C

Hydrolysis rate constant:

0.006 h-1

DT50:

116.3 h

Type:

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

Remarks on result:

other: calculated using Arrhenius equation: Ln(K) = f(1/T).

pH:

4

Temp.:

15 °C

Hydrolysis rate constant:

0.002 h-1

DT50:

385.1 h

Type:

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

Other kinetic parameters:

None

Details on results:

For pseudo-first order behaviour, the values of hydrolysis rate constant (K.obs) can be obtained from the plots of logarithms of the concentration versus time using the expression: K.obs = - slope.
The hydrolysis rate constant derived from linear regression analysis was subsequently used to calculate the half-life for each set of test conditions, using the following equation: Half-life (t 1/2) = Ln2 / K.obs

Table 5.1.2/1: Hydrolysis of the test item at pH 4 and 50°C - definitive test

Hydrolysis of the test substance at pH 4 and 50°C
Time (hours)	pH	Measured concentration (mg/L)			Measured hydrolysis
		Sample 1	Sample 2	Mean	Remaining concentration (%)	Ln Remaining	Hydrolysis (%)
0 1 2 4.5 5.5 6.5 24.5 28.5	4	8.00 7.85 7.74 4.47 3.45 3.09 0.42 0.32	8.00 7.32 7.66 4.85 3.74 4.17 0.45 0.30	8.00 7.58 7.70 4.66 3.60 3.63 0.43 0.31	100 94.78 96.27 58.27 44.96 45.38 5.43 3.88	4.61 4.55 4.57 4.07 3.81 3.82 1.69 1.35	0.00 5.22 3.73 41.73 55.04 54.62 94.57 96.13

Table 5.1.2/2: Hydrolysis of the test item at pH 4 and 37°C - definitive test

Hydrolysis of the test substance at pH 4 and 37°C
Time (hours)	pH	Measured concentration (mg/L)			Measured hydrolysis
		Sample 1	Sample 2	Mean	Remaining concentration (%)	Ln Remaining	Hydrolysis (%)
0 1 2 6.5 24.5 30.5 48.5 53.5 149.5	4	8.00 7.41 8.55 6.77 3.48 2.74 1.59 1.01 0.30	7.32 8.70 7.72 3.08 2.74 1.33 1.21 0.34	8.00 7.37 3.47 3.08 3.28 2.74 1.46 1.11 0.32	100 92.06 43.39 38.54 40.94 34.25 18.25 13.88 4.00	4.61 4.52 3.77 3.65 3.71 3.53 2.90 2.63 1.39	0.00 7.94 56.61 61.46 59.06 65.75 81.75 86.13 96.00

Table 5.1.2/3: Hydrolysis of the test item at pH 4 and 15°C - definitive test

Hydrolysis of the test substance at pH 4 and 15°C
Time (hours)	pH	Measured concentration (mg/L)			Measured hydrolysis
		Sample 1	Sample 2	Mean	Remaining concentration (%)	Ln Remaining	Hydrolysis (%)
0 1 2 6.5 24.5 30.5 48.5 149.5 341.5 557.5 581.5	4	8.00 6.30 8.30 7.16 6.80 8.22 6.65 9.70 4.19 3.25 2.47	6.60 8.20 8.40 6.60 7.96 7.15 9.30 4.17 2.79 2.32	8.00 6.45 8.25 7.78 6.70 8.09 6.90 9.50 4.18 3.02 2.40	100 80.63 103.13 97.25 83.75 101.13 86.25 118.75 52.25 37.75 29.94	4.61 4.39 4.64 4.58 4.43 4.62 4.46 4.78 3.96 3.63 3.40	0.00 19.38 -3.13 2.75 16.25 -1.13 13.75 -18.75 47.75 62.25 70.06

Validity criteria fulfilled:

no

Remarks:

The hydrolysis test at 15°C was stopped at 24 days and 70% hydrolysis instead of 30 days or 90% hydrolysis.

Conclusions:

The half-life time for the test substance at pH 4 and 25°C was determined using Arrhenius equation to be 116.3 hours.

Executive summary:

This study was performed according to OECD Guideline 111 with GLP statement to determine the rate of hydrolysis of the test substance at pH 4.

In the preliminary test, the test substance was added into each buffer (pH 1.2, 4, 7 and 9; de-oxygenated by bubbling nitrogen) as follow: 10 μL of test item were mixed with 1L of each buffer during 45 min under stirring. The solutions were then separated by decantation and two times 500 mL of clear solution were transferred to 500 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. One can conclude that a strong hydrolysis is observed at every pH (1.2, 4, 7 and 9) after 5 days at 50 °C. As hydrolysis of the test substance was already studied at pH 7 and 9, this study was only performed at pH 4.

In the definitive test, the test substance was addedd into the buffer (de-oxygenated by bubbling nitrogen) as follow: 10 µL of test item were mixed with 1L of buffer during 45 min under stirring (slow stir flask). The solution was then separated by decantation and 3 samples of 100 mL were prepared. These solutions were transferred to 100 mL flasks, closed with butyl rubber caps (head space should be avoided). Two replicates were prepared for pH 4 buffer. All test vessels were incubated at 50, 37 and 15°C. The solutions were then analysed along with time.

At 50°C, 96.1% hydrolysis was obtained after 28.5 hours. For the other temperature, 96% of the test item was hydrolysed in 149.5 hours at 37°C and 70% in 581.5 hours at 15°C. The results of this test indicated pseudo-first order reaction kinetics. Therefore, the half-life time at 25°C was extrapolated from the results obtained at the 3 temperatures tested.

The half-life time for the test substance at pH 4 and 25°C was determined using Arrhenius equation to be 116.3 hours.

Reference 2

Endpoint:

hydrolysis

Type of information:

experimental study

Adequacy of study:

key study

Study period:

From 27/01/2012 to 03/01/2013

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: This study was performed according to OECD Guideline 111 with GLP statement. No deviations were observed but first order kinetics is not proved for all experiments.

Reason / purpose for cross-reference:

reference to other study

Qualifier:

according to guideline

Guideline:

OECD Guideline 111 (Hydrolysis as a Function of pH)

Deviations:

no

Principles of method if other than guideline:

Not applicable

GLP compliance:

yes (incl. QA statement)

Remarks:

2012-07-18

Specific details on test material used for the study:

Details on properties of test surrogate or analogue material (migrated information):
None

Radiolabelling:

no

Analytical monitoring:

yes

Details on sampling:

- Sampling method: dilution 2 to 20 in acetonitrile/buffer (final composition 50/50).

Buffers:

- pH 1.2: potassium chloride (3.7275 g) - HCl 0.2M (322.5 mL), adjustment to 1 L with ultra-pure water.
- pH4: potassium phthalate monobasic (10.211 g) - NaOH 0.1M (4 mL), adjustment to 1 L with ultra-pure water.
- pH7: potassium dihydrogen phosphate (6.805 g) - NaOH 0.1M (296.3 mL), adjustment to 1 L with ultra-pure water.
- pH9: boric acid (3.0915 g) - potassium chloride (3.7275 g) - NaOH 0.1M (213 mL), adjustment to 1 L with ultra-pure water.

Estimation method (if used):

Not applicable

Details on test conditions:

PRELIMINARY TEST:
The test substance was added into each buffer (pH 1.2, 4, 7 and 9; de-oxygenated by bubbling nitrogen) as follow: 10 μL of test item were mixed with 1L of each buffer during 45 min under stirring. The solutions were then separated by decantation and two times 500 mL of clear solution were transferred to 500 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.

DEFINITIVE TEST (pH 7 and 9):
The test substance was added into each buffer (pH 7 and 9; de-oxygenated by bubbling nitrogen) as follow: 10 μL of test item were mixed with 1 L of buffer during 45 min under stirring (Slow Stir flasks). The solutions were then separated by decantation and 3 samples of 100 mL were prepared for each buffer. These solutions were transferred to 100 mL flasks, closed with butyl rubber caps (head space should be avoided). Two replicates were prepared for each buffer. All test vessels were incubated at 50, 37 and 15 °C. The solutions were then analysed along with time.

Duration:

96 h

pH:

7

Temp.:

50 °C

Initial conc. measured:

4.4 mg/L

Duration:

144 h

pH:

7

Temp.:

37 °C

Initial conc. measured:

4.4 mg/L

Duration:

792 h

pH:

7

Temp.:

15 °C

Initial conc. measured:

4.4 mg/L

Duration:

96 h

pH:

9

Temp.:

50 °C

Initial conc. measured:

6.62 mg/L

Duration:

144 h

pH:

9

Temp.:

37 °C

Initial conc. measured:

6.62 mg/L

Duration:

792 h

pH:

9

Temp.:

15 °C

Initial conc. measured:

6.62 mg/L

Number of replicates:

2

Positive controls:

no

Negative controls:

no

Statistical methods:

None

Preliminary study:

See table 5.1.2/1 in "Any other information on results incl. tables".
One can conclude that a strong hydrolysis is observed at every pH (1.2, 4, 7 and 9) after 5 days at 50 °C. In this study, a definitive test was conducted at pH 7 and 9. A test at pH 4 will be performed afterwards.

Test performance:

See tables 5.1.2/2 to 5.1.2/7 in "Any other information on results incl. tables".
At pH 7 and 50°C, 97.8% hydrolysis was obtained in 28 hours. For the other temperatures, 90.8% of the test item was hydrolyzed in 96 hours at 37°C and 53.1% in 33 days at 15°C.
At pH 9 and 50°C, 97.7% hydrolysis was obtained in 28 hours. For the other temperatures, 95.7% of the test item was hydrolyzed in 96 hours at 37°C and 78.3% in 33 days at 15°C.

Transformation products:

not measured

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

Not applicable

pH:

7

Temp.:

50 °C

Hydrolysis rate constant:

0.143 h-1

DT50:

5 h

Type:

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

pH:

7

Temp.:

37 °C

Hydrolysis rate constant:

0.024 h-1

DT50:

29 h

Type:

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

pH:

7

Temp.:

25 °C

Hydrolysis rate constant:

0.004 h-1

DT50:

188 h

Type:

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

Remarks on result:

other: calculated using Arrhenius equation: Ln(K) = f(1/T).

pH:

7

Temp.:

15 °C

Hydrolysis rate constant:

0.001 h-1

DT50:

990 h

Type:

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

pH:

9

Temp.:

50 °C

Hydrolysis rate constant:

0.139 h-1

DT50:

4.99 h

Type:

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

pH:

9

Temp.:

37 °C

Hydrolysis rate constant:

0.045 h-1

DT50:

15.3 h

Type:

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

pH:

9

Temp.:

25 °C

Hydrolysis rate constant:

0.007 h-1

DT50:

106 h

Type:

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

Remarks on result:

other: calculated using Arrhenius equation: Ln(K) = f(1/T).

pH:

9

Temp.:

15 °C

Hydrolysis rate constant:

0.001 h-1

DT50:

630 h

Type:

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

Other kinetic parameters:

None

Details on results:

For pseudo-first order behaviour, the values of hydrolysis rate constant (K.obs) can be obtained from the plots of logarithms of the concentration versus time using the expression: K.obs = - slope.
The hydrolysis rate constant derived from linear regression analysis was subsequently used to calculate the half-life for each set of test conditions, using the following equation: Half-life (t 1/2) = Ln2 / K.obs

Table 5.1.2/1: Hydrolysis of the test item at 50°C - preliminary test

Hydrolysis of the test substance at 50°C
Days	pH	Measured concentrations (mg/L)
0	1.2	4.6 - 6.9 / 4.8 - 7.1
5		<DL	<DL
0	4	4.7 - 6.9 / 4.5 - 6.3
5		<DL	<DL
0	7	3.3 - 3.8 / 3.4 - 3.7
5		<DL	<DL
0	9	7.7 - 5.9 / 6.3 - 5.5
5		<DL	<DL

DL = 3 µg/L at pH 1.2; 0.5 µg/L at pH 4; 5 µg/L at pH 7; 5 µg/L at pH 9.

Table 5.1.2/2: Hydrolysis of the test item at pH 7 and 50°C - definitive test

Hydrolysis of the test substance at pH 7 and 50 °C
Time (hours)	pH	Measured concentrations (mg/L)
		Sample 1	Sample 2	Mean
0 4 20 24 28 96	7.04	4.40 1.56 0.20 0.20 0.19 <DL	4.40 1.77 0.03 0.01 0.00 <DL	4.40 1.67 0.11 0.10 0.10 0.00

Table 5.1.2/3: Hydrolysis of the test item at pH 7 and 37°C - definitive test

Hydrolysis of the test substance at pH 7 and 37 °C
Time (hours)	pH	Measured concentrations (mg/L)
		Sample 1	Sample 2	Mean
0 4 20 24 28 96 144	7.04	4.40 3.05 1.72 1.79 1.61 0.40 <DL	4.40 3.89 2.19 1.95 1.65 0.41 <DL	4.40 3.47 1.96 1.87 1.63 0.41 <DL

Table 5.1.2/4: Hydrolysis of the test item at pH 7 and 15°C - definitive test

Hydrolysis of the test substance at pH 7 and 15 °C
Time (hours)	pH	Measured concentrations (mg/L)
		Sample 1	Sample 2	Mean
0 4 20 24 28 96 144 192 288 504 675 792	7.04	4.40 3.00 4.67 4.54 4.88 3.37 5.15 4.06 5.17 3.12 3.31 2.34	4.40 3.50 4.86 4.81 4.39 3.82 5.20 4.91 4.54 4.39 2.68 1.79	4.40 3.25 4.77 4.68 4.63 3.60 5.17 4.49 4.85 3.75 3.00 2.06

Table 5.1.2/5: Hydrolysis of the test item at pH 9 and 50°C - definitive test

Hydrolysis of the test substance at pH 9 and 50 °C
Time (hours)	pH	Measured concentrations (mg/L)
		Sample 1	Sample 2	Mean
0 4 20 24 28 96	9.09	6.62 1.97 0.21 0.14 0.15 <DL	6.62 2.11 0.23 0.11 0.15 <DL	6.62 2.04 0.22 0.13 0.15 0.00

Table 5.1.2/6: Hydrolysis of the test item at pH 9 and 37°C - definitive test

Hydrolysis of the test substance at pH 9 and 37 °C
Time (hours)	pH	Measured concentrations (mg/L)
		Sample 1	Sample 2	Mean
0 4 20 24 28 96 144	9.09	6.62 3.7 1.38 1.52 0.72 0.27 0.00	6.62 3.92 1.50 1.40 0.79 0.30 0.00	6.62 3.83 1.44 1.46 0.76 0.29 0.00

Table 5.1.2/7: Hydrolysis of the test item at pH 9 and 15°C - definitive test

Hydrolysis of the test substance at pH 9 and 15 °C
Time (hours)	pH	Measured concentrations (mg/L)
		Sample 1	Sample 2	Mean
0 4 20 24 28 96 144 192 288 504 672 792	9.09	6.62 4.47 3.83 3.89 3.35 2.26 3.53 2.56 3.33 3.12 2.12 1.41	6.62 5.60 3.26 3.31 3.31 2.26 3.50 2.57 3.68 3.14 2.12 1.47	6.62 5.03 3.54 3.60 3.33 2.26 3.52 2.56 3.51 3.13 2.12 1.44

The first order kinetics is not proved at pH 9 / 15°C.

Validity criteria fulfilled:

yes

Conclusions:

The half-life times for the test substance at pH 7 and 9 at 25°C are 188 and 106 hours, respectively.

Executive summary:

The hydrolysis as a function of pH of the test substance was assessed according to the OECD Guideline 111 with GLP statement.

The objective of the study was to determine the rate of hydrolysis of the test substance in different buffers and at different temperatures.

In the preliminary test, the test substance was added into each buffer (pH 1.2, 4, 7 and 9; de-oxygenated by bubbling nitrogen) as follow: 10 μL of test item were mixed with 1L of each buffer during 45 min under stirring. The solutions were then separated by decantation and two times 500 mL of clear solution were transferred to 500 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.

One can conclude that a strong hydrolysis is observed at every pH (1.2, 4, 7 and 9) after 5 days at 50 °C. In this study, a definitive test was conducted at pH 7 and 9. A test at pH 4 will be performed afterwards.

In the definitive test, the test substance was added into each buffer (pH 7 and 9; de-oxygenated by bubbling nitrogen) as follow: 10 μL of test item were mixed with 1 L of buffer during 45 min under stirring (Slow Stir flasks). The solutions were then separated by decantation and 3 samples of 100 mL were prepared for each buffer. These solutions were transferred to 100 mL flasks, closed with butyl rubber caps (head space should be avoided). Two replicates were prepared for each buffer. All test vessels were incubated at 50, 37 and 15 °C. The solutions were then analysed along with time.

At pH 7 and 50°C, 97.8% hydrolysis was obtained in 28 hours. For the other temperatures, 90.8% of the test item was hydrolyzed in 96 hours at 37°C and 53.1% in 33 days at 15°C.

At pH 9 and 50°C, 97.7% hydrolysis was obtained in 28 hours. For the other temperatures, 95.7% of the test item was hydrolyzed in 96 hours at 37°C and 78.3% in 33 days at 15°C.

The half-life times for the test substance at pH 7 and 9 at 25°C were determined using Arrhenius equation to be 188 and 106 hours, respectively.

Description of key information

key studies, OECD Guideline 111, GLP, validity 2:
- Half-life (pH 4; 25°C) = 116.3 hours;
- Half-life (pH 7; 25°C)= 188 hours;
- Half-life (pH 9; 25°C) = 106 hours.

Key value for chemical safety assessment

Half-life for hydrolysis:

188 h

at the temperature of:

25 °C

Additional information

Two valid key studies are available to assess the hydrolysis potential of the substance 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: 10 μL of test item were mixed with 1L of each buffer during 45 min under stirring. The solutions were then separated by decantation and two times 500 mL of clear solution were transferred to 500 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. One can conclude that a strong hydrolysis is observed at every pH (1.2, 4, 7 and 9) after 5 days at 50 °C.

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: 10 μL of test item were mixed with 1 L of buffer during 45 min under stirring (Slow Stir flasks). The solutions were then separated by decantation and 3 samples of 100 mL were prepared for each buffer. 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, 37 and 15 °C. The solutions were then analysed along with time.

At pH 7 and 50°C, 97.8% hydrolysis was obtained in 28 hours. For the other temperatures, 90.8% of the test item was hydrolyzed in 96 hours at 37°C and 53.1% in 33 days at 15°C. At pH 9 and 50°C, 97.7% hydrolysis was obtained in 28 hours. For the other temperatures, 95.7% of the test item was hydrolyzed in 96 hours at 37°C and 78.3% in 33 days at 15°C. At pH 4 and 50°C, 96.1% hydrolysis was obtained after 28.5 hours. For the other temperature, 96% of the test item was hydrolysed in 149.5 hours at 37°C and 70% in 581.5 hours at 15°C. The results of these studies indicated pseudo-first order reaction kinetics. Therefore, the half-life time at 25°C was 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; 25°C) = 116.3 hours;

- Half-life (pH 7; 25°C)= 188 hours;

- Half-life (pH 9; 25°C) = 106 hours.