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Hydrolysis

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Reference
Endpoint:
hydrolysis
Type of information:
experimental study
Adequacy of study:
key study
Study period:
2014
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to guideline
Guideline:
OECD Guideline 111 (Hydrolysis as a Function of pH)
Deviations:
yes
Remarks:
1. No thymol was added to the buffer solutions. 2. Test temperatures of 12°C and 37°C were used. 3. Only Tier 1 of OECD guideline 111 was conducted in this screening study.
GLP compliance:
yes (incl. QA statement)
Specific details on test material used for the study:
EC name: tert-pentyl peroxypivalate
Trade name: Trigonox 125-C75
CAS: 29240-17-3
Batch/Lot no.: 1205442102
Purity: 71.4%
Water solubility: 815 mg/L (Akzo, 1994)
Composition: see CoA
Appearance: Colorless clear liquid
Expiry date: December 1, 2014
Storage: -25°C
Radiolabelling:
no
Analytical monitoring:
yes
Details on sampling:
At the moment the test vials were placed in the water bath, the first sample was taken and analyzed using the analytical method.
Subsequent samples were taken on different time intervals and analyzed to determine the percentage of hydrolysis. Samples were analyzed directly after sampling in order to prevent further hydrolysis.
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.
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.
Details on test conditions:
Main experiment
A stock solution with a test substance concentration of 714 mg/L was prepared in acetonitrile. From
this, a diluted stock solution with a concentration of 50 mg/L was prepared in acetonitrile. An amount of
1 mL of the diluted stock solution was transferred to a volumetric flask of 100 mL and was filled up with
the respective buffer solutions. Subsequently about 10 mL of the spiked buffer solutions was transferred
to sterile glass test vials. The vials were tightly closed and placed in the dark in a thermostatically
controlled water bath at a temperature of 12 ± 0.5°C.

Additional experiment
A stock solution with a test substance concentration of 756 mg/L was prepared in acetonitrile. From
this, a diluted stock solution with a concentration of 50 mg/L was prepared in acetonitrile. An amount of
1 mL of the diluted stock solution was transferred to a volumetric flask of 100 mL and was filled up with
the pH 1.2 buffer solution. Subsequently about 10 mL of the spiked buffer solution was transferred to
sterile glass test vials. The vials were tightly closed and placed in the dark in a thermostatically
controlled water bath at a temperature of 37 ± 0.5°C.
Duration:
120 h
pH:
4
Temp.:
12 °C
Initial conc. measured:
491.7 µg/L
Duration:
120 h
pH:
7
Temp.:
12 °C
Initial conc. measured:
502.6 µg/L
Duration:
120 h
pH:
9
Temp.:
12 °C
Initial conc. measured:
499.6 µg/L
Duration:
6 h
pH:
1.2
Temp.:
37 °C
Initial conc. measured:
497.2 µg/L
Number of replicates:
1
Transformation products:
no
Key result
pH:
4
Temp.:
12 °C
Hydrolysis rate constant:
0.002 h-1
DT50:
384 h
Type:
(pseudo-)first order (= half-life)
Key result
pH:
7
Temp.:
12 °C
Hydrolysis rate constant:
0.002 h-1
DT50:
362 h
Type:
(pseudo-)first order (= half-life)
Key result
pH:
9
Temp.:
12 °C
Hydrolysis rate constant:
0.002 h-1
DT50:
300 h
Type:
(pseudo-)first order (= half-life)
Key result
pH:
1.2
Temp.:
37 °C
Hydrolysis rate constant:
0.057 h-1
DT50:
12.2 h
Type:
(pseudo-)first order (= half-life)
Details on results:
Results of screening experiment, pH 4
Sample name Time Conc. (Ct) Hydrolysis Log Ct
hrs µg/L %
T14009 H pH 4 T=0 0 491.7 0.0 2.69
T14009 H pH 4 T=2h 2 455.9 7.3 2.66
T14009 H pH 4 T=5.5h 5.5 479.7 2.4 2.68
T14009 H pH 4 T=24h 24 471.2 4.2 2.67
T14009 H pH 4 T=48h 48 456.1 7.2 2.66
T14009 H pH 4 T=120h 120 383.3 22.1 2.58

Results of screening experiment, pH 7
Sample name Time Conc. (Ct) Hydrolysis Log Ct
hrs µg/L %
T14009 H pH 7 T=0 0 502.6 0.0 2.70
T14009 H pH 7 T=2h 2 499.2 0.7 2.70
T14009 H pH 7 T=4.3h 4.3 492.1 2.1 2.69
T14009 H pH 7 T=24h 24 474.5 5.6 2.68
T14009 H pH 7 T=48h 48 473.3 5.8 2.68
T14009 H pH 7 T=120h 120 394.7 21.5 2.60

Results of screening experiment, pH 9
Sample name Time Conc. (Ct) Hydrolysis Log Ct
hrs µg/L %
T14009 H pH 9 T=0 0 499.6 0.0 2.70
T14009 H pH 9 T=2h 2 489.7 2.0 2.69
T14009 H pH 9 T=4.3h 4.3 488.3 2.2 2.69
T14009 H pH 9 T=24h 24 464.3 7.1 2.67
T14009 H pH 9 T=48h 48 460.8 7.8 2.66
T14009 H pH 9 T=120h 120 372.2 25.5 2.57

Results of additional experiment, pH 1.2
Sample name Time Conc. (Ct) Hydrolysis Log Ct
hrs µg/L %
T14009 H pH 1.2 T=0 0 497.2 0.0 2.70
T14009 H pH 1.2 T=0.5h 0.5 496.0 0.2 2.70
T14009 H pH 1.2 T=1h 1 491.0 1.2 2.69
T14009 H pH 1.2 T=2h 2 464.7 6.5 2.67
T14009 H pH 1.2 T=4h 4 414.3 16.7 2.62
T14009 H pH 1.2 T=5h 5 376.1 24.4 2.58
T14009 H pH 1.2 T=6h 6 363.2 27.0 2.56

Calculation half-lives

pH

 

Kobs

t0.5

value

slope

(min-1)

(hrs)

pH 1.2

-0.024616056

0.056680563

12.2

pH 4

-0.000783981

0.001805183

384

pH 7

-0.000830706

0.001912772

362

pH 9

-0.001004288

0.002312458

300

Validity criteria fulfilled:
yes
Conclusions:
pH 4
The pH value at the start of the test was measured to be 4.0. The temperature during the test varied between 12.0 and 12.1°C. It was observed that about 22% of the test substance was hydrolysed after 5 days. Using the information, gathered during the screening hydrolysis test, also a calculation of the half-life (t0.5) was done by applying the Arrhenius relationship. The Arrhenius relationship is given by the relation between the logarithmic value of the test substance concentration and time . The half-life for the test substance was calculated to be 384 hours.

pH 7
The pH value at the start of the test was measured to be 7.0. The temperature throughout the test was measured to be 12.0°C. It was observed that about 21% of the test substance was hydrolysed after 5 days. Using the information, gathered during the screening hydrolysis test, also a calculation of the half-life (t0.5) was done by applying the Arrhenius relationship. The Arrhenius relationship is given by the relation between the logarithmic value of the test substance concentration and time. The half-life for the test substance was calculated to be 362 hours.

pH 9
The pH value at the start of the test was measured to be 9.0. The temperature throughout the test was measured to be 12.0°C. It was observed that about 25% of the test substance was hydrolysed after 5 days. Using the information, gathered during the screening hydrolysis test, also a calculation of the half-life (t0.5) was done by applying the Arrhenius relationship. The Arrhenius relationship is given by the relation between the logarithmic value of the test substance concentration and time. The half-life for the test substance was calculated to be 300 hours.

Additional experiment
pH 1.2
The pH value at the start of the test was measured to be 1.2. The temperature during the test varied between 37.0 and 37.2°C. It was observed that about 27% of the test substance was hydrolysed after 6 hours. Using the information, gathered during the screening hydrolysis test, also a calculation of the half-life (t0.5) was done by applying the Arrhenius relationship. The Arrhenius relationship is given by the relation between the logarithmic value of the test substance concentration and time. The half-life for the test substance was calculated to be 12.2 hours.

During the screening experiment it was observed that the half-life decreased at increasing pH values. Moreover the half-life observed in the additional experiment, was much lower. This value can be used for physiological purposes.
Executive summary:

The purpose of this study was to determine if tert-pentyl peroxypivalate would hydrolyze at environmentally and physiologically relevant pH values, complying with the OECD Guideline No. 111. Hydrolysis of tert-pentyl peroxypivalate was observed at pH values 4, 7 and 9.

 

At pH value 4 the half-life (t0.5) for tert-pentyl peroxypivalate at a temperature of 12°C was calculated to be 384 hours.

 

At pH value 7 the half- life (t0.5) for tert-pentyl peroxypivalate at a temperature of 12°C was calculated to be 362 hours.

 

At pH value 9 the half- life (t0.5) for tert-pentyl peroxypivalate at a temperature of 12°C was calculated to be 300 hours.

 

In an additional test, it was determined if tert-pentyl peroxypivalate would hydrolyze at a pH value of 1.2, a physiological relevant pH, complying with the OECD guideline 111. Hydrolysis was observed.

 

At pH value 1.2 the half- life (t0.5) for tert-pentyl peroxypivalate at a temperature of 37°C was calculated to be 12.2 hours.

Description of key information

The purpose of this study was to determine if tert-pentyl peroxypivalate would hydrolyze at environmentally and physiologically relevant pH values, complying with the OECD Guideline No. 111. Hydrolysis of tert-pentyl peroxypivalate was observed at pH values 4, 7 and 9.

 

At pH value 4 the half-life (t0.5) for tert-pentyl peroxypivalate at a temperature of 12°C was calculated to be 384 hours.

At pH value 7 the half- life (t0.5) for tert-pentyl peroxypivalate at a temperature of 12°C was calculated to be 362 hours.

At pH value 9 the half- life (t0.5) for tert-pentyl peroxypivalate at a temperature of 12°C was calculated to be 300 hours.

 

In an additional test, it was determined if tert-pentyl peroxypivalate would hydrolyze at a pH value of 1.2, a physiological relevant pH, complying with the OECD guideline 111. Hydrolysis was observed.

At pH value 1.2 the half- life (t0.5) for tert-pentyl peroxypivalate at a temperature of 37°C was calculated to be 12.2 hours.

No hydrolysis products were identified during the study, but the theoretical hydrolysis products are Pivalic acid (CAS 75 -98 -9) and Tert-amyl hydroperoxide (CAS 3425 -61 -4).

Key value for chemical safety assessment

Half-life for hydrolysis:
362 h
at the temperature of:
12 °C

Additional information