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Environmental fate & pathways

Hydrolysis

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Reference
Endpoint:
hydrolysis
Type of information:
experimental study
Adequacy of study:
key study
Study period:
06-Apr-2010 to 13-Sep-2010
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Remarks:
Study conducted in compliance with agreed protocols, with no or minor deviations from standard test guidelines and/or minor methodological deficiencies, which do not affect the quality of the relevant results. The study report was conclusive, done to a valid guideline and the study was conducted under GLP conditions.
Qualifier:
according to
Guideline:
OECD Guideline 111 (Hydrolysis as a Function of pH)
Deviations:
no
Qualifier:
according to
Guideline:
EU Method C.7 (Degradation: Abiotic Degradation: Hydrolysis as a Function of pH)
Deviations:
no
GLP compliance:
yes (incl. certificate)
Remarks:
Date of Certificate: November 12, 2008
Radiolabelling:
no
Analytical monitoring:
yes
Details on sampling:
Before and after incubation at different temperatures, 20 µL aliquots of the test solutions at each pH value were analyzed without dilution by measuring the UV/VIS signals of tert-butyl perbenzoate (CAS# 614-45-9) and of benzoic acid after HPLC separation of the injected sample solution.
Buffers:
Buffer Solution pH 4.0
Biphthalate buffer, pH 4.0 ± 0.02, Fluka, Art. No. 82566

Buffer Solution pH 7.0
Phosphate buffer, pH 7.0 ± 0.02, Fluka, Art. No. 82571

Buffer Solution pH 9.0
Borate buffer, pH 9.0 ± 0.02, Fluka, Art. No. 82574



Estimation method (if used):
Not used.
Duration:
188.8 h
pH:
4
Initial conc. measured:
69.19 mg/L
Duration:
605.4 h
pH:
4
Initial conc. measured:
63.1 mg/L
Duration:
843.5 h
pH:
4
Initial conc. measured:
76.1 mg/L
Duration:
188.8 h
pH:
7
Initial conc. measured:
72.4 mg/L
Duration:
605.4 h
pH:
7
Initial conc. measured:
49.7 mg/L
Duration:
843.5 h
pH:
7
Initial conc. measured:
88.3 mg/L
Duration:
9.9 h
pH:
9
Initial conc. measured:
62.5 mg/L
Duration:
54.6 h
pH:
9
Initial conc. measured:
53.4 mg/L
Duration:
167 h
pH:
9
Initial conc. measured:
56.7 mg/L
Number of replicates:
Duplicate aliquots (A and B) of sample solution were diluted by a factor of 100 using glass double-distilled water.
Positive controls:
not specified
Negative controls:
not specified
Statistical methods:
Not specified.
Transformation products:
not specified
No.:
#1
No.:
#2
Details on hydrolysis and appearance of transformation product(s):
Due to the instability of the test item one proposed major degradation product was identified by comparison of the respective retention times. Therefore, solutions of benzoic acid was prepared and analyzed. Because in the proposed decomposition pathway benzoic acid and tert-butanol are formed in equimolar quantities and because quantification of benzoic acid was more practical, benzoic acid was quantified and tert-butanol was calculated.
% Recovery:
17
pH:
4
Temp.:
50 °C
Duration:
188.8 h
% Recovery:
26
pH:
4
Temp.:
40 °C
Duration:
605.4 h
% Recovery:
51
pH:
4
Temp.:
30 °C
Duration:
843.5 h
% Recovery:
8
pH:
7
Temp.:
50 °C
Duration:
188.8 h
% Recovery:
9
pH:
7
Temp.:
40 °C
Duration:
605.4 h
% Recovery:
34
pH:
7
Temp.:
30 °C
Duration:
843.5 h
% Recovery:
4
pH:
9
Temp.:
50 °C
Duration:
9.9 h
% Recovery:
18
pH:
9
Temp.:
30 °C
Duration:
54.6 h
% Recovery:
20
pH:
9
Temp.:
20 °C
Duration:
167 h
Key result
pH:
4
Temp.:
25 °C
Hydrolysis rate constant:
0
DT50:
79.2 d
Type:
(pseudo-)first order (= half-life)
Remarks on result:
other: calculated value
Key result
pH:
7
Temp.:
25 °C
Hydrolysis rate constant:
0.001
DT50:
976 h
Type:
(pseudo-)first order (= half-life)
Remarks on result:
other: calculated value
Key result
pH:
9
Temp.:
25 °C
Hydrolysis rate constant:
0.018
DT50:
38 h
Type:
(pseudo-)first order (= half-life)
Remarks on result:
other: calculated value
Other kinetic parameters:
None.

General

In general all given values represent rounded results obtained by calculation using the exact raw data.

 

A representative calibration curveis given in the attached Figure1. Examples of the calibration data for test item-standards are given in Table1. The coefficient of determination r² as well as the correlation coefficient r of all calibration data used for quantification was found to be more than 0.99 (optimum 1.000). This reflects the linearity of the HPLC-system within the used calibration range of about 1 µg/mL to 97 µg/mL of the test item.

 

A typical chromatogram of a standard solution is given in the attached Figure 2. Typical chromatograms of the test solutions after incubation at pH 4.0, pH 7.0 and pH 9.0 are given in the attached Figure 3, Figure 4 and Figure 5.

Table1       Calibration Data oftert-butyl perbenzoate (CAS# 614-45-9)

Concentration
[μg/mL]

Peak Area

Deviation

(Bias)

(X)

(Y)

[%]

96.930304

579411

0.2

72.697728

432098

-0.4

48.465152

289484

0.1

24.232576

143973

-0.4

7.2697728

43413

0.1

4.8465152

29250

1.2

1.09046592

6778

4.4

 

 

Hydrolysis at 50 °C

The hydrolysis preliminary test was performed with tert-butyl perbenzoate (CAS# 614-45-9) at 50.0 °C ± 0.1 °C at each of pH 4.0, pH 7.0, and pH 9.0 in duplicate. The test solutions of tert-butyl perbenzoate (CAS# 614-45-9) were thermostated to 50.0 °C and analyzed in time intervals.

 

The results of the preliminary test show, that tert-butyl perbenzoate (CAS# 614-45-9) is not stable at pH 9.0. Therefore the test at 50 °C was repeated in the range of 10% to 90% degradation. The results found in the main study are discussed in respective chapter.

 

The results obtained for hydrolysis at pH 4.0 and 7.0 at 50°C are in the range of 10 to 90% and therefore discussed in the respective chapter.

 

 

Hydrolysis at pH 4.0 and Different Temperatures

 Calculation of the Half-Life Time

The hydrolysis reaction at pH 4.0 is relatively fast. Peroxides are known to be thermal instable. Therefore, the further hydrolysis tests were performed additionally at 40°C and 30 °C, each in duplicate. Each buffered test solution was analyzed in time intervals.

 

The results found are summarized inTable2,Table4, andTable6. The tabulated values represent rounded results, which were obtained by calculation using the exact raw data.

 

The decrease of the tert-butyl perbenzoate (CAS# 614-45-9) concentration at pH 4.0 in each sample is shown in the attached Figure 6, Figure 8, Figure 10, Figure 12, Figure 14 and Figure16. The data in the range from 10% to 90% hydrolysis are plotted at ln ctversus t in the atttached Figure 7, Figure 9, Figure 11, Figure 13, Figure 15 and Figure 17. The obtained linear plot of each sample proves that the hydrolysis reaction is pseudo first order at 50 °C, 40 °C and 30 °C.

 

The reaction rate constant k was calculated for all three temperatures by regression analysis. The results of these calculations are summarized in Table 3, Table 5 and Table 7.

 

The half-life time of tert-butyl perbenzoate (CAS# 614-45-9) at 50.0 °C and pH 4.0 was calculated to be 79 hours (3.3 days)

 

The half-life time of tert-butyl perbenzoate (CAS# 614-45-9) at 40.0 °C and pH 4.0 was calculated to be 309 hours (12.9 days).

 

The half-life time of tert-butyl perbenzoate (CAS# 614-45-9) at 30.0 °C and pH 4.0 was calculated to be 924 hours (38.5 day).

 

The mass balance is given for the hydrolysis reaction of tert-butyl perbenzoate (CAS# 614-45-9) at pH 4.0 for all pH values in a recovery range of 88 to 98 %. The calculated mass balances are shown in Table 10 to Table 15.

 

 Evaluation of the Half-Life Time at 25 °C

The calculated results of the activation energy and the k25value (at 25 °C) for pH 4.0 are summarized in Table 8.

 

The half-life time of the hydrolysis reaction of tert-butyl perbenzoate (CAS# 614-45-9) at 25 °C and pH 4.0 was calculated to be 1900 hours (79 days).

 

 

 Hydrolysis at pH 7.0 and Different Temperatures

Calculation of the Half-Life Time at pH 7.0

The hydrolysis reaction at pH 7.0 is relatively fast. Peroxides are known to be thermal instable. Therefore, the further hydrolysis tests were performed additionally at 40°C and 30 °C, each in duplicate. Each buffered test solution was analyzed in time intervals.

 

The results found are summarized in Table16, Table18 and Table 20. The tabulated values represent rounded results, which were obtained by calculation using the exact raw data.

 

The decrease of the tert-butyl perbenzoate (CAS# 614-45-9) concentration at pH 7.0 in each sample is shown in the attached Figure18, Figure 20, Figure 22, Figure 24, Figure 26 and Figure 28. The data in the range from 10% to 90% hydrolysis are plotted at ln ctversus t in the attached Figure 19, Figure 21, Figure 23, Figure 25, Figure 27 and Figure 29. The obtained linear plot of each sample proves that the hydrolysis reaction is pseudo first order at 50 °C, 40 °C and 30 °C.

 

The reaction rate constant k was calculated for all three temperatures by regression analysis. The results of these calculations are summarized in Table 17, Table 19, and Table 21.

 

The half-life time of tert-butyl perbenzoate (CAS# 614-45-9) at 50.0 °C and pH 7.0 was calculated to be 54 hours (2.2 days)

 

The half-life time of tert-butyl perbenzoate (CAS# 614-45-9) at 40.0 °C and pH 7.0 was calculated to be 177 hours (7.4 days).

 

The half-life time of tert-butyl perbenzoate (CAS# 614-45-9) at 30.0 °C and pH 7.0 was calculated to be 514 hours (21.4 day).

 

The mass balance is given for the hydrolysis reaction of tert-butyl perbenzoate (CAS# 614-45-9) at pH 7.0 for all pH values in a recovery range of 96 to 100 %. The calculated mass balances are shown in Table 24 to Table 29.

 

 

 Evaluation of the Half-Life Time at 25 °C

The calculated results of the activation energy and the k25value (at 25 °C) for pH 7.0 are summarized in Table 22.

 

The half-life time of the hydrolysis reaction of tert-butyl perbenzoate (CAS# 614-45-9) at 25 °C and pH 7.0 was calculated to be 976 hours (41 days).

 

 

 Hydrolysis at pH 9.0 and Different Temperatures

Calculation of the Half-Life Time at pH 9.0

The hydrolysis reaction at pH 9.0 is extremely fast. Therefore, the further hydrolysis tests were performed additionally at 30°C and 20 °C, each in duplicate. Each buffered test solution was analyzed in time intervals.

 

The results found are summarized in Table 30, Table 32, and Table 34. The tabulated values represent rounded results, which were obtained by calculation using the exact raw data.

 

The decrease of the tert-butyl perbenzoate (CAS# 614-45-9) concentration at pH 9.0 in each sample is shown in the attached Figure 30, Figure 32, Figure 34, Figure 36, Figure 38 and Figure 40. The data in the range from 10% to 90% hydrolysis are plotted at ln ctversus t in the attached Figure 31, Figure 33, Figure 35, Figure 37, Figure 39, and Figure 41. The obtained linear plot of each sample proves that the hydrolysis reaction is pseudo first order at 50 °C, 30 °C and 20 °C.

 

The reaction rate constant k was calculated for all three temperatures by regression analysis. The results of these calculations are summarized in Table 31, Table 33, and Table 35.

 

The half-life time of tert-butyl perbenzoate (CAS# 614-45-9) at 50.0 °C and pH 9.0 was calculated to be 2.6 hours (0.1 days)

 

The half-life time of tert-butyl perbenzoate (CAS# 614-45-9) at 30.0 °C and pH 9.0 was calculated to be 21 hours (0.9 days).

 

The half-life time of tert-butyl perbenzoate (CAS# 614-45-9) at 20.0 °C and pH 9.0 was calculated to be 71 hours (3 day).

 

The mass balance is given for the hydrolysis reaction of tert-butyl perbenzoate (CAS# 614-45-9) at pH 7.0 for all pH values in a recovery range of 96 to 100 %. The calculated mass balances are shown inTable38toTable43.

 

Evaluation of the Half-Life Time at 25 °C

The calculated results of the activation energy and the k25value (at 25 °C) for pH 9.0 are summarized in Table 36.

 

The half-life time of the hydrolysis reaction of tert-butyl perbenzoate (CAS# 614-45-9) at 25 °C and pH 9.0 was calculated to be 38 hours (1.6 days).

 

Validity criteria fulfilled:
yes
Conclusions:
pH 4.0
At pH 4.0 a main test was performed at 50 °C, 40 °C and 30 °C, respectively. The half-life time of the hydrolysis reaction of tert-butyl perbenzoate (CAS# 614-45-9) at 25 °C and pH 4.0 was calculated to be 1900 hours (79 days).

pH 7.0
At pH 7.0 a main test was performed at 50 °C, 40 °C and 30 °C, respectively. The half-life time of the hydrolysis reaction of tert-butyl perbenzoate (CAS# 614-45-9) at 25 °C and pH 7.0 was calculated to be 976 hours (41 days).

pH 9.0
At pH 9.0 a main test was performed at 50 °C, 30 °C and 20 °C, respectively. The half-life time of the hydrolysis reaction of tert-butyl perbenzoate (CAS# 614-45-9) at 25 °C and pH 9.0 was calculated to be 38 hours (1.6 days).
Executive summary:

The purpose of this study was to determine the hydrolysis behavior of tert-butyl peroxy benzoate (CAS# 614-45-9) in aqueous buffered solutions adjusted to pH 4.0, pH 7.0 and pH 9.0.

 

Hydrolysis is one of the most common reactions controlling abiotic degradation in the environment. This reaction is particularly relevant for substances with low biodegradability.

The hydrolysis determination of tert-butyl perbenzoate (CAS# 614-45-9) at different pH values was based on the OECD Guideline No. 111, “Hydrolysis as a Function of pH"; adoptedApril 13, 2004and the Council Regulation (EC) 440/2008 C.7.

The hydrolysis of the test item was performed at 50.0 °C ± 0.1 °C at each of pH 4.0, pH 7.0 and pH 9.0.

 

Tert-butyl perbenzoate (CAS# 614-45-9) was not stable at pH 4.0, pH 7.0 and at pH 9.0. Further testing was required in order to calculate the rate constant (k25) and the half-life time of the hydrolysis at pH 4.0, pH 7.0, and pH 9.0 at 25 °C. In order to avoid thermal degradation the testing was performed at reduced temperatures.

The results are summarized below (the values typed in italics were calculated using the Arrhenius equation):

 

pH

Temperature

Reaction rate constant

k

Reaction rate constant

k

Half-life time

t 1/2

 

[°C]

[1/hours]

[1/s]

[hours]

4.0

25

3.67 x 10-4

1.01 x 10-7

1900

50

8.80 x 10-3*

2.44 x 10-6

79

40

2.24 x 10-3*

6.24 x 10-7

309

30

7.52 x 10-4*

2.09x 10-7

924

7.0

25

7.11 x 10-4

1.98 x 10-7

976

50

1.29x 10-2*

3.57x 10-6

54

40

3.92x 10-3*

1.09x 10-6

177

30

1.35x 10-3*

3.75x 10-7

514

9.0

25

1.81x 10-2

5.02 x 10-6

38

50

2.68x 10-1*

7.45x 10-5

2.6

30

3.32x 10-2*

9.23x 10-6

21

20

9.75x 10-3*

2.71x 10-6

71

* The tabulated value is the mean of two samples.

 

Tert-butyl perbenzoate (CAS# 614-45-9) at pH 4.0 has a half-life time of 1900 hours (79 days) at 25 °C.

 

Tert-butyl perbenzoate (CAS# 614-45-9) at pH 7.0 has a half-life time of 976 hours (40.5 days) at 25 °C.

 

Tert-butyl perbenzoate (CAS# 614-45-9) at pH 9.0 has a half-life time of 38 hours (1.6 days) at 25 °C.

 

Description of key information

At 25°C and pH 4 the substance has a hydrolysis 1/2 life of 1900 h (79 days)

At 25°C and pH 7 the substance has a hydrolysis 1/2 life of 976 h (40.5 days)

At 25°C and pH 9 the substance has a hydrolysis 1/2 life of 38 h (1.6 days)

Key value for chemical safety assessment

Half-life for hydrolysis:
40.5 d
at the temperature of:
25 °C

Additional information

Critical half-lives under most common environmental conditions and those used in the standard guideline studies are between 40.5 days at pH 7 and 1.6 days at pH 9 at 25°C. Degradation of the substance to hydrolytic by products during studies where pHs were close to pH 9, such as the algae study may then be expected. However, in such cases the organisms would then be exposed to the degradation products.