4-tert-butylpyrocatechol

Hydrolysis

Link to relevant study record(s)

Reference

Endpoint:

hydrolysis

Type of information:

experimental study

Adequacy of study:

key study

Study period:

from 17-Sept-2009 to 05-Aug-2010

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:

no

Qualifier:

according to guideline

Guideline:

EU Method C.7 (Degradation: Abiotic Degradation: Hydrolysis as a Function of pH)

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Radiolabelling:

no

Analytical monitoring:

yes

Details on sampling:

- Standard solutions: For example: 45.95 mg of 4-tert-butylpyrocatechol (4-TBC) were dissolved in 100 mL of a solvent mixture of acetonitrile and water (30:70; v/v) to prepare a stock solution of 459.5 µg/mL 4-tert-butylpyrocatechol (4-TBC). Calculated volumes of this stock solution were diluted with the same solvent mixture to obtain six standard solutions in the range from 9.19 µg/mL to 137.8 µg/mL 4-tert-butylpyrocatechol (4-TBC). These standard solutions were used to calibrate the HPLC-system.
- Sample preparation: Aliquots of the test solutions at each pH value were analyzed after dilution in a 1:10 ratio with a solvent mixture of acetonitrile and water (30:70; v/v) and by measuring the UV/VIS signal of 4-tert-butylpyrocatechol (4-TBC) after HPLC separation of the injected sample solution.
- Sampling intervals for the parent/transformation products: 0h, 2.4h and 5 days
- Sampling method: in duplicate
- Volatile compounds, if any: not volatile
- Sampling intervals/times for pH measurements: 0 and 120 hours
- Sampling intervals/times for sterility check: after each main test
- Sample storage conditions before analysis: no storage, direct analysis
- Other observation, if any (e.g.: precipitation, color change etc.): All filtrate samples were colored reddish bron and the samples of each residue were colored yellow.

Buffers:

- pH: 4.0, 7.0 and 9.0
- Type of buffer:
Buffer pH 4.0: Biphthalate
Buffer pH 7.0: Phosphate
Buffer pH 9.0: Borate
- Composition of buffer: no data

Details on test conditions:

TEST SYSTEM:
- Type, material and volume of test flasks, other equipment used: All glassware, which must be inert in the pH range applied, was rinsed with sterile buffer. The hydrolysis was carried out in flasks, which were stoppered or sealed with an inert material (e.g. glass).
- Sterilisation method: The buffer solutions were sterilized for 25 minutes in an autoclave prior to first use.
- Lighting: The test item was incubated in the dark. at a specific temperature.
- Measures to exclude oxygen: Nitrogen was passed through the buffer solutions for 5 minutes to reduce the oxygen in the solution in the preliminary test and in the main test at pH 7.0 and 50°C.

PRELIMINARY TEST (Tier 1):
According to the guideline, a preliminary hydrolysis test was performed at 50.0 °C ± 0.5 °C at pH 4.0, pH 7.0 and pH 9.0, each. Aliquots of each test solution were analyzed at the beginning, after 2.4 hours and after 120 hours using the analytical method.

An aliquot of 4-tert-butylpyrocatechol (4-TBC) was dissolved in 100 mL of buffer solution (pH 4.0). Two aliquots of this test solution of approximately 50 mL each were transferred into 50 mL Erlenmeyer flasks in order to perform a duplicate test.

The samples for the initial concentration were sonicated for 15 minutes. The solutions after 120 hours at pH 7.0 and pH 9.0 were filtrated after sampling (0.2 µm, Nylon). All samples at each sampling time were diluted in a 1:10 ratio with a solvent mixture of acetonitrile and water (30:70; v/v) prior to quantification.

HYDROLYSIS OF UNSTABLE SUBSTANCES (Tier 2):
Due to the instability of the test item found in the preliminary test at 50.0 °C, further hydrolysis tests were performed at 40 °C, 50 °C and 60°C in the buffered test solution at pH 7.0 and pH 9.0. The test temperature was kept constant ±0.5 °C. To test for first order behaviour the concentration of the test item in each test solution was determined immediately after preparation and at time intervals, which provide a minimum of six spaced data points between approximately 10% and approximately 90% of hydrolysis of the test item (exception: at pH 7.0 and 40°C and for the second sample at pH 9.0 and 40°C only 5 spaced data points are applicable). After each main test, a sterility test was performed by incubating some drops of sample solution on caso-agar plates for about 3 days at 37 °C. All tests were found to be negative.

- Test at 50.0°C and a pH of 7.0:
An aliquot of 4-tert-butylpyrocatechol (4-TBC) was dissolved 250 mL with buffer solution pH 7.0. This solution was filtered (0.2 µm, Nylon) and diluted in a 1:2 ratio with the same buffer solution. Two aliquots of this test solution of approximately 250 mL were each transferred into 2 Erlenmeyer flasks in order to perform a duplicate test. The initial weighings are listed in the following table. Both vessels were shaken at the respective temperature in a water bath.

For sampling at each time point, 20 mL from the test vessels were transferred into a test tube and stored for about 2 minutes in the refrigerator in order to stop the degradation process. Afterwards, 15 mL of the sample were filtered (0.45 µm, Nylon) into a 50 mL Erlenmeyer flask. The filter will be placed into a second 50 mL Erlenmeyer flask, which contains 15 mL of acetonitrile and will be used for the residue samples.

- Test at pH 9.0 at all temperatures and at pH 7.0 and 40.0°C and 60.0°C:
An aliquot of 4-tert-butylpyrocatechol (4-TBC) were dissolved 250 mL with buffer solution. This solution was filtered (0.2 µm, Nylon) and diluted in a 1:2 ratio with the respective buffer solution. Several aliquots (about 10) of this test solution of approximately 10 mL each were transferred into headspace vials in order to perform a duplicate test and the remaining solution was transferred into a Erlenmeyer flask as reserve vessel. The initial weighings are listed in the following table. All vessels were shaken at the respective temperature in a water bath.

For sampling at each time point, each 2 headspace vial were transferred for about 3 minutes into a refrigerator in order to stop the hydrolysis. All 10 mL of the headspace vial were then filtrated into a second headspace vial. The filter was transferred into the first headspace vial and the remaining on the filter was re-dissolved with 10 mL of acetonitrile.

Duration:

186.65 h

pH:

7

Temp.:

40

Initial conc. measured:

808.24 mg/L

Duration:

159.9 h

pH:

7

Temp.:

50

Initial conc. measured:

827.34

Duration:

163.4 h

pH:

7

Temp.:

60

Initial conc. measured:

721.58 mg/L

Duration:

186.45 h

pH:

9

Temp.:

40

Initial conc. measured:

793.04 mg/L

Duration:

217.7 h

pH:

9

Temp.:

50

Initial conc. measured:

832.5 mg/L

Duration:

164.07 h

pH:

9

Temp.:

60

Initial conc. measured:

792.8 mg/L

Number of replicates:

2 replicates

Positive controls:

no

Negative controls:

no

Preliminary study:

The results of pH 4.0 showed no significant degradation of 4-tert-butylpyrocatechol (4-TBC) at 50 °C. According to the OECD 111, it can be concluded, that the estimated half-life time is higher than one year under representative environmental conditions (25 °C). Therefore, 4-tert-butylpyrocatechol (4-TBC) can be considered to be hydrolytically stable at pH 4.0 and no further testing was necessary at this pH-value.
The results of pH 7.0 and pH 9.0 showed degradation of 4-TBC at 50°C, so it was found to be not stable, therefore further testing was performed at elevated temperature in order to calculate the rate constant (k25) and the half-life time of the hydrolysis at pH 7.0, pH 9.0 at 25°C.

Transformation products:

no

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

At pH 7.0, the samples of the residue on the filter only show peaks of 4-TBC and the concentrations are below the smallest point of calibration for 50.0 °C and 60.0 °C. Additional peaks up to a retention time of 5 minutes could be observed for the samples of the filtrates after incubation at the several temperatures. The individual peaks could not be clearly separated and identified.

At pH 9.0, the samples of the residue on the filter showed no peaks. The samples of the filtrate showed additionally several peaks up to a retention time of about 3 minutes under these HPLC conditions.

It is likely that the degradation of the test item is not caused by hydrolysis, but by oxidation of the test item at the specific pH value. It is well-known in the specific literature that catechols can be oxidized to quinones. This is supported by the fact that a compound likely to be 4-tert butyl 1,2-benzoquinone was identified in the samples at all pH values by LC-MS.

Key result

pH:

4

Temp.:

25 °C

DT50:

> 1 yr

Type:

other: Estimation due to no observed degradation after 5 days at pH4/T 50°C.

Remarks on result:

hydrolytically stable based on preliminary test

Key result

pH:

7

Temp.:

25 °C

Hydrolysis rate constant:

0.005 h-1

DT50:

141 h

Type:

other: Estimation using Arrhenius equation

pH:

7

Temp.:

40 °C

Hydrolysis rate constant:

0.008 h-1

DT50:

84 h

Type:

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

pH:

7

Temp.:

50 °C

Hydrolysis rate constant:

0.011 h-1

DT50:

62 h

Type:

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

pH:

7

Temp.:

60 °C

Hydrolysis rate constant:

0.015 h-1

DT50:

47 h

Type:

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

pH:

9

Temp.:

40 °C

Hydrolysis rate constant:

0.008 h-1

DT50:

83 h

Type:

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

pH:

9

Temp.:

50 °C

Hydrolysis rate constant:

0.008 h-1

DT50:

84 h

Type:

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

pH:

9

Temp.:

60 °C

Hydrolysis rate constant:

0.004 h-1

DT50:

177 h

Type:

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

Details on results:

At pH 7.0, the results of the preliminary test show, that 4-tert-butylpyrocatechol (4-TBC) is not stable. The concentration of 4-TBC was decreased for each duplicate sample. The linear plots prove that the degradation is of pseudo first order in the range from 10% to 90% degradation at pH 7.0.
The reaction rate constant k for pH 7.0 was calculated by regression analysis and the half-life time at pH 7.0 and at 25°C was calculated (see table 1 below).

At pH 9.0, The results of the preliminary test show, that 4-tert-butylpyrocatechol (4-TBC) is not stable. The concentration of 4-TBC was decreased in each sample. The obtained linear plot of each sample prove that the degradation reaction is pseudo first order at 40.0 °C, 50.0 °C and 60.0 °C.
The reaction rate constant k was calculated for both temperatures by regression analysis. The individual results did not lead to a reasonable result and therefore neither the half life time nor the reaction rate constant at 25 °C could be calculated for this pH value.

Table 1: Half-life time of 4 -TBC at pH 7.0

	40.0 °C	50.0 °C	60.0 °C	25.0°C
Half life time [hours]	84	62	47	141
Half life time [days]	3.5	2.6	1.9	5.9

Table 2: Half-life time of 4 -TBC at pH 9.0

	40.0 °C	50.0 °C	60.0 °C	25.0°C
Half life time [hours]	83	84	177	Not extrapolable
Half life time [days]	3.5	3.5	7.4

Validity criteria fulfilled:

yes

Remarks:

(Recovery within the specified range of 90-110%; Analytical method repetable and sensitive enough (LOQ < 1.5% initial concentration))

Conclusions:

The test item is considered to be stable at pH 4.0. Therefore, the half-life time is longer than one year at 25 °C.
The test item is not stable at pH 7.0 and has a half-life time of 141 hours (6 days) at 25 °C.
The test item is not stable at pH 9.0. However, the half life time and the reaction rate constant could not be calculated as the results of the individual temperatures did not lead to a reasonable coherence.

Executive summary:

In a study (harlan, 2010), the hydrolysis as a function of pH was determined for 4 -tert-butylpyrocatechol (4 -TBC) according to the OECD Guideline for Testing of Chemicals, n°111 (2004). The hydrolysis preliminary test of 4 -TBC was performed at 50.0 °C ± 0.5 °C at each of pH 4.0, pH 7.0 and pH 9.0 for 5 days and sampled at 0h, 2.4h and 120h by HPLC. According to this test, 4 -TBC was found to be stable at pH 4.0 and 50 °C. Therefore no further testing was performed at this pH-value and 4 -TBC was found to be stable at pH 4.0 (t_½(25 °C) > 1 year).

4 -TBC was found to be not stable at pH 7.0 and at pH 9.0 at 50.0°C, therefore further testing was performed at elevated temperature in order to calculate the rate constant (k₂₅) and the half-life time of the hydrolysis at pH 7.0, pH 9.0 at 25°C.

The half-life time of the degradation of 4 -TBC at 25°C was calculated to be 141 hours (6 days) at pH 7.0.

4 -TBC at pH 9.0 is not stable, however the results at the individual temperatures in the main test did not lead to a reasonable coherence. Therefore, no half life time and reaction rate constant at 25 °C can be calculated.

The degradation of the test item at pH 7.0 and pH 9.0 may not caused by hydrolysis but oxidation reactions. It is well-known in the specific literature that catechols can be oxidized to quinones. This is supported by the fact that a compound likely to be 4-tert butyl 1,2-benzoquinone was identified in the samples at all pH values by LC-MS.

Description of key information

At pH 4.0, 4-tert-butylpyrocatechol (4-TBC) was found to be stable at 25°C: t 1/2 > 1 year.
At pH 7.0; the half-life time of the degradation of 4-TBC at 25°C was calculated to be 141 hours (6 days).
At pH 9.0, 4-TBC was not stable.   

Key value for chemical safety assessment

Half-life for hydrolysis:

141 h

at the temperature of:

25 °C

Additional information

One study (Harlan, 2010), scored as reliability 1 according to Klimisch and selected as key study, was performed according to OECD guideline n°111. The hydrolysis preliminary test of 4 -TBC was performed at 50°C at each of pH 4.0, 7.0 and 9.0 for 5 days. 4 -TBC was found to be stable only at pH 4.0 and 50°C. Therefore, the half-life time at pH 4.0 and 25°C was > 1 year. The half-life time of the degradation of 4 -TBC at 25°C was calculated to be 141 hours (6 days) at pH 7.0. At pH 9.0, 4 -TBC was not stable; therefore, no half-life time and reaction rate constant at 25°C can be calculated.