dimethyl 1,2-benzenedicarboxylate;reaction mass of: 1,2-dimethylpropylidene dihydroperoxide

Hydrolysis

Link to relevant study record(s)

Reference

Endpoint:

hydrolysis

Type of information:

experimental study

Adequacy of study:

key study

Study period:

26 June 2002 - 16 August 2002

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

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

GLP compliance:

yes

Radiolabelling:

no

Analytical monitoring:

yes

Details on sampling:

- Sampling intervals for the parent/transformation products: peliminary test: 0h, 2.4h and 5 days.
- Sampling method:No data
- Sampling methods for the volatile compounds, if any: NA
- Sampling intervals/times for pH measurements: For each test solution, the pH value at room temperature was determined at the beginning and
at the end of each test.
- Sampling intervals/times for sterility check:NA
- Sample storage conditions before analysis: The samples taken at t>0 were cooled to room temperature by running tap-water immediately after sampling. Thereafter, each sample was diluted with acetonitrile in a 1:1 ratio to obtain concentrations within the calibration range and analysed.
- Other observation, if any (e.g.: precipitation, color change etc.): None

Buffers:

A sterile 0.05 M acetate buffer pH 4: sodium acetate/acetic acid/Milli-Q water.
A sterile 0.05 M phosphate buffer pH 7: potassium dihydrogen phosphate/ sodium hydroxide/Milli-Q water.
A sterile 0.05 M borate buffer pH 9: boric acid/potassium chloride/sodium hydroxide/Milli-Q water.

Details on test conditions:

TEST SYSTEM
- Type, material and volume of test flasks, other equipment used: EC C.7
- Sterilisation method: Prior to the start of each test, the test solutions were freshly prepared. For the preparation of the test solutions, 50 ml of each buffer solution (pH 4, pH 7 or pH 9) was filter-sterilised through a 0.2 µm membrane filter (FP 30/0.2 CA-S, Schleicher & Schuell, Dassel, Germany) and transferred into sterile glass vessels.
- Lighting: in the dark
- Measures taken to avoid photolytic effects:
- Measures to exclude oxygen: To exclude oxygen, nitrogen gas was bubbled through each solution for 5 minutes. Each vessel was tightly sealed with a septum-crimpcap.

TEST MEDIUM
- Volume used/treatment: 500 µl of a 23.6 g/l solution of the test substance in acetonitrile was added to each of the sterile buffer solutions.
- Kind and purity of water: MilliQ
- Preparation of test medium: see above
- Renewal of test solution: none
- Identity and concentration of co-solvent: acetonitrile

Number of replicates:

single samples, duplicate analysis

Positive controls:

no

Negative controls:

no

Statistical methods:

None

Preliminary study:

MIPK is a degradation product of the other compounds present in the formulation. Therefore it was not possible to determine the hydrolysis of this component.
At pH 9 for MIPKP-T4, a decrease in concentration < 10% was observed after 5 days (half-life time at 25°C> 1 year). Therefore, no further testing was necessary at pH 9 for MIPKP-T4.
At pH 4 (for MIPKP-T3 and MIPKP-T4), pH 7 (for MIPKP-T3 and MIPKP-T4) and pH 9 (for MIPKP-T3), a decrease in concentration < 50% after 2.4 hours but> 10% after 5 days was observed. In order to determine if hydrolysis of MIPKP is a pseudo-first order reaction and to determine the half-life time at 25°C, subsequent tests were performed at these pH values and for these compounds.

Test performance:

The analytical results of the subsequent hydrolysis tests are summarised in the attached Tables. No test substance was measured in the blank buffer solutions.

Transformation products:

not measured

pH:

4

Temp.:

25 °C

DT50:

411 h

Type:

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

Remarks on result:

other: for MIPKP-T4

pH:

7

Temp.:

25 °C

DT50:

7 943 h

Type:

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

Remarks on result:

other: for MIPKP-T4

pH:

4

Temp.:

25 °C

DT50:

145 h

Type:

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

Remarks on result:

other: for MIPKP-T3 peak 1

pH:

7

Temp.:

25 °C

DT50:

1 438 h

Type:

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

Remarks on result:

other: for MIPKP-T3 peak 1

pH:

9

Temp.:

25 °C

DT50:

147 h

Type:

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

Remarks on result:

other: for MIPKP-T3 peak 1

pH:

4

Temp.:

25 °C

DT50:

98.8 h

Type:

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

Remarks on result:

other: for MIPKP-T3 peak 2

pH:

7

Temp.:

25 °C

DT50:

1 221 h

Type:

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

Remarks on result:

other: for MIPKP-T3 peak 2

pH:

9

Temp.:

25 °C

DT50:

61.1 h

Type:

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

Remarks on result:

other: for MIPKP-T3 peak 2

Other kinetic parameters:

Testing of pseudo-first order kinetics
For the test solutions at pH 4 (for MIPKP-T3 and MIPKP-T4), pH 7 (for MIPKP-T3 and MIPKP-T4) and pH 9 (for MIPKP-T3), the plots of the logarithms of the relative concentrations between 80% and 30% (i.e. between 20% and 70% hydrolysis) against time were straight lines. Therefore, the reactions at pH 4, pH 7 and pH 9 are considered to be (pseudo)-first order. Hence, the half-life times at 25°C were estimated in a subsequent test.

Determination of the half life at 25 °C
The logarithms of all relative concentrations were plotted against time and a linear regression program (least-squares method) was used to calculate the regression line, see attached tables.
The half-life time for MIPKP-T4 at 25°C is 411 and 7943 hours in aqueous solutions buffered at pH 4 and pH 7 respectively.
The half-life time for MIPKP-T3 peak 1 at 25°C is 145, 1438 and 147 hours in aqueous solutions buffered at pH 4, pH 7 and pH 9 respectively.
The half-life time for MIPKP-T3 peak 2 at 25°C is 98.8, 1221 and 61.1 hours in aqueous solutions buffered at pH 4, pH 7 and pH 9 respectively.

Details on results:

See attached Tables.

Validity criteria fulfilled:

yes

Conclusions:

MIPKP-T4 is hydrolytically stable (half-life time at 25°C> 1 year) in aqueous solutions buffered at pH 9.
The half-life time for MIPKP-T4 at 25°C is 411 and 7943 hours in aqueous solutions buffered at pH 4 and pH 7 respectively.
The half-life time for MIPKP-T3 peak 1 at 25°C is 145, 1438 and 147 hours in aqueous solutions buffered at pH 4, pH 7 and pH 9 respectively.
The half-life time for MIPKP-T3 peak 2 at 25°C is 98.8, 1221 and 61.1 hours in aqueous solutions buffered at pH 4, pH 7 and pH 9 respectively.

Executive summary:

The determination of the hydrolysis rate of the test substance as a function of pH was based on the EEC-Directive 92/69 EEC, Part C, Methods for the determination of Ecotoxicity, C.7: "Abiotic degradation: Hydrolysis as a function of pH", EEC Publication no. L383, December 1992.

According to information supplied by the sponsor, the substance is a formulation containing several components (see the certificate of analysis). Measurements were performed on the following components: MIPK, MIPKP-T4 and MIPKP-T3 (peak 1 and peak 2). Due to the fact that DMP, which was used for preparation of this formulation, is a very well known compound, which cannot be determined in the same chromatographic run as the other compounds due to a large difference in sensitivity (see also Notox Project 338805 "Development and validation of an analytical method for Trigonox R-938"), analyses were not based on this compound. Due to an interfering peak in blank buffer solutions at the retention time of Hydrogen peroxide it was not possible to determine the hydrolysis of this component. Hydrogen peroxide is a very well known compound and therefore this was not considered to have an effect on this study.

MIPK is a degradation product of the other compounds present in the formulation. Therefore it was not possible to determine the hydrolysis of this component.

MIPKP-T4 is hydrolytically stable (half-life time at 25°C> 1 year) in aqueous solutions buffered at pH 9.

The half-life time for MIPKP-T4 at 25°C is 411 and 7943 hours in aqueous solutions buffered at pH 4 and pH 7 respectively.

The half-life time for MIPKP-T3 peak 1 at 25°C is 145, 1438 and 147 hours in aqueous solutions buffered at pH 4, pH 7 and pH 9 respectively.

The half-life time for MIPKP-T3 peak 2 at 25°C is 98.8, 1221 and 61.1 hours in aqueous solutions buffered at pH 4, pH 7 and pH 9 respectively.

Description of key information

MIPKP-T4 is hydrolytically stable (half-life time at 25°C> 1 year) in aqueous solutions buffered at pH 9.

The half-life time for MIPKP-T4 at 25°C is 411 and 7943 hours in aqueous solutions buffered at pH 4 and pH 7 respectively.

The half-life time for MIPKP-T3 peak 1 at 25°C is 145, 1438 and 147 hours in aqueous solutions buffered at pH 4, pH 7 and pH 9 respectively.

The half-life time for MIPKP-T3 peak 2 at 25°C is 98.8, 1221 and 61.1 hours in aqueous solutions buffered at pH 4, pH 7 and pH 9 respectively.