Dibutyl peroxydicarbonate

Hydrolysis

Link to relevant study record(s)

Reference

Endpoint:

hydrolysis

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2018-03-29 to 2018-04-16 (experimental phase)

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

comparable to guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 111 (Hydrolysis as a Function of pH)

Qualifier:

according to guideline

Guideline:

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

Qualifier:

according to guideline

Guideline:

EPA OPPTS 835.2120 (Hydrolysis of Parent and Degradates as a Function of pH at 25°C)

Principles of method if other than guideline:

The results on the stability of the test item versus hydrolysis are supposed to be used as arguments for tests on further physico-chemical properties, especially the water solubility. The determination of hydrolysis is performed to find whether the water solubility of the test item can be determined or not. Therefore, the determination of hydrolysis in this study is limited to a modified pre-test (Tier 1). During this modified pre-test samples of the test item are incubated at room temperature (approx. 22°C) and repeated measurements by NMR are performed. The identity of hydrolysis products is determined both by NMR spectrometry as well as by GC-MS measurements.
Assuming pseudo-first order kinetics as mentioned above the reaction rate k depends only on the pH value and the temperature. In order to determine the hydrolysis reaction, to acetonitrile-d3 solutions of the test item a defined amount of water was added and the solutions were incubated at a room temperature (approx. 22°C) without adjustment of pH. The hydrolysis results in the decrease of the test item concentration as a function of time.
The logarithms of the concentrations are plotted against time and the slope of the resulting straight line (assuming first-order or pseudo-first order behavior) gives the rate constant from the formula: kobs = - slope.

GLP compliance:

yes (incl. QA statement)

Specific details on test material used for the study:

SOURCE OF TEST MATERIAL
- Source and lot/batch No.of test material: 1252508-01
- Expiration date of the lot/batch: 04/2018
- Purity test date: CoA of Peroxan NBC-50, dated 08-Jan-2018, PERGAN GmbH

Radiolabelling:

no

Analytical monitoring:

yes

Details on sampling:

Due to the known tendency of the test item to fast hydrolysis the standard Tier 1 was not performed. To be able to show the fast hydrolysis of the test item, samples were prepared in NMR tubes and repeated measurements were performed at room temperature (approx. 22°C).

For determination of the 1H-NMR spectra of the test item prior to hydrolysis, a test solution of 21 mg of the test item in 0.6 mL of acetonitrile-d3 (with 0.2 % of tetramethylsilane for referencing) was prepared. This solution was measured directly after preparation, the resulting spectra correspond to the t=0 values.
Afterwards an amount of 100 μL of distilled water was added to this NMR tube to initialize hydrolysis. This sample was then measured subsequently over a total period of 73 min. Since, for determination of hydrolysis rate constants, the slope of the starting hydrolysis reaction is relevant, longer hydrolysis reaction times were not analyzed.

Preliminary study:

See below ''Any other information on results incl. tables'

Transformation products:

yes

Remarks:

n-Butanol could be identified as the main hydrolysis product by NMR and GC-MS. Carbon dioxide must also have formed as a complementary hydrolysis product that was not detectable by NMR and GC-MS.

No.:

#1

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

The hydrolysis process is a simple conversion from the unhydrolysed test item to one individual hydrolysis product. The reaction therefore can be seen as a hydrolysis reaction of first order. The hydrolysis product is n-butanol.

Key result

Temp.:

22 °C

Hydrolysis rate constant:

0.01 min-1

DT50:

66.6 min

Type:

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

Remarks on result:

other: The test item was dissolved in acetonitrile-d3 and water was added to start hydrolysis. Due to the need for modified testing conditions (high content of organic modifier), the test was performed without adjustment of pH.

Details on results:

The measured data showed that the test item was instable after addition of water with rapid hydrolysis starting from the preparation of the test item solutions even at 22°C. After 73 min of hydrolysis time the concentration of the unhydrolysed test item dropped below 50 %.

Results of the Preliminary Test

The measured values and calculated results of the preliminary test are summarized in the following Table 1. For calculation of half-life times and hydrolysis rate constants the 1H purities at each test point were taken into account. The initial purity of 100.00 % was used as c₀ (concentration at t=0). The concentrations of the samples are calculated as 1H purities, since the total amount of terminal methylene groups (signal 4 was used for evaluation) in the sample cannot change during hydrolysis. For this signal group a significant difference in chemical shift – depending on the chemical structure of the molecule – can be observed. While signal group 4 shows a approx. 4.45 ppm, the shift is reduced to 3.80 ppm in the hydrolysis product. As long as there is no precipitation (which was not observed), all species present in the sample will lead to a 1H-NMR signal. Measured signal intensities are molar intensities. Due to the fact that the test itemdibutyl peroxydicarbonate is expected to hydrolyse to form n-butanol, the amount of group 4 signals is supposed to be identical for both the unhydrolysed test item as well as for the hydrolysis product.

Test conditions: Temperature = approx. 22°C

Table 1. Results of the Preliminary Tests – Summary

Sample name	Time of incubation at 22°C [min]	Concentration [^1H-%]	Hydrolysed portion [%]	Result
Start value	0.00	100.00	0.00	Half-life time
Measurement 1	17.00	80.87	19.13
Measurement 2	36.00	68.79	31.21
Measurement 3	49.00	61.62	38.38	66.6 min
Measurement 4	61.00	53.55	46.45
Measurement 5	73.00	45.96	54.04

Evaluation of Hydrolysis Rate Constants and Half-Life Times

Due to the results from the preliminary test, the single measurements of the preliminary test are used for the estimation of hydrolysis rate constants as well as the half-life time of the test item at approx. 22°C.

In the following table the results from the measurement of the preliminary test are summarized, the concentrations of the test item and the calculated ln (c0/ct) values are given.

Table 2. Calculated results for the Preliminary Test at approx. 22°C

Time [min]	Concentration of Test Item [^1H-%]	ln (c0/ct)	Hydrolysis [%]
0.00	100.00	0.000000	0.00
17.00	80.87	0.212327	19.13
36.00	68.79	0.374112	31.21
49.00	61.62	0.484184	38.38
61.00	53.55	0.624554	46.45
73.00	45.96	0.777399	54.04

The slope of the linear regression was determined to be 0.01041 which directly gives the observed hydrolysis rate constant at approx. 22°C. According to the theory, only the starting slope of the reaction of pseuo-first order follows the linear correlation between c0 and ct. Therefore the measured five time points are sufficient to fully describe the hydrolysis behavior of the test item.

The calculated value for the hydrolysis rate constant at approx. 22°C is: kobs = 0.01041 [min-1] corresponding to a half-life time of t0.5 = 66.6 min (22°C)

Validity criteria fulfilled:

not specified

Conclusions:

For the given experimental set-up, the measured half-life time of the test item without pH adjustment was 66.6 min. n-Butanol could be identified as the main hydrolysis product by NMR and GC-MS.

Executive summary:

The abiotic degradation of the test item dibutyl peroxydicarbonate (50 % w/w in isododecane) was determined based on OECD-Guideline 111, European Commission Council Regulation (EC) No 440/2008, Annex, Part C, method C.7. and US EPA OCSPP 835.2120. Within this study a modified pre-test was performed to find out whether the test item is sufficiently stable in water to perform the determination of the water solubility.

Due to the known tendency of the test item to fast hydrolysis the standard Tier 1 was not performed. To be able to show the fast hydrolysis of the test item, samples were prepared in NMR tubes and repeated measurements were performed at room temperature (approx. 22°C). The test item was dissolved in acetonitrile-d3 and water was added to start hydrolysis. Due to the need for modified testing conditions (high content of organic modifier), the test was performed without adjustment of pH.

At room temperature (approx. 22°C) the test item was found to be instable upon addition of water. Hydrolysis started immediately after addition of water to the dissolved test item. The analytical determination of the t = 0 min concentration was possible prior to addition of water. The first measurement of the test item after addition of water, that was achieved after approx. 17 min of hydrolysis time (incl. measuring time), showed hydrolysis at a level of approx. 19 %. The half-life time as well as the hydrolysis rate constant at room temperature (approx. 22°C) could be estimated. For the given experimental set-up, the measured half-life time of the test item without pH adjustment was 66.6 min.

n-Butanol could be identified as the main hydrolysis product by NMR and GC-MS. Carbon dioxide must also have formed as a complementary hydrolysis product that was not detectable by NMR and GC-MS.

Description of key information

The abiotic degradation of dibutyl peroxydicarbonate (50 % w/w in isododecane) was determined based on OECD-Guideline 111, European Commission Council Regulation (EC) No 440/2008, Annex, Part C, method C.7. and US EPA OCSPP 835.2120. Within this study a modified pre-test was performed to find out whether the test item is sufficiently stable in water to perform the determination of the water solubility.

For the given experimental set-up, the measured half-life time of the test item without pH adjustment was 66.6 min. n-Butanol could be identified as the main hydrolysis product by NMR and GC-MS.

Key value for chemical safety assessment

Half-life for hydrolysis:

66.6 min

at the temperature of:

22 °C