2,2'-azobis[2-methylbutyronitrile]

Hydrolysis

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

hydrolysis

Type of information:

read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

weight of evidence

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: see 'Remark'

Remarks:

This study was selected as the key study because the information provided for the hazard endpoint is sufficient for the purpose of classification and labeling and/or risk assessment. This study is used for read-across and therefore has been assigned a reliability of 2 (reliable with restrictions). Otherwise the study has a reliability of 1 (reliable without restriction). Conducted according to appropriate OECD Guideline. Meets generally accepted scientific principles, acceptable for assessment.

Justification for type of information:

see 13.2 for attached read across rationale

Reason / purpose for cross-reference:

read-across source

Qualifier:

according to guideline

Guideline:

OECD Guideline 111 (Hydrolysis as a Function of pH)

Deviations:

not specified

GLP compliance:

yes

Specific details on test material used for the study:

Details on properties of test surrogate or analogue material:
PHYSICO-CHEMICAL PROPERTIES
- Vapour pressure: 0.81 Pa
- Water solubility: 350 mg/L at 25 ±1°C

Radiolabelling:

not specified

Analytical monitoring:

not specified

Details on sampling:

No details provided

Buffers:

- pH: 4, 7 and 9
- Type and final molarity of buffer: Not reported
- Composition of buffer: Not reported

Details on test conditions:

TEST SYSTEM
- Type, material and volume of test flasks, other equipment used: Glass flask with a stopper
No other details supplied

Number of replicates:

2

Positive controls:

not specified

Negative controls:

not specified

Statistical methods:

No details of any statistical analysis

Preliminary study:

No data

Test performance:

No data

Transformation products:

not specified

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

- Formation and decline of each transformation product during test: No details supplied

pH:

4

Temp.:

25 °C

Hydrolysis rate constant:

0 h-1

DT50:

263 d

Type:

not specified

Remarks on result:

other: Actual rate constant is 1.08 x 10-4 per hour

pH:

7

Temp.:

25 °C

Hydrolysis rate constant:

0 h-1

DT50:

304 d

Type:

not specified

Remarks on result:

other: Actual rate constant is 9.50 x 10-5 per hour

pH:

9

Temp.:

25 °C

Hydrolysis rate constant:

0 h-1

DT50:

210 d

Type:

not specified

Remarks on result:

other: Actual rate constant is 1.38 x 10-4 per hour

Details on results:

TEST CONDITIONS No details provided

The rate constants and half-lives of the test substance determined at 25°C were as follows:

 

pH	Rate constant (hours^-1)	Half-life (days)
4	1.08 x 10^-4	263
7	9.50 x 10^-5	304
9	1.38 x 10^-4	210

 

Validity criteria fulfilled:

yes

Conclusions:

This study and the conclusions which are drawn from it fulfill the quality criteria (validity, reliability, repeatability).
The rate constant and half-lives of the test substance at different pH was as follows:
1.08E-4 and half life of 263 days at pH 4; 9.50E-5 and half life of 304 days at pH 7; 1.38E-4 and half life of 210 days at pH 9

Executive summary:

Determination of the physicochemical properties of azobis(cyanoisopropyl) also known as 2,2’-Azobis (isobutyronitrile), was conducted at Kurume Research Laboratories, which included the test for hydrolysis as a function of pH. The test was conducted according to OECD Guideline 111 at temperature of 60±1°C, 70±1°C and 80±1°C and extrapolated to 25°C. The results were as follows: Rate constant 1.08x 10-4 and half life of 263 days at pH 4; Rate constant 9.50x10-5 and half life of 304 days at pH 7; and Rate constant 1.38x10-4 and half life of 210 days at pH 9.

On this basis azobis(cyanoisopropyl) can be considered as a stable substance not subject to hydrolysis.

Reference 2

Endpoint:

hydrolysis

Type of information:

experimental study

Adequacy of study:

weight of evidence

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: GLP study according to protocol.

Qualifier:

according to guideline

Guideline:

OECD Guideline 111 (Hydrolysis as a Function of pH)

Deviations:

yes

Remarks:

No thymol was added to the buffer solutions; A test temperature of 25°C was used; only tier 1 of the guideline was conducted

GLP compliance:

yes (incl. QA statement)

Radiolabelling:

no

Analytical monitoring:

yes

Details on sampling:

An amount of stock solution was spiked to a 100 mL volumetric flask and filled up with the respective buffer solutions, resulting in an initial concentration of 20 mg/L. Subsequently about 10 mL of the spiked buffer solutions was transferred to multiple sterile glass test vials. The vials were closed tightly and placed in a thermostatically controlled water bath in the dark at a temperature of 25 ± 0.5°C. At the moment the test vials were placed in the water bath, the first sample was taken and analyzed using the analytical method described in Annex 3. 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:

Buffer solutions of the different pH values were prepared according to the buffer systems of CLARK and LUBS as described in Annex 3 of OECD 111 (OECD, 2004).

Details on test conditions:

Screening experiment (Tier 1):
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 (OECD, 2004) and purged with nitrogen for at least 5 minutes. A stock solution with a test substance concentration of approximately 3 g/L was prepared in acetonitrile. An amount of stock solution was spiked to a 100 mL volumetric flask and filled up with the respective buffer solutions, resulting in an initial concentration of 20 mg/L. Subsequently about 10 mL of the spiked buffer solutions was transferred to multiple sterile glass test vials. The vials were closed tightly and placed in a thermostatically controlled water bath in the dark at a temperature of 25 ± 0.5°C.

Additional experiment:
A sterile buffer solution of pH 1.2 was prepared in a glass bottle according to the description in Annex 3 of OECD 111 (OECD, 2004) and purged with nitrogen for at least 5 minutes. A stock solution with a test substance concentration of approximately 2.5 g/L was prepared in acetonitrile. An amount of stock solution was spiked to a 100 mL volumetric flask and filled up with the pH 1.2 buffer solution, resulting in an initial concentration of 20 mg/L. Subsequently about 10 mL of the spiked buffer solution was transferred to multiple 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. Same procedure was followed as described above for sampling of the test and pH measurement of the buffer solution.

Duration:

5 d

pH:

4

Temp.:

25

Initial conc. measured:

14.7 mg/L

Duration:

5 d

pH:

7

Temp.:

25

Initial conc. measured:

20 mg/L

Duration:

5 d

pH:

9

Temp.:

25

Initial conc. measured:

20.3 mg/L

Duration:

6 h

pH:

1.2

Temp.:

37

Initial conc. measured:

20.5 mg/L

Number of replicates:

singlefold

Statistical methods:

No statistics have been performed

Preliminary study:

The test substance showed less than 10% hydrolysis after 5 days for all tested pH values, i.e. pH, 4, 7 and 9. Based on these results the test substance is considered to be hydrolytically stable. The additional test at pH 1.2 showed also less than 10% hydrolysis, after 6 hours. Therefore, the test substance is considered to be hydrolytically stable at this pH as well.

Transformation products:

not measured

Remarks on result:

other: see Remarks

Remarks:

preliminary study indicates that the substance is hydrolytically stable and no further study was performed

Details on results:

pH 4
The pH value at the start of the test was measured to be 4.0. The temperature during the test varied between 24.9 and 25.0°C. A maximum of 4.0 % hydrolysis of the test substance was reached during the 5 days test. Because less than 10% hydrolysis was observed during the test, no accurate Arrhenius relationship could be calculated.

pH 7
The pH value at the start of the test was measured to be 7.0. The temperature during the test varied between 24.8 and 25.0°C. A maximum of 2.7 % hydrolysis of the test substance was reached during the 5 days test. Because less than 10% hydrolysis was observed during the test, no accurate Arrhenius relationship could be calculated.

pH 9
The pH value at the start of the test was measured to be 9.0. The temperature during the test varied between 24.9 and 25.0°C. A maximum of 2.1 % hydrolysis of the test substance was reached during the 5 days test. Because less than 10% hydrolysis was observed during the test, no accurate Arrhenius relationship could be calculated.

pH 1.2
The pH value at the start of the test was measured to be 1.2. The temperature throughout the test was measured to be 37.0°C. No hydrolysis was observed after 6 hours. Because no hydrolysis occurred during the test, no Arrhenius relationship could be calculated.

Validity criteria fulfilled:

yes

Conclusions:

For all pH values tested less than 10 % hydrolysis was observed. Based on these results the test substance is considered to be hydrolytically stable and will be reported as half-life > 1 year.

Executive summary:

The purpose of this study was to determine if 2,2’azobis[2-methylbutyronitrile] would hydrolyze at environmentally and physiologically relevant pH values, complying with OECD Guideline No. 111.

The test substance showed less than 10% hydrolysis after 5 days for all tested pH values, i.e. pH, 4, 7 and 9. Based on these results the test substance is considered to be hydrolytically stable. The additional test at pH 1.2 showed also less than 10% hydrolysis, after 6 hours. Therefore, the test substance is considered to be hydrolytically stable at this pH as well.

Description of key information

Stable; not subject to hydrolysis

Key value for chemical safety assessment

Half-life for hydrolysis:

210 d

at the temperature of:

25 °C

Additional information

No full hydrolysis study with the test substance is available, only a screening study demonstrating hydrolytic stability. A hydrolysis study with 2,2’-azobis(isobutyronitrile) was also used as weight of evidence to fulfill the data gap for the test substance.The underlying hypothesis for the read-across is that based on the structural and functional group similarity, the presence of the nitrile group in both substances is likely driving any hydrolysis. Additional documentation, provided within the IUCLID Assessment Reports section, supports the read-across approach.  

A hydrolysis study following OECD Guideline 111 was performed with 2,2’-azobis(isobutyronitrile). The half-life is 263 days at pH 4, 304 days at pH 7, and 210 days at pH 9. 

 

A GLP screening hydrolysis study with 2,2’-azobis[2-methylbutyronitrile] was conducted at environmentally relevant pH levels and 25 °C to support this read across. After 5 days at all pH levels less than 10% hydrolysis was observed, showing that this substance is hydrolytically stable and reacts similar to 2,2’-azobis(isobutyronitrile) with water.