2,2'-azobis[4-methoxy-2,4-dimethylvaleronitrile]

Hydrolysis

Link to relevant study record(s)

Reference

Endpoint:

hydrolysis

Type of information:

experimental study

Adequacy of study:

key study

Study period:

29.08.17-05.03.18

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)

GLP compliance:

yes (incl. QA statement)

Analytical monitoring:

yes

Buffers:

- pH: 4
- Type and final molarity of buffer:
- Composition of buffer:CH3COOH (2 M); CH3COONa; water

- pH: 7
- Type and final molarity of buffer:
- Composition of buffer:KH2PO4, NaOH (2 M); water

- pH: 9
- Type and final molarity of buffer:
- Composition of buffer:H3BO3, KCl, NaOH(2 M), water

Duration:

741 h

pH:

4

Temp.:

12 °C

Initial conc. measured:

91 mg/L

Duration:

741 h

pH:

7

Temp.:

12 °C

Initial conc. measured:

90.98 mg/L

Duration:

839 h

pH:

9

Temp.:

12 °C

Initial conc. measured:

80.92 mg/L

Duration:

768 h

pH:

4

Temp.:

25 °C

Initial conc. measured:

95.69 mg/L

Duration:

720 h

pH:

7

Temp.:

25 °C

Initial conc. measured:

94.02 mg/L

Duration:

720 h

pH:

9

Temp.:

25 °C

Initial conc. measured:

80.44 mg/L

Duration:

6 h

pH:

4

Temp.:

50 °C

Initial conc. measured:

97.84 mg/L

Duration:

6 h

pH:

7

Temp.:

50 °C

Initial conc. measured:

83.43 mg/L

Duration:

4.2 h

pH:

9

Temp.:

50 °C

Initial conc. measured:

83.84 mg/L

Number of replicates:

20

Negative controls:

yes

Remarks:

2 blanks, analysed at start and end of testing period

Preliminary study:

Complete degradation of the test item was observed at all three pH values. The test item was considered unstable and Tier 2 was triggered.

Transformation products:

not measured

% Recovery:

50

pH:

4

Temp.:

12 °C

Duration:

741 h

Remarks on result:

other: The test item appears stable over the first 332.5 h, then a drop to about 50 % of the initial con-centration occurs between 332.5 and 507.3 h. The concentration remains stable for the remain-ing duration of the test.

% Recovery:

54.8

pH:

7

Temp.:

12

Duration:

741 h

Remarks on result:

other: The test item appears stable over the first 332.5 h, then a drop to about 50 % of the initial con-centration occurs between 332.5 and 507.3 h. The concentration remains stable for the remain-ing duration of the test.

% Recovery:

56.4

pH:

9

Temp.:

12 °C

Duration:

839 h

Remarks on result:

other: The test item appears stable over the first 501.7 h, then a drop to about 50 % of the initial con-centration occurs between 501.7 and 676.6 h. The concentration remained stable for the re-maining duration of the test.

% Recovery:

17.1

pH:

4

Temp.:

25 °C

Duration:

433 h

% Recovery:

14.3

pH:

7

Temp.:

25 °C

Duration:

480 h

pH:

9

Temp.:

25 °C

Duration:

720 h

Remarks on result:

not determinable

% Recovery:

20.5

pH:

4

Temp.:

50 °C

Duration:

6 h

% Recovery:

20

pH:

7

Temp.:

50 °C

Duration:

6 h

% Recovery:

34.6

pH:

9

Temp.:

50 °C

Duration:

4.2 h

pH:

4

Temp.:

12 °C

Remarks on result:

not determinable because of methodological limitations

pH:

7

Temp.:

12 °C

Remarks on result:

not determinable because of methodological limitations

pH:

9

Temp.:

12 °C

Remarks on result:

not determinable because of methodological limitations

Key result

pH:

4

Temp.:

25 °C

Hydrolysis rate constant:

0.004 h-1

DT50:

190.7 h

Type:

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

Key result

pH:

7

Temp.:

25 °C

Hydrolysis rate constant:

0.004 h-1

DT50:

173.2 h

Type:

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

Key result

pH:

9

Temp.:

25 °C

Hydrolysis rate constant:

0.003 h-1

DT50:

253.9 h

Type:

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

pH:

4

Temp.:

50 °C

Hydrolysis rate constant:

0.237 h-1

DT50:

2.9 h

Type:

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

pH:

7

Temp.:

50 °C

Hydrolysis rate constant:

0.243 h-1

DT50:

2.9 h

Type:

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

pH:

9

Temp.:

50 °C

Hydrolysis rate constant:

0.233 h-1

DT50:

3 h

Type:

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

Validity criteria fulfilled:

yes

Conclusions:

All validity criteria regarding the analytical methods and determination of hydrolysis were met; repeatability of the values was very good, and coefficients of determination all lay
≥ 0.95 (rounded values). The measurements of the test at pH = 7 and 12 °C couldn’t be evaluat-ed because of the lack of evaluable data points during the test period.
Temperature dependency of the hydrolysis constants fits very well the ARRHENIUS equation indi-cating that the reaction is indeed following pseudo-first order pattern
At pH values 4, 7 and 9, complete degradation of the test item was observed in the preliminary study. Therefore, Tier 2 was necessary for all three pH values.
The hydrolysis mechanism is largely independent from the pH value, indicated by the finding that the half-lives determined at 25 °C and 50 °C are similar for all three tested temperatures. The test item appeared stable at 12 °C at all three tested concentrations. However, due to an apparent systematic error in the measurements, the kinetics at 12 °C was not evaluable at all three pH values.

Executive summary:

Tier 1

200 µL of a test item solution (10 g/L in methanol) were mixed with 20 mL buffer solution with pH values: 4; 7; and 9 for each individual assay. The resulting solutions with test item concentration 100 mg/L were sterile filtrated into HPLC vials, purged with sterile Argon and closed tightly immediately after preparation. The closed vials were incubated at 50 °C for a period of five days. Samples were analysed at the beginning and after incubation. The analysis of the samples using LC-MS-MS showed complete degradation of the test item at all three tested pH values.

 Results Tier 1

pH	% of start concentration after 5 days	% decrease within 5 days
4	0	100
7	0	100
9	0	100

 

 Tier 2

400 µL of a test item solution (10 g/L in methanol) were mixed with 40 mL buffer solution with pH values: 4; 7; and 9 for each individual assay. The resulting solutions with test item concentration 100 mg/L were incubated at 12, 25, and 50 °C. Sampling was performed in suitable time intervals in order to monitor the hydrolysis behaviour of the test item at the different temperatures and pH values. Two vials were sampled and analysed with LC-MS-MS at each time point.

The following hydrolysis constants were determined:

 

Results Tier 2

Temperature [°C]	pH	kobs, i ± standard deviation	Half-life t1/2[h^-1] ± standard deviation	kobstotal [h^-1]	t1/2(total) [h^-1]
50	4.0	0.237255 ± 0.018263	2.9 ± 0.2	0.713011	0.97214041
	7.0	0.004002 ± 0.001043	173.2 ± 45.1
	9.0	0.233120 ± 0.044285	3.0 ± 0.6
25	4.0	0.003635 ± 0.000831	190.7 ± 43.6	0.010367	66.8592216
	7.0	0.242637 ± 0.027085	2.9 ± 0.3
	9.0	0.002730 ± 0.001513	253.9 ± 140.7
12	4.0	n.c.	n.c.	n.c.	n.c.
	7.0	n.c.	n.c.
	9.0	n.c.	n.c.

n.c. = not calculable

 

Kinetic constants could not be evaluated at 12 °C. The test item appeared stable at all pH values, but measurements showed a systematic error (drop to measured concentration of about 50 % of the initial concentration, remaining stable after the drop).

Therefore k_obsat a temperature of 20 °C (293.15 K) was calculated using theArrheniusequation based on the results of 25 °C and 50 °C only:

k_obs(293.15 K)=                         0.004090 h^-1

t_1/2(293.15 K) =                          169.5 h

Description of key information

The substance is considered to be hydrolytically instable based on the findings in an OECD 111 guideline study. The half-life is calculated using the experimental data and the Arrhenius Equation.

Key value for chemical safety assessment

Half-life for hydrolysis:

169.5 h

at the temperature of:

25 °C