Pentasodium 2,2'-((2,4-diamino-5-(4-methoxy-2-sulfophenylazo)-1,3-phenylene)bis(azo))bis(5-(2-(sulfonatooxyethyl)sulfonyl)benzenesulfonate

Hydrolysis

Link to relevant study record(s)

Reference

Endpoint:

hydrolysis

Type of information:

experimental study

Adequacy of study:

key study

Study period:

From June 20, 2006 to July 17, 2006

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)

Deviations:

no

Qualifier:

according to guideline

Guideline:

OECD Guideline 111 (Hydrolysis as a Function of pH)

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Radiolabelling:

no

Analytical monitoring:

yes

Details on sampling:

Preliminary tests:
pH 4.0 and 50°C: 2.4 and 120 h
pH 7.0 and 50°C: 2.4 and 120 h
pH 9.0 and 50°C: 2.4 and 120 h

Main test:
Test 1 at pH 7.0 and 50°C: 1.3, 2.6, 4.3, 6.1, 22 and 23 h
Test 1 at pH 7.0 and 70°C: 0.3, 0.4, 0.7, 0.9, 1.3, 1.7 and 2.0 h
Test 1 at pH 7.0 and 30°C: 19, 26.3, 43, 66.2, 89.9, 97.6 and 165.3 h

Buffers:

pH 4, 7 and 9

Details on test conditions:

Preparation of the Test Samples:
Solutions of the test item were prepared by weighing about 0.39 g to 0.45 g of the test item in 50 mL volumetric flasks and dissolving the test item in the relevant buffers. This preparation was done in a glove box filled with nitrogen.

Hydrolysis Procedure:
The flasks containing the hydrolysis mixtures were placed in a thermostatically controlled water bath at the selected temperature for the specified time.

METHOD
Pretests:
- The pretests were done at 50±0.5°C with buffers at pH 4, 7 and 9.

Test 1:
- At 50±0.5°C with buffer at pH 7. At least 6 aliquots were taken between a decomposition rate of 10 and 90%.
- At 70±0.5°C with buffer at pH 7. At least 6 aliquots were taken between a decomposition rate of 10 and 90%.
- At 30±0.5°C with buffer at pH 7. At least 6 aliquots were taken between a decomposition rate of 10 and 90%.

Each sample was measured twice.

Duration:

5 d

pH:

4

Temp.:

50 °C

Initial conc. measured:

7.89 g/L

Duration:

5 d

pH:

7

Temp.:

50 °C

Initial conc. measured:

8.29 g/L

Duration:

5 d

pH:

9

Temp.:

50 °C

Initial conc. measured:

7.67 g/L

Duration:

23 h

pH:

7

Temp.:

50 °C

Initial conc. measured:

8.12 g/L

Duration:

2 h

pH:

7

Temp.:

70 °C

Initial conc. measured:

8.32 g/L

Duration:

165.3 h

pH:

7

Temp.:

30 °C

Initial conc. measured:

8.4 g/L

Number of replicates:

Preliminary Test: All experiments were run in duplicates
Main test: All experiments were run in duplicates

Positive controls:

no

Negative controls:

no

Transformation products:

not measured

pH:

4

Temp.:

50 °C

DT50:

> 120 h

Remarks on result:

other: Based on the preliminary test, the degree of hydrolysis was <10 % within 120 h

pH:

7

Temp.:

50 °C

DT50:

> 2.4 - < 120 h

Remarks on result:

other: Based on the preliminary test, the degree of hydrolysis was 21.6% at 2.4 h and >99% at 121 h.

pH:

7

Temp.:

50 °C

Hydrolysis rate constant:

0.093 h-1

DT50:

7.4 h

Type:

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

Remarks on result:

other: Correlation coefficient (r) = 0.999

pH:

7

Temp.:

70 °C

Hydrolysis rate constant:

1.05 h-1

DT50:

0.7 h

Type:

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

Remarks on result:

other: Correlation coefficient (r) = 0.999

pH:

7

Temp.:

30 °C

Hydrolysis rate constant:

0.007 h-1

DT50:

97.1 h

Type:

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

Remarks on result:

other: Correlation coefficient (r) = 0.999

pH:

7

Temp.:

25 °C

Hydrolysis rate constant:

0.003 h-1

DT50:

204 h

Remarks on result:

other: Calculated by extrapolation. Correlation coefficient (r) = 0.999

pH:

9

Temp.:

50 °C

DT50:

< 2.4 h

Remarks on result:

other: Based on the preliminary test

Details on results:

- At pH 4, less than 10% of the reaction was observed after 120 h (5 d) at 50°C (half life >1 y). Thus the test substance was considered hydrolytically stable and according to the guidelines no additional testing was required.
- The decomposition at pH 7 was below 50% after 2.4 h at 50°C and above 10% after 120 h (5 d) at 50°C. Therefore, examination of the hydrolysis kinetics was essential. For pH 7 at 25°C, the half-life was determined by extrapolation of the results of the experiments at 30, 50 and 70°C, and was found to be 204 h (8.5 d).
- At pH 9, more than 50 % of the reaction was observed after 2.4 h at 50°C. Thus the test substance was considered hydrolytically unstable and according to the guidelines no additional testing was required.

TABLE 1: PRELIMINARY TEST

 

Test conditions	Time point (h)	% hydrolysis	Comment
Test at pH 4.0 and 50°C	2.4	-	Further testing not required as the degree of hydrolysis was lower than 10% within 120 h.
	120	5.07
Test at pH 7.0 and 50°C	2.4	21.6	Further testing necessary as the degree of hydrolysis was lower than 50% within 2.4 h and higher than 10% within 120 h.
	120	>99.0
Test at pH 9.0 and 50°C	2.4	>99.0	No further testing necessary as the degree of hydrolysis was higher than 50% within 2.4 h.
	120	>99.0

 

 

 TABLE 2: MAIN TEST

 

Test conditions	Kobs	t1/2	Comment
Test 1 at pH 7.0 and 50°C	0.093 h^-1	7.4 h	Results indicated a pseudo first order reaction.
Test 1 at pH 7.0 and 70°C	1.05 h^-1	0.7 h	Results indicated a pseudo first order reaction.
Test 1 at pH 7.0 and 30°C	0.0071 h^-1	97.1 h	Results indicated a pseudo first order reaction.

 

Validity criteria fulfilled:

yes

Conclusions:

Under the conditions of the study, the half-life of the test substance at pH 7 was found to be 7.4 h, 0.7 h and 97.1 h at 50, 70 and 30°C, respectively. 
From these results, the rate constant at pH 7 and 25°C was calculated to be 0.0034 h-1, leading to a half-life of 204 h.

Executive summary:

A study was conducted to determine hydrolysis as a function of pH for the test substance according to EU Method C.7 and OECD Guideline 111, in compliance with GLP.

 

Based on the results of a preliminary test which demonstrated >50% hydrolysis within 2.4 h at pH 9.0 and <10% hydrolysis within 120 h (5 d) at pH 4.0, additional testing was only required at pH 7. Results of the main test (Test 1) at pH 7 demonstrated a pseudo first order reaction at 30, 50 and 70°C. From the results, the rate constant (K_obs) and the half-life (t_1/2) of the test substance were derived or calculated for different temperatures at pH 7.

Under the conditions of the study, the half-life of the test substance at pH 9 was <2.4 h and at pH 4 was >120 h. The half-life of the test substance at pH 7 was found to be 7.4 h, 0.7 h and 97.1 h at 50, 70 and 30°C, respectively.

From these results, the rate constant at pH 7 and 25°C was calculated to be 0.0034 h-1, leading to a half-life of 204 h.

Description of key information

The rate constant for hydrolysis at pH 7 and 25°C was calculated to be 0.0034/h, leading to a half-life of 204 h.

Key value for chemical safety assessment

Half-life for hydrolysis:

204 h

at the temperature of:

25 °C

Additional information

A study was conducted to determine hydrolysis as a function of pH for the test substance according to EU Method C.7 and OECD Guideline 111, in compliance with GLP. Based on the results of a preliminary test which demonstrated >50% hydrolysis within 2.4 h at pH 9.0 and <10% hydrolysis within 120 h (5 d) at pH 4.0, additional testing was only required at pH 7. Results of the main test (Test 1) at pH 7 demonstrated a pseudo first order reaction at 30, 50 and 70°C.From the results, the rate constant (K_obs) and the half-life (t_1/2) of the test substance were derived or calculated for different temperatures at pH 7. Under the conditions of the study, the half-life of the test substance at pH 9 was <2.4 h and at pH 4 was >120 h. The half-life of the test substance at pH 7 was found to be 7.4 h, 0.7 h and 97.1 h at 50, 70 and 30°C, respectively. From these results, the rate constant at pH 7 and 25°C was calculated to be 0.0034 h^-1, leading to a half-life of 204 h (Moller, 2006a).