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Hydrolysis

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Endpoint:
hydrolysis
Type of information:
experimental study
Adequacy of study:
key study
Study period:
from 1985-10-01 to 1985-10-29
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
GLP compliance:
yes
Radiolabelling:
no
Analytical monitoring:
no
Buffers:
- pH: 4, 7 , 9
- Type and final molarity of buffer: 0.05 mol/L
- Composition of buffer:
Buffer solution pH 4: Potassium in dist. water,
(C6H4 (000H) COOK) adjusted = 0.05 mol/L sodium hydroxide added to pH 4.0

Buffer solution pH 7: potassium hydroxide and water,
(KH2P04) = 0.05 mol/L, adjusted to pH 7.0 by sodium hydroxide addition

Buffer solution pH 9 boric acid in aqueous KCl solution
(KCl) = 0.05 mol/L
(H3BO3) = 0.05 mol/L,
adjusted by sodium hydroxide added to pH 9.0
Details on test conditions:
TEST SYSTEM
- Type, material and volume of test flasks, other equipment used: 100 mL flask
- Sterilisation method: yes , boiling glassware for 30 minute and after at 180 °C (in oven) for 2 hours

TEST MEDIUM
- Preparation of test medium:
c.a 0.2 ± 1g of item substance was dissolved in 100 ml of buffer (the buffers used was been at an pH = 4, pH = 7 and pH = 9).
In flasks, 10.0 mL of this latter solution were diluited to 100 ml with same buffers (pH 4, 7 and 9).
The flaskes were put in an thermostated bath and before the HPLC analisy, rapidily cooled in an iced bath.

OTHER TEST CONDITIONS
- Adjustment of pH: yes
- concentration was 0.2 ± 1 g/L, on the pure dye converted to about 0.17 g/L, or about 3 x 10^-4 mol/L.
Duration:
5 d
pH:
4
Temp.:
25 °C
Initial conc. measured:
ca. 0.2 g/L
Duration:
5 d
pH:
7
Temp.:
38 °C
Initial conc. measured:
ca. 0.2 g/L
Duration:
5 d
pH:
7
Temp.:
50 °C
Initial conc. measured:
ca. 0.2 g/L
Duration:
5 d
pH:
9
Temp.:
25 °C
Initial conc. measured:
ca. 0.2 g/L
Positive controls:
no
Negative controls:
no
Preliminary study:
The substance was unstable at pH 4 and pH 9. At pH 9 the concentration of the substance decreased to < 10 % of the initial value by 2.4 hours. At pH 4 the substance decreased its initial concentration by less than 10 % in less than 5 days.
No further tests were carried out for these pH values. For pH 7 the hydrolysis results were measured at temperatures of 38 and 50 °C.
Transformation products:
no
% Recovery:
ca. 98.5
pH:
4
Temp.:
25 °C
Duration:
ca. 2.4 h
% Recovery:
ca. 98
pH:
4
Temp.:
25 °C
Duration:
ca. 5 d
% Recovery:
ca. 70
pH:
7
Temp.:
25 °C
Duration:
ca. 2.4 h
% Recovery:
< 1
pH:
7
Temp.:
25 °C
Duration:
ca. 5 d
% Recovery:
< 1
pH:
9
Temp.:
25 °C
Duration:
ca. 2.4 h
% Recovery:
< 1
pH:
9
Temp.:
25 °C
Duration:
ca. 5 d
pH:
7
Temp.:
50 °C
Hydrolysis rate constant:
0.116 h-1
DT50:
6 h
Type:
(pseudo-)first order (= half-life)
pH:
7
Temp.:
38 °C
Hydrolysis rate constant:
0.027 h-1
DT50:
25.7 h
Type:
(pseudo-)first order (= half-life)
Key result
pH:
7
Temp.:
25 °C
Hydrolysis rate constant:
0.005 h-1
DT50:
6 d
Type:
(pseudo-)first order (= half-life)
Remarks on result:
other: A=5284; B=15.4
pH:
4
Temp.:
25 °C
DT50:
> 1 yr
pH:
9
Temp.:
25 °C
DT50:
< 1 d
Details on results:
TEST CONDITIONS
- pH, sterility, temperature, and other experimental conditions maintained throughout the study: yes
- Anomalies or problems encountered: no

MAJOR TRANSFORMATION PRODUCTS
No determined

MINOR TRANSFORMATION PRODUCTS
No determined

MINERALISATION
No determined

INDICATION OF UNSTABLE TRANSFORMATION PRODUCTS:
No

VOLATILIZATION (at end of study)
No

UNIDENTIFIED RADIOACTIVITY
No

Results with reference substance:
No results with reference substance were determined.

log K= -A/T + B

A= 5284

B=15.4

Kobs= 0.0049 h^-1

t1/2(ph7) at 25°C ~ 6 d

test 1 (50°C, pH=7)

time c (0) c (t) c(t)/c(0)  - Log c(t)/c(0)
2 0.2001 0.1583 0.7909 0.1019
3 0.2001 0.1413 0.7062 0.1511
4 0.2001 0.1261 0.6304 0.2004
6 0.2001 0.1007 0.5035 0.298
8 0.2001 0.079 0.3949 0.4035

test 3 (38°C, pH=7)

time c (0) c (t) c(t)/c(0)  -Log c(t)/c(0)
1.33 0.201 0.192 0.9551 0.01995
21 0.2 0.1136 0.5681 0.2455
24 0.2006 0.1034 0.5155 0.2878
27 0.2006 0.0968 0.4825 0.3165
31 0.2006 0.0877 0.437 0.3595
Validity criteria fulfilled:
yes
Conclusions:
Based on results of the hydrolysis study, the half life at 25 °C is > 1 year, 6 days, and < 1 day at pH 4, 7, and 9, respectively.
Executive summary:

The structural analogue 01 as lithium salt was tested by EU method C.7 'Hydrolysis as function of pH' at ph 4, 7 and 9. Based on results of a preliminary study, the half-life at pH 4 and 9 is estimated to be one year and maximum one day, respectively. At pH 7 (measured at at 38 and 50°C) the hydrolysis showed a pseudo-first order curve. The half life at 25°C was calculated to be 6 days (Bartsch 1985).

Endpoint:
hydrolysis
Type of information:
experimental study
Adequacy of study:
supporting study
Study period:
1989
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
Radiolabelling:
no
Analytical monitoring:
yes
Details on sampling:
Sample storage conditions before analysis: inert gas atmosphere; at the dark; the period from dissolution up to the testing at thermostated temeprature was kept as short as possible
Buffers:
- pH: 4, 7, 9
- Composition of buffer:
pH4: potassium hydrogene phthtalate in water; adjustment of the pH by sodium hydroxide
pH7: monopotassium dihydrogene phosphate in water; adjustment of the pH by sodium hydroxide
pH9: boric acid in aqueous potassium chloride solution; adjustment of the pH with sodium hydroxide
Estimation method (if used):
not applicable
Duration:
19 d
pH:
4
Temp.:
60 °C
Initial conc. measured:
209.8 mg/L
Duration:
168 h
pH:
4
Temp.:
70 °C
Initial conc. measured:
211 mg/L
Duration:
71 h
pH:
4
Temp.:
80 °C
Initial conc. measured:
230 mg/L
Duration:
52 h
pH:
7
Temp.:
25 °C
Initial conc. measured:
221 mg/L
Duration:
60 min
pH:
9
Temp.:
20 °C
Initial conc. measured:
226 mg/L
Positive controls:
no
Negative controls:
no
Preliminary study:
at 50°C after 2.4h the following results were observed:
pH4: 1.7% degradation
pH7: 98.9% degradation
pH9: > 99% degradation
at 50°C and pH 4 after 5 d a degradation of 10% was observed
Transformation products:
yes
No.:
#1
No.:
#2
No.:
#2
No.:
#3
Details on hydrolysis and appearance of transformation product(s):
#1: retention time in HPLC: 11.4 minutes: after 2.4 h 75% at 50°C and pH7
#2: retention time in HPLC of both isomers: 8.6 min;
#3: retention time in HPLC: 8.2 min
% Recovery:
33.5
pH:
4
Temp.:
80 °C
Duration:
71.5 h
% Recovery:
42.3
pH:
4
Temp.:
70 °C
Duration:
168 h
% Recovery:
48
pH:
4
Temp.:
60 °C
Duration:
18.98 d
% Recovery:
41.7
pH:
7
Temp.:
25 °C
Duration:
51.9 h
% Recovery:
45.3
pH:
9
Temp.:
20 °C
Duration:
60 min
pH:
4
Temp.:
25 °C
Hydrolysis rate constant:
0 d-1
DT50:
258.5 wk
pH:
7
Temp.:
25 °C
Hydrolysis rate constant:
0.02 d-1
DT50:
> 1 - < 2 d
pH:
9
Temp.:
20 °C
Hydrolysis rate constant:
0.01 min-1
DT50:
48 min
Details on results:
The test substance was determined to be hydrolytically unstable at pH 7 and 9 and hydrolytically stable at pH 4. The t1/2 was determined to be 258.5 weeks at pH4 and 25 °C, 1.9 days at pH7 and 25 °C and 48 minutes at pH9 and 20 °C.
Results with reference substance:
No results with reference substance were determined.
Validity criteria fulfilled:
yes
Conclusions:
Hydrolytically unstable at pH 7 and 9; hydrlotically stable at pH 4. The t1/2 was determined to be 258.5 weeks at pH4 and 25 °C, 1.9 days at pH7 and 25 °C and 48 minutes at pH9 and 20 °C.
Executive summary:

Overall results:

pH

T [°C]

k=<

t1/2

4

25

0.0004 1/d

258.5 weeks

7

25

0.0152 1/d

1.9 days

9

20

0.0146 1/min

48 minutes

 

Description of key information

Based on results of the hydrolysis study, the half life at 25°C is estimated to be > 1 year, 6 days, and < 1 day at pH 4, 7, and 9, respectively.

Key value for chemical safety assessment

Half-life for hydrolysis:
6 d
at the temperature of:
25 °C

Additional information

The structural analogue 01 as lithium salt was tested by EU method C.7 'Hydrolysis as function of pH' at ph 4, 7 and 9. Based on results of a preliminary study, the half-life at pH 4 and 9 is estimated to be one year and maximum one day, respectively. At pH 7 (measured at 38 and 50°C) the hydrolysis showed a pseudo-first order curve. The half-life at 25°C was calculated to be 6 days (Bartsch 1985)

In the preliminary experiments with structural analogue 03 at pH 7 and 50°C, was observed that in 2.4 hours the presence of the vinyl branch "[[4-[[2-(sulphonatooxy)ethyl]sulphonyl]phenyl]azo]" were less than 1%. (Appel 1989) This part of molecule is identical to Reactive Orange 72/78. It is reasonable to suppose that the reaction is the same for Reactive Orange 72/78.