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Hydrolysis

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Reference
Endpoint:
hydrolysis
Type of information:
experimental study
Adequacy of study:
key study
Study period:
February 9, 2005
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Remarks:
According to EU Method C.7, with GLP.
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:
yes
Details on sampling:
- Sampling intervals for the parent/transformation products: the concentrations of the 3 main components MMAC2, MAC3 and MM2AC of the test substance were determined at the earliest possible time, i.e. 0.75 h after the start of the dissolution. Later sampling times were not required as the concentrations were already below the limit of quantification at 0.75 h.
Buffers:
Buffer pH 4:
- pH (actual pH preliminary test): 4.0
- Composition of buffer: 250 ml 0.1 mol/l potassium dihydrogencitrate (Fluka; lot. No. 364546/1) and 45 mL 0.1 mol/l sodium hydroxide (Titrisol; Merck, Lot. No. OC489094) filled up to 500 ml with water.

Buffer pH 7:
- pH (actual pH preliminary test): 7.0
- Composition of buffer: 250 ml 0.1 mol/l potassium dihydrogenphosphate (Merck, lot. No. A531473427) and 148.2 ml 0.1 mol/l sodium hydroxide filled up to 500 ml with water.

Buffer pH 9:
- pH (actual pH preliminary test): 9.0
- Composition of buffer: 250 ml 0.1 mol/l boric acid (Merck, lot. No. K20380665) in 0.1 mol/l potassium chloride (Merck, lot. No. K31517236313) and 106.5 ml 0.1 mol/l sodium hydroxide filled up to 500 ml with water.

The water (for analysis; Merck; lot. No. OC409681 was autoclaved before use.
Details on test conditions:
Preparation of the test medium:

The hydrolysis assay should be performed with a concentration of the test substance of ca. 50 % saturation. The water solubility of the test substance could not be determined, because of the rapid hydrolysis. A concentration of nominally 50 mg test substance per litre was selected, as this concentration is within the range of the calculated results and as a clear solution (checked by eye) was obtained.

Solutions of the test substance were prepared by dissolving 24.9, 24.1 and 24.5 mg respectively of the test substance in 100 mL of the appropriate buffers and 400 mL water (for analysis, Merck, Lot No. OC522462), using ultrasonication. Afterwards nitrogen was bubbled through each solution to expel oxygen. The solutions were kept for fifteen minutes in a water bath (DL 30 V26 1, accuracy ± 0.01 °C; Haake, Karlsruhe, Germany) at 25.0 °C in the dark.
Duration:
0.75 h
pH:
4.01
Temp.:
25 °C
Remarks:
See details below
Duration:
0.75 h
pH:
6.99
Temp.:
25 °C
Remarks:
See details below
Duration:
0.75 h
pH:
8.98
Temp.:
25 °C
Remarks:
See details below
Number of replicates:
There were no replicates.
Positive controls:
no
Negative controls:
no
Preliminary study:
The preliminary test indicated that the half-lives of the 3 main components MMAC2, MAC3 and MM2AC of the test substance at 25 °C and at pH 4, pH 7 and pH 9 were shorter than 1 hour in each case. Therefore the test substance is considered to be easily hydrolysable and no main test was performed, according to the guideline.
Test performance:
The concentrations of the 3 main components of the test substance were determined at the earliest possible time, i.e. 0.75 h after the start of the dissolution. Later sampling times were not required as the concentrations were already below the limit of quantification at 0.75 h.
Transformation products:
no
Details on hydrolysis and appearance of transformation product(s):
The test substance is composed of several compounds, including the 3 main components MMAC2, MAC3 and MM2AC. They polymerise, triggered by hydrolysis.
Key result
pH:
4
Temp.:
25 °C
Hydrolysis rate constant:
> 1 h-1
DT50:
< 1 h
Type:
(pseudo-)first order (= half-life)
Remarks on result:
other: (for the 3 main components)
Key result
pH:
7
Temp.:
25 °C
Hydrolysis rate constant:
> 1 h-1
DT50:
< 1 h
Type:
(pseudo-)first order (= half-life)
Remarks on result:
other: (for the 3 main components)
Key result
pH:
9
Temp.:
25 °C
Hydrolysis rate constant:
> 1 h-1
DT50:
< 1 h
Type:
(pseudo-)first order (= half-life)
Remarks on result:
other: (for the 3 main components)
Other kinetic parameters:
No kinetic of the hydrolysis could be determined because of the slow dissolution of the test substance and the fast hydrolysis.

Rate constants of hydrolysis and half life times (for the 3 main components):

pH

temperature (°C)

rate constant (h-1)

rate constant (s-1)

half life (h)

4

25

>1

>0.0003

<1

7

25

>1

>0.0003

<1

9

25

>1

>0.0003

<1

Results of the hydrolysis at 25 °C, pH = 4 (preliminary test):

MM2AC:

time of exposure [h]

pH

concentration
[mg/L]

decrease of the initial concentr. [%]

0

4.01

5.83 *

/

0.75

4.01

< 0.47 **

>90

MMAC2:

time of exposure [h]

pH

concentration
[mg/L]

decrease of the initial concentr. [%]

0

4.01

27.39 *

/

0.75

4.01

< 11.1 **

>55

MAC3:

time of exposure [h]

pH

concentration
[mg/L]

decrease of the initial concentr. [%]

0

4.01

11.95 *

/

0.75

4.01

< 4.8 **

>55

Results of the hydrolysis at 25 °C, pH = 7 (preliminary test):

MM2AC:

time of exposure [h]

pH

concentration
[mg/L]

decrease of the initial concentr. [%]

0

6.99

5.64 *

/

0.75

6.99

< 0.47 **

>90

MM2AC:

time of exposure [h]

pH

concentration
[mg/L]

decrease of the initial concentr. [%]

0

6.99

26.5 *

/

0.75

6.99

< 11.1 **

>55

MM2AC:

time of exposure [h]

pH

concentration
[mg/L]

decrease of the initial concentr. [%]

0

6.99

11.57 *

/

0.75

6.99

< 4.8 **

>55

Results of the hydrolysis at 25 °C, pH = 9 (preliminary test):

MM2AC:

time of exposure [h]

pH

concentration
[mg/L]

decrease of the initial concentr. [%]

0

8.98

5.76 *

/

0.75

8.98

< 0.47 **

>90

MM2AC:

time of exposure [h]

pH

concentration
[mg/L]

decrease of the initial concentr. [%]

0

6.99

27.06 *

/

0.75

6.99

< 11.1 **

>55

MM2AC:

time of exposure [h]

pH

concentration
[mg/L]

decrease of the initial concentr. [%]

0

6.99

11.81 *

/

0.75

6.99

< 4.83 **

>55

* Concentration calculated from the nominal initial concentration of the test substance and the content of the component.

** Below the limit of quantification.

Validity criteria fulfilled:
yes
Conclusions:
The concentrations of the tree main components were below the limit of quantification (1.04 mg/mL) at 0.75 h after starting the dissolution of the test substance. More than 50 % of this component at pH 4, pH 7 and pH 9 hydrolysed in less than 1 hour at 25 °C. Therefore, the half-life of the test substance Wasox-MMAC2 was determined to be < 1 h.
Executive summary:

The hydrolysis as a function of pH study was carried out for the test substance Wasox-MMAC2 according to EU Method C.7. This test material is composed of several compounds, including the 3 main components MMAC2 (Propan-2-one-O,O'-(methoxymethylsilandiyl) dioxime), MAC3 (Propan-2-one-O,O',O''-(methylsilantriyl)trioxime) and MM2AC (Propan-2-one-O-(dimethoxymethylsilyl)oxime). They polymerise, triggered by hydrolysis. The rate constants of the 3 main components were determined at pH 4, pH 7 and pH 9. Due to the predicted instability of the test substance, communicated by the sponsor, the test was performed at 25°C and not at 50°C as described in the guideline for the "preliminary test". No "main test" was performed in agreement with the guideline, as the half-life time was < 1 h in each case. The test substance dissolved slowly in water, and the hydrolysis was fast, therefore the concentration was determined only at one time (0.75 h) after the start of the dissolution. The chemical analysis was performed by gaschromatography. Each of the analysed concentrations was below the limit of quantification at 0.75 h after starting the dissolution of the test substance. More than 50 % of the main component of the main components at pH 4, pH 7 and pH 9 hydrolysed in less than 1 hour at 25°C. Therefore, the substance is easily hydrolysable at test conditions and its half-life was determined to be < 1 h under test conditions.

 

Description of key information

Key study: EU Method C.7 and GLP. The half-life of test item Wasox-MMAC2's components MMAC2, MAC3 and MM2AC were <1h at pH 4, pH 7 and pH 9 hand 25°C. Therefore, the test item Wasox-MMAC2 is determined to be easily hydrolysable at test conditions.

Key value for chemical safety assessment

Half-life for hydrolysis:
1 h
at the temperature of:
25 °C

Additional information

Key study: The hydrolysis as a function of pH study was carried out for the test substance Wasox-MMAC2 according to EU Method C.7 and GLP. This test material is composed of several compounds, including the 3 main components MMAC2 (Propan-2-one-O,O'-(methoxymethylsilandiyl) dioxime), MAC3 (Propan-2-one-O,O',O''-(methylsilantriyl)trioxime) and MM2AC (Propan-2-one-O-(dimethoxymethylsilyl)oxime). They polymerise, triggered by hydrolysis. More than 50 % of the components MMAC2, MAC3 and MM2AC of the test item hydrolysed in less than 1 hour at 25 ºC and at pH 4, pH 7 and pH 9. The half-life time in each case was <1h and therefore, the test item Wasox-MMAC2 is determined to be easily hydrolysable at test conditions.