Estr-5(10)-en-17-one, 3,3-dimethoxy-

Hydrolysis

Link to relevant study record(s)

Reference

Endpoint:

hydrolysis

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2000

Reliability:

2 (reliable with restrictions)

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

Analytical monitoring:

yes

Details on sampling:

Sampling
Due to the fast hydrolytic degradation at pH 4 each sample was prepared individually in a vial, stored in the sample compartment of the HPLC autosampler and then injected once. The concentration of the sample analyzed immediately after preparation was taken as initial concentration.
The concentrations of the test solutions at pH 7 were determined after addition of 0.1 ml 0.1 M sodium hydroxide solution to 4 ml of the test solution whereas the concentrations of the test solutions at pH 9 were directly determined.
One vessel at each pH value was used exclusively for pH measurements. The pH values of the test solutions were measured at the start of incubation and at each sampling time.

Buffers:

Buffer solutions
- 0.05 M acetate buffer solution pH 4
0.651 g = 0.008 mol sodium acetate p.a. Merck Art. 106268 (M = 82.03 g/mol) and 2.4 mL = 0.042 mol acetic acid 100 % p.a. Merck Art. 63 E (M = 60.05 g/mol, density = 1.05 g/mL).
were dissolved to 1000 mL with double distilled water. The pH value was adjusted to 4 by adding 1 M sodium hydroxide solution (Merck Art. 109956).

- 0.05 M phosphate buffer solution pH 7
4.35 g = 0.031 mol disodium hydrogen phosphate Merck Art. 106566 (M = 141.96 g/mol) and 2.64 g = 0.019 mol potassium dihydrogen phosphate Merck Art. 105108 (M = 136.09 g/mol)
were dissolved to 1000 mL with double distilled water. The pH value was adjusted to 7 by adding 1 M sodium hydroxide solution (Merck Art. 109956).

- 0.05 M borate buffer solution pH 9
2.51 g = 0.0125 mol disodium tetraborate Merck Art. 106309 (M = 201.22 g/mol) and 46 mL = 0.0046 mol hydrochloric acid Titrisol Merck Art. 109973 (0.1 M) were dissolved to 1000 mL with double distilled water.

Details on test conditions:

Methods
The rate of hydrolysis of the substance in aqueous solutions buffered to pH values of 4, 7 and 9 was studied according to Testing Guideline C.7 of the European Community.
For pH 4 and pH 7, the hydrolysis experiments were directly conducted at 25 °C since hydrolytic instability was expected due to the ketal function in the molecule.
As the hydrolytic behaviour of the test substance was at pH 9 was unknown, the preliminary test defined by the guideline (incubation at 50 ± 0.1 °C) was performed to assess whether more than 50 % of the test substance are degraded within 2.4 hours at 50 °C (corresponding to a half-life of less than 24 hours at 25 °C) or if the test substance can be considered hydrolytically stable (less than 10 % hydrolytic degradation within 5 days at 50 °C corresponding to t1/2 > 1 year at 25 °C). For pH values where this is not the case, hydrolysis experiments at two elevated temperatures have to be conducted in order to extrapolate from the experimentally determined hydrolysis rate constants at higher temperatures to the rate constant at 25 °C by using the Arrhenius equation and the experimental data.

pH9: Since more than 10 % of the test substance were degraded within 5 days at 50 °C, hydrolysis experiments at elevated temperatures were necessary. Experiments were conducted at 70 and 80 °C with replication at 70 °C.

Preparation of the test solutions
Test solutions, buffered to pH values of 4, 7 and 9, each with a substance concentration of approx. 5 mg/I, were prepared by adding a stock solution of the substance in acetonitrile to the corresponding buffer solution. Prior to preparation of the test solutions, the buffer solutions had been equilibrated at the corresponding test temperature for one hour followed by purging with nitrogen to remove dissolved oxygen.
All experiments were conducted using sterilized equipment and buffer solutions.

Incubation
Aliquots of the test solutions were filled into sterilized 5 ml autosampler vials which were tightly closed with screw caps. The vials were incubated in a thermostatic water bath at the corresponding test temperature or, in the case of the experiment at pH 4, in the thermostated sample compartment of an autosampler. The temperature was kept constant within ± 0.1 °C
During the incubation of the test solutions possible photolytic degradation of the test substance was prevented by exclusion of light from the hydrolysis solutions.

Transformation products:

yes

No.:

#1

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

The substance is hydrolyzed with half-lives of 1.8 minutes at pH 4, 27.3 h at pH 7 and 86.4 days at pH 9. The hydrolysis is therefore acid-catalyzed.
An acid-catalyzed hydrolysis is to be expected since ketals like the substance under investigation are readily cleaved by acids to form alcohols and ketones. In the case of the substance, two molecules methanol and the corresponding ketone are expected to be the hydrolysis products.

pH:

4

Temp.:

25 °C

Hydrolysis rate constant:

23.04 h-1

DT50:

1.8 min

pH:

7

Temp.:

25 °C

Hydrolysis rate constant:

0.025 h-1

DT50:

27.3 h

pH:

9

Temp.:

25 °C

Hydrolysis rate constant:

0 h-1

DT50:

86.4 d

The rate of hydrolysis of the substance was determined according to EC guideline C.7 at pH 4, 7 and 9. The rate constants were directly determined at 25 °C (pH 4, pH 7) or extrapolated from measurements at elevated temperatures by using the Arrhenius equation and the experimental data (pH 9).

The rate constants and half-lives at 25 °C are:

pH	k [h^-1]	95 % confidence intervales for k [h^-1]	half-life	95 % confidence intervales for half-life
4	23.04	19.43 - 26.65	1.8 min	1.6 - 2.1 min
7	0.0254	0.02513 - 0.02566	27.3 h	27.0 - 27.6 h
9	0.0003344	0.0003216 - 0.0003472	86.4 d	83.2 - 89.8 d

Validity criteria fulfilled:

not specified

Conclusions:

The hydrolysis of the substance showed a half-life at 25 °C of 1.8 min at pH 4, 27.3 h at pH 7 and 86.4 d at pH 9.
An acid-catalyzed hydrolysis is to be expected since ketals like the substance are readily cleaved by acids to form alcohols and ketones. In the case of the substance, two molecules methanol and the corresponding ketone (5(10)-Estrene-3,17-dion) are expected to be the hydrolysis products.

Executive summary:

The rate of hydrolysis of the substance was determined according to EC guideline C.7 at pH 4, 7 and 9. The rate constants were directly determined at 25 °C (pH 4, pH 7) or extrapolated from measurements at elevated temperatures by using the Arrhenius equation and the experimental data (pH 9). The rate constants and half-lives at 25 °C are:

pH 4: k = 23.04 h^-1 and half-life = 1.8 min

pH 7: k = 0.0254 h^-1 and half-life = 27.3 hours

pH 9: k = 0.0003344 h^-1 and half-life = 86.4 days.

An acid-catalyzed hydrolysis is to be expected since ketals like the substance are readily cleaved by acids to form alcohols and ketones. In the case of the substance, two molecules methanol and the corresponding ketone (5(10)-Estrene-3,17-dion) are expected to be the hydrolysis products.

Description of key information

The rate of hydrolysis of the substance was determined according to EC guideline C.7 at pH 4, 7 and 9. The rate constants were directly determined at 25 °C (pH 4, pH 7) or extrapolated from measurements at elevated temperatures by using the Arrhenius equation and the experimental data (pH 9).
The half-lives at 25 °C are:
pH4= 1.8 min
pH7= 27.3 h
pH9= 86.4 d

Key value for chemical safety assessment

Half-life for hydrolysis:

1.8 min

at the temperature of:

25 °C

Additional information

The key value was reported at pH 4.