13-β-ethyl-3-methoxygona-2,5(10)-dien-17-one

Hydrolysis

Link to relevant study record(s)

Reference

Endpoint:

hydrolysis

Type of information:

experimental study

Adequacy of study:

key study

Study period:

1994

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

guideline study with acceptable restrictions

Justification for type of information:

D-Ethyldienon is the D-enantiomer of ethyldienon which is a racemic mixture. The rate of hydrolysis of ethyldienon was determined in this study. As, except in chiral environment, D-enantiomer and racemate should show the same behaviour, the same rate of hydrolysis as determined for ethyldienon can be expected for D-Ethyldienon.

Reason / purpose for cross-reference:

read-across: supporting information

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:

Immediately after preparation of the test solutions and after defined times intervals, samples were taken and analyzed by HPLC.

Buffers:

buffer solutions:
0.05 M acetate buffer solution pH 4
2.87 g = 0.035 M sodium acetate p.a. Merck
Art. 6268 (M = 82.03 g/mol)
were dissolved to 1000 mL with double-distilled water.
The pH value was adjusted to 4 by adding acetic acid 100 % p.a. (Merck Art. 63 E).

0.05 M phosphate buffer solution pH 7
4.34 g = 0.031 M disodium hydrogen phosphate
Merck Art. 6589 (M = 141.96 g/mol)
2.65 g = 0.019 M potassium dihydrogen phosphate
Merck Art. 4881 (M = 136.09 g/mol)
were dissolved to 1000 mL with double-distilled water.

0.05 M borate buffer solution pH 9
4.76 g = 0.012 M disodium tetraborate
Merck Art. 6315 (M = 381.37 g/mol)
46 mL = 0.0046 M 0.1 M hydrochloric acid Titrisol
Merck Art. 9944 (M = 36.46 g/mol)
were dissolved to 1000 mL with double-distilled water.

Details on test conditions:

Preparation of the test solutions
Three test solutions, buffered to pH values of 4, 7 and 9, each with a test concentration of approx. 0.5 mg/L containing 1 % acetonitrile, were prepared by adding a test stock solution in acetonitrile to the corresponding buffer solution which had been equilibrated at 50 °C for one hour followed by purging with nitrogen to remove dissolved oxygen. All experiments were conducted using sterilized equipment, buffer solutions and double-distilled water.

Positive controls:

no

Negative controls:

no

Transformation products:

not measured

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

Hydroiysis products
The only hydrolyzable functional group is the enol ether group at position 3. Enol ethers are known to be very sensitive to acids. In synthesis they are used for protection of the keto function which is recovered after acid hydrolysis of the enol ethers. The rate of this reaction is decreasing with increasing pH value as observed in this study.
Thus in the case of the present substance, the diketo compound 18-methyl-5(10)-estren-3,17-dione should have been formed. This is consistent with the appearance of a HPLC peak with retention time ¿ 3.2 min in all hydrolyzed solutions which is increasing during hydrolysis.

pH:

4

Temp.:

25 °C

Hydrolysis rate constant:

> 6.9 h-1

DT50:

< 0.1 h

Type:

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

pH:

7

Temp.:

25 °C

Hydrolysis rate constant:

0.079 h-1

DT50:

8.7 h

Type:

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

pH:

9

Temp.:

25 °C

Hydrolysis rate constant:

0.001 h-1

DT50:

22.3 d

Type:

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

Details on results:

The rate constant of the substance at pH 7 and 9 at 25 °C was calculated by applying the Arrhenius equation.

Times of sampling, pH values of the hydrolysis solutions at 50 °C and the measured concentrations of the test item in the hydrolysis solutions.

	time	pH value	concentration	percent of intial concentration
	[hours]		[mg/L]	[%]
pH 4	0	4.02	0.440	100
	0.1	3.99	0.073	16.6
	0.2	4.01	0	0
	0.3	4.02	0
	0.5	4.00	0
pH 7	0	*	0.615	100
	0.5	6.99	0.440	71.5
	1.0	6.99	0.373	60.7
	1.5	7.00	0.346	56.3
	2.0	7.00	0.314	51.1
	3.0	7.01	0.252	41.0
	4.0	7.00	0.200	32.5
	6.0	7.00	0.122	19.8
pH 9	0	9.02	0.455	100
	72.6	9.03	0.326	71.6
	143	9.02	0.250	54.9
	188.5	9.02	0.262	57.6
	216	9.02	0.233	51.2
	338	9.00	0.141	31.0
	406	9.03	0.083	18.5

* no pH measurements because of the necessity of sample preparation

The data for the test solution at pH 4 indicate more than 50 % decay of the test substance within 2.4 hours at 50 ± 0.1 °C, corresponding to a half-life of less than 24 hours at 25 °C. Therefore no further testing was necessary at this pH value.

At pH 7 and pH 9, less than 50 % decay of the test substance within 2.4 hours, but more than 10 % degradation within 5 days at 50 ± 0.1 °C were observed. The measurements at pH 7 and 9 at 50 °C fulfilled both the requirements of the preliminary test and of test no. 1 in the EC test guideline. Although hydrolytic degradation at pH 7 and pH 9, 50 °C followed first-order kinetics and therefore hydrolysis experiments according to test no. 3 in the guideline would have been sufficient (one sampling point at t = 0 and two sampling points at more than 30 % hydrolytic degradation), experiments according to test no. 2 were conducted at pH 7 and pH 9 to obtain higher accuracy.

Validity criteria fulfilled:

yes

Conclusions:

The rate of hydrolysis of the substance was determined as t1/2 = <0.1 hours at pH 4, t1/2 = 8.7 hours at pH7 and t1/2 = 534 hours (22.3 days) at pH 9 in a read-across approach with results from a chemically relate substance.

Executive summary:

D-Ethyldienon is the D-enantiomer of ethyldienon which is a racemic mixture. The rate of hydrolysis of ethyldienon was determined in this study. As, except in chiral environment, D-enantiomer and racemate should show the same behaviour, the same rate of hydrolysis as determined for ethyldienon can be expected for D-Ethyldienon. The half-lives for ethyldienon at 25°C which were extrapolated from measurements at elevated temperatures using the Arrhenius equation and the experimental data are: t1/2 (pH4) <0.1h, t1/2 (pH7) = 8.7 hours and t1/2 (pH9) = 534 hours (22.3 days).

Description of key information

The rate of hydrolysis of the substance was determined as t1/2 = <0.1 hours at pH 4, t1/2 = 8.7 hours at pH7 and t1/2 = 534 hours (22.3 days) at pH 9 in a read-across approach from a chemically related substance.
Thus in the case of the present substance, the diketo compound 18-methyl-5(10)-estren-3,17-dione should have been formed. This is consistent with the appearance of a HPLC peak with retention time ¿ 3.2 min in all hydrolyzed solutions which is increasing during hydrolysis.

Key value for chemical safety assessment

Half-life for hydrolysis:

8.7 h

at the temperature of:

25 °C

Additional information

D-Ethyldienon is the D-enantiomer of ethyldienon which is a racemic mixture. The rate of hydrolysis of ethyldienon was determined in this study. As, except in chiral environment, D-enantiomer and racemate should show the same behaviour, the same rate of hydrolysis as determined for ethyldienon can be expected for D-Ethyldienon. The half-lives for ethyldienon at 25°C which were extrapolated from measurements at elevated temperatures using the Arrhenius equation and the experimental data are: t1/2 (pH4) <0.1h, t1/2 (pH7) = 8.7 hours and t1/2 (pH9) = 534 hours (22.3 days).

The key value reported at pH 7.