19-Norpregn-5(10)-ene-21-nitrile, 17-hydroxy-3-oxo-, (17.alpha.)-

Hydrolysis

Link to relevant study record(s)

Reference

Endpoint:

hydrolysis

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2003

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

guideline study with acceptable restrictions

Qualifier:

according to guideline

Guideline:

EU Method C.7 (Degradation: Abiotic Degradation: Hydrolysis as a Function of pH)

Deviations:

no

GLP compliance:

no

Radiolabelling:

no

Analytical monitoring:

yes

Details on sampling:

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. The temperature was kept constant within ± 0.1 °C. Prior to incubation the initial concentration of the test item was measured on the test solutions of pH 4, 7 and 9.
During the incubation of the test solutions in the thermostatic water bath possible photolytic degradation of the test substance was prevented by exclusion of light from the hydrolysis solutions by using a thermostatic bath made of stainless steel with a metal cover.
At each sampling time two vials from each of the hydrolysis solutions were removed from the thermostatic bath and aliquots of each vessel were analyzed by HPLC.

Buffers:

BUFFER SOLUTIONS:
- 0.05 M acetate buffer solution pH 4:
0.659 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. 100063 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 acetic acid

- 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 2.66 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 dilute phosphoric acid (10 % v/v)

- 0.05 M borate buffer solution pH 9:
2.52 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.

As the pH value of borate buffer solutions decreases with increasing temperature, the pH value had to be adjusted to 9.17 at 25 °C in order to obtain a pH value of 9.00 at 50 °C. For the experiment at 60 °C, the pH value had to be adjusted to 9.28 at 25 °C. The pH value was adjusted with 0.1 M sodium hydroxide solution.

Details on test conditions:

Test solutions with concentrations of approx. 10 mg/L in 0.05 M buffer solution pH 4, 7 and 9 with 1 % acetonitrile were prepared by adding a stock solution of the substance in acetonitrile to the corresponding buffer solution. All buffer solutions had been purged with nitrogen to remove dissolved oxygen. Experiments were conducted using sterilized equipment and buffer solutions.

Positive controls:

no

Negative controls:

no

Transformation products:

not specified

Remarks:

The cyano group is hydrolyzed leading to the corresponding amide. This is a reaction common to nitriles.The product can be identified by a peak at 3.4 min in the chromatograms of the hydrolysis solutions increasing with hydrolysis time.

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

The cyano group is hydrolyzed leading to the corresponding amide. This is a reaction common to nitriles.The product can be identified by a peak at 3.4 min in the chromatograms of the hydrolysis solutions increasing with hydrolysis time.

pH:

4

Temp.:

25 °C

Hydrolysis rate constant:

0.001 h-1

DT50:

56 d

pH:

7

Temp.:

25 °C

Hydrolysis rate constant:

0 h-1

DT50:

59 d

pH:

9

Temp.:

25 °C

Hydrolysis rate constant:

0.005 h-1

DT50:

6 d

Details on results:

Since more than 10 % of the test substance were degraded at pH 4, 7 and 9 within 5 days at 50 °C, hydrolysis experiments at elevated temperatures were necessary for all pH values. Therefore additional experiments were conducted at pH 4 and 7, 80 °C and at pH 9, 60 °C.

The rate constants for the substance at pH 4, 7 and 9, 25 °C were calculated by applying the Arrhenius equation.

Validity criteria fulfilled:

not specified

Conclusions:

The half-lives at pH 4 and 7 were nearly identical with 56 and 59 days determined at 25 °C. The half life at pH 9 was 6.0 days.

Executive summary:

The hydrolysis of the substance was determined according to EU Guideline Method C.7 in aqueous solutions buffered to pH values of 4, 7 and 9. Since the hydrolytic behaviour of the test substance was unknown, the preliminary test defined by the guideline (incubation at 50 ± 0.1 °C) was performed at pH 4, 7 and 9 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). Since more than 10 % of the test substance were degraded at pH 4, 7 and 9 within 5 days at 50 ± 0.1 °C, additional hydrolysis experiments had to be conducted at pH 4 and 7, 80 °C and at pH 9, 60 °C. The rate constants at 25 °C were then calculated by using the Arrhenius equation and the experimental data. Extrapolated first-order rate constant [k] and half-lives [t_1/2] for the test item were calculated at pH 4 k = 0.0005158/h and t_1/2 = 56 days, pH 7 k = 0.0004909/h and t _1/2 = 59 days and pH 9 k = 0.004823/h and t_1/2 = 6.0 days. Hydrolytic degradation is therefore clearly base-catalyzed. The cyanogroup is hydrolyzed leading to the corresponding amide. This is a reaction common to nitriles.

Description of key information

The half-lives at pH 4 and 7 were nearly identical with 56 and 59 days determined at 25 °C. The half life at pH 9 was 6.0 days.

Key value for chemical safety assessment

Half-life for hydrolysis:

6 d

at the temperature of:

25 °C

Additional information

The key value is reported at pH 9.