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Hydrolysis

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Reference
Endpoint:
hydrolysis
Type of information:
experimental study
Adequacy of study:
key study
Study period:
2002
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
guideline study with acceptable restrictions
Qualifier:
equivalent or similar 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
Buffers:
Buffer solutions:
- 0.05 M acetate buffer solution pH 4
- 0.05 M phosphate buffer solution pH 7
- 0.05 M borate buffer pH 9

Buffer solutions for calibration of pH meter and electrode:
- standard buffer solutions pH 4 (Art. 1.09475), pH 7 (Art. 1.09477) and pH 9 (Art. 1.09476), Merck
Details on test conditions:
Preparation of the test solutions:
- Test solutions with concentrations of approx. 8 mg/L in 0.05 M buffer solution pH 4, 7 and 9 with 1 % acetonitrile were prepared by adding a stock solution of methyl pentanoate 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

lncubation and sampling:
- aliquots of the test solutions were filled into sterilized 5 mL autosampler vials which were tigbtly closed with screw caps
- 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 methyl pentanoate was measured on the test solutions of pH 4, 7 and 9
- during tbe 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
Duration:
55.3 h
pH:
7
Temp.:
80 °C
Initial conc. measured:
7.92 mg/L
Duration:
7.1 h
pH:
9
Temp.:
60 °C
Initial conc. measured:
7.96 mg/L
Duration:
118.4 h
pH:
4
Temp.:
50 °C
Initial conc. measured:
8.02 mg/L
Remarks:
Preliminary test
Preliminary study:
At pH 4 less than 10 % of the initial concentration of methyl valerate were hydrolyzed within 5 days at 50 +/- 0.1 °C, which is considered as equivalent to t 1/2 > 1 year at 25 °C. According to the EC test guideline C.7, a substance can be considered hydrolytically stable if t 1/2 > 1 year at 25 °C. Therefore no further testing was necessary at this pH value.

Since more than 10 % of the test substance were degraded at pH 7 and pH 9 within 5 days at 50 °C, hydrolysis experiments at elevated temperatures were necessary for pH 7 and 9. Therefore additional experiments were conducted at pH 7, 80 °C and at pH 9, 60 °C.
Transformation products:
yes
No.:
#1
No.:
#2
Details on hydrolysis and appearance of transformation product(s):
Methanol (CAS 67-56-1) and valeric acid (CAS 109-52-4) were the hydrolysis products. Valeric acid could be identified by a peak in the HPLC diagrams of the hydrolysis solutions at approx. 4.5 min increasing with hydrolysis time.
% Recovery:
95.3
pH:
4
Temp.:
50 °C
Duration:
118.4 h
Remarks on result:
hydrolytically stable based on preliminary test
% Recovery:
38
pH:
7
Temp.:
50 °C
Duration:
675.2 h
% Recovery:
34.8
pH:
7
Temp.:
80 °C
Duration:
55.3 h
% Recovery:
23.7
pH:
9
Temp.:
50 °C
Duration:
16 h
% Recovery:
16
pH:
9
Temp.:
60 °C
Duration:
7.1 h
pH:
4
Temp.:
25 °C
DT50:
> 1 yr
pH:
7
Temp.:
25 °C
Hydrolysis rate constant:
>= 0 - <= 0 h-1
DT50:
322 d
Remarks on result:
other: 95% confidence intervals for half-life: 278-383 d
pH:
9
Temp.:
25 °C
Hydrolysis rate constant:
>= 0.002 - <= 0.005 h-1
DT50:
8 d
Remarks on result:
other: 95% confidence intervals for half-life: 5.4-15.1 d
Validity criteria fulfilled:
yes
Conclusions:
Methyl valerate is hydrolytically stable at pH 4 and 7 with half lives between more than 1 year and 322 days at 25°C. However, in the alkaline pH range (pH 9) methyl valerate must be considered as hydrolytically instable with a half-life of 8 days.
Executive summary:

The rate of hydrolysis of methyl valerate in aqueous solution buffered to pH values of 4, 7 and 9 was studied according to EU testing guideline C.7. Methyl valerate is hydrolytically stable at pH 4 and 7 with a half lives between more than 1 year and 322 days at 25 °C. However, in the alkaline pH range (pH 9) methyl valerate must be considered as hydrolytically instable with a half-life of 8 days. Therefore the hydrolysis is base-catalyzed.

Description of key information

Methyl valerate is hydrolytically stable at pH 4 and 7 with half lives between more than 1 year and 322 days at 25°C. But in the alkaline pH range methyl valerate must be considered as hydrolytically instable with a half-life of 8 days.

Key value for chemical safety assessment

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

Additional information

"Should read: 322 days, measured at pH 7"

The hydrolysis is base-catalyzed.

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