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Environmental fate & pathways

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
Guideline:
other: no data
GLP compliance:
no
Radiolabelling:
no
Analytical monitoring:
yes
Details on sampling:
Immediately after preparation of the test solutions and after defined time intervals, samples were taken and anayzed by HPLC.
Buffers:
Buffer solutions
- 0.05 M acetate buffer solution pH 4
0.657 g = 0.008 mol sodium acetate p.a. (M = 82.03 g/mol) and 2.4 mL = 0.042 mol acetic acid 100 % p.a. (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
4.34 g = 0.031 mol disodium hydrogen phosphate (M = 141.96 g/mol) and 2.65 g = 0.019 mol potassium dihydrogen phosphate (M = 136.09 g/mol) were dissolved to 1000 mL with double distilled water. The pH value was adjusted to 7 by adding phosphoric acid 10 % v/v.

- 0.05 M borate buffer solution pH 9
2.52 g = 0.0125 mol disodium tetraborate (M = 201.22 g/mol) and 46 mL = 0.0046 mol hydrochloric acid Titrisol (0.1 M) were dissolved to 1000 mL with double distilled water. The pH was 9.00.

- buffer solutions for calibration of pH meter
standard buffer solutions pH 2 (Riedel-de Haen Art. 33543), pH 7 (Fluka Art. 82596) and pH 10 (Fluka Art. 82597)
Details on test conditions:
Kinetics of degradation
Since the substance is an anhydride the test substance was expected to be hydrolytically instable at pH 4, 7 and 9. Therefore the hydrolysis experiments were directly conducted at room temperature (approx. 25 °C).

Two sets of test solutions, buffered to pH values of 4, 7 and 9, each with a concentration of approx. 10 mg/L, were prepared by adding a stock solution of test item in acetonitrile to the corresponding buffer solution.

Preparation of the test solutions
Two sets of test solutions, buffered to pH values of 4, 7 and 9, each with a the substance concentration of approx. 10 mg/l, were prepared by adding a stock solution of the substance in acetonitrile to the corresponding buffer solution.

Incubation and sampling
Aliquots of the test solutions were filled into autosampler vials which had been pre-rinsed with the test solutions and which were tightly closed with crimp caps. The vials were incubated in an autosampler at room temperature (approx. 25 °C). The concentration of the sample analyzed immediately after preparation was taken as initial concentration. The test solutions were analyzed after certain time intervals. The pH values of the test solutions were measured in a separate solution at the start and at the end of hydrolysis.

Calculation of rate constants and half-lives
The rate constants k at 25 °C, half-lives t¿ and 95 % confidence limits for k and t¿ were calculated with a kinetic data analysis program (PC based software KIM version 1.0). Plots of the experimental data and fitted curves and results of the parameter estimations were done with the program KIM.
Duration:
2.4 h
pH:
4
Temp.:
25 °C
Initial conc. measured:
7.8 mg/L
Duration:
2 h
pH:
7
Temp.:
25 °C
Initial conc. measured:
8.09 mg/L
Duration:
50 min
pH:
9
Temp.:
25 °C
Initial conc. measured:
10.04 mg/L
Transformation products:
yes
No.:
#1
% Recovery:
100
pH:
4
Temp.:
25 °C
pH:
4
Temp.:
25 °C
Hydrolysis rate constant:
2.669 h-1
DT50:
16 min
Type:
(pseudo-)first order (= half-life)
pH:
7
Temp.:
25 °C
Hydrolysis rate constant:
2.906 h-1
DT50:
14 min
Type:
(pseudo-)first order (= half-life)
pH:
9
Temp.:
25 °C
Hydrolysis rate constant:
21.52 h-1
DT50:
2 min
Type:
(pseudo-)first order (= half-life)

The result values represent an estimation since due to the fast hydrolysis only a few data points could be measured. Therefore also no confidence intervals can be given.

Validity criteria fulfilled:
not specified
Conclusions:
The hydrolysis half-lifes of pentanoic anhydride were determined at pH 4( t1/2: 16 minutes), pH 7 (t1/2: 14 minutes) and pH 9 (t1/2: 2 mintes) at 25 °C. The hydrolysis product was determined as valeric acid.
Executive summary:

The rate of hydrolysis of pentanoic anhydride was determined at pH 4, 7 and 9 at 25 °C. The hydrolysis rates measured were in the range 2-16 minutes. These values represent an estimation since due to the fast hydrolysis only a few data points could be measured. The hydrolysis product was determined as valeric acid. Therefore also no confidence intervals can be given.

Description of key information

The hydrolysis half-lifes of pentanoic anhydride were determined at pH 4( t1/2: 16 minutes), pH 7 (t1/2: 14 minutes) and pH 9 (t1/2: 2 mintes) at 25 °C. The hydrolysis  product was determined as valeric acid.

Key value for chemical safety assessment

Half-life for hydrolysis:
14 min
at the temperature of:
25 °C

Additional information