bis(branched-alkyl) 2-{[(1-phenylethyl)amino]methyl}alkanedioate

Hydrolysis

Link to relevant study record(s)

Reference

Endpoint:

hydrolysis

Type of information:

experimental study

Adequacy of study:

key study

Study period:

29 April 2015 to 03 July 2015

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 111 (Hydrolysis as a Function of pH)

Deviations:

yes

Remarks:

test item storage temperature exceeded upper limit on three occasions with no impact on results or integrity of study (see below)

Qualifier:

according to guideline

Guideline:

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

Deviations:

yes

Remarks:

test item storage temperature exceeded upper limit on three occasions with no impact on results or integrity of study (see below)

GLP compliance:

yes (incl. QA statement)

Radiolabelling:

no

Analytical monitoring:

yes

Details on sampling:

SAMPLING
- Sample solutions were taken from the water bath at various times and the pH of each solution recorded.

ANALYSIS OF SAMPLE SOLUTIONS
- The concentration of test item in the stock solutions and sample solutions was determined by high performance liquid chromatography – mass spectrometry (HPLC-MS).
- Samples: An aliquot of each sample was diluted by a factor of 1.25 using tetrahydrofuran.
- Standards: Duplicate standard solutions of test item were prepared in purified water : tetrahydrofuran (80:20 v/v) at a nominal concentration of 0.02 mg/L.
- Matrix blanks: Purified water : tetrahydrofuran (80:20 v/v) and relevant buffer : tetrahydrofuran (80:20 v/v).
- The standard, stock, sample and blank solutions were analyzed by HPLC-MS using the conditions shown in the table below.

Buffers:

TEST SYSTEM
- The test system consisted of buffer solutions at pH 4, 7 and 9 (see Table 3.1, below).
- The buffer solutions were subjected to ultrasonication and degassing with nitrogen to minimise the dissolved oxygen content.

Details on test conditions:

PREPARATION OF TEST SOLUTIONS
- Stock solutions were prepared in glass flasks at a nominal concentration of 0.025 mg/L in the three buffer solutions.
- A 1% co-solvent of tetrahydrofuran was used to aid dissolution.
- The stock solutions were split into individual sealed glass vials (with minimal headspace purged with nitrogen) for each data point.
- The sample solutions were shielded from light whilst maintained at the test temperature.

PRELIMINARY TEST / TIER 1
- Sample solutions at pH 4, 7 and 9 were maintained at 50.0 ± 0.5 °C for a period of 192 hours for pH 4 and 120 hours for pH 7 and 9.

TIER 2
- Results from the Preliminary test/Tier 1 showed it was necessary to undertake further testing at pH 7 and pH 9, with solutions being maintained at 40.0 ± 0.5 °C, 50.0 ± 0.5 °C, 60.0 ± 0.5 °C and 70.0 ± 0.5 °C for various periods of time.

TIER 3
- Identification of hydrolysis products was assessed.

CALCULATION
- The response factors of the standard peak areas (unit peak area per mg/L) were calculated using the equation RF = Rstd / Cstd where RF = response factor of the standard solution; Rstd = mean peak area ratio for the standard solution; Cstd = concentration for the standard solution (mg/L).
- The sample solution concentration (g/L) was calculated using the equation C = (Rspl / RFstd) * (D / 1.00 x 10E+03) where C = sample solution concentration (g/L); Rspl = mean peak area ratio for the sample solution; RFstd = mean response factor for the standard solutions (unit peak area per mg/L); D = dilution factor (1.25).
 
DEGREE OF HYDROLYSIS
- The decrease in concentration as a percentage of initial concentration was calculated using the equation % of initial concentration = (Ct / C0) * 100 where Ct = concentration of time t; C0 = concentration of time 0.
 
TESTING THE REACTION FOR PSEUDO FIRST ORDER
- The general rate expression for a first order reaction is d(c) / dt = -k * c
- The integrated form of the equation is -ln(C0 / Ct) = -k * t or ln Ct = (-k) * t -lnC0
- Therefore, the rate constant k is the slope of a plot of ln Ct versus t. The data were plotted as ln Ct versus t. The linear plots prove that the hydrolysis reaction is pseudo first order. The reaction rate constant k can be calculated by regression analysis or the equation -k = -(1/t) * ln(C0/Ct)
- The half-life time was calculated from the equation t1/2 = 0.693/k where C0 = concentration of the test solution at time 0 [μg/mL]; Ct = concentration of the test solution at time t [μg/mL]; k = first order rate constant [hours-1]; t1/2 = half-life time [hours].
 
EVALUATION OF RATE CONSTANT AT 25°C
- When the rate constants are known for two temperatures the rate constants at other temperatures can be calculated using the Arrhenius equation ln k = -(E/R) * 1/T + lnA where k = rate constant, measured at different temperatures; E = activation energy [kJ/mol]; T = absolute temperature [K]; R = gas constant [8.314 J/mol K]; A = pre-exponential factor.
- The half-life at 25 °C was extrapolated directly from the graph.

Duration:

192 h

pH:

4

Temp.:

50 °C

Remarks:

Tier 1

Duration:

120 h

pH:

7

Temp.:

50 °C

Remarks:

Tier 1

Duration:

120 h

pH:

9

Temp.:

50 °C

Remarks:

Tier 1

Duration:

78 h

pH:

7

Temp.:

40 °C

Remarks:

Tier 2

Duration:

54 h

pH:

9

Temp.:

40 °C

Remarks:

Tier 2

Duration:

30 h

pH:

7

Temp.:

50 °C

Remarks:

Tier 2

Duration:

30 h

pH:

9

Temp.:

50 °C

Remarks:

Tier 2

Duration:

6 h

pH:

7

Temp.:

60 °C

Remarks:

Tier 2

Duration:

6 h

pH:

9

Temp.:

60 °C

Remarks:

Tier 2

Duration:

6 h

pH:

7

Temp.:

70 °C

Remarks:

Tier 2

Duration:

6 h

pH:

9

Temp.:

70 °C

Remarks:

Tier 2

Number of replicates:

Two

Positive controls:

no

Negative controls:

no

Transformation products:

not measured

pH:

4

Temp.:

25 °C

DT50:

> 1 yr

Remarks on result:

other: rate constant not determined

pH:

7

Temp.:

25 °C

Hydrolysis rate constant:

0.006 h-1

DT50:

117 h

Type:

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

pH:

9

Temp.:

25 °C

Hydrolysis rate constant:

0.007 h-1

DT50:

96.9 h

Type:

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

Details on results:

RESULTS
- Typical chromatograms are attached.
- Tier 1 mean peak areas relating to the standard and sample solutions are shown in Table 3.2 (attached).
- Tier 1 test item concentrations at given time points are shown in Tables 3.3, 3.4 and 3.5 (attached).
- Tier 2 mean peak areas relating to the standard and sample solutions are shown in Table 3.6 (attached).
- Tier 2 test item concentrations at given time points are shown in Tables 3.7 to 3.14 (attached) and associated graphs are presented in Figures 3.1 to 3.8 (attached).
- Data relating to Tier 3 are presented in Tables 3.15 and 3.16 plus Figures 3.9 and 3.10 (attached).

VALIDATION
- The linearity of the detector response with respect to concentration in a matrix of purified water : tetrahydrofuran (80:20 v/v) was assessed over the nominal concentration range of 0.003 to 0.05 mg/L.
- The results were satisfactory with a correlation coefficient (r) of 0.999 being obtained.

IDENTIFICATION OF HYDROLYSIS PRODUCTS – TIER 3
- The hydrolysis products were not analytically determined as the mode of hydrolysis could be ascertained from the structure provided by the Sponsor.
- The structure contained two ester function groups which both will have been able to hydrolyse and each release a 4-methyl-2-pentanol molecule.
- The test result only measured rate of first ester group to be hydrolysed.

Validity criteria fulfilled:

yes

Conclusions:

The estimated half-life at 25 °C of the test item was determined to be > 1 year at pH 4, 117 h at pH 7 and 96.9 h at pH 9. Rate constants were reported as 5.93 x 10E-03 h-1 at pH 7 and 7.15 x 10E-03 h-1 at pH 9 (OECD 111 and EU Method C.7).

Executive summary:

GUIDELINE

Assessment of hydrolytic stability was carried out using a procedure designed to be compatible with Method C7 Abiotic Degradation, Hydrolysis as a Function of pH of Commission Regulation (EC) No 440/2008 of 30 May 2008 and Method 111 of the OECD Guidelines for Testing of Chemicals, 13 April 2004.

 

METHODS

The test system consisted of buffer solutions at pH 4, 7 and 9.The buffer solutions were subjected to ultrasonication and degassing with nitrogen to minimise the dissolved oxygen content.

 

Sample solutions at pH 4, 7 and 9 were maintained at 50.0 ± 0.5 °C for a period of 192 hours for pH 4 and 120 hours for pH 7 and 9 (preliminary test / Tier 1). Results from the Preliminary test/Tier 1 showed it was necessary to undertake further testing at pH 7 and pH 9, with solutions being maintained at 40.0 ± 0.5 °C, 50.0 ± 0.5 °C, 60.0 ± 0.5 °C and 70.0 ± 0.5 °C for various periods of time (Tier 2). Identification of hydrolysis products was then assessed (Tier 3).

 

Sample solutions were taken from the water bath at various times and the pH of each solution recorded. The concentration of test item in the stock solutions and sample solutions was determined by high performance liquid chromatography – mass spectrometry (HPLC-MS).

 

RESULTS

The estimated half-life at 25 °C of the test item was determined to be > 1 year at pH 4, 117 h at pH 7 and 96.9 h at pH 9. Rate constants were reported as 5.93 x 10E-03 h-1 at pH 7 and 7.15 x 10E-03 h-1 at pH 9 (OECD 111 and EU Method C.7).

Description of key information

The estimated half-life at 25 °C of the test item was determined to be > 1 year at pH 4, 117 h at pH 7 and 96.9 h at pH 9. Rate constants were reported as 5.93 x 10E-03 h-1 at pH 7 and 7.15 x 10E-03 h-1 at pH 9 (OECD 111 and EU Method C.7).

Key value for chemical safety assessment

Half-life for hydrolysis:

117 h

at the temperature of:

25 °C

Additional information

GUIDELINE

Assessment of hydrolytic stability was carried out using a procedure designed to be compatible with Method C7 Abiotic Degradation, Hydrolysis as a Function of pH of Commission Regulation (EC) No 440/2008 of 30 May 2008 and Method 111 of the OECD Guidelines for Testing of Chemicals, 13 April 2004.

 

METHODS

The test system consisted of buffer solutions at pH 4, 7 and 9. The buffer solutions were subjected to ultrasonication and degassing with nitrogen to minimise the dissolved oxygen content.

 

Sample solutions at pH 4, 7 and 9 were maintained at 50.0 ± 0.5 °C for a period of 192 hours for pH 4 and 120 hours for pH 7 and 9 (preliminary test / Tier 1). Results from the Preliminary test/Tier 1 showed it was necessary to undertake further testing at pH 7 and pH 9, with solutions being maintained at 40.0 ± 0.5 °C, 50.0 ± 0.5 °C, 60.0 ± 0.5 °C and 70.0 ± 0.5 °C for various periods of time (Tier 2). Identification of hydrolysis products was then assessed (Tier 3).

 

Sample solutions were taken from the water bath at various times and the pH of each solution recorded. The concentration of test item in the stock solutions and sample solutions was determined by high performance liquid chromatography – mass spectrometry (HPLC-MS).

 

RESULTS

The estimated half-life at 25 °C of the test item was determined to be > 1 year at pH 4, 117 h at pH 7 and 96.9 h at pH 9. Rate constants were reported as 5.93 x 10E-03 h-1 at pH 7 and 7.15 x 10E-03 h-1 at pH 9 (OECD 111 and EU Method C.7).