Ethyl 4-dimethylaminobenzoate

Hydrolysis

Link to relevant study record(s)

Reference

Endpoint:

hydrolysis

Type of information:

experimental study

Adequacy of study:

key study

Study period:

07 June 2017 to 15 November 2017

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:

no

Qualifier:

according to guideline

Guideline:

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

Version / remarks:

2008

Deviations:

no

Qualifier:

according to guideline

Guideline:

other: REACH Regulation (EU) No 1907/2006 of the European Parliament and of the Council.

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Radiolabelling:

no

Analytical monitoring:

yes

Details on sampling:

- At each sampling time, two samples were removed from the bath and an aliquot (1 mL) of each was diluted to volume (10 mL) with mobile phase for analysis by high performance liquid chromatography (HPLC).
- Extended testing at pH 9: Duplicate samples were taken immediately to serve as t0 samples, and then several pairs of samples were analysed in the range 10 to 90 % hydrolysis to test for pseudo-first order behaviour.

Buffers:

Buffer solutions were prepared as follows:
- pH 4: 0.2 M aqueous potassium dihydrogen orthophosphate (110 mL) was mixed with 0.07 M aqueous disodium hydrogen orthophosphate dodecahydrate (250 mL) and purified water (640 mL). The pH was adjusted to 4.0 ± 0.05 with orthophosphoric acid.
- pH 7: 0.2 M aqueous potassium dihydrogen orthophosphate (250 mL) was mixed with 1 M sodium hydroxide (30 mL) and purified water (720 mL). The pH was adjusted to 7.0 ± 0.05 with 1 M hydrochloric acid.
- pH 9: 0.1 M boric acid in 0.1 M aqueous potassium chloride (500 mL) was mixed with 1 M sodium hydroxide (21 mL) and purified water (480 mL). The pH was adjusted to 9.0 ± 0.05 with 1 M hydrochloric acid.

Details on test conditions:

PRELIMINARY TEST
The following procedure was carried out at each of pH 4, 7 and 9:
- Aliquots (0.1 mL) of a stock solution in purified water (3 g/L) were added to separate Wheaton vials containing buffer solution (10 mL), which had been purged with nitrogen and pre-equilibrated at test temperature (50 ± 0.5 °C).
- The samples, of nominal concentration 30 mg/L, were placed in a 50 °C water bath in the dark until sampling was required (immediately, and then after 2.4, 24 and 120 hours).
- At each sampling time, two samples were removed from the bath and an aliquot (1 mL) of each was diluted to volume (10 mL) with mobile phase for analysis by high performance liquid chromatography (HPLC).
- Sample pH and incubation temperature were monitored over the period of the test.

EXTENDED TESTING AT PH 9
- Separate tests were conducted at temperatures of 50, 60 and 70 °C in the dark, and the procedure followed was as detailed for the preliminary test. Duplicate samples were taken immediately to serve as t0 samples, and then several pairs of samples were analysed in the range 10 to 90% hydrolysis to test for pseudo-first order behaviour.

Duration:

120 h

pH:

4

Temp.:

50 °C

Initial conc. measured:

28.5 mg/L

Duration:

120 h

pH:

7

Temp.:

50 °C

Initial conc. measured:

31.7 mg/L

Duration:

120 h

pH:

9

Temp.:

50 °C

Initial conc. measured:

29.7 mg/L

Duration:

480 h

pH:

9

Temp.:

50 °C

Initial conc. measured:

31.84 mg/L

Duration:

168 h

pH:

9

Temp.:

60 °C

Initial conc. measured:

29.26 mg/L

Duration:

64 h

pH:

9

Temp.:

70 °C

Initial conc. measured:

28.91 mg/L

Number of replicates:

The test was performed in duplicate

Positive controls:

no

Negative controls:

no

Preliminary study:

- The preliminary study showed that at pH 4 and pH 7 and 50 ± 0.5 ºC, less than 10 % hydrolysis had occurred after 120 hours (5 days), equivalent to an environmental (25 °C) half-life (te½) of greater than 1 year. No further testing was therefore necessary at these pH values.
- At pH 9 and 50 ± 0.5 ºC, however, more than 10 % hydrolysis had occurred after 120 hours (5 days), indicating a te½ value of less than 1 year. This necessitated proceeding to definitive testing at this pH value.

Test performance:

LINEARITY
Under the conditions described, the calibration of the test material was found to be linear over the range 0 to 5 mg/L with a regression coefficient of 1.0000. It was considered that the analytical method was sufficiently sensitive to quantify test material concentrations down to 10 % or less of the initial concentration.

PH OF TEST SOLUTIONS
- The results show that there were no significant changes in pH with time.

Transformation products:

not specified

Key result

pH:

4

Temp.:

25 °C

DT50:

> 1 yr

Remarks on result:

hydrolytically stable based on preliminary test

Key result

pH:

7

Temp.:

25 °C

DT50:

> 1 yr

Remarks on result:

hydrolytically stable based on preliminary test

Key result

pH:

9

Temp.:

25 °C

Hydrolysis rate constant:

0 h-1

DT50:

398 d

Type:

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

Details on results:

EXTENDED TESTING AT PH 9
- At pH 9, definitive tests were conducted at temperatures of 50, 60 and 70 °C, and the hydrolysis rate constant (k) and te½ at 25 °C were extrapolated from
the measured values of log10k at the selected temperatures using the Arrhenius relationship. A te½ value of 398 days was obtained at this pH value.
- The hydrolysis reactions for the test material at pH 9 were shown to follow pseudo-first order behaviour.

Table 1: Preliminary test results for hydrolysis of the test material

pH	Concentration of the test material in solution at time th (in hours) (mg/L)
	t0h		t2.4h		t24h		t120h
	Measured	Mean	Measured	Mean	Measured	Mean	Measured	Mean
4	28.7, 28.3	28.5	29.3, 29.3	29.3	28.2, 28.1	28.2	28.8, 28.9	28.8
7	32.2, 31.3	31.7	31.5, 31.5	31.5	30.6, 30.8	30.7	30.5, 31.1	30.8
9	28.9, 30.6	29.7	30.7, 30.4	30.5	30.4, 29.7	30.1	23.8, 24.1	23.9

 

Table 2: Results for hydrolysis of the test material at pH 9 and 50 °C

Time (hours)	Concentration (mg/L)	Mean concentration (mg/L)	log10Ct
0	31.93, 31.74	31.84	1.503
72	28.84, 28.60	28.72	1.458
144	25.57, 25.56	25.57	1.408
216	22.23, 23.18	22.71	1.356
336	18.20, 18.36	18.28	1.262
408	16.30, 17.04	16.67	1.222
480	14.83, 15.25	15.04	1.177

Exponential regression, log₁₀C_t= 1.505 - 0.00069t

                                                       r = -0.9992

rate constant, k_obs= -slope x 2.303 = 0.001598 hour^-1

 

Table 3: Results for hydrolysis of the test material at pH 9 and 60 °C

Time (hours)	Concentration (mg/L)	Mean concentration (mg/L)	log10Ct
0	29.54, 28.97	29.26	1.466
24	25.95, 25.93	25.94	1.414
48	22.28, 22.86	22.57	1.354
72	20.34, 21.18	20.76	1.317
120	16.68, 16.39	16.54	1.218
144	14.86, 15.37	15.12	1.179
168	13.51, 13.45	13.48	1.130

Exponential regression, log₁₀C_t= 1.459 - 0.00197t

                                                       r = -0.9989

Rate constant, k_obs= -slope x 2.303 = 0.004548 hour^-1

 

Table 4: Results for hydrolysis of the test material at pH 9 and 70 °C

Time (hours)	Concentration (mg/L)	Mean concentration (mg/L)	log10Ct
0	28.79, 29.02	28.91	1.461
7	25.98, 26.26	26.12	1.417
16	20.96, 20.97	20.97	1.321
31	18.76, 18.91	18.84	1.275
40	15.19, 15.09	15.14	1.180
55	12.60, 13.23	12.92	1.111
64	12.58, 12.35	12.47	1.096

Exponential regression, log₁₀C_t= 1.445 - 0.00588t

                                                       r = -0.9872

Rate constant, k_obs= -slope x 2.303 = 0.01354 hour^-1

Validity criteria fulfilled:

yes

Conclusions:

Under the conditions of this study, the test material was determined to be hydrolytically stable under acidic and neutral conditions, but to hydrolyse slowly under basic conditions with a half-life of 398 days.

Executive summary:

The rate of hydrolysis of the test material as a function of pH was investigated in accordance with the standardised guidelines OECD 111 and EU Method C.7., under GLP conditions.

The preliminary study showed that at pH 4 and pH 7 and 50 ± 0.5 °C, less than 10 % hydrolysis had occurred after 120 hours (5 days), equivalent to an environmental (25 °C) half-life (te½) of greater than 1 year. No further testing was therefore necessary at these pH values.

At pH 9 and 50 ± 0.5 °C, however, more than 10 % hydrolysis had occurred after 120 hours (5 days), indicating a te½ value of less than 1 year. This necessitated proceeding to definitive testing at this pH value.

The hydrolysis reactions for the test material were shown to follow pseudo-first order behaviour in definitive testing at pH 9. Definitive tests were conducted at temperatures of 50, 60 and 70 °C, and the hydrolysis rate constant (k) and te½ at 25 °C were extrapolated from the measured values of log10k at the selected temperatures using the Arrhenius relationship. A te½ value of 398 days was obtained at pH 9.

Under the conditions of this study, the test material was determined to be hydrolytically stable under acidic and neutral conditions, but to hydrolyse slowly under basic conditions with a half-life of 398 days.

Description of key information

The rate of hydrolysis of the test material as a function of pH was investigated in accordance with the standardised guidelines OECD 111 and EU Method C.7., under GLP conditions.

 

The preliminary study showed that at pH 4 and pH 7 and 50 ± 0.5 °C, less than 10 % hydrolysis had occurred after 120 hours (5 days), equivalent to an environmental (25 °C) half-life (te½) of greater than 1 year. No further testing was therefore necessary at these pH values.

 

At pH 9 and 50 ± 0.5 °C, however, more than 10 % hydrolysis had occurred after 120 hours (5 days), indicating a te½ value of less than 1 year. This necessitated proceeding to definitive testing at this pH value.

The hydrolysis reactions for the test material were shown to follow pseudo-first order behaviour in definitive testing at pH 9. Definitive tests were conducted at temperatures of 50, 60 and 70 °C, and the hydrolysis rate constant (k) and te½ at 25 °C were extrapolated from the measured values of log10k at the selected temperatures using the Arrhenius relationship. A te½ value of 398 days was obtained at pH 9.

 

Under the conditions of this study, the test material was determined to be hydrolytically stable under acidic and neutral conditions, but to hydrolyse slowly under basic conditions with a half-life of 398 days.

 

Key value for chemical safety assessment

Half-life for hydrolysis:

398 d

at the temperature of:

25 °C