N-Phenyl-diethanolamine, reaction products with formaldehyde

Hydrolysis

Link to relevant study record(s)

Reference

Endpoint:

hydrolysis

Type of information:

experimental study

Adequacy of study:

key study

Study period:

01 July 2020 to 02 October 2020

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Reason / purpose for cross-reference:

reference to other study

Reason / purpose for cross-reference:

reference to same study

Qualifier:

according to guideline

Guideline:

OECD Guideline 111 (Hydrolysis as a Function of pH)

Version / remarks:

2004

Deviations:

no

Qualifier:

according to guideline

Guideline:

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

Version / remarks:

2016

Deviations:

no

Qualifier:

according to guideline

Guideline:

EPA OPPTS 835.2120 (Hydrolysis of Parent and Degradates as a Function of pH at 25°C)

Version / remarks:

2008

Deviations:

no

GLP compliance:

yes

Remarks:

Date of inspection: 10-17 December 2019 Date on certificate: 24 February 2020

Analytical monitoring:

yes

Buffers:

Acetate buffer pH 4, 0.01 M: Solution of 16.7% 0.01 M sodium acetate in water and 83.3% 0.01 M acetic acid in water. Buffer contained 0.0009% (w/v) sodium azide.
Phosphate buffer pH 7, 0.01 M: Solution of 0.01 M potassium di-hydrogen-phosphate in water adjusted to pH 7 using 1 M sodium hydroxide. Buffer contained 0.0009% (w/v) sodium azide.
Borate buffer pH 9, 0.01 M: Solution of 0.01 M boric acid in water and 0.01 M potassium chloride in water adjusted to pH 9 using 1 M sodium hydroxide. Buffer contained 0.0009% (w/v) sodium azide

Details on test conditions:

The rate of hydrolysis of the test item as a function of pH was determined at pH values normally found in the environment (pH 4-9).
Only the results of the measurements at pH 4 are reported. The hydrolysis measurements at pH 7 and at pH 9 were technically not possible due to rapid hydrolysis the test item at these pH values.
All solutions containing the test item were protected from light.

From the initial results obtained in Test Facility Study No. 20194899 (study record cross-referenced) it is observed that degradation/hydrolysis of the reaction product of N-Phenyl-diethanolamine with a single molecule of formaldehyde occurs rapidly and therefore preliminary test has not been performed, but only the main study in a short time period has been performed.

Due to observed rapid degradation/hydrolysis test solutions has been incubated at three temperatures, 10.1°C, 15°C and 20°C until 90% hydrolysis of the substance is observed or for 30 days whichever comes first. Temperatures has been controlled within ± 0.5°C. The concentration of the test item in duplicate test solutions has been determined immediately after preparation and at a minimum of six sampling times afterwards to cover the hydrolysis range of 10% to 90%. Linear regression analysis on the logarithm of the relative concentration between 10% and 90% of hydrolysis and time has been performed to investigate the pseudo-first order behaviour of the test item. During the study only the the reaction product of N-Phenyl-diethanolamine with a single molecule of formaldehyde curve has been made and m/z 212.4 has been quantified in connection with monitoring degradation.

Duration:

1.5

pH:

4

Temp.:

20 °C

Initial conc. measured:

4.88 mg/L

Duration:

43.87 h

pH:

4

Temp.:

15 °C

Initial conc. measured:

5.52 mg/L

Duration:

5 h

pH:

4

Temp.:

10 °C

Initial conc. measured:

4.96 mg/L

Number of replicates:

2

Positive controls:

no

Negative controls:

no

Preliminary study:

From the initial results preformed in Test Facility Study No. 20194899 (cross-referenced above) it is observed that degradation/hydrolysis of the test item occurs rapidly and therefore preliminary test has not been performed, but only the main study in a short time period has been performed.

Test performance:

At pH 7 and pH 9 it was technically not possible to determine hydrolysis rate due to rapid degradation of the test item at these pH values.

Transformation products:

not specified

Remarks:

Not identified as part of this study alone but in study number 20194899 it was confirmed that in an aqueous solution the reaction product of N-Phenyl-diethanolamine with a single molecule of formaldehyde is converted back to N-Phenyl-diethanolamine

% Recovery:

98

pH:

4

Temp.:

10 °C

Duration:

5.1 h

% Recovery:

109

pH:

4

Temp.:

15 °C

Duration:

43.87 h

% Recovery:

96

pH:

4

Temp.:

20

Duration:

1.5 h

pH:

4

Temp.:

10 °C

Hydrolysis rate constant:

0.49 h-1

Type:

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

pH:

4

Temp.:

15 °C

Hydrolysis rate constant:

1.06 h-1

Type:

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

pH:

4

Temp.:

20 °C

Hydrolysis rate constant:

2.27 h-1

Type:

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

Key result

pH:

4

Temp.:

25 °C

Hydrolysis rate constant:

4.7 h-1

Type:

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

Table 1        
Main Test pH 4: Hydrolysis of the reaction product of N-Phenyl-diethanolamine with a single molecule of formaldehyde at 10°C

Sampling time [hours]	Analyzed concentration [mg/L]	Relative concentration [%]	Logarithm relative concentration	pH
0.00	4.96	101	2.01	4.1
0.00	4.82	99	1.99	4.1
0.18	4.25	87	1.94	n.a.
0.18	4.99	102	2.01	n.a.
0.35	4.22	86	1.94	n.a.
0.35	4.28	87	1.94	n.a.
0.50	4.11	84	1.92	n.a.
0.50	3.78	77	1.89	n.a.
0.68	3.58	73	1.87	n.a.
0.68	3.20	65	1.82	n.a.
1.20	2.79	57	1.76	n.a.
1.20	3.01	62	1.79	n.a.
2.08	1.65	34	1.53	n.a.
2.08	1.59	33	1.51	n.a.
3.20	1.02	21	1.32	n.a.
3.20	0.913	19	1.27	n.a.
4.15	0.52 ^1	11	1.03	n.a.
4.15	0.63 ^1	13	1.11	n.a.
5.10	0.45 ^1	9.2	0.97	4.1
5.10	0.48 ^1	10	0.99	4.1

¹     Estimated value, calculated by extrapolation of the calibration curve.

n.a. Not applicable.

 

Table 2     
Main Test at pH 4: Hydrolysis of the reaction product of N-Phenyl-diethanolamine with a single molecule of formaldehyde at 15°C

Sampling time [hours]	Analyzed concentration [mg/L]	Relative concentration [%]	Logarithm relative concentration	pH
0.00	5.52	102	2.01	4.1
0.00	5.33	98	1.99	4.1
0.17	4.58	84	1.93	n.a.
0.17	4.46	82	1.92	n.a.
0.33	3.74	69	1.84	n.a.
0.33	3.97	73	1.86	n.a.
0.50	3.25	60	1.78	n.a.
0.50	3.16	58	1.76	n.a.
0.67	3.04	56	1.75	n.a.
0.67	2.65	49	1.69	n.a.
0.83	2.19	40	1.61	n.a.
0.83	2.39	44	1.64	n.a.
1.00	2.14	39	1.60	n.a.
1.00	2.02	37	1.57	n.a.
1.17	1.60	30	1.47	n.a.
1.17	1.70	31	1.50	n.a.
1.33	1.54	28	1.45	n.a.
1.33	1.22	22	1.35	n.a.
1.50	1.03	19	1.28	n.a.
1.50	1.03	19	1.28	n.a.
43.87	n.d.	n.a.	n.a.	4.1
43.87	n.d.	n.a.	n.a.	4.1

      n.d. Not detected.

       n.a. Not applicable.

 

Table 3       
Main Test at pH 4: Hydrolysis of the reaction product of N-Phenyl-diethanolamine with a single molecule of formaldehyde at 20°C

Sampling time [hours]	Analyzed concentration [mg/L]	Relative concentration [%]	Logarithm relative concentration	pH
0.00	4.88	101	2.01	4.1
0.00	4.76	99	1.99	4.1
0.17	4.26	88	1.95	n.a.
0.17	3.38	70	1.85	n.a.
0.33	2.94	61	1.79	n.a.
0.33	2.40	50	1.70	n.a.
0.50	1.62	34	1.53	n.a.
0.50	1.78	37	1.57	n.a.
0.67	1.30	27	1.43	n.a.
0.67	1.40	29	1.46	n.a.
0.83	0.964	20	1.30	n.a.
0.83	0.907	19	1.27	n.a.
1.00	0.65 ^1	14	1.13	n.a.
1.00	0.55 ^1	11	1.06	n.a.
1.17	0.44 ^1	9.1	0.96	n.a.
1.17	0.36 ^1	7.6	0.88	n.a.
1.33	0.20 ^1	4.2	0.62	n.a.
1.33	0.29 ^1	6.0	0.78	n.a.
1.50	0.16 ^1	3.4	0.53	4.1
1.50	0.17 ^1	3.5	0.54	4.1

¹     Estimated value, calculated by extrapolation of the calibration curve.

n.a. Not applicable.

 

 

Table 4        
Main Test pH 4: Recoveries

Temperature (°C)	Nominal concentration [mg/L]	Analyzed concentration [mg/L]	Recovery [%]
			Individual	Mean
10	5.00	4.96	99	98
	5.00	4.82	96
15	5.00	5.52	110	109
	5.00	5.33	107
20	5.00	4.88	98	96
	5.00	4.76	95

 

For testing of pseudo-first order kinetics the mean logarithms of the relative concentrations between 10% and 90% were plotted against time. At all temperatures linear relationships were obtained.

The half-life time of the reaction product of N-Phenyl-diethanolamine with a single molecule of formaldehyde was determined according to the model for pseudo-first order reactions. All logarithms of the relative concentrations were correlated with time using linear regression analysis. Table 5 shows the statistical parameters.

 

Table 5       
Main Test pH 4: Statistical Parameters Regression Curves

Temperature (°C)	Slope [hours^-1]	Intercept	Coefficient of correlation
10	-2.13 ´ 10^-1	2.00	0.995
15	-4.59 ´ 10^-1	2.01	0.992
20	-9.88 ´ 10^-1	2.06	0.994

The rate constant (k_obs) and half-life time of the test item at each temperature was obtained and the Arrhenius equation was used to determine the rate constant and half-life time at 25°C (see Table 6).

 

 

Table 6      
Main Test pH 4: Rate Constants (k_obs) and Half-life Time (t_½)

Temperature [°C]	kobs [hours^-1]	t½
10	4.90 ´ 10^-1	1.42 hours
15	1.06 ´ 10^0	0.66 hours
20	2.27 ´ 10^0	0.30 hours
25	4.70 ´ 10^0	0.15 hours ^1

¹     calculated with the Arrhenius equation

For testing of pseudo-first order kinetics the mean logarithms of the relative concentrations between 10% and 90% were plotted against time. At all temperatures linear relationships were obtained.

Validity criteria fulfilled:

yes

Conclusions:

The hydrolysis rate of the test item was determined at pH 4 to range from 0.15 hours at 25°C to 1.42 hours at 10°C.

Executive summary:

Hydrolysis of the test item was investigated in accordance with OECD 111 and EU C7. The hydrolysis measurements at pH 7 and pH 9 were technically not possible due to rapid hydrolysis of the test item at these pH values. The half lives were determined to be as follows at pH 4: 1.42 hours at 10°C, 0.66 hours at 15°C, 0.30 hours at 20°C, 0.15 hours at 25°C.

Description of key information

At pH 4: t_1/2(10°C) = 1.42 hours, t_1/2(15°C) = 0.66 hours, t_1/2(20°C) = 0.30 hours, t_1/2(25°C) = 0.15 hours; OECD 111; Petrovic, D. (2020)

Key value for chemical safety assessment

Half-life for hydrolysis:

0.15 h

at the temperature of:

25 °C