N-(1,4-dimethylpentyl)-N'-phenylbenzene-1,4-diamine

Hydrolysis

Link to relevant study record(s)

Reference

Endpoint:

hydrolysis

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2016

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Remarks:

including GLP

Qualifier:

according to guideline

Guideline:

OECD Guideline 111 (Hydrolysis as a Function of pH)

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Radiolabelling:

no

Analytical monitoring:

yes

Buffers:

Buffer pH 4 Citric acid/NaOH/NaCl;
Buffer pH 7 KH2PO4/Na2HPO4,
Buffer pH 9 Na2B4O7/HCl,
The buffer solutions were 1:10 diluted with Millipore water and tempered to respective hydrolysis temperature before applying to the test item.

Estimation method (if used):

Concentration of water remains essentially constant during hydrolysis. Hence the kinetics of hydrolysis is generally pseudo-first order at fixed pH and temperature.
Concentration of the test substance is determined as a function of time. The logarithms of the concentrations are plotted against time and the slope of the resulting straight line gives the rate constant from the formula: k(obs) = - slope x 2.303 (if log10 is used).
When the rate constants are known for two or more temperatures, the rate constants at other temperatures can be calculated using the Arrhenius equation:
k = A x e -E / (R x T) or ln k = -E / (R x T) + ln A

Details on test conditions:

Preparation was carried out under nitrogen as flushing gas, to avoid oxygen. The vials were closed and incubated at 20 °C in a heat regulator under dark to avoid any photolytic effects.
10.1 mg of the test item Santoflex 7PPD was dissolved in 100 mL acetonitrile. This stock solution was 1:100 diluted with buffer solution pH 4, leading to a test item concentration of 1.01 mg/L (Hydrolysis at 20 °C).
10.7 mg of the test item Santoflex 7PPD was dissolved in 100 mL acetonitrile. This stock solution was 1:100 diluted with buffer solution pH 4, leading to a test item concentration of 1.07 mg/L (Hydrolysis at 50 °C).
Aliquots of the test solution were taken to obtain individual vials for every test point.

Duration:

741 h

pH:

4

Temp.:

20 °C

Initial conc. measured:

0.903 mg/L

Duration:

31.7 h

pH:

4

Temp.:

50 °C

Initial conc. measured:

1.111 mg/L

Duration:

721 h

pH:

7

Temp.:

20 °C

Initial conc. measured:

0.847 mg/L

Duration:

2.9 h

pH:

7

Temp.:

50 °C

Initial conc. measured:

0.893 mg/L

Remarks:

first determination

Duration:

6 h

pH:

7

Temp.:

50 °C

Initial conc. measured:

1.076 mg/L

Remarks:

second determination

Duration:

720 h

pH:

9

Temp.:

20 °C

Initial conc. measured:

0.84 mg/L

Duration:

3.3 h

pH:

9

Temp.:

50 °C

Initial conc. measured:

0.976 mg/L

Number of replicates:

Single determinations

Positive controls:

no

Negative controls:

no

Preliminary study:

Test item Santoflex 7PPD was assumed to be instable at environmental relevant temperatures and pH values

Transformation products:

yes

No.:

#1

No.:

#2

No.:

#3

No.:

#4

No.:

#5

Details on hydrolysis and appearance of transformation product(s):

These components were calibrated separately using certified standard compounds. During the study an additional hydrolysis product was detected in the hydrolysis test solutions at pH 7 and pH 9 only.
The LC-MS spectrum of the originally unknown component shows a molecular ion signal at m/z = 200.0712, which can be assigned to the protonated molecular ion [M+H]+ of C12H9NO2, M = 199 g/mol. The unknown component therefore appears to have a molecular weight of 199 Dalton linked to a formula C12H9NO2. This would probably fit to “overoxidised 4-HDPA” (4-(phenylnitroso)benzen-1-olate or 4-phenylnitroso)cyclohexa-2,5-dien-1-one) (short name: N-Oxide).
This component was also quantified using the response factor of the parent compound 7PPD at 202 nm assuming similar UV absorption of their chemical structures (4-(phenylnitroso)benzen-1-olate or 4-phenylnitroso)cyclohexa-2,5-dien-1-one).

% Recovery:

< 10

pH:

4.2

Temp.:

20 °C

Duration:

741 h

% Recovery:

< 10

pH:

4.2

Temp.:

50 °C

Duration:

31.7 h

% Recovery:

< 10

pH:

7.3

Temp.:

20 °C

Duration:

721 h

% Recovery:

< 10

pH:

7.3

Temp.:

50 °C

Duration:

6 h

% Recovery:

< 10

pH:

9.1

Temp.:

20 °C

Duration:

720 h

% Recovery:

< 10

pH:

9.1

Temp.:

50 °C

Duration:

3.3 h

pH:

4

Temp.:

20 °C

DT50:

ca. 370 h

Type:

other: DT50 value (time at which the concentration is reduced by 50 %)

Remarks on result:

other: estimated

Remarks:

For pH 4 and pH 9 the rate at which the concentrations of the test item decreases does not follow a first order reaction. Therefore the hydrolysis reaction cannot be described by first order kinetics and no half-life-time (t(1/2)) can be calculated by linear regression. Based on the experimental data a DT50 value (time at which the concentration is reduced by 50 %) can be estimated instead.

pH:

4

Temp.:

50 °C

DT50:

ca. 15 h

Type:

other: DT50 value (time at which the concentration is reduced by 50 %)

Remarks on result:

other: estimated

Remarks:

For pH 4 and pH 9 the rate at which the concentrations of the test item decreases does not follow a first order reaction. Therefore the hydrolysis reaction cannot be described by first order kinetics and no half-life-time (t(1/2)) can be calculated by linear regression. Based on the experimental data a DT50 value (time at which the concentration is reduced by 50 %) can be estimated instead.

pH:

7

Temp.:

20 °C

Hydrolysis rate constant:

0 s-1

DT50:

7 h

Type:

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

Remarks on result:

other: DT50 calculated by linear regression

pH:

7

Temp.:

50 °C

Hydrolysis rate constant:

0 s-1

DT50:

1 h

Type:

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

Remarks on result:

other: DT50 calculated by linear regression

pH:

9

Temp.:

20 °C

DT50:

ca. 10 h

Type:

other: DT50 value (time at which the concentration is reduced by 50 %)

Remarks on result:

other: estimated

Remarks:

For pH 4 and pH 9 the rate at which the concentrations of the test item decreases does not follow a first order reaction. Therefore the hydrolysis reaction cannot be described by first order kinetics and no half-life-time (t(1/2)) can be calculated by linear regression. Based on the experimental data a DT50 value (time at which the concentration is reduced by 50 %) can be estimated instead.

pH:

9

Temp.:

50 °C

DT50:

ca. 1 h

Type:

other: DT50 value (time at which the concentration is reduced by 50 %)

Remarks on result:

other: estimated

Remarks:

For pH 4 and pH 9 the rate at which the concentrations of the test item decreases does not follow a first order reaction. Therefore the hydrolysis reaction cannot be described by first order kinetics and no half-life-time (t(1/2)) can be calculated by linear regression. Based on the experimental data a DT50 value (time at which the concentration is reduced by 50 %) can be estimated instead.

Results of hydrolysis and kinetics at 20 °C for pH 4

Table1: Overall hydrolysis of test item and concentration of hydrolysis products expressed in µmole/L

Hydrolysis time (hours)	7PPD	"N-Oxide"	4-HDPA	Aniline	p-Hydroquinone	p-Benzoquinone	Sum [µmole/L)
0	3.20	--	--	--	--	--	3.20
0.5	3.34	--	--	--	--	--	3.34
2.1	3.28	--	--	--	--	--	3.28
18	3.27	--	--	--	--	--	3.27
25	3.19	--	--	--	--	--	3.19
43	3.11	--	--	--	--	--	3.11
68	3.33	--	--	--	--	--	3.33
92	3.24	--	--	--	--	--	3.24
164	2.96	--	--	0.32	--	--	3.28
333	1.86	--	--	1.02	0.38	0.16	3.42
402	1.28	--	--	1.49	0.67	0.36	3.80
500	1.03	--	--	1.68	0.89	0.39	3.99
668	0.65	--	--	2.02	1.15	0.48	4.30
741	0.16	--	--	2.30	1.19	0.74	4.38

Results of hydrolysis and kinetics at 20 °C for pH 7

Table 2: Overall hydrolysis of test item and concentration of hydrolysis products expressed in µmole/L

Hydrolysis time (hours)	7PPD	"N-Oxide"	4-HDPA	Aniline	p-Hydroquinone	p-Benzoquinone	Sum [µmole/L)
0	3.00	--	--	--	--	--	3.00
1.0	2.61	--	--	--	--	--	2.61
3.1	1.82	--	--	--	--	--	1.82
5.2	1.36	--	--	--	--	--	1.36
21	0.34	1.26	0.33	--	--	--	1.92
25	0.17	1.67	--	--	--	--	1.84
46	0.14	1.71	0.36	--	--	--	2.21
70	--	1.75	0.35	--	--	--	2.11
142	--	1.76	0.29	0.19	--	0.15	2.39
214	--	1.83	--	0.28	--	0.21	2.31
310	--	1.83	--	0.40	--	0.31	2.54
480	--	1.59	--	0.56	--	0.38	2.53
648	--	1.46	--	0.73	--	0.44	2.63
721	--	1.40	--	0.76	--	0.44	2.61

Results of hydrolysis and kinetics at 20 °C for pH 9

Table 3: Overall hydrolysis of test item and concentration of hydrolysis products expressed in µmole/L

Hydrolysis time (hours)	7PPD	"N-Oxide"	4-HDPA	Aniline	p-Hydroquinone	p-Benzoquinone	Sum [µmole/L)
0	2.98	--	--	--	--	--	2.98
1.0	2.39	--	--	--	--	--	2.39
2.1	2.53	--	--	--	--	--	2.53
3.1	2.33	--	--	--	--	--	2.33
20	0.61	0.79	0.31	--	--	--	1.71
24	0.21	1.25	0.19	--	--	--	1.66
45	--	1.82	0.17	--	--	--	1.99
69	--	1.88	--	--	--	--	1.88
141	--	1.74	0.23	--	--	--	1.97
213	--	1.68	0.28	0.27	--	--	2.22
309	--	1.46	0.36	0.42	--	--	2.24
479	--	1.27	0.23	0.61	--	--	2.10
647	--	1.24	--	0.78	--	--	2.01
720	--	1.21	0.24	0.90	--	--	2.35

Validity criteria fulfilled:

yes

Remarks:

The recovery and the repeatability were checked on every day of application. According to OECD 111 Guideline a sterility test was conducted at the end of 90 % hydrolysis. No microbes (colonies) were found. Therefore biotic degradation can be excluded.

Conclusions:

The test item Santoflex 7PPD was found to be hydrolytically instable at pH 4, pH 7 and pH 9.

The following degradation products were detected:
pH 4: aniline, p-benzoquinone, p-hydroquinone
pH 7: aniline, p-benzoquinone, unknown component
pH 9: aniline, unknown component
The LC-MS spectrum of the unknown component shows a molecular ion signal at m/z = 200.0712, which can be assigned to the protonated molecular ion [M+H]+ of C12H9NO2, M = 199 g/mol.
The unknown component therefore appears to have a molecular weight of 199 Dalton linked to a formula C12H9NO2. This would probably fit to “overoxidised 4-HDPA” (4-(phenylnitroso)benzen-1-olate or 4-phenylnitroso)cyclohexa-2,5-dien-1-one) (short name: "N-Oxide").

Recoveries of the test item are near 100 % indicating a satisfying repeatability of the method applied to quantify the test item concentrations. The requirements of OECD 111 are met.

Executive summary:

The hydrolysis of the test item Santoflex 7PPD was investigated for pH 4, pH 7 and pH 9 at 20 °C and 50 °C based on OECD TG 111. The stability was monitored by HPLC analysis using UV-detection until > 90 % hydrolysis of 7PPD as parent compound was observed.

The test item Santoflex 7PPD was found to be hydrolytically instable at pH 4, pH 7 and pH 9. Recoveries of the test item are near 100 % indicating a satisfying repeatability of the method applied to quantify the test item concentration.The requirements of OECD 111 are met.

The hydrolysis tests at 20 °C were prolonged up to 30 days monitoring 7PPD and in addition primary and secondary hydrolysis products ending up with the final hydrolysis products. The following hydrolysis products were determined: 4-Hydroxydiphenylamine, Aniline, p-Benzoquinone, p-Hydroquinone

During the study an additional hydrolysis product was detected in the hydrolysis test solutions at pH 7 and pH 9 only. The LC-MS spectrum of the component shows a molecular ion signal at m/z = 200.0712, which can be assigned to the protonated molecular ion [M+H]+ of C12H9NO2, M = 199 g/mol. The component therefore appears to have a molecular weight of 199 Dalton linked to a formula C12H9NO2. This would probably fit to “overoxidised 4-HDPA” (4-(phenylnitroso)benzen-1-olate or 4-phenylnitroso)cyclohexa-2,5-dien-1-one) (short name: “N-Oxide”).

The kinetic behavior of Santoflex 7PPD and identified hydrolysis products were monitored and evaluated.

Identified primary hydrolysis products of Santoflex 7PPD are 4-Hydroxydiphenylamine (4-HDPA) and “N-Oxide”. 4-HDAP was built by release of 1,4-dimethylpentylamine. Oxidation of 4-HDAP resulted in “N-Oxide”. Due to subsequent hydrolysis of primary degradation products secondary hydrolysis products are Aniline, p-Benzoquinone, and p-Hydroquinone.

At pH 4 the degradation products 4-HDPA and N-Oxide could not be measured, while Aniline, p-Benzoquinone, and p-Hydroquinone were formed. Therefore, it was supposed that 4-HDPA and N-Oxide are highly instable at pH 4 and immediately degrade to Aniline and quinones (p-Benzoquinone, and p-Hydroquinone).

Therefore, it is assumed that the same reported hydrolysis mechanism occurs at hydrolysis of Santoflex 7PPD at all investigated pH values 4, 7, and 9.

Additionally the mass balance of Santoflex 7PPD including primary and secondary hydrolysis products was monitored over 30 days of hydrolysis. Comparison of the starting concentration of Santoflex 7PPD to the summarized concentration of measured degradation products after 30 days showed deviations at all investigated pH values:

pH 4: At the beginning of measurement the concentration of Santoflex 7 PPD was determined to be 3.2 µmol/L. After 30 days the sum of all measured degradation products was reported to be 4.38 µmol/L. It is assumed that deviation in mass balancing could be a result of measuring inaccuracy of the analytical method. Real starting concentration of Santoflex 7PPD in hydrolysis test was reported to be 3.58 µmol/L. Due to delayed starting of measurement (caused by preparation of the sample, like dilution, mixing) the concentration of 7PPD at t=0 hrs was measured to be 3.2 µmol /L instead of 3.58 µmol/L. This deviation could result in higher mass balance at the end of measurement. Additional, several reported concentrations of Aniline, p-Benzoquinone, and p-Hydroquinone were measured to be outside calibration range (below the lowest calibration level) but taken into account for the mass balance. This could also result in inaccuracy of reported values.

pH 7 and pH 9: At pH 7 a starting concentration of Santoflex 7PPD 3.0 µmol/L (at pH 9: 2.98 µmol/L) was measured at the beginning of hydrolysis. After 30 days the sum of all measured degradation products was reported to be 2.61 µmol/L (at pH 9: 2.35 µmol/L). It is assumed that deviations in mass balancing are caused by calibration inaccuracy of “N-Oxide”. This degradation product was quantified using the response factor of the parent compound 7PPD at 202 nm assuming similar UV absorption of their chemical structures. This calibration could influence the reported values of concentration and therefore has an influence on correct mass balane. Additionally deviation in mass balancing could be a result of measuring inaccuracy of the analytical method. Several reported concentrations of 7PPD, Aniline, and p-Benzoquinone were measured to be outside calibration range (below the lowest calibration level) but taken into account for the mass balance. This could result in inaccuracy of reported values. Additionally it is assumed that the concentration of p-Hydroquinone at pH 7 (p-Hydroquinone and p-Benzoquinone at pH 9) was below limit of detection and therefore could not be included into the sum of all degradation products.

Description of key information

The hydrolysis of Santoflex 7PPD (N-(1,4-dimethylpentyl)-N'-phenylbenzene-1,4-diamine) was investigated for pH 4, pH 7 and pH 9 at 20 °C and 50 °C based on OECD TG 111. The half-life of 7PPD was determined to be 7 hours at 20 °C (pH 7) and 1 hour at 50 °C (pH 7).

The following hydrolysis products were determined: 4-Hydroxydiphenylamine, Aniline, p-Benzoquinone, p-Hydroquinone. During the study an additional hydrolysis product was detected in the hydrolysis test solutions at pH 7 and pH 9 only. The LC-MS spectrum of the component shows a molecular ion signal at m/z = 200.0712, which can be assigned to the protonated molecular ion [M+H]+ of C12H9NO2, M = 199 g/mol. The component therefore appears to have a molecular weight of 199 Dalton linked to a formula C12H9NO2. This would probably fit to “overoxidised 4-HDPA” (4-(phenylnitroso)benzen-1-olate or 4-(phenylnitroso)cyclohexa-2,5-dien-1-one) (short name: “N-Oxide”).

7PPD was found to be hydrolytically instable at pH 4, pH 7 and pH 9. Recoveries of the test item are near 100 % indicating a satisfying repeatability of the method applied to quantify the test item concentration.

The hydrolysis tests at 20 °C were prolonged up to 30 days monitoring 7PPD and in addition primary and secondary hydrolysis products. Identified primary hydrolysis products of Santoflex 7PPD are 4-Hydroxydiphenylamine (4-HDPA) and “N-Oxide”. 4-HDAP was built by release of 1,4-dimethylpentylamine. Oxidation of 4-HDAP resulted in “N-Oxide”. Due to subsequent hydrolysis of primary degradation products secondary hydrolysis products are Aniline, p-Benzoquinone, and p-Hydroquinone.

At pH 4 the degradation products 4-HDPA and N-Oxide could not be measured, while Aniline, p-Benzoquinone, and p-Hydroquinone were formed. Therefore, it was supposed that 4-HDPA and N-Oxide are highly instable at pH 4 and immediately degrade to Aniline and quinones (p-Benzoquinone, and p-Hydroquinone).

Therefore, it is assumed that the same reported hydrolysis mechanism occurs at hydrolysis of Santoflex 7PPD at all investigated pH values 4, 7, and 9.

Key value for chemical safety assessment

Half-life for hydrolysis:

7 h

at the temperature of:

20 °C

Additional information

Mass balance of Santoflex 7PPD including primary and secondary hydrolysis products was monitored over 30 days of hydrolysis. Comparison of the starting concentration of Santoflex 7PPD to the summarized concentration of measured degradation products after 30 days showed deviations at all investigated pH values:

 

pH 4:At the beginning of measurement the concentration of Santoflex 7 PPD was determined to be 3.2 µmol/L. After 30 days the sum of all measured degradation products was reported to be 4.38 µmol/L. It is assumed that deviation in mass balancing could be a result of measuring inaccuracy of the analytical method. Real starting concentration of Santoflex 7PPD in hydrolysis test was reported to be 3.58 µmol/L. Due to delayed starting of measurement (caused by preparation of the sample, like dilution, mixing) the concentration of 7PPD at t=0 hrs was measured to be 3.2 µmol /L instead of 3.58 µmol/L. This deviation could result in higher mass balance at the end of measurement. Additional, several reported concentrations of Aniline, p-Benzoquinone, and p-Hydroquinone were measured to be outside calibration range (below the lowest calibration level) but taken into account for the mass balance. This could also result in inaccuracy of reported values.

 

pH 7 and pH 9:At pH 7 a starting concentration of Santoflex 7PPD 3.0 µmol/L (at pH 9: 2.98 µmol/L) was measured at the beginning of hydrolysis. After 30 days the sum of all measured degradation products was reported to be 2.61 µmol/L (at pH 9: 2.35 µmol/L). It is assumed that deviations in mass balancing are caused by calibration inaccuracy of “N-Oxide”. This degradation product was quantified using the response factor of the parent compound 7PPD at 202 nm assuming similar UV absorption of their chemical structures. This calibration could influence the reported values of concentration and therefore has an influence on correct mass balane. Additionally deviation in mass balancing could be a result of measuring inaccuracy of the analytical method. Several reported concentrations of 7PPD, Aniline, and p-Benzoquinone were measured to be outside calibration range (below the lowest calibration level) but taken into account for the mass balance. This could result in inaccuracy of reported values. Additionally it is assumed that the concentration of p-Hydroquinone at pH 7 (p-Hydroquinone and p-Benzoquinone at pH 9) was below limit of detection and therefore could not be included into the sum of all degradation products (Currenta, 2016).