Diammonium peroxodisulphate

Hydrolysis

Link to relevant study record(s)

Reference

Endpoint:

hydrolysis

Type of information:

experimental study

Adequacy of study:

key study

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)

Version / remarks:

2004-11-23

Deviations:

no

GLP compliance:

no

Remarks:

In-house quality and environmental management system in place. Certified in accordance with ISO 9001:2015 and ISO 14001:2015.

Radiolabelling:

no

Analytical monitoring:

yes

Remarks:

Ion chromatography

Buffers:

1) pH-4 buffer solution:
20.43 g potassium hydrogen phthalate were dissolved in 1 L distilled water at 20 °C. To 500 mL of that solution 4.0 mL NaOH 0.1 M and water are added to an overall volume of 1.0 L.

2) pH-7 buffer solution:
13.61 g potassium hydrogen phosphate were dissolved in 1 L distilled water at 20 °C. To 500 mL of that solution 296.3 mL NaOH 0.1 M and water are added to an overall volume of 1.0 L.

3) pH-9 buffer solution:
6.19 g boric acid were dissolved in 1 L distilled water at 20 °C. To 500 mL of that solution 213.0 mL NaOH 0.1 M and water are added to an overall volume of 1.0 L.

Details on test conditions:

TEST SYSTEM
- Type, material and volume of test flasks, other equipment used: standard laboratory glassware
- Sterilisation method: none
- Lighting: darkness
- Measures taken to avoid photolytic effects:yes, the test was performed unter total darkness.
- Measures to exclude oxygen: none.

TEST MEDIUM
- Volume used/treatment: 50 mL
- Kind and purity of water: distilled water

OTHER TEST CONDITIONS
- Adjustment of pH: none

Duration:

4 d

pH:

9

Temp.:

60 °C

Duration:

4 d

pH:

7

Temp.:

60 °C

Duration:

4 d

pH:

4

Temp.:

60 °C

Duration:

32 d

pH:

9

Temp.:

25 °C

Duration:

32 d

pH:

7

Temp.:

25 °C

Duration:

32 d

pH:

4

Temp.:

25 °C

Duration:

31 d

pH:

9

Temp.:

10 °C

Duration:

31 d

pH:

7

Temp.:

10 °C

Duration:

31 d

pH:

4

Temp.:

10 °C

Number of replicates:

2

Positive controls:

no

Negative controls:

no

Preliminary study:

The preliminary hydrolysis test was performed at 50 °C at pH values of 4, 7 and 9. The samples were incubated for five days and analyzed afterwards.

S2O8[2-] (t = 0) S2O8[2-] (t = 5 days)
pH 4 88.21 7.77
pH 7 84.93 13.37
pH 9 97.45 12.33

The persulfate was hydrolyzed to similar degrees at all tested pH values. Given the fact, that in each case the amount of hydrolyzed substance is more than 10 %, the substance cannot be considered hydrolytically stable. Thus, an in-detail study was conducted.

Transformation products:

not specified

Key result

pH:

7

Temp.:

12 °C

Hydrolysis rate constant:

0 h-1

DT50:

1 698.18 h

Type:

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

Key result

pH:

4

Temp.:

60 °C

Hydrolysis rate constant:

0.025 h-1

DT50:

27.7 h

Type:

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

pH:

7

Temp.:

60 °C

Hydrolysis rate constant:

0.019 h-1

DT50:

36.5 h

Type:

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

pH:

9

Temp.:

60 °C

Hydrolysis rate constant:

0.019 h-1

DT50:

36.5 h

Type:

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

As the APS was found to be unstable at all tested pH values, advanced tests were conducted for all three conditions. The buffered APS solutions were thermostated at 10, 25, as well as 60 °C, respectively.

Hydrolysis at 10 °C

Table 1: Analytic results of the hydrolysis of APS at 10 °C and pH = 4.

APS (10 °C, pH = 4)
Day	Sample-ID	weighed-in sample [g]	S2O8^2- [%]		pH	SO4^2-
			Sample 1	Sample 2
1	0 (Start)	0.1171	85.40	85.35	4.03
4	1	0.1151	85.91	85.71	4.05
8	2	0.1142	85.99	85.43	4.10
11	3	0.1157	87.98	88.00	4.08
15	4	0.1142	88.54	88.39	4.10
18	5	0.1162	88.65	87.68	3.97
22	6	0.1147	90.90	92.08	3.90
25	7	0.1149	91.79	92.33	4.08
29	8	0.1143	92.38	92.47	4.10
31	9	0.1182	94.54	94.78	4.06	0.5

APS is hydrolytically stable at 10 °C and pH=4. Interestingly, the measured APS content was found to increase over the measurement period. The sulfate content of the final sample 9 was determined to be 0.5 %, further confirming the stability of APS under these conditions.

Table 2: Analytic results of the hydrolysis of APS at 10 °C and pH = 7.

APS (10 °C, pH = 7)
Day	Sample-ID	weighed-in sample [g]	S2O8^2- [%]		pH	SO4^2-
			Sample 1	Sample 2
1	0 (Start)	0.1201	85.53	85.06	6.97
4	1	0.1148	86.40	84.98	6.97
8	2	0.1143	85.85	86.16	7.03
11	3	0.1142	88.27	88.29	7.04
15	4	0.1177	88.94	88.00	7.05
18	5	0.1155	89.37	87.87	6.96
22	6	0.1165	91.54	91.77	6.88
25	7	0.1159	82.02	91.78	7.00
29	8	0.1160	92.56	93.17	7.00
31	9	0.1185	94.89	93.52	6.96	0.1

The results from the study at pH = 4 can be confirmed for pH = 7. APS is hydrolytically stable under these conditions (10 °C and pH=7) as well. Likewise, the measured APS content was found to increase over the measurement period. The sulfate content of the final sample 9 was determined to 0.1 %, confirming the stability of APS under these conditions.

Table 3: Analytic results of the hydrolysis of APS at 10 °C and pH = 9.

APS (10 °C, pH = 9)
Day	Sample-ID	weighed-in sample [g]	S2O8^2- [%]		pH	SO4^2-
			Sample 1	Sample 2
1	0 (Start)	0.1155	84.05	84.16	8.86
4	1	0.1148	84.80	85.16	8.75
8	2	0.1152	85.95	85.25	8.80
11	3	0.1149	88.24	88.60	8.86
15	4	0.1161	88.60	88.14	8.86
18	5	0.1176	89.19	87.77	8.85
22	6	0.1166	90.30	91.72	8.70
25	7	0.1151	91.07	92.13	8.80
29	8	0.1145	92.56	92.68	8.70
31	9	0.1183	93.78	93.52	8.75	0.6

The results from the study at pH = 4 and 7 can be confirmed for pH = 9 as well. APS is hydrolytically stable under these conditions (10 °C and pH=9) as well. Likewise, the measured APS content was found to increase over the measurement period. The sulfate content of the final sample 9 was determined to 0.6 %, confirming the stability of APS under these conditions.

Hydrolysis at 25 °C

Table 4: Analytic results of the hydrolysis of APS at 25 °C and pH = 4.

APS (25 °C, pH = 4)
Day	Sample-ID	weighed-in sample [g]	S2O8^2- [%]		pH	SO4^2-
			Sample 1	Sample 2
1	0 (Start)	0.1117	85.66	85.95	4.08
5	1	0.1133	85.62	85.57	4.09
8	2	0.1128	85.57	85.40	4.05
12	3	0.1180	85.95	86.14	3.94
15	4	0.1121	85.21	85.41	4.03
19	5	0.1138	85.20	85.40	4.01
22	6	0.1125	84.72	84.21	4.05
26	7	0.1123	84.45	84.39	3.99
29	8	0.1142	77.80	78.07	3.81
32	9	0.1121	68.94	68.82	3.82	3.22

APS is hydrolytically stable until after sample 7 (after approx. 3 weeks). Afterwards, the APS content was found to decrease significantly. Likewise, the pH value drops to 3.8 indicating that the buffer is used up at this point. The sulfate content was analysed to 3.2% which is a lower value than anticipated from the decreased amount of persulfate. This might be explained by the fact that persulfates can decompose via a different pathway in the acidic milieu and form monoperoxosulfate SO₅^2- as an intermediate decomposition product which was not determined analytically during this study.

Table 5: Analytic results of the hydrolysis of APS at 25 °C and pH = 7.

APS (25 °C, pH = 7)
Day	Sample-ID	weighed-in sample [g]	S2O8^2- [%]		pH	SO4^2-
			Sample 1	Sample 2
1	0 (Start)	0.1122	84.63	84.97	7.03
5	1	0.1135	85.64	85.77	6.99
8	2	0.1158	86.19	86.12	6.96
12	3	0.1157	86.50	86.69	6.93
15	4	0.1183	86.78	86.84	6.97
19	5	0.1134	86.67	86.57	6.94
22	6	0.1122	87.95	87.67	7.00
26	7	0.1113	87.95	88.00	6.93
29	8	0.1170	82.39	82.82	6.85
32	9	0.1136	82.98	83.43	6.81	2.40

The results from the study at pH = 7 indicate that almost no hydrolysis was observed under these conditions. After one month the persulfate content was reduced by approx. 2.5 %. The analysed amount of SO₄^2- in the terminal sample was 2.40 % which is in good accordance to the decomposed amount of persulfate. Analogous to the study at pH = 4 the final pH-value of the sample is slightly lower than the original sample at the beginning of the measurement indicating that the buffer was at its limit.

Table 6: Analytic results of the hydrolysis of APS at 25 °C and pH = 9.

APS (25 °C, pH = 9)
Day	Sample-ID	weighed-in sample [g]	S2O8^2- [%]		pH	SO4^2-
			Sample 1	Sample 2
1	0 (Start)	0.1130	85.66	85.95	8.76
5	1	0.1121	85.77	85.99	8.72
8	2	0.1144	86.51	86.43	8.71
12	3	0.1130	86.49	86.52	8.69
15	4	0.1144	86.75	87.00	8.71
19	5	0.1146	87.46	87.09	8.67
22	6	0.1122	87.07	86.94	8.70
26	7	0.1121	87.46	87.21	8.68
29	8	0.1135	82.07	82.77	8.51
32	9	0.1124	83.00	82.58	8.52	2.94

The results from the study at pH = 9 is very similar to the result obtained at pH = 7. APS is hydrolytically stable under these conditions as well. After one month the persulfate content was reduced by approx. 3 %. The analysed amount of SO₄^2- in the terminal sample was 2.94 % which is in good accordance to the decomposed amount of persulfate. Analogous to the study at pH = 4 the final pH-value of the sample is slightly lower than the original sample at the beginning of the measurement indicating that the buffer was at its limit.

Hydrolysis at 60 °C

Table 7: Analytic results of the hydrolysis of APS at 60 °C and pH = 4.

APS (60 °C, pH = 4)
Date, Time	Sample-ID	weighed-in sample [g]	S2O8^2- [%]		pH	SO4^2-
			Sample 1	Sample 2
2019-03-25, 07:00	0 (Start)	0.1138	84.48	84.37	4.09
2019-03-25, 15:00	1	0.1127	59.51	59.42	3.83
2019-03-26, 06:00	2	0.1136	37.68	38.58	3.60
2019-03-26, 11:00	3*	0.1138	28.74	28.76	3.47
2019-03-26, 15:00	4*	0.1134	28.56	28.94	3.46
2019-03-27, 06:00	5*	0.1130	20.00	19.09	3.43
2019-03-27, 13:00	6*	0.1134	15.97	15.82	3.42
2019-03-28, 06:00	7**	0.1150	11.06	11.05	3.35
2019-03-28, 13:00	8**	0.1123	10.45	10.43	3.36
2019-03-29, 06:00	9**	0.1130	7.53	7.53	3.36	81.87***

* dilution factor for ion chromatographic analysis = 8000

** dilution factor for ion chromatographic analysis = 4000

*** dilution factor for ion chromatographic analysis = 80000

APS decomposes rather quickly under the test conditions. After approx. 4 days less than 10 % of the original content was found in the respective samples. The amount of sulfate detected in the terminal sample is in good agreement with that finding. At this temperature it was not possible to hold the pH value of the buffered solutions at 4. It drifted steadily to 3.36 throughout the study.

Table 8: Analytic results of the hydrolysis of APS at 60 °C and pH = 7.

APS (60 °C, pH = 7)
Date, Time	Sample-ID	weighed-in sample [g]	S2O8^2- [%]		pH	SO4^2-
			Sample 1	Sample 2
2019-03-25, 07:00	0 (Start)	0.1146	85.23	85.19	7.05
2019-03-25, 15:00	1	0.1123	74.68	74.19	6.96
2019-03-26, 06:00	2	0.1128	53.73	54.32	6.63
2019-03-26, 11:00	3*	0.1138	49.63	48.97	6.57
2019-03-26, 15:00	4*	0.1143	46.77	46.95	6.55
2019-03-27, 06:00	5*	0.1129	32.42	32.33	6.41
2019-03-27, 13:00	6*	0.1128	30.41	30.42	6.40
2019-03-28, 06:00	7**	0.1139	22.69	22.90	6.21
2019-03-28, 13:00	8**	0.1127	20.82	21,06	6.20
2019-03-29, 06:00	9**	0.1158	14.29	14.22	6.06	72.04***

* dilution factor for ion chromatographic analysis = 8000

** dilution factor for ion chromatographic analysis = 4000

*** dilution factor for ion chromatographic analysis = 40000

APS decomposes rather quickly at these conditions, however somewhat slower than at pH = 4. The amount of sulfate detected in the terminal sample (72.04 %) is in good agreement with the corresponding APS content. As for the previous study at pH = 4 it was also not possible to keep the pH value of the buffered solutions at 7. It drifted steadily to a final value of 6.06 during the study.

Table 9: Analytic results of the hydrolysis study of APS at 60 °C and pH = 9.

APS (60 °C, pH = 9)
Date, Time	Sample-ID	weighed-in sample [g]	S2O8^2- [%]		pH	SO4^2-
			Sample 1	Sample 2
2019-03-25, 07:00	0 (Start)	0.1160	85.86	85.77	8.88
2019-03-25, 15:00	1	0.1165	69.94	70.58	8.71
2019-03-26, 06:00	2	0.1122	50.78	51.25	8.34
2019-03-26, 11:00	3*	0.1116	45.03	44.50	8.19
2019-03-26, 15:00	4*	0.1136	43.53	43.38	8.16
2019-03-27, 06:00	5*	0.1130	35.42	35.33	7.68
2019-03-27, 13:00	6*	0.1143	31.89	31.59	7.60
2019-03-28, 06:00	7**	0.1117	21.52	21.65	7.00
2019-03-28, 13:00	8**	0.1165	19.21	19.26	3.30
2019-03-29, 06:00	9**	0.1159	13.60	12.93	2.93	78.17***

* dilution factor for ion chromatographic analysis = 8000

** dilution factor for ion chromatographic analysis = 4000

*** dilution factor for ion chromatographic analysis = 40000

APS decomposes at 60 °C and pH=9 with a similar rate compared to the study at pH = 7. The amount of sulfate detected in the terminal sample is again in good agreement with the corresponding APS content. As for the previous studies at 60 °C it was also not possible to keep the pH value of the buffered solutions at 9. Especially close to the end of the study the pH value of the sample fell rapidly to a final value of 2.93.

Validity criteria fulfilled:

yes

Conclusions:

APS was shown to be hydrolitically stable at 10 °C and pH 4, 7 and 9, a minor hydrolysis was observed at 25 °C, whereas, a very strong hydrolysis at 60 °C was observed within 4 days. The DT50 at pH 4 and 60 °C was determined to be 27.2 h, at pH 7 and 9 and 60 °C the DT50 was determined to be 36.5 h. The DT50 at environmentally relevant temperature (12 °C) and pH 7 was extrapolated to be 1698.18 h (70.76 d).

Executive summary:

A study according to OECD TG 111 was performed to determine the hydrolysis potential of the test item. Inittialla, a Tier 1 tests at for 5 days at 50 °C and H 4, 7 and 9 was performed. Hydrolisys of more than 10 % was observed at all pH levels. Thus, a Tier 2 hydrolysis test was conducted at 10, 25 and 60 °C and pH 4, 7 and 9. Hydrolysis studies at 10 and 25 °C run for ca. 30 days, while at 60 °C the hydrolysis process was finished after 4 days. APS was shown to be hydrolitically stable at 10 °C and pH 4, 7 and 9, a minor hydrolysis was observed at 25 °C, whereas, a very strong hydrolysis at 60 °C was observed within 4 days. The DT50 at pH 4 and 60 °C was determined to be 27.2 h. The DT50 at environmentally relevant temperature (12 °C) was extrapolated to be 1288.76 h (53.7 d).

Description of key information

Persulfates dissociate in water to the corresponding cation and persulfate anion. Hydrolysis is temperature and pH dependent. The persulfate anion, independent from the cation, undergoes decomposition in normal water or acid conditions, readily oxidizing water to oxygen, producing acid conditions. All degradation products are ubiquitous to the environment. APS was shown to be hydrolitically stable at 10 °C and pH 4, 7 and 9, a minor hydrolysis was observed at 25 °C, whereas, a very strong hydrolysis at 60 °C was observed within 4 days. The DT50 at pH 4 and 60 °C was determined to be 27.2 h, at pH 7 and 9 and 60 °C the DT50 was determined to be 36.5 h. The DT50 at environmentally relevant temperature (12 °C) and pH 7 was extrapolated to be 1698.18 h (70.76 d).

Key value for chemical safety assessment

Half-life for hydrolysis:

70.76 d

at the temperature of:

12 °C

Additional information

A study according to OECD TG 111 was performed to determine the hydrolysis potential of the test item. Initially, a Tier 1 tests at for 5 days at 50 °C and H 4, 7 and 9 was performed. Hydrolisys of more than 10 % was initially observed at all pH levels. Thus, a Tier 2 hydrolysis test was conducted at 10, 25 and 60 °C and pH 4, 7 and 9. Hydrolysis studies at 10 and 25 °C run for ca. 30 days, while at 60 °C the hydrolysis process was finished after 4 days. APS was shown to be hydrolitically stable at 10 °C and pH 4, 7 and 9, a minor hydrolysis was observed at 25 °C, whereas, a very strong hydrolysis at 60 °C was observed within 4 days. The DT50 at pH 4 and 60 °C was determined to be 27.2 h, at pH 7 and 9 and 60 °C the DT50 was determined to be 36.5 h. The DT50 at environmentally relevant temperature (12 °C) and pH 7 was extrapolated to be 1698.18 h (70.76 d).