2,4-diethyl-9H-thioxanthen-9-one

Hydrolysis

Link to relevant study record(s)

Reference

Endpoint:

hydrolysis

Type of information:

read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

supporting study

Study period:

18 July 2017 to 20 September 2017

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: guideline study on closely related supporting substance

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)

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Radiolabelling:

no

Analytical monitoring:

yes

Details on sampling:

- For the determination of the concentrations of the test material in the different measuring cylinders at different time intervals, samples were taken under nitrogen atmosphere and measured undiluted by means of HPLC with UV-detection.
- Whenever samples were measured also standard solutions freshly prepared from the test material in acetonitrile and blank buffer solutions were measured for verification of the analytical method

Buffers:

- The buffer solutions used for pH 4, 7 and 9 were:
pH 4: acetic acid (0.05 mol/L) / sodium acetate (0.01 mol/L) 1:1 v/v
pH 7: Solution A: potassium dihydrogen phosphate (0.07 mol/L). Solution B: di-potassium hydrogen phosphate (0.07 mol/L). Buffer solution: 306 mL solution B + 194 mL solution A
pH 9: ammoniac 25 % (14 mol/L) / ammonium chloride (0.05 mol/L) 1:1 v/v (adjusted to the pH with HCl (1 mol/L))
- The pH value of each buffer solution was checked with a calibrated pH meter to a precision of 0.1.

Details on test conditions:

- The study was performed in measuring flasks, which were dried in a drying chamber at 200 °C for 48 hours, under dark and sterile conditions (under inert atmosphere) in temperature controlled water baths.
- The test material was dissolved in acetonitrile and applied into the different buffer solutions under nitrogen atmosphere.
- Preliminary test (Tier 1): The preliminary test was carried out at 50 ± 0.5 °C and pH values of 4.0, 7.0 and 9.0, respectively, in duplicate. The concentration of the test material in the test solutions was 332.4 mg/L. Due to the fact that the test material proved to be unstable at all three pH values further kinetic tests (Tier 2) were carried out.
- Hydrolysis of unstable substances (Tier 2): Due to the fact that the test material was unstable at all three pH values further kinetic tests (Tier 2) were carried out at temperatures of 20, 25 and 30 °C. At each pH-value and each temperature at least two parallel tests (a and b) were performed. Each reaction solution was analysed in time intervals, which were set up to allow at least six data points between 10 and 90 % hydrolysis to be measured.

Duration:

240 h

pH:

4

Temp.:

20 °C

Initial conc. measured:

>= 6.766 - <= 7.739 mg/L

Duration:

98.7 h

pH:

4

Temp.:

50 °C

Initial conc. measured:

>= 5.933 - <= 9.346 mg/L

Duration:

31 h

pH:

4

Temp.:

60 °C

Initial conc. measured:

>= 6.279 - <= 6.694 mg/L

Duration:

190.1 h

pH:

7

Temp.:

20 °C

Initial conc. measured:

>= 6.425 - <= 6.808 mg/L

Duration:

95.6 h

pH:

7

Temp.:

50 °C

Initial conc. measured:

>= 6.224 - <= 6.71 mg/L

Duration:

30.9 h

pH:

7

Temp.:

60 °C

Initial conc. measured:

>= 6.182 - <= 7.134 mg/L

Duration:

164.1 h

pH:

9

Temp.:

20 °C

Initial conc. measured:

>= 6.745 - <= 6.873 mg/L

Duration:

75.7 h

pH:

9

Temp.:

50 °C

Initial conc. measured:

>= 6.497 - <= 6.978 mg/L

Duration:

30.3 h

pH:

9

Temp.:

60 °C

Initial conc. measured:

>= 0.083 - <= 0.215 mg/L

Number of replicates:

The test was performed in duplicate

Positive controls:

no

Negative controls:

no

Preliminary study:

TIER 1: The preliminary test at pH 4, 7 and 9 was performed at a temperature of 50 °C. Samples were taken and measured after 17 and 116 hours. The nominal start concentration of the test material was 7.9 mg/L. It was observed, that the test material was hydrolysed by more than 10 % at all three pH values after 5 hours. Thus, Tier 2 was performed for all three pH values.

Test performance:

The HPLC-method was checked several times on every day that samples of the tests were taken and measured. The recovery rates of the standard solutions in acetonitrile range from 93.3 to 109.9 % and show a sufficient accuracy of the analytical method. Only one standard (2017-08-23) is outside the acceptable range. Due to the fact that all other standards are in a good range, these three measurements of 2017-08-23, which are outside the acceptable range, can be neglected.

Transformation products:

not specified

Key result

pH:

4

Temp.:

20 °C

Hydrolysis rate constant:

0.006 h-1

DT50:

126.5 h

Key result

pH:

4

Temp.:

50 °C

Hydrolysis rate constant:

0.014 h-1

DT50:

51.1 h

Key result

pH:

4

Temp.:

60 °C

Hydrolysis rate constant:

0.018 h-1

DT50:

39.5 h

Key result

pH:

7

Temp.:

20 °C

Hydrolysis rate constant:

0.009 h-1

DT50:

88.3 h

Key result

pH:

7

Temp.:

50 °C

Hydrolysis rate constant:

0.012 h-1

DT50:

58.7 h

Key result

pH:

7

Temp.:

60 °C

Hydrolysis rate constant:

0.011 h-1

DT50:

65.8 h

Key result

pH:

9

Temp.:

20 °C

Hydrolysis rate constant:

0.013 h-1

DT50:

54.1 h

Key result

pH:

9

Temp.:

50 °C

Hydrolysis rate constant:

0.018 h-1

DT50:

39.1 h

Key result

pH:

9

Temp.:

60 °C

Hydrolysis rate constant:

0.021 h-1

DT50:

32.8 h

Details on results:

TIER 2 (pH 4)
- For the test at pH 4 and 20 °C a nominal concentration of the test material in the buffer solution of 8.01 mg/L was used. The degree of hydrolysis for the tests a and c at the respective sampling times was calculated in comparison to the measured c0-value at t = 0 h. Results can be seen in Table 1. The calculated results of the measurements at pH 4 at 20 °C are:
10a: kobs = 0.0047 h^-1, t0.5 = 148.6 h
10b: kobs = 0.0066 h^-1, t0.5 = 104.3 h

- For the test at pH 4 and 50 °C a concentration of the test material in the buffer solution of 7.76 and 7.84 mg/L was used. The degree of hydrolysis for the tests a and b at the respective sampling times was calculated in comparison to the measured c0-value at t = 0 h. The test was started with the parallel tests 6a and 6b. Due to the very different slope of the hydrolysis, two further tests were performed (21 a and 21 b). The tests 21 a and 21 b show the same tendency as test 6b. Therefore, these three tests are reported. Results can be seen in Table 2. The results of the measurements at pH 4 at 50 °C are:
6b: kobs = 0.0118 h^-1, t0.5 = 58.8 h
21a: kobs = 0.0145 h^-1, t0.5 = 47.9 h
21b: kobs = 0.0149 h^-1, t0.5 = 46.5 h

- For the test at pH 4 and 60 °C a concentration of the test material in the buffer solution of 7.84 mg/L was used. The degree of hydrolysis for the tests a and b at the respective sampling times was calculated in comparison to the measured c0-value at t = 0 h. Results can be seen in Table 3. The results of the measurements at pH 4 at 60 °C are:
18a: kobs = 0.0168 h^-1, t0.5 = 41.2 h
18b: kobs = 0.0184 h^-1, t0.5 = 37.7 h

- Calculation of the Arrhenius parameters for pH 4 can be seen in Table 4.

TIER 2 (pH 7)
- For the test at pH 7 and 20 °C a concentration of the test material in the buffer solution of 8.01 and 7.84 mg/L was used. The degree of hydrolysis for the tests 11 a, 11 c and 22b at the respective sampling times was calculated in comparison to the measured c0-value at t = 0 h.
The test was started with the parallel tests 11 a and 11 b. Due to the much too fast hydrolysis in test 11 b during the first two time steps, test 11 b was stopped and a further test 11 c carried out. Due to the different slope of the hydrolysis of test 11 a and 11 c, one further test was performed (22a). Although the test 11 a, 11 c and 22a show a different slope of hydrolysis these three tests are reported and used for the calculation of the activation energy. Results can be seen in Table 5. The results of the measurements at pH 7 at 20 °C are:
11a: kobs = 0.0056 h^-1, t0.5 = 124.6 h
11c: kobs = 0.0123 h^-1, t0.5 = 56.4 h
22a: kobs = 0.0083 h^-1, t0.5 = 83.8 h

- For the test at pH 7 and 50 °C a concentration of the test material in the buffer solution of 7.76 mg/L was used. The degree of hydrolysis for the tests a and b at the respective sampling times was calculated in comparison to the measured c0-value at t = 0 h. Results can be seen in Table 6. The results of the measurements at pH 7 at 50 °C are:
7a: kobs = 0.0112 h^-1, t0.5 = 61.9 h
7b: kobs = 0.0125 h^-1, t0.5 = 55.5 h

- For the test at pH 7 and 60 °C a concentration of the test material in the buffer solution of 7.84 mg/L was used. The degree of hydrolysis for the tests a and b at the respective sampling times was calculated in comparison to the measured c0-value at t = 0 h. Results can be seen in Table 7. The results of the measurements at pH 7 at 60 °C are:
19a: kobs = 0.0088 h^−1, t0.5 = 78.6 h
19b: kobs = 0.0131 h^−1, t0.5 = 53.0 h

- Calculation of the Arrhenius parameters for pH 7 can be seen in Table 8.

TIER 2 (pH 9)
- For the test at pH 9 and 20 °C a concentration of the test material in the buffer solution of 331.8 mg/L was used. The degree of hydrolysis for the tests a and b at the respective sampling times was calculated in comparison to the measured c0-value at t = 0 h. Results can be seen in Table 9. The results of the measurements at pH 9 at 20 °C are:
12a: kobs = 0.0125 h^-1, t0.5 = 55.4 h
12b: kobs = 0.0132 h^-1, t0.5 = 52.7 h

- For the test at pH 9 and 50 °C a concentration of the test material in the buffer solution of 7.76 mg/L was used. The degree of hydrolysis for the tests a and b at the respective sampling times was calculated in comparison to the measured c0-value at t = 0 h. Results can be seen in Table 10. The results of the measurements at pH 9 at 50 °C are:
8a: kobs = 0.0191 h^-1, t0.5 = 36.3 h
8b: kobs = 0.0166 h^-1, t0.5 = 41.8 h

- For the test at pH 9 and 60 °C a concentration of the test material in the buffer solution of 7.84 mg/L was used. The degree of hydrolysis for the tests a and b at the respective sampling times was calculated in comparison to the measured c0-value at t = 0 h. Results can be seen in Table 11. The results of the measurements at pH 9 at 60 °C are:
20a: kobs = 0.0206 h^−1, t0.5 = 33.7 h
20b: kobs = 0.0217 h^−1, t0.5 = 31.9 h

- Calculation of the Arrhenius parameters for pH 9 can be seen in Table 12.

Table 1: Results of Tier 2 at pH 4 and 20 °C

Sample no.	t[h]	Measuredct [mg/L]	lnc0/ct	Degree of hydrolysis [%]
10a-0	0	6.766	--	--
10a-1	3.6	5.846	0.146	13.6
10a-2	71.4	4.593	0.387	32.1
10a-3	94.9	4.418	0.426	34.7
10a-4	100.0	4.459	0.417	34.1
10a-5	116.9	4.100	0.501	39.4
10a-6	123.6	3.548	0.646	47.6
10a-7	140.8	3.630	0.623	46.4
10a-8	147.8	3.518	0.654	48.0
10a-9	163.9	3.315	0.714	51.0
10a-10	167.9	3.195	0.750	52.8
10a-11	240.0	1.835	1.305	72.9
10c-0	0	7.739	--	--
10c-1	3.6	6.881	0.118	11.1
10c-2	20.9	6.778	0.133	12.4
10c-3	27.8	6.216	0.219	19.7
10c-4	44.0	6.366	0.195	17.7
10c-5	48.0	5.927	0.267	23.4
10c-6	120.0	3.719	0.733	51.9
10c-7	124.2	3.500	0.794	54.8
10c-8	147.8	2.589	1.095	66.5

Table 2: Results of Tier 2 at pH 4 and 50 °C

Sample no.	t[h]	Measuredct [mg/L]	lnc0/ct	Degree of hydrolysis [%]
6b-0	0.0	6.346	--	--
6b-1	3.1	5.833	0.084	8.1
6b-2	21.0	3.728	0.532	41.2
6b-3	26.9	3.380	0.630	46.7
6b-4	45.2	2.175	1.071	65.7
6b-5	50.6	2.374	0.983	62.6
6b-6	70.1	1.986	1.161	68.7
6b-7	75.6	1.996	1.157	68.5
6b-8	98.7	1.822	1.248	71.9
21a-0	0	5.933	--	--
21a-1	3.9	4.291	0.324	26.1
21a-2	19.9	3.198	0.618	43.5
21a-3	23.7	2.880	0.723	48.5
21a-4	27.8	2.798	0.752	49.9
21a-5	43.8	2.346	0.928	57.0
21a-6	47.9	2.160	1.011	60.0
21a-7	51.7	2.079	1.049	61.3
21b-0	0	6.055	--	--
21b-1	3.7	5.225	0.147	13.1
21b-2	19.7	4.038	0.405	31.8
21b-3	23.5	3.726	0.485	36.7
21b-4	27.5	3.433	0.567	41.3
21b-5	43.6	2.843	0.756	50.6
21b-6	47.7	2.694	0.810	53.0

Table 3: Results of Tier 2 at pH 4 and 60 °C

Sample no.	t[h]	Measuredct [mg/L]	lnc0/ct	Degree of hydrolysis [%]
18a-0	0	6.279	--	--
18a-1	2.5	5.337	0.163	15.0
18a-2	5.4	4.797	0.269	23.6
18a-3	23.9	3.434	0.603	45.2
18a-4	26.3	3.428	0.605	45.3
18a-5	28.8	3.261	0.655	48.0
18a-6	31.0	3.377	0.620	46.1
18b-0	0	6.694	--	--
18b-1	2.6	6.008	0.108	10.8
18b-2	5.5	5.514	0.194	18.6
18b-3	23.9	3.997	0.516	42.5
18b-4	26.1	3.807	0.565	45.5
18b-5	28.6	3.651	0.606	48.0
18b-6	30.9	3.560	0.631	49.4

Table 4: Calculation of the Arrhenius Parameters for pH 4

T[°C]	T[K]	1/T[1/K]	kobsh^-1]	lnkobs
20	293.15	0.00341	0.00466	-5.37
20	293.15	0.00341	0.00665	-5.01
50	323.15	0.00309	0.01179	-4.44
50	323.15	0.00309	0.01447	-4.24
50	323.15	0.00309	0.01492	-4.21
60	333.15	0.00300	0.01684	-4.08
60	333.15	0.00300	0.01836	-4.00
lnA	4.42		A[h^-1]	82.7
-EA/R	-2815.6		EA[kJ/mol]	23.41

Table 5: Results of Tier 2 at pH 7 and 20 °C

Sample no.	t[h]	Measuredct [mg/L]	lnc0/ct	Degree of hydrolysis [%]
11a-0	0.0	6.425	--	--
11a-1	3.7	5.443	0.166	15.3
11a-2	71.5	4.441	0.369	30.9
11a-3	95.0	3.902	0.499	39.3
11a-4	100.0	3.916	0.495	39.1
11a-5	116.9	3.333	0.656	48.1
11a-6	123.7	3.112	0.725	51.6
11a-7	140.9	3.051	0.745	52.5
11a-8	147.8	2.779	0.838	56.7
11a-9	164.0	2.635	0.935	60.7
11a-10	168.0	1.952	1.159	68.6
11c-0	0	6.808	--	--
11c-1	3.7	6.285	0.080	7.7
11c-2	20.9	5.598	0.196	17.8
11c-3	28.0	5.572	0.200	18.2
11c-4	44.0	4.487	0.417	34.1
11c-5	48.0	4.415	0.433	35.1
11c-6	120.1	1.867	1.294	72.6
11c-7	124.3	1.857	1.299	72.7
11c-8	147.8	0.969	1.949	85.8

Sample no.	t[h]	Measuredct [mg/L]	lnc0/ct	Degree of hydrolysis [%]
22a-0	0	6.703	--	--
22a-1	6.1	6.111	0.093	1.8
22a-2	22.1	5.196	0.255	22.6
22a-3	29.9	5.161	0.262	17.1
22a-4	46.0	4.819	0.330	28.2
22a-5	53.8	4.386	0.424	29.5
22a-6	142.9	2.423	1.017	63.9
22a-7	149.8	2.197	1.115	64.7
22a-8	166.0	1.794	1.318	73.3
22a-9	173.6	1.546	1.467	75.2
22a-10	190.1	1.097	1.810	83.6

Table 6: Results of Tier 2 at pH 7 and 50 °C

Sample no.	t[h]	Measuredct [mg/L]	lnc0/ct	Degree of hydrolysis* [%]
7a-0	0	6.224	--	--
7a-1	3.1	5.793	0.072	6.9
7a-2	21.0	4.152	0.405	33.3
7a-3	26.9	3.900	0.468	37.4
7a-4	45.2	3.202	0.665	48.6
7a-5	50.6	2.949	0.747	52.6
7a-6	70.2	2.468	0.925	60.3
7a-7	75.7	2.385	0.959	61.7
7a-8	95.6	1.959	1.156	68.5
7b-0	0	6.710	--	--
7b-1	3.2	5.621	0.177	16.2
7b-2	21.0	4.040	0.507	39.8
7b-3	26.9	3.591	0.625	46.5
7b-4	45.3	2.632	0.936	60.8
7b-5	50.6	2.571	0.960	61.7
7b-6	70.2	2.208	1.111	67.1
7b-7	75.6	2.023	1.199	69.8
7b-8	95.6	1.721	1.361	74.3

Table 7: Results of Tier 2 at pH 7 and 60 °C

Sample no.	t[h]	Measuredct [mg/L]	lnc0/ct	Degree of hydrolysis* [%]
19a-0	0	6.182	--	--
19a-1	2.8	5.175	0.178	16.9
19a-2	5.5	5.103	0.192	18.0
19a-3	24.0	4.231	0.379	32.0
19a-4	26.3	4.102	0.410	34.1
19a-5	28.8	4.081	0.415	34.4
19a-6	30.9	4.203	0.386	32.5
19b-0	0	7.134	--	--
19b-1	2.6	6.433	0.103	4.1
19b-2	5.6	6.036	0.167	10.1
19b-3	23.8	4.658	0.426	30.6
19b-4	26.1	4.531	0.454	32.5
19b-5*	28.7	6.021	0.170	10.3
19b-6	30.6	4.582	0.443	31.7

*This measurement is not included in the further calculation

Table 8: Calculation of the Arrhenius Parameters for pH 7

T[°C]	T[K]	1/T[1/K]	kobs[h^-1]	lnkobs
20	293.15	0.00341	0.00556	-5.19
20	293.15	0.00341	0.01229	-4.40
20	293.15	0.00341	0.00827	-4.80
50	323.15	0.00309	0.01119	-4.49
50	323.15	0.00309	0.01249	-4.38
60	333.15	0.00300	0.00881	-4.73
60	333.15	0.00300	0.01307	-4.34
lnA	-2.11		A[h^-1]	0.12
-EA/R	-781.7		EA[kJ/mol]	6.50

Table 9: Results of Tier 2 at pH 9 and 20 °C

Sample no.	t[h]	Measuredct [mg/L]	lnc0/ct	Degree of hydrolysis* [%]
12a-0	0	6.873	--	--
12a-1	3.7	4.907	0.337	28.6
12a-2	71.5	2.031	1.219	70.5
12a-3	95.0	1.677	1.411	75.6
12a-4	100.0	1.597	1.459	76.8
12a-5	117.0	1.197	1.748	82.6
12a-6	123.7	0.995	1.933	85.5
12a-7	141.0	0.714	2.265	89.6
12a-8*	147.9	0.607	2.426	91.2
12a-9	164.0	0.766	2.194	88.9
12b-0	0	6.745	--	--
12b-1	3.8	5.224	0.256	22.6
12b-2	71.5	2.179	1.130	67.7
12b-3	95.0	1.869	1.283	72.3
12b-4	100.1	1.875	1.280	72.2
12b-5	117.0	1.452	1.536	78.5
12b-6	123.7	1.222	1.708	81.9
12b-7	141.0	0.762	2.180	88.7
12b-8	147.9	0.770	2.170	88.6
12b-9*	164.1	0.492	2.618	92.7

*This measurement is not included in the further calculation

Table 10: Results of Tier 2 at pH 9 and 50 °C

Sample no.	t[h]	Measuredct [mg/L]	lnc0/ct	Degree of hydrolysis* [%]
8a-0	0	6.978	--	--
8a-1	3.2	4.652	0.405	33.3
8a-2	21.0	1.731	1.394	75.2
8a-3	27.0	1.094	1.853	84.3
8a-4	45.3	0.868	2.084	87.6
8a-5	50.6	0.825	2.136	88.2
8a-6	70.2	0.999	1.944	85.7
8a-7	75.7	0.851	2.104	87.8
8b-0	0	6.497	--	--
8b-1	3.3	4.819	0.299	25.8
8b-2	21.1	2.801	0.841	56.9
8b-3	27.0	2.133	1.114	67.2
8b-4	45.3	1.534	1.443	76.4
8b-5	50.7	1.544	1.437	76.2
8b-6	70.3	1.373	1.554	78.9
8b-7	75.7	1.342	1.577	79.3

Table 11: Results of Tier 2 at pH 9 and 60 °C

Sample no.	t[h]	Measuredct [mg/L]	lnc0/ct	Degree of hydrolysis* [%]
20a-0	0	6.740	--	--
20a-1	3.1	5.439	0.215	20.9
20a-2	5.8	5.000	0.299	27.3
20a-3	24.0	3.322	0.707	51.7
20a-4	26.3	3.307	0.712	51.9
20a-5	28.8	3.179	0.751	53.7
20a-6	30.3	3.132	0.766	54.4
20b-0	0	6.712	--	--
20b-1	3.0	6.180	0.083	8.4
20b-2	5.7	5.761	0.153	14.6
20b-3	23.9	3.925	0.537	41.8
20b-4	26.1	3.683	0.600	45.4
20b-5	28.6	3.444	0.667	48.9
20b-6	29.9	3.511	0.648	47.9

Table 12: Calculation of the Arrhenius Parameters for pH 9

T[°C]	T[K]	1/T[1/K]	kobs[h^-1]	lnkobs
20	293.15	0.00341	0.0125	-4.38
20	293.15	0.00341	0.0132	-4.33
50	323.15	0.00309	0.0191	-3.96
50	323.15	0.00309	0.0166	-4.10
60	333.15	0.00300	0.0206	-3.88
60	333.15	0.00300	0.0217	-3.83
lnA	-0.37		A[h^-1]	0.69
-EA/R	-1170.8		EA[kJ/mol]	9.73

Validity criteria fulfilled:

yes

Conclusions:

Under the conditions of this study, at pH 4 average half-lives were 126.5, 51.1 and 39.5 hours at 20, 50 and 60 °C, respectively.
At pH 7 average half-lives were 88.3, 58.7 and 65.8 hours at 20, 50 and 60 °C, respectively.
At pH 9 average half-lives were 54.1, 39.1 and 32.8 hours at 20, 50 and 60 °C, respectively.

Executive summary:

The hydrolysis of the test material 2-Isopropylthioxanthone ("ITX", CAS 5495-84-1, EC 226-827-9) 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 test at pH 4, 7 and 9 was performed at a temperature of 50 °C. Samples were taken and measured after 17 and 116 hours. The nominal start concentration of the test material was 7.9 mg/L. It was observed, that the test material was hydrolysed by more than 10 % at all three pH values after 5 days. Thus, Tier 2 was performed for all three pH values.

The half-life values of the test material were determined at pH 4, 7 and 9 at 20, 50 and 60 °C using HPLC. The test was performed in duplicate.

Under the conditions of this study, at pH 4 average half-lives were 126.5, 51.1 and 39.5 hours at 20, 50 and 60 °C, respectively. At pH 7 average half-lives were 88.3, 58.7 and 65.8 hours at 20, 50 and 60 °C, respectively. At pH 9 average half-lives were 54.1, 39.1 and 32.8 hours at 20, 50 and 60 °C, respectively.

Description of key information

- pH 4: average half-lives were 126.5, 51.1 and 39.5 hours at 20, 50 and 60 °C [OECD 111; GLP; test material: 2-Isopropylthioxanthone ("ITX", CAS 5495-84-1, EC 226-827-9)];

- pH 7 average half-lives were 88.3, 58.7 and 65.8 hours at 20, 50 and 60 °C [OECD 111; GLP; test material: 2-Isopropylthioxanthone ("ITX", CAS 5495-84-1, EC 226-827-9)];

- pH 9 average half-lives were 54.1, 39.1 and 32.8 hours at 20, 50 and 60 °C [OECD 111; GLP; test material: 2-Isopropylthioxanthone ("ITX", CAS 5495-84-1, EC 226-827-9)].

Key value for chemical safety assessment

Half-life for hydrolysis:

88.3 h

at the temperature of:

20 °C

Additional information

Supporting data from the closely related substance 2-Isopropylthioxanthone ("ITX", CAS 5495-84-1, EC 226-827-9) are used to draw conclusions on the expected half-lives of the registration substance 2,4-diethyl-9H-thioxanthen-9-one ("DETX", CAS 82799-44-8, EC 280-041-0):

The hydrolysis of the test material ITX as a function of pH was investigated in accordance with the standardised guidelines OECD 111 and EU Method C.7 under GLP conditions. The study was awarded a reliability score of 1 in accordance with the criteria set forth by Klimisch et al. (1997).

The preliminary test at pH 4, 7 and 9 was performed at a temperature of 50 °C. Samples were taken and measured after 17 and 116 hours. The nominal start concentration of the test material was 7.9 mg/L. It was observed, that the test material was hydrolysed by more than 10 % at all three pH values after 5 days. Thus, Tier 2 was performed for all three pH values.

The half-life values of the test material were determined at pH 4, 7 and 9 at 20, 50 and 60 °C using HPLC. The test was performed in duplicate.

Under the conditions of this study, at pH 4 average half-lives were 126.5, 51.1 and 39.5 hours at 20, 50 and 60 °C, respectively. At pH 7 average half-lives were 88.3, 58.7 and 65.8 hours at 20, 50 and 60 °C, respectively. At pH 9 average half-lives were 54.1, 39.1 and 32.8 hours at 20, 50 and 60 °C, respectively.