6-methyl-3,4-dihydro-2H-1,4-benzoxazine

Hydrolysis

Link to relevant study record(s)

Reference

Endpoint:

hydrolysis

Type of information:

experimental study

Adequacy of study:

key study

Study period:

09 January 2019 - 18 June 2019

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:

13 April 2004

Deviations:

no

Qualifier:

according to guideline

Guideline:

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

Version / remarks:

Commission Regulation (EC) No 440/2008 (as amended), 30 May 2008

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Radiolabelling:

no

Analytical monitoring:

yes

Buffers:

- pH: 4
- Composition of buffer:
Citric acid 6 (mmol dm-3);
Sodium chloride 4 (mmol dm-3);
Sodium hydroxide 7 (mmol dm-3).

- pH: 7
- Composition of buffer:
Disodium hydrogen orthophosphate (anhydrous) 3 (mmol dm-3);
Potassium dihydrogen orthophosphate 2 (mmol dm-3);
Sodium chloride 2 (mmol dm-3).

- pH: 9
- Composition of buffer:
Boric acid 5 (mmol dm-3);
Potassium chloride 5 (mmol dm-3);
Sodium hydroxide 2 (mmol dm-3).

Details on test conditions:

Preliminary Test/Tier 1:
Stock solutions of test item were prepared at a nominal concentration of 200 mg/L in the three buffer solutions; a 1% co-solvent of methanol was used to aid solubility. The stock solutions were split into individual glass vessels and sealed with minimal headspace for each data point. These sample solutions were maintained at 50.0 ± 0.5 °C for a period of 120 hours while being shielded from light.

Preliminary Test/Tier 1 (pH 4 Repeat):
A stock solution of test item was prepared at a nominal concentration of 200 mg/L in pH 4 buffer solution; a 1% co-solvent of acetonitrile was used to aid solubility. The stock solutions were split into individual plastic vessels and sealed with minimal headspace for each data point. These sample solutions were maintained at 50.0 ± 0.5 °C for a period of 120 hours while being shielded from light.

Tier 2:
Results from the preliminary test/tier 1 indicated it was necessary to undertake further testing at pH 4. A stock solution of test item was prepared at a nominal concentration of 200 mg/L in pH 4 buffer solution; a 1% co-solvent of acetonitrile was used to aid solubility. The stock solutions were split into individual deactivated glass vessels and sealed with minimal headspace for each data point. These sample solutions were maintained at 50.0 ± 0.5 °C,
60 ± 0.5 °C and 70 ± 0.5 °C for a period of 336, 215 and 96 hours respectively while being shielded from light.

Duration:

120 h

pH:

4

Temp.:

50 °C

Initial conc. measured:

200 mg/L

Remarks:

Tier 1 test / co-solvent methanol

Duration:

120 h

pH:

7

Temp.:

50 °C

Initial conc. measured:

200 mg/L

Remarks:

Tier 1 test / co-solvent methanol

Duration:

120 h

pH:

9

Temp.:

50 °C

Initial conc. measured:

200 mg/L

Remarks:

Tier 1 test / co-solvent methanol

Duration:

120 h

pH:

4

Temp.:

50 °C

Initial conc. measured:

200 mg/L

Remarks:

Tier 1 test (pH 4 repeat) / co-solvent acetonitrile

Duration:

336 h

pH:

4

Temp.:

50 °C

Initial conc. measured:

200 mg/L

Remarks:

Tier 2 test / co-solvent acetonitrile

Duration:

215 h

pH:

4

Temp.:

60 °C

Initial conc. measured:

200 mg/L

Remarks:

Tier 2 test / co-solvent acetonitrile

Duration:

96 h

pH:

4

Temp.:

70 °C

Initial conc. measured:

200 mg/L

Remarks:

Tier 2 test / co-solvent acetonitrile

Number of replicates:

Duplicate sample solutions were taken initially and from the waterbath at various time points. The pH of each solution was recorded.

Positive controls:

no

Negative controls:

no

Test performance:

Validation:
The linearity of the detector response with respect to concentration was assessed over the nominal concentration range of 25 to 150 mg/L for the methanol:pH 4 buffer solution (50:50 v/v) matrix. The result was satisfactory with a correlation coefficient (r) of 1.000 being obtained.
The linearity of the detector response with respect to concentration was assessed over the nominal concentration range of 10 to 250 mg/L for the methanol:pH 7 buffer solution (50:50 v/v) matrix. The result was satisfactory with a correlation coefficient (r) of 1.000 being obtained.

Transformation products:

no

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

The test item was considered to be hydrolytically stable at pH 4, pH 7 and pH 9 under the conditions of the test.

Key result

pH:

4

Temp.:

50 °C

DT50:

115 h

Type:

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

Remarks on result:

other:

Remarks:

after being stored in glass vessels and using a methanol co-solvent

Key result

pH:

7

Temp.:

50 °C

DT50:

1 510 h

Type:

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

Remarks on result:

other:

Remarks:

after being stored in glass vessels and using a methanol co-solvent

Key result

pH:

9

Temp.:

50 °C

DT50:

575 h

Type:

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

Remarks on result:

other:

Remarks:

after being stored in glass vessels and using a methanol co-solvent

Key result

pH:

4

Temp.:

50 °C

DT50:

57.3 h

Type:

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

Remarks on result:

other:

Remarks:

Repeated. stored in plastic vessels and using acetonitrile co-solvent

Preliminary Test/Tier 1:

The test item concentrations at the given time points, after being stored in glass vessels and using a methanol co-solvent,are shown in the following tables:

pH 4 at 50 ºC

Time (Hours)	Concentration (mg/L)		% of Mean Initial Concentration
	A	B	A	B
0	256	256	100	100
22	215	215	83.9	83.8
120	123	123	47.8	47.9

pH 4 at 50 °C half-life:          115 hours

pH 7 at 50 ºC

Time (Hours)	Concentration (mg/L)		% of Mean Initial Concentration
	A	B	A	B
0	265	265	100	100
22	262	262	98.8	98.8
120	251	251	94.6	94.5

pH 7 at 50 °C half-life:          1.51 x 10³hours

pH 9 at 50 ºC

Time (Hours)	Concentration (mg/L)		% of Mean Initial Concentration
	A	B	A	B
0	286	286	100	100
22	284	284	99.3	99.2
120	250	249	87.2	87.0

pH 9 at 50 °C half-life:          575 hours

The test item concentrations at the given time points, after being stored in plastic vessels and using an acetonitrile co-solvent, are shown in the following table:

Repeated pH 4 at 50 ºC

Time (Hours)	Concentration (mg/L)		% of Mean Initial Concentration
	A	B	A	B
0	193	193	99.9	100
120	46.2	44.0	24.0	22.8

pH 4 at 50 °C result:  half-life = 57.3 hours

Tier 2

The test item concentrations at the given time points are shown in the following tables:

pH 4 at 50 ºC

Time (Hours)	Concentration (mg/L)		% of Mean Initial Concentration
	A	B	A	B
0	240	241	99.9	100.1
23	190	187	78.7	77.8
48	159	153	66.0	63.6
96	123	125	51.2	51.9
168	93.9	92.0	39.0	38.2
240	74.7	74.8	31.0	31.1
336	74.3	75.2	30.9	31.2

pH 4 at 60 ºC

Time (Hours)	Concentration (mg/L)		% of Mean Initial Concentration
	A	B	A	B
0	264	265	99.8	100.2
24	198	199	74.8	75.4
47	155	158	58.7	59.9
52	150	152	56.9	57.4
72	139	138	52.4	52.1
96	112	112	42.5	42.5
165	81.7	81.6	30.9	30.9
215	65.0	65.0	24.6	24.6

pH 4 at 70 ºC

Time (Hours)	Concentration (mg/L)		% of Mean Initial Concentration
	A	B	A	B
0	240	241	99.9	100.1
3	228	228	94.8	94.7
6	215	217	89.4	90.0
22	162	162	67.5	67.3
28	150	151	62.4	62.7
48	117	115	48.7	47.6
54	106	109	44.2	45.2
75.5	82.4	88.0	34.2	36.6
96	73.8	75.5	30.7	31.4

Validity criteria fulfilled:

yes

Conclusions:

The test item was considered to be hydrolytically stable at pH 4, pH 7 and pH 9 under the conditions of the test. However, a decrease in concentration of the test item in solution was observed, especially at pH 4, but this finding was assessed to have been due to oxidation.

Description of key information

The hydrolysis as a function of pH of the test substance has been evaluated using a procedure designed to be compatible with both Method C.7 Abiotic Degradation, Hydrolysis as a Function of pH of Commission Regulation (EC) No 440/2008 of 30 May 2008, and Method 111 of the OECD Guidelines for Testing of Chemicals, 13 April 2004. The test item was considered to be hydrolytically stable at pH 4, pH 7 and pH 9 under the conditions of the test. However, a decrease in concentration of the test item in solution was observed, especially at pH 4, but this decrease was assessed to have been due to oxidation and not hydrolysis.

Key value for chemical safety assessment

Half-life for hydrolysis:

1 510 h

at the temperature of:

50 °C