Dicyclopentyldimethoxysilane

Hydrolysis

Link to relevant study record(s)

Reference

Endpoint:

hydrolysis

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2011-10-04 to 2011-12-12

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)

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:

The concentrations of the test substance were determined immediately after preparation (t=0) and at several sampling points after t=0. The samples taken were cooled to room temperature using running tap water. Immediately after cooling, 4 ml of each sample was added to 4 ml hexane for extraction of the test substance by shaking for 30 seconds. The extracts were subsequently analysed.

Samples have to be extracted with n-hexane as soon as possible to maximise accuracy and repeatability.

Buffers:

- pH: 4
- Type and final molarity of buffer: Acetate
- Composition of buffer: 0.1 M solution of 16.6% (v/v) 0.1 M sodium acetate and 83.4% (v/v) 0.1 M acetic acid. The buffer contains 0.0009% (w/v) sodium azide.

- pH: 7
- Type and final molarity of buffer: Phosphate
- Composition of buffer: Phosphate buffer pH 7, 0.1 M solution of 0.1 M potassium dihydrogenphosphate adjusted to pH 7 using 10 N sodium hydroxide. The buffer contains 0.0009% (w/v) sodium azide.

- pH: 9
- Type and final molarity of buffer: Borate
- Composition of buffer: 0.1 M solution of 0.1 M boric acid and 0.1 M potassium chloride adjusted to pH 9 using 10 N sodium hydroxide. The buffer contains 0.0009% (w/v) sodium azide.

Details on test conditions:

TEST SYSTEM (main study)
- Type, material and volume of test flasks, other equipment used: For each sampling time, duplicate sterile vessels under vacuum were filled with 6 ml test solution and placed in the dark in a temperature controlled environment.
- Sterilisation method: filtration
- Lighting: test conducted in the dark
- Measures to exclude oxygen: purged with N2 gas for 5 minutes
- Is there any indication of the test material adsorbing to the walls of the test apparatus? No

TEST MEDIUM
- Volume used/treatment: 6 ml
- Kind and purity of water: Tap water purified by a Milli-Q water purification system
- Identity and concentration of co-solvent: The test substance was spiked to the solutions at a target concentration of
2.5 mg/l using a spiking solution in acetone.

OTHER TEST CONDITIONS
- Adjustment of pH: refer to information on buffers.

Duration:

1.1 h

pH:

4

Initial conc. measured:

1.68 mg/L

Duration:

0.6 h

pH:

4

Initial conc. measured:

1.99 mg/L

Duration:

91.5 h

pH:

7

Initial conc. measured:

2.14 mg/L

Duration:

54.5 h

pH:

7

Initial conc. measured:

2.09 mg/L

Duration:

95.5 h

pH:

9

Initial conc. measured:

2.52 - 2.55 mg/L

Duration:

69.5 h

pH:

9

Initial conc. measured:

2.1 - 2.14 mg/L

Number of replicates:

two

Positive controls:

no

Negative controls:

no

Transformation products:

not measured

Key result

pH:

4

Temp.:

20 °C

Hydrolysis rate constant:

2.87 h-1

DT50:

0.24 h

Type:

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

Remarks on result:

other: Coefficient of correlation 0.998

Key result

pH:

4

Temp.:

25 °C

Hydrolysis rate constant:

4.15 h-1

DT50:

0.17 h

Type:

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

Remarks on result:

other: Coefficient of correlation 0.996

Key result

pH:

7

Temp.:

20 °C

Hydrolysis rate constant:

0.029 h-1

DT50:

24 h

Type:

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

Remarks on result:

other: Coefficient of correlation 0.98

Key result

pH:

7

Temp.:

25 °C

Hydrolysis rate constant:

0.031 h-1

DT50:

19 h

Type:

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

Remarks on result:

other: Interpolated conclusion

Key result

pH:

7

Temp.:

30 °C

Hydrolysis rate constant:

0.047 h-1

DT50:

15 h

Type:

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

Remarks on result:

other: Coefficient of correlation 0.98

Key result

pH:

7

Temp.:

50 °C

Hydrolysis rate constant:

0.149 h-1

DT50:

4.7 h

Type:

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

Remarks on result:

other: Coefficient of correlation 0.992

Key result

pH:

9

Temp.:

20 °C

Hydrolysis rate constant:

0.024 h-1

DT50:

29 h

Type:

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

Remarks on result:

other: Coefficient of correlation 0.97

Key result

pH:

9

Temp.:

25 °C

Hydrolysis rate constant:

0.031 h-1

DT50:

22 h

Type:

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

Key result

pH:

9

Temp.:

30 °C

Hydrolysis rate constant:

0.04 h-1

DT50:

18 h

Type:

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

Remarks on result:

other: Coefficient of correlation 0.98

Key result

pH:

9

Temp.:

50 °C

Hydrolysis rate constant:

0.15 h-1

DT50:

4.6 h

Type:

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

Remarks on result:

other: Coefficient of correlation 0.994

Other kinetic parameters:

A rate constant and half-life at 50°C at pH 4 could not be determined due to the very fast rate of reaction.

Details on results:

TEST CONDITIONS
- pH, sterility, temperature, and other experimental conditions maintained throughout the study: Yes
- Anomalies or problems encountered (if yes): none

Table 1: Hydrolysis of dicyclopentyldimethoxysilane, expressed as percentage of the applied substance based on GC-FID analysis, at pH 7 and 20˚C

Compound	Sampling times (hours)
	0	0.5	1	19.5	22	27	43	46.3	50	72	91.5
Parent compound (mg.L)	2.14 2.14	2.05 1.99	2.01 2.11	0.958 0.864	0.912 1.01	0.759 0.901	0.500 0.539	0.382 0.396	0.284 0.388	0.231 0.263	0.168 0.168
Total % recovery	100 100	96 93	94 98	45 40	43 47	35 42	23 25	18 18	13 18	11 12	7.9 7.8

Table 2: Hydrolysis of dicyclopentyldimethoxysilane, expressed as percentage of the applied substance based on GC-FID analysis, at pH 7 and 30˚C

Compound	Sampling times (hours)
	0	3.5	5	7	23	25.5	28.75	30.75	47.25	54.5
Parent compound (mg.L)	2.09 2.09	1.73 1.81	1.44 1.49	1.27 1.30	0.499 0.488	0.574 0.559	0.431 0.424	0.414 0.411	0.244 0.272	0.186 0.157
Total % recovery	100 100	83 87	69 71	61 62	24 23	27 27	21 20	20 20	12 13	8.9 7.5

 

Table 3: Hydrolysis of dicyclopentyldimethoxysilane, expressed as percentage of the applied substance based on GC-FID analysis, at pH 4 and 20˚C

Compound	Sampling times (hours)
	0	0.083	0.17	0.25	0.33	0.42	0.50	0.58	0.67	0.75	1.1*
Parent compound (mg.L)	1.68 1.73	1.32 1.33	1.04 1.09	0.770 0.811	0.625 0.674	0.504 0.452	0.392 0.382	0.326 0.328	0.252 0.267	0.199 0.194	0.0711 0.0755
Total % recovery	99 102	78 78	61 64	45 48	37 40	30 27	23 22	19 19	15 16	12 11	4.2 4.4

* extrapolated results

 

Table 4: Hydrolysis of dicyclopentyldimethoxysilane, expressed as percentage of the applied substance based on GC-FID analysis, at pH 4 and 25˚C

Compound	Sampling times (hours)
	0	0.067	0.13	0.20	0.27	0.33	0.40	0.47	0.53	0.60
Parent compound (mg.L)	1.99 1.91	1.26 1.26	0.942 0.901	0.672 0.764	0.614 0.633	0.427 0.472	0.326 0.345	0.263 0.257	0.172 0.194	0.148 0.149
Total % recovery	102 98	65 65	48 46	35 39	32 33	22 24	17 18	14 13	8.8 10	7.6 7.7

 

 

Table 5: Hydrolysis of dicyclopentyldimethoxysilane, expressed as percentage of the applied substance based on GC-FID analysis, at pH 9 and 20˚C

Comp-ound	Sampling times (hours)
	0	0.3	0.7	1	1.3	2	4.5	23.5	31	47	54.5	76	95.5
Parent comp-ound (mg.L)	2.55 2.52	2.23*	2.14 2.21	2.12 2.16	2.17 2.18	2.07 2.13	1.82 2.03	0.886 0.85	0.932 0.816	0.626 0.53	0.447 0.467	0.515 0.389	0.288 0.213
Total % recovery	101 99	88	84 87	84 85	85 86	82 84	72 80	35 33	37 32	25 21	18 18	20 15	11 8.4

* misinjection

 

Table 6: Hydrolysis of dicyclopentyldimethoxysilane, expressed as percentage of the applied substance based on GC-FID analysis, at pH 9 and 30˚C

Compound	Sampling times (hours)
	0	3	4.5	6	21.5	24	26.3	29	46	53	69.5
Parent compound (mg.L)	2.14 2.10	1.75 1.85	1.80 1.73	1.60 1.59	0.657 0.649	0.559 0.547	0.530 0.519	0.462 0.430	0.326 0.315	0.212 0.217	0.150 0.151
Total % recovery	101 99	83 87	85 82	75 75	31 31	26 26	25 24	22 20	15 15	10 10	7.1 7.1

 

Validity criteria fulfilled:

yes

Conclusions:

A half-life of 19 h for hydrolysis of dicyclopentyl(dimethoxy)silane at pH 7 at 25ºC was determined in a reliable study, conducted according to an appropriate test protocol, and in compliance with GLP.

Description of key information

Hydrolysis: 0.17 hours at pH 4, 19 hours at pH 7 and 22 hours at pH 9 and 25°C (EU Method C.7)

Key value for chemical safety assessment

Half-life for hydrolysis:

19 h

at the temperature of:

25 °C

Additional information

Four measured hydrolysis studies are available for the submission substance. Hydrolysis of the substance was determined in a study conducted in accordance with EU Method C.7 and in compliance with GLP (Brekelmans 2012). The result is considered to be reliable and is selected as the key study. The half-lives obtained are:

pH 4: 0.24 h at 20°C and 0.17 hours at 25°C

pH 7: 24 hours at 20°C, 19 hours at 25°C, 15 hours at 30°C and 4.7 hours at 50°C

pH 9: 29 hours at 20°C, 22 hours at 25°C, 18 hours at 30°C and 4.6 hours at 50°C

In addition, three preliminary studies are available for dicyclopentyl(dimethoxy)silane, CAS 126990-35-0; EC No. 404-370-8. In Dow Corning Corporation (1991), hydrolysis half-lives of 119.5 minutes at pH 3.9, 110 minutes at pH 7.1 and 49.1 minutes at pH 9.2 and 50°C were obtained for the substance. Also, in Hogg (1995), hydrolysis half-lives of <2.4 hours at pH 4, pH 7 and pH 9 and 25°C were obtained for the submission substance in accordance with EU Method C.7. Similarly, in Greinert 1995, hydrolysis half-lives of 4.7 hours at pH 7 and 4.2 hours at pH 9 and 50°C were obtained for the substance according to EU Method C.7. In the same study, half-lives of 10 hours at pH 7.07 and 11.6 hours at pH 8.96 and 39°C were obtained for the substance.

Analysis of parent substance in test media by gas chromatography was undertaken as part of an algal inhibition study performed using dicyclopentyl(dimethoxy)silane (SafePharm Laboratories Ltd. 1996d). This suggests that the half-life of the substance is approximately 24 hours at 24⁰C and pH range 8-10. This is limited evidence for understanding of the half-life, but may be indicative.

The hydrolysis products are dicyclopentylsilanediol (1 mole) and methanol (2 moles).

The hydrolysis data for substances used for read-across purposes for other endpoints are discussed below.

Hydrolysis of the read-across substance cyclohexyl(dimethoxy)methylsilane (CAS 17865-32-6)

Data for the substance, cyclohexyl(dimethoxy)methylsilane (CAS 17865-32-6) are read-across to the submission substance, dicyclopentyl(dimethoxy)silane (CAS 126990-35-0) for genetic toxicity in vivo endpoint. The structural similarity, silanol hydrolysis products and the rate of hydrolysis of the two substances are relevant to this read-across, as discussed in the appropriate section for the endpoint.

For cyclohexyl(dimethoxy)methylsilane, the hydrolysis half-lives are read-across from the submission substance itself as discussed above.

The hydrolysis products are cyclohexylmethylsilanediol (1 mole) and methanol (2 moles).

Hydrolysis of the read-across substance dichloro(dicyclopentyl)silane (CAS 139147-73-2)

Data for the substance, dichloro(dicyclopentyl)silane, CAS 139147-73-2 are read-across to the submission substance dicyclopentyl(dimethoxy)silane (CAS 126990-35-0) for the short-term toxicity to fish, short-term toxicity to aquatic invertebrates and toxicity to microorganims endpoints. The formation of the same silanol hydrolysis products and the rate of hydrolysis of the two substances are relevant to this read-across, as discussed in the appropriate sections for the endpoints.

For dichloro(dicyclopentyl)silane, hydrolysis half-lives of <1 minute at pH 4, pH 7 and pH 9 and 25°C were read-across from other dichlorosilanes.

The hydrolysis products are dicyclopentylsilanediol (1 mole) and hydrochloric acid (2 moles).

Hydrolysis of the read-across substance dicyclopentylsilanediol (CAS 211495-85-1)

Data for the substance, dicyclopentylsilanediol, CAS 211495-85-1 are read-across to the submission substance dicyclopentyl(dimethoxy)silane (CAS 126990-35-0) for the repeated dose toxicity oral endpoint. For the bacteria mutagenicity and in vitro cytogenicity endpoints, the data for dicyclopentylsilanediol are used as a supporting study.

Dicyclopentylsilanediol is the silanol hydrolysis product of the submission substance, dicyclopentyl(dimethoxy)silane (CAS 126990-35-0).

Dicyclopentylsilanediol does not have functional groups that are susceptible to hydrolysis.