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Hydrolysis

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Endpoint:
hydrolysis
Type of information:
experimental study
Adequacy of study:
key study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
guideline study with acceptable restrictions
Remarks:
The study was conducted according to an appropriate OECD test guideline but was not in compliance with GLP.
Qualifier:
according to
Guideline:
OECD Guideline 111 (Hydrolysis as a Function of pH)
GLP compliance:
no
Radiolabelling:
no
Analytical monitoring:
yes
Buffers:
- Buffer solutions were not sterilized.
- Co-solvent: <1% acetonitrile
- Buffer volume for hydrolysis: 50 mL

Target pH Buffer System Measured pH (before addition of test material
4.0 Acetic acid/sodium hydroxide 4.00
7.0 Sodium dihydrogen phosphate/sodium hydroxide 7.01
9.0 Boric acid/sodium hydroxide 8.99
Details on test conditions:
- Plastic, instead of glass containers were used since it is known that the SiOH layer on glass will react with SiCl compounds.
- Temperature: 1.5 +/- 0.5 °C
- Vessels: Low-density polyethylene bottles of 90-mL capacity with screw caps. Vessels were not sterilized.
- Co-solvent: <1% acetonitrile
Number of replicates:
One at pH 4, 7, and 9
Statistical methods:
- Data treatment: For given solution conditions, the hydrolysis of parent was followed to completion as indicated by a stable chloride ion concentration measurement (< 2% change between concentration readings). The elapsed time between the addition of the test material to the aqueous buffer solution and the observation of a stable chloride ion concentration was used to estimate an upper limit on t1/2 (seconds) assuming that 10 half-lives represents exhaustive hydrolysis (99.9% complete).
Transformation products:
yes
No.:
#1
No.:
#2
pH:
4
Temp.:
1.5 °C
DT50:
< 1 min
pH:
7
Temp.:
1.5 °C
DT50:
< 1 min
pH:
9
Temp.:
1.5 °C
DT50:
< 1 min
Details on results:
Nominal: 1x10-3 M (149 mg/L) Methyltrichlorosilane

Measured value (the value with units preferably mg/L):
3.0x10-3 M (106 mg/L) Chloride ion at pH 4
3.2x10-3 M (113 mg/L) Chloride ion at pH 7
2.7x10-3 M (96 mg/L) Chloride ion at pH 9

Half-life (t(1/2) in seconds at a specific pH (pH 4, 7, 9, or other) at 1.5 +/- 0.5 °C:
pH 4.0: 7 seconds
pH 7.0: 9 seconds
pH 9.0: 6 seconds

Remarks Field for Results:
- Values of upper limit on t1/2 (shown above) refer to disappearance of test material, i.e. complete hydrolysis, from measurement of chloride ion concentration formed.
- Since the hydrolysis is so rapid, there is insufficient data to determine the rate constants (k1, k2, and k3) for the hydrolysis reactions by regression modeling.
- Rate constants and half-lives could not be determined quantitatively, although the data is certainly adequate for estimating the upper limit of t1/2.
- The chloride ion concentration measured was stoichiometrically equivalent to the methyltrichlorosilane concentration added to each buffer. This confirmed the quantitative completion of hydrolysis.
- First order or pseudo-first order behavior could not be confirmed because: a) sparse nature of the data during the critical portion of the process (20-70% hydrolyzed), b) the inherent limitation caused by measuring co-product concentration, and c) the relationship between k1, k2, and k3 is not known.
- Breakdown products from hydrolysis: Hydrogen chloride and silanol. For given solution conditions, the degradation product hydrogen chloride was observed to be stable during data collection. Consequently, HCl was considered stable. The stability of silanol was not measured, however silanols will undergo condensation reactions to form siloxanes. The stabilities of silanols lie in the order R3SiOH > R2Si(OH)2 > RSi(OH)3, with the bulkier R groups lending more stability to the SiOH function.2
Conclusions:
Hydrolysis half-lifes at 1.5 °C of <1 min at pH 4, 7 and 9 were determined in a study conducted according to OECD 111 but not under GLP.
Endpoint:
hydrolysis
Type of information:
read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
key study
Justification for type of information:
Please refer to the attached justification below and the overall justification for grouping of substances attached in IUCLID Section 13.
Reason / purpose:
read-across source
Transformation products:
yes
No.:
#1
No.:
#2
pH:
4
Temp.:
1.5 °C
DT50:
< 1 min
pH:
7
Temp.:
1.5 °C
DT50:
< 1 min
pH:
9
Temp.:
1.5 °C
DT50:
< 1 min

Description of key information

Hydrolysis half-life: < 1 min at pH 4-9 and 1.5 °C (OECD 111)

Key value for chemical safety assessment

Additional information

No data on the hydrolysis of trichloro(4-methylphenyl)silane (CAS 701-35-9) are available. Therefore good quality data from the similar substance trichloro(methyl)silane (CAS 75-79-6) were read across. Details on the read across justification can be found in the attached justification in the respective target entry and in the overall justification for grouping of substances attached in IUCLID Section 13.

The hydrolysis study for the chlorosilane trichloro(methyl)silane (CAS 75-79-6) was performed according to OECD guideline 111 (2001). The hydrolysis was rapid so that no t1/2 could be determined quantitatively. The chloride ion concentration measured was stochiometrically equivalent to the parent substance concentration added to each buffer. This confirmed the quantitative completion of hydrolysis. In conclusion the half-lives for pH 4, 7 and 9 were < 1 min (at 1.5 °C). This result is in line with further available experimental data for chlorosilanes (PFA, 2013).

On this basis the hydrolysis of the substance is expected to be rapid. The hydrolysis products are (4-methylphenyl)silanetriol and hydrochloric acid based on the chemical structure of the target substance.