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EC number: 201-127-6 | CAS number: 78-62-6
- Life Cycle description
- Uses advised against
- Endpoint summary
- Appearance / physical state / colour
- Melting point / freezing point
- Boiling point
- Density
- Particle size distribution (Granulometry)
- Vapour pressure
- Partition coefficient
- Water solubility
- Solubility in organic solvents / fat solubility
- Surface tension
- Flash point
- Auto flammability
- Flammability
- Explosiveness
- Oxidising properties
- Oxidation reduction potential
- Stability in organic solvents and identity of relevant degradation products
- Storage stability and reactivity towards container material
- Stability: thermal, sunlight, metals
- pH
- Dissociation constant
- Viscosity
- Additional physico-chemical information
- Additional physico-chemical properties of nanomaterials
- Nanomaterial agglomeration / aggregation
- Nanomaterial crystalline phase
- Nanomaterial crystallite and grain size
- Nanomaterial aspect ratio / shape
- Nanomaterial specific surface area
- Nanomaterial Zeta potential
- Nanomaterial surface chemistry
- Nanomaterial dustiness
- Nanomaterial porosity
- Nanomaterial pour density
- Nanomaterial photocatalytic activity
- Nanomaterial radical formation potential
- Nanomaterial catalytic activity
- Endpoint summary
- Stability
- Biodegradation
- Bioaccumulation
- Transport and distribution
- Environmental data
- Additional information on environmental fate and behaviour
- Ecotoxicological Summary
- Aquatic toxicity
- Endpoint summary
- Short-term toxicity to fish
- Long-term toxicity to fish
- Short-term toxicity to aquatic invertebrates
- Long-term toxicity to aquatic invertebrates
- Toxicity to aquatic algae and cyanobacteria
- Toxicity to aquatic plants other than algae
- Toxicity to microorganisms
- Endocrine disrupter testing in aquatic vertebrates – in vivo
- Toxicity to other aquatic organisms
- Sediment toxicity
- Terrestrial toxicity
- Biological effects monitoring
- Biotransformation and kinetics
- Additional ecotoxological information
- Toxicological Summary
- Toxicokinetics, metabolism and distribution
- Acute Toxicity
- Irritation / corrosion
- Sensitisation
- Repeated dose toxicity
- Genetic toxicity
- Carcinogenicity
- Toxicity to reproduction
- Specific investigations
- Exposure related observations in humans
- Toxic effects on livestock and pets
- Additional toxicological data
Hydrolysis
Administrative data
Link to relevant study record(s)
- Endpoint:
- hydrolysis
- Type of information:
- (Q)SAR
- Adequacy of study:
- key study
- Reliability:
- 2 (reliable with restrictions)
- Rationale for reliability incl. deficiencies:
- results derived from a valid (Q)SAR model and falling into its applicability domain, with adequate and reliable documentation / justification
- Principles of method if other than guideline:
- The result was obtained using an appropriate QSAR method (see attached QMRF and QPRF for details)
- GLP compliance:
- no
- Transformation products:
- yes
- No.:
- #1
- No.:
- #2
- Key result
- pH:
- 7
- DT50:
- 5.5 h
- Type:
- (pseudo-)first order (= half-life)
- Remarks on result:
- other: 20-25 °C
- pH:
- 4
- DT50:
- 0.3 h
- Type:
- (pseudo-)first order (= half-life)
- Remarks on result:
- other: 20-25 °C
- pH:
- 5
- DT50:
- 0.3 h
- Type:
- (pseudo-)first order (= half-life)
- Remarks on result:
- other: 20-25 °C
- pH:
- 9
- DT50:
- 0.1 h
- Type:
- (pseudo-)first order (= half-life)
- Remarks on result:
- other: 20-25 °C
- Conclusions:
- A hydrolysis half life of approximately 5.5 h at 20-25°C and pH 7 was obtained using an accepted calculation method. The result is considered to be reliable.
Reference
Description of key information
Diethoxy(dimethyl)silane CAS 78-62-6: hydrolysis half-life = 5.5 h at 20-25 °C and pH7 (QSAR)
Key value for chemical safety assessment
- Half-life for hydrolysis:
- 5.5 h
Additional information
Once released into the water phase, hydrolysis contributes significantly to the degradation of this substance. A QSAR that was developed (Peter Fisk Associates 2012) predicts half-lives at 20-25 °C of 0.3 h at pH 4, 0.3 h at pH 5, 5.5 h at pH 7 and 0.1 h at pH 9. As the hydrolysis reaction may be acid or base catalysed, the rate of reaction is expected to be slowest at pH 7 and increase as the pH is raised or lowered.
For an acid-base catalysed reaction in buffered solution, the measured rate constant is a linear combination of terms describing contributions from the uncatalyzed reaction as well as catalysis by hydronium, hydroxide, and general acids or bases.
kobs= k0+ kH3O+[H3O+] + kOH-[OH-] + ka[acid] + kb[base]
At extreme pH values and under standard hydrolysis test conditions, it is reasonable to suggest that the rate of hydrolysis is dominated by either the hydronium or hydroxide catalysed mechanism. This is supported by studies for various organosilicon compounds in which calculation of kH3O+and kOH- from the experimental results at pH 4 and 9, respectively, resulted in reasonable estimates of the half-life at pH 7.
Therefore, at low pH:
kobs≈kH3O+[H3O+]
At pH 4 [H3O+]=10-4mol dm-3and at pH2 [H3O+]=10-2mol dm-3; therefore, kobsat pH 2 should be approximately 100 times greater than kobsat pH 4.
The half-life of a substance at pH 2 is calculated based on:
t1/2(pH 2) = t1/2(pH 4) / 100
Reaction rate increases with temperature therefore hydrolysis will be faster at physiologically relevant temperatures compared to standard laboratory conditions. Under ideal conditions, hydrolysis rate can be recalculated according to the equation:
DT50(XºC) = DT50(T) x e(0.08*(T-X))
Where T = temperature for which data are available and X = target temperature.
Thus, for diethoxy(dimethyl)silane CAS 78-62-6, the hydrolysis half-life at 37.5°C and pH 2 (relevant for oral exposure) is < 5 s.
The initial hydrolysis products are and dimethylsilanediol and ethanol. It can be concluded that the submission substance will hydrolyse rapidly under environmentally relevant conditions.
Reference:
Mabey W. & Mill T. (1978). Critical review of hydrolysis of organic compounds in water under environmental conditions. J Phys Chem Ref Data. 7(2): 383-415.
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