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EC number: 236-704-1
CAS number: 13465-77-5
There are no in vivo or in vitro data on the
toxicokinetics of hexachlorodisilane. The following summary has
therefore been prepared based on physicochemical properties of the
substance itself and its hydrolysis products. Hexachlorodisilane is an
inorganic, moisture-sensitive liquid that hydrolyses very rapidly in
contact with water (half-life approximately 5 seconds at 25°C and pH 4,
7 and 9 (analogue read-across)). This half-life relates to hydrolysis of
the Si-Cl bonds to give hexahydroxydisilane and hydrochloric acid.
Further hydrolysis of the Si-Si bonds in hexahydroxydisilane is expected
to occur rapidly, producing monosilicic acid (Si(OH)4), which
condenses at concentrations above approximately 100-150 mg/l as SiO2
to give insoluble amorphous polysilicic acid (SAS). Hexahydroxydisilane
is also likely to form condensation products (polyhydroxy-polysilanes)
at similar concentrations (in terms of SiO2 equivalents). The
structure and predicted properties of the Si-Si containing hydrolysis
products (polyhydroxy-polysilanes) and (poly)silicic acid are very
similar, and distinguishing between them would be very difficult
exposure can occur via the inhalation or dermal routes. Relevant
inhalation exposure would be to the hydrolysis products (hydrolysis
would occur rapidly when inhaled, even if a mixture of parent and
hydrolysis products were present in air). The substance would also
hydrolyse rapidly in contact with moist skin. The resulting HCl
hydrolysis product would be severely irritating or corrosive.
oral exposure is not expected for this corrosive substance. Should it
occur then gastrointestinal absorption of insoluble condensation
products will be insignificant as compared to the absorption of the
soluble species (Carlisle, 1986).
high water solubility of
hexahydroxydisilane and monosilicic acid might
lead to some of this hydrolysis product being retained in the mucous of
the lungs. Damage to membranes caused by the corrosive nature of the HCl
hydrolysis product might enhance the uptake. Absorption of the insoluble
condensation products is not expected.
molecular weights of the parent and hydrolysis products favour
absorption across the skin. However, the very high water solubility (
which is a theoretical value and does not take into account the
condensation reaction) and low predicted log Kow
the silanol hydrolysis products, hexahydroxydisilane and monosilicic acid,
suggest that they are too hydrophilic to cross the lipid rich stratum
corneum. Since the other hydrolysis product, HCl is corrosive to the
skin, damage to the skin might increase penetration. Absorption
of the insoluble condensation products is not expected.
All absorbed material is likely to be in the form of the hydrolysis
products, hexahydroxydisilane, monosilicic acid and hydrogen chloride.
Hexahydroxydisilane and monosilicic acid are small molecules, and
therefore have potential to be widely distributed, but their hydrophilic
nature will limit their diffusion across membranes (including the
blood-brain and blood-testes barriers) and their accumulation in fatty
tissues. Human blood contains 1 mg SiO2/l of monosilicic acid
(Iler, 1979). Hydrogen and chloride ions will enter the body's natural
Hexachlorodisilane is rapidly hydrolysed generating HCl and
hexahydroxydisilane, which will then further hydrolyse to monosilicic
acid, both will then condense to give an amorphous
are no data regarding the metabolism of hexahydroxydisilane. Silicon is
an essential trace element participating in the normal metabolism of
higher animals. It is required in bone, cartilage and connective tissue
formation as well as participating in other important metabolic
processes. The silicon is present almost entirely as free soluble
monosilicic acid (Carlisle 1986).
The low molecular weight and high water solubility of
hexahydroxydisilane and monosilicic acid suggest that they are likely to
be rapidly eliminated via the kidneys in urine. There is therefore no
evidence to suggest that this substance will accumulate in the body.
Carlisle E.M. (1986) Silicon is an essential trace element in animal
nutrition in Silicon Biochemistry, Ciba Foundation Symposium 121, Wiley,
Iler, R.K. (1979) The Chemistry of Silica: Solubility, Polymerization,
Colloid and Surface Properties and Biochemistry of Silica, Wiley, p. 13.
Information on Registered Substances comes from registration dossiers which have been assigned a registration number. The assignment of a registration number does however not guarantee that the information in the dossier is correct or that the dossier is compliant with Regulation (EC) No 1907/2006 (the REACH Regulation). This information has not been reviewed or verified by the Agency or any other authority. The content is subject to change without prior notice.Reproduction or further distribution of this information may be subject to copyright protection. Use of the information without obtaining the permission from the owner(s) of the respective information might violate the rights of the owner.
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