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EC number: 236-704-1
CAS number: 13465-77-5
Hexachlorodisilane is a liquid at standard temperature and pressure,
with a measured melting point of 3°C, and boiling point of 144°C at 980
mbar. A boiling point of 146°C at 1 bar is reported in a handbook of
data that is peer-reviewed and in which the original sources of the data
are cited. It has a predicted density of 1.6 g/cm³ at 20°C and a
predicted vapour pressure of 280 Pa at 25°C, based on a boiling point of
The substance is not classified
for flammability on the basis of a measured flash point of 77°C. It has
a measured auto-ignition temperature of 315°C, does not represent
an explosion hazard and is not oxidising on the basis of structural
violently with water initially giving hexahydroxydisilane and HCl.
Further hydrolysis of the Si-Si
bonds in hexahydroxydisilane is expected to happen rapidly and produces
monosilicic acid. At concentrations above about 100-150 mg/l (measured asSiO2equivalents),
condensation products of monosilicic acid can also form. At
concentrations >100-150 mg/l of SiO2, monomeric
monosilicic acid condenses into colloidal particles of polysilicic acid
(silica sol) or a highly cross-linked network (silica gel).
Hexahydroxydisilane is also likely to form condensation products
(polyhydroxy-polysilanes) at similar concentrations (in terms of SiO2equivalents).
The structure and predicted properties of Si-Si containing
hydrolysis products (polyhydroxy-polysilanes) and (poly)silicic acid are
very similar, and distinguishing between them would be very difficult
Therefore, the requirements for
testing of water based physicochemical properties for the
substance are waived on the basis of instability in water. The
properties of the initial and final hydrolysis products,
hexahydroxydisilane and monosilicic acid, are assessed instead. Both
substances have high predicted water solubilities, but in reality the
solubility is limited by the condensation reactions as discussed above.
Their volatility is expected to be low. They are not surface active and
do not undergo significant dissociation within the environmentally
relevant pH range; the first dissociation constant is approximately 10.
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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