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Please be aware that this old REACH registration data factsheet is no longer maintained; it remains frozen as of 19th May 2023.

The new ECHA CHEM database has been released by ECHA, and it now contains all REACH registration data. There are more details on the transition of ECHA's published data to ECHA CHEM here.

Diss Factsheets

Physical & Chemical properties

Endpoint summary

Administrative data

Description of key information

Additional information

The substance, dichlorosilane, is not stable in water, which affects the approach to the determination of physicochemical properties. The significance of this for read-across is discussed in Section 1.4.1 of the CSR.

Dichlorosilane is a gas at standard temperature and pressure, with a melting point of -112°C and a boiling point of 8.3°C. It has a density of 4.129 g/l at 25°C. The vapour pressure of the substance is expected to be greater than the limit of measurement, i.e. 1E+05 Pa at 20°C, as it is a gas.

Dichlorosilane is classified as an extremely flammable gas (Category 1) in accordance with Regulation (EC) No. 1272/2008. In addition, based on read-across from a related chlorosilane substance, it is also expected to rapidly emit a flammable gas (hydrogen) in contact with water. 

Dichlorosilane does not have any chemical structures that are associated with explosive properties and was found to be not explosive under EU Method A14.

Dichlorosilane reacts violently with water, to form silanediol as intermediate hydrolysis product and hydrochloric acid according to the following equation:

H2SiCl2+ 2H2O → H2Si(OH)2+ 2HCl

The Si-H bond is also unstable, resulting in further reaction to monosilicic acid Si(OH)4 with hydrogen as a by-product. The rate of this reaction has not been determined but is expected to be rapid. The overall equation is given below:

H2SiCl2+ 4H2O → Si(OH)4+ 2HCl + 2H2

Both silanediol and monosilicic acid exist only in dilute aqueous solutions and readily condense at concentrations above approximately 100 -150 mg/l as SiO2 to give a dynamic equilibrium between monomer, oligomers and insoluble amorphous polysilicic acid.

Many of the physicochemical properties have been waived because the substance is an inorganic gas that produces a flammable gas in contact with water. The properties of the initial and final silanol hydrolysis products, silanediol and monosilicic acid, are assessed instead. Both substances have high predicted water solubility but in reality solubility is limited by condensation reactions as discussed above. Their volatility is expected to be very 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.