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Please be aware that this old REACH registration data factsheet is no longer maintained; it remains frozen as of 19th May 2023.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

Tetraethyl orthosilicate (TEOS, CAS 78-10-4; EC No. 201-083-8) is a liquid at standard temperature and pressure, with a measured melting point of <-100°C at 1013 hPa and a measured boiling point of 167.3°C at 1013 hPa. It has a measured relative density of 0.934 at 20°C and a measured kinematic viscosity of 0.772 mm2/s at 20°C. The substance has measured vapour pressure values of 20 Pa at 20°C and 660 Pa at 50°C.

The substance is classified for flammability according to Regulation (EC) No 1272/2008, on the basis of a measured flash point of 54°C at 1013 hPa and measured boiling point of 167.3°C at 1013 hPa. It has a measured auto-ignition temperature of 222°C at 960.8 to 962.6 hPa, and is not explosive and not oxidising on the basis of structural examination.

In contact with water, tetraethyl orthosilicate reacts rapidly to form monosilicic acid (CAS 10193-36-9; EC No. 233-477-0) and ethanol (CAS 64-17-5; EC No. 200-578-6) (measured half-life of 0.11 hours at pH 4, 4.4 h at pH 7 and 0.22 hours at pH 9 and 25°C) according to the following equation:

Si(OC2H5)4 + 4H2O → Si(OH)4 + 4C2H5OH

Therefore, requirements for testing of water-based physicochemical properties for the submission substance are waived on the basis of instability in water. However, the key physicochemical properties of tetraethyl orthosilicate have been predicted using validated QSAR estimation methods. The submission substance has a predicted log Kow of 1.4 at 20°C and a predicted water solubility value of 8600 mg/L at 20°C.

Ethanol is miscible with water, has a low log Kow (-0.3) and high vapour pressure (7910 Pa at 25°C).

Monosilicic acid exists only in dilute aqueous solutions and readily condenses at concentrations above approximately 100-150 mg/L as SiO2, to give a dynamic equilibrium between monomer, oligomers and insoluble amorphous polysilicic acid. Silicic acid is expected to have negligible vapour pressure and is not surface active. Log Kow is not relevant for inorganic compounds such as silicic acid. Silicic acid does not undergo significant dissociation within the environmentally-relevant pH range; the first dissociation constant is approximately 10.

Additional information