Triethoxy(3,3,4,4,5,5,6,6,7,7,8,8,8-tridecafluorooctyl)silane

Endpoint summary

Description of key information

[2-(Perfluorohexyl)ethyl]triethoxysilane is a liquid at standard temperature and pressure, with a measured melting point of <-100°C, and a measured boiling point of 225°C at 1007 hPa. It has a measured relative density of 1.3417 at 20°C and a predicted vapour pressure of 9.8 Pa at 25°C.

 

The registration substance has a predicted log K_ow value of 7.2 at 20°C and a measured water solubility limit of <2 mg/L at 20°C and pH 6.29. The predicted water solubility of [2-(perfluorohexyl)ethyl]triethoxysilane is 6.4E-06 mg/L at 20°C. A surface tension value of 72.2 mN/m at 20°C and 10 mg/L was obtained for the substance.

 

The substance is not classified for flammability according to Regulation (EC) No. 1272/2008 on the basis of a measured flash point of 108.5°C at 1013 hPa. It has a measured auto-ignition temperature of 245°C at 1003-1017 hPa and is not explosive and not oxidising on the basis of chemical structure.

 

In contact with water under dilute conditions, [2-(perfluorohexyl)ethyl]triethoxysilane reacts moderately rapidly (half-life of 12.5 hours at pH 7, 1.44 hours at pH 4, 5.18 hours at pH 9, and at 20°C) to produce [2-(perfluorohexyl)ethyl]silanetriol and ethanol according to the following equation:

 

C₁₄H₁₉F₁₃O₃Si + 3H₂O → C₈H₇F₁₃O₃Si + 3C₂H₅OH

 

Silanetriols may undergo condensation reactions to give siloxane dimers, oligomers and polymers, according to the scheme:

 

RSi(OH)₃  ⇌  RSi(OH)₂OSi(OH)₂R  ⇌  RSi(OH)₂O[Si(R)(OH)O]_nSi(OH)₂R

(where R is an alkyl or aryl side-chain)

 

A highly cross-linked gel may form. The degree of condensation that will occur may vary with:

• Concentration of the silanol; the greater the initial concentration, the greater the degree of condensation. Significant condensation is not expected at concentrations less than approximately 100 mg/l, but is dependent on specific conditions.
• pH; the condensation reaction may be either acid or base catalysed.
• Temperature.
• Other species present.  
• The nature of the R group 
•  Timescale
• The number of Si-OH groups; silanetriols condense more rapidly than silanediols

In the case of this substance the R group contains a perfluorohexyl chain; fluorocarbons have very low solubility in water, relative to hydrocarbons of equivalent chain length (e.g. Horvath 1982), so it would be expected that a substance with this R group would be of low solubility; the corresponding monomeric silanetriol is expected to be surface active based on measured and read across data. The presence of fluorocarbon chains may mean that condensation products could have some surface activity. For these reasons, the effective limits of solubility of both the parent substance and monomeric silanol hydrolysis products are very low and all forms of the substance may have a tendency to enrich at surfaces rather than forming stable dispersions in solution. These phenomena may limit the extent of hydrolysis under conditions at which the solubility of either parent or oligomer is exceeded. The measured rates presented above relate to dilute conditions. These factors are important in any consideration of aqueous behaviour and properties.

 

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

 

The silanol hydrolysis product, [2-(perfluorohexyl)ethyl]silanetriol has a predicted water solubility of 0.58 mg/l at 20°C and a predicted log K_ow of 2.8 at 20°C. It is considered to be surface active based on a measured surface tension value of <22 mN/m at 20°C and 1 g/l. [2-(Perfluorohexyl)ethyl]silanetriol is much less volatile than the parent substance (vapour pressure of 6.9E-03 Pa at 25°C, predicted).

 

Reference:

Horvath, A.L (1982). Halogenated hydrocarbons: solubility-Miscibility with water. CRC press 26 Feb 1982