[3-(triethoxysilyl)propyl]urea

Endpoint summary

Additional information

Physico-chemical properties

3-(triethoxysilyl)propyl]urea is a white solid at standard temperature and pressure, with a measured melting point of 51°C and a measured boiling point of 316.9°C. It has a measured density of 1.06g/cm³at 20°C, and a predicted vapour pressure of 3.1E-03 Pa at 25°C.

The substance is classified as non-flammable. It is not pyrophoric or flammable in contact with water, and it is not explosive and not oxidising on the basis of chemical structure. It is not self-heating.

It is not surface active. A first pKa value of 1.0 was determined for the amine groups (parent compound) using an appropriate calculation method.

In contact with water, 3-(triethoxysilyl)propyl]urea reacts rapidly (calculated half-life of approximately 16.4 hours at 20-25°C, pH 7) to produce [3-(trihydroxysilyl)propyl]urea and ethanol according to the following equation:

           (CH₃CH₂O)₃SiCH₂CH₂CH₂NHC(=O)NH₂ + 3H₂O 

           → (HO)₃SiCH₂CH₂CH₂NHC(=O)NH_2 + 3CH₃CH₂(OH)

Therefore, requirements for testing of the water-based physicochemical properties for the substance and measurement of the surface tension are waived on the basis of instability in water. The properties of the hydrolysis products are assessed in instead.

The silanol hydrolysis product, [3-(trihydroxysilyl)propyl]urea, is predicted to be very soluble in water at 20^oC (1.0E+06 mg/l) and has a log K_ow of -3.3 at 20°C (predicted). It is less volatile than the parent substance with a vapour pressure of 4.1E-07 at 25°C (predicted). The first dissociation constant (hydroxyl groups) of a structurally analogous silanetriol (phenylsilanediol) has been reported to be around pK_a10.

Ethanol is miscible with water, has low log K_ow(-0.3) and high vapour pressure (7910 Pa at 20°C).

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
• The number of Si-OH groups; silanetriols condense more rapidly than silanediols.