Bis(triethoxysilylpropyl)tetrasulfide
# Bis(triethoxysilylpropyl)tetrasulfide

Bis(triethoxysilylpropyl)tetrasulfide is an organosulfur compound with the formula $S_4[C_3H_6Si(OEt)_3]_2$ (Et = $C_2H_5).$ The molecule consists of two trialkoxysilyl propyl groups linked with a polysulfide. It is often sold as a mixture with the trisulfide. The compound is a colorless viscous liquid that is soluble in ordinary organic solvents such as toluene. Commercial samples often are yellowish. The compound is added to rubber compositions that contain silica filler.

## Synthesis and reactivity

The compound was first prepared by the reaction of 3-(triethoxysilyl)propyl chloride with sodium tetrasulfide:

    $Na_2S_4$ + 2 $ClC_3H_6Si(OEt)_3$ → $S_4[C_3H_6Si(OEt)_3]_2$ + 2 NaCl

Bis(triethoxysilylpropyl)tetrasulfide is a bifunctional molecule in that it contains two kinds of reactive functional groups. The tetrasulfide group is a polysulfide, which means that it consists of a chain of sulfur atoms. S-S bonds are susceptible to reduction (to thiols), attachment to metals (e.g., for protection against corrosion), and vulcanization. The triethoxysilyl groups are susceptible to hydrolysis, resulting in cross-linking via sol-gel condensation. In the usual application of this chemical, the hydrolyzed siloxy groups attach to silica particles and the polysulfide groups link to the organic polymer.

