Bis(triethoxysilylpropyl)tetrasulfide is an organosulfur compound with the formula S4[C<sub>3</sub>H<sub>6</sub>Si(OEt)<sub>3</sub>]2 (Et = C2H5). 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.[1] [2] [3]
thumb|left|ReactionThe compound was first prepared by the reaction of 3-(triethoxysilyl)propyl chloride with sodium tetrasulfide:[4]
Na2S4 + 2 ClC3H6Si(OEt)3 → S4[C<sub>3</sub>H<sub>6</sub>Si(OEt)<sub>3</sub>]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.[5]