Bis(triethoxysilylpropyl)tetrasulfide

Bis(triethoxysilylpropyl)tetrasulfide is an organosulfur compound with the formula S₄[C₃H₆Si(OEt)₃]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]

Bis(triethoxysilylpropyl)­tetrasulfide

Names
Preferred IUPAC name [Tetrasulfanediyldi(propane-3,1-diyl)]bis(triethoxysilane)
Other names Bis[3-(triethoxysilyl)propyl]tetrasulfide Bis(3-triethoxysilylpropyl)tetrasulfane Si-69 TESPT
Identifiers
CAS Number	40372-72-3
3D model (JSmol)	Interactive image
ChEMBL	ChEMBL3188179
ChemSpider	142291
ECHA InfoCard	100.049.888
EC Number	254-896-5
PubChem CID	162012
UNII	J98V193ZRY
CompTox Dashboard (EPA)	DTXSID3029362
InChI InChI=1S/C18H42O6S4Si2/c1-7-19-29(20-8-2,21-9-3)17-13-15-25-27-28-26-16-14-18-30(22-10-4,23-11-5)24-12-6/h7-18H2,1-6H3 Key: VTHOKNTVYKTUPI-UHFFFAOYSA-N
SMILES CCO[Si](CCCSSSSCCC[Si](OCC)(OCC)OCC)(OCC)OCC
Properties
Chemical formula	C18H42O6S4Si2
Molar mass	538.95
Appearance	yellow syrup
Density	1.08 g/cm3
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Infobox references

Synthesis and reactivity

Reaction

The compound was first prepared by the reaction of 3-(triethoxysilyl)propyl chloride with sodium tetrasulfide:^[4]

Na₂S₄ + 2 ClC₃H₆Si(OEt)₃ → S₄[C₃H₆Si(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.^[5]

References

1. Kohjiya, Shinzo; Ikeda, Yuko (2000). "Reinforcement of general-purpose grade rubbers by silica generated in situ". Rubber Chemistry and Technology. 73 (3): 534–550. doi:10.5254/1.3547604.
2. Wolff, Siegfried (1996). "Chemical aspects of rubber reinforcement by fillers". Rubber Chemistry and Technology. 69 (3): 325–346. doi:10.5254/1.3538376.
3. Vilmin, F.; Bottero, I.; Travert, A.; Malicki, N.; Gaboriaud, F.; Trivella, A.; Thibault-Starzyk, F. (2014). "Reactivity of Bis[3-(triethoxysilyl)propyl] Tetrasulfide (TESPT) Silane Coupling Agent over Hydrated Silica: Operando IR Spectroscopy and Chemometrics Study". The Journal of Physical Chemistry C. 118 (8): 4056–4071. doi:10.1021/jp408600h.
4. Thurn, Friedrich; Meyer-Simon, Eugen; Michel, Rudolf "Verfahren zur Herstellung von Organosiliziumverbindungen (Continuous manufacture of bis[3-(triethoxysilyl)propyl] tetrasulfide)" Ger. Offen. (1973), DE 2212239 A1 19731004.
5. Choi, S.-S.; Kim, I.-S.; Woo, C.-S. (2007). "Influence of TESPT Content on Crosslink Types and Rheological Behaviors of Natural rubber compounds reinforced with Silica". Journal of Applied Polymer Science. 106 (4): 2753–2758. doi:10.1002/app.25744.