Sulfur donors are used commonly in rubber crosslinking, usually in conjunction with elemental sulfur. In the crosslinking process, sulfur donors release in situ free sulfur. The difference between two sulfur donors, bis(triethoxysilylpropyl)-tetrasulfide (TESPT) and cyclic tetrasulfide (CTS), both of which contain at least one tetrasulfidic group in the molecule, is analyzed. Chemical model studies are deployed to assess the chemical reactivity of the two molecules. The difference in reactivity of the two sulfur donors was observed in chemical model studies in reaction with 2,3-dimethyl-2-butene, as followed by Raman spectroscopy, gas chromatography coupled with mass spectroscopy, and nuclear magnetic resonance analysis of the products of reaction. These studies represent a fundamental analysis and comparison between the two tetrasulfidic compounds, and the findings of these experiments can be extrapolated to crosslinking processes in rubber.