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. This study analyses the difference between two sulfur donors, bis(triethoxysilylpropyl)- tetrasulfide (TESPT) and cyclic tetrasulfide (CTS), both containing at least one tetrasulfidic group in the molecule. 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, GC-MS and NMR 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.