Optimization of the Reaction of Hexamethyldisilazane on a Fumed Silica Surface

Hexamethyldisilazane (HMDS) is commonly used to transfer trimethylsilyl (TMS) groups to silica surfaces. While studies have been done examining individual factors that influence the reaction, no investigations have reported how these factors affect each other. The factors examined in this study include temperature, presence of catalyst (butylamine), pretreatment, time, concentration, solvent, and presence of water in the solvent. The purpose of this study is to examine potential factors and two-way interactions to determine which significantly affect the yield and produce an optimum set of conditions. The HMDS reactions occurred in an organic solvent slurry under nitrogen. Using statistical experimental design, the factors under study were implemented at preset values for each reaction of the design. From this study, four factors and interactions were found to influence the silylation reaction. The only independent factor observed was the solvent chosen, showing TMS yields favoring cyclohexane\u3ebenzene\u3eacetonitrile. Solvent showed the weakest influence on the reaction of all significant effects. The three significant interactions observed were catalyst-time, temperature-time, and temperature-concentration. Catalyst-time favors reaction times of at least five hours or one hour in the presence of 50 μL butylamine. The temperature-time interaction prefers at least 5 hours or reaction times as short as 1 hour at higher temperatures. Temperature-concentration favors higher temperatures (\u3e80 °C) to allow smaller concentrations of HMDS/g silica to produce the same TMS yields as larger concentrations at room temperature