Reaction of Silica Gel with Trimethylsilyl Donors Using Conditions Useful for End-Capping HPLC Bonded Phase Packings

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Abstract
Several trimethylsilyl (TMS) donors including bis-N, O-trimethylsilylacetamide (BSA), bis-N, O-trimethylsilyltrifluoro-acetamide (BSTFA), hexamethyldisilane (HMDS), trimethylchlorosilane (TMCS) with and without pyridine, 2-trimethylsiloxypent-2-en-A-one (TMSOP), trimethylsilyldimethylamine (TMSDMA), and trimethylsilylimidazole (TMSIM) were reacted with 60 Å silica. TMSIM at 60°C with reaction times of one hour or less gave coverage of silica gel equivalent to that provided by refluxing TMCS and pyridine in toluene for 67 hrs. Reactivity of the TMS donors studied may be ranked in the following order: TMSIM > TMSDMA > BSTFA > BSA > TMCS > TMSOP > HMDS. TMSIM appears to be the reagent of choice for end-capping of alkyl bonded HPLC phases.