Bonded Phases - The Use of Alkoxysilane Reagents in Bonded Phase Synthesis
The Use of Alkoxysilane Reagents in Bonded Phase Synthesis
If the alternative alkoxysilane reagents are employed for bonding, the method of synthesis remains very similar. The same solvents can be used but, as no hydrochloric acid is generated, there is no need to have any pyridine present as a scavenger. The most reactive alkoxy reagents are the methoxy and ethoxysilanes and their reaction with a hydroxyl group is accompanied by the release of methanol or ethanol.
Consequently, the reaction is best carried out in a distillation flask and the methanol removed as it is formed, the heating rate being adjusted to ensure that the aromatic solvent is not removed as well. The reaction is again allowed to proceed for 5 hours and the product is then filtered through a sintered glass filter and washed with the same sequence of solvents as those used in the chlorsilane synthesis. The product is then refluxed with the THF/water mixture, filtered and again washed with the appropriate solvents and dried. The final capping process is also the same as that employed in the method using the chlorsilanes reagents, utilizing hexamethyldisilazane as the capping reagent. The alkoxysilanes are almost as readily available as the chlorsilanes and are easier and more pleasant to handle. They are, however, just as hygroscopic as the chlorsilanes and must be kept under the same anhydrous conditions. Approximately the same yields can be expected and the same degree of bonding.