Endcapping of Octadecylsilyl-Silica Gels Using Supercritical Fluid as Reaction Medium

Abstract

A method for endcapping of octadecylsilyl (ODS)-silica gels was developed using supercritical carbon dioxide as a silylation medium. The effects of temperature and pressure of carbon dioxide on the deactivation of the gels were investigated under the silylation conditions at 100 -220˚C and 11.8 -24.5 MPa. High-performance liquid chromatographic evaluation using caffeine and phenol as test compounds indicated that the most inert gels were obtained from the endcapping under 180˚C and 24.5 MPa. Endcapped ODS-silica gels, which were commercially available, could be further deactivated under these conditions. The inertness of the gels was also evaluated by supercritical fluid chromatography (SFC) using pyridine and phenol as test compounds. The effectiveness of the proposed method was clearly observed in the SFC evaluation.

Synthesis, characterisation and chromatographic evaluation of pentafluorophenyl and phenyl bonded silica phases prepared using supercritical carbon dioxide as a reaction solvent

“…Also, the increase in the carbon content of the endcapped bonded phases is due to methylation of residual silica surface silanols while the decreased observed for 3.0 m Ex-PFP-E BSA is likely due to stripping of pentafluorophenylsilyl group or ligand on silica by endcapping reagent. Other authors have also noted a decreased in carbon loading for ODS after sc-CO 2 endcapping [7,59]. However, the surface coverages of the scgenerated pentafluorophenyl and phenyl bonded phases including the endcapped phases are comparable with commercially available columns cited in literature (Table 2), despite most available commercial supports today employing a double endcapping treatment [60,61] compared to a single endcapping process used in this research work.…”

“…Yarita et al endcapped an octadecyl silica (ODS) using sc-CO 2 as a silylation solvent [7], while Robson et al prepared silica bonded stationary phases in an autoclave using sc-CO 2 at 150 • C for 20 h [8]. Myers et al reported the derivatisation of silica with a polyaminosilane in sc-CO 2 at 150 • C and low pressure [9].…”

Polymer synthesis and processing using supercritical carbon dioxide

“…226 Finally, Yarita et al have developed a method for end-capping octadecylsilyl (ODS) silica gels using scCO 2 as a silylation medium. 227 The effects of temperature and pressure on the deactivation of the gels were investigated, and HPLC (or SFC) evaluation of the resulting materials indicated that the most inert gels were obtained via silylation at 180 ³C and 245 bar. It was found that commercially available end-capped ODS-silica gels could be further deactivated by this technique.…”

Silica hydride intermediate for octadecylsilica and phenyl bonded phase preparation via heterogeneous hydrosilation in supercritical carbon dioxide

“…Yarita et al demonstrated a method for endcapping octadecylsilyl (ODS)-silica gels using supercritical carbon dioxide as a silylation medium [6], while Robson et al prepared bonded silica stationary phases in sc-CO 2 using an autoclave at 150 degrees for 20 h [7]. Healy et al exploited the high diffusivity and mass transfer kinetics of sc-CO 2 to gendesired organic compound, in general via a terminal olefin, onto the hydride silica surface is typically facilitated by the use of Speier's catalyst (a 2-propanol solution of hexachloroplatinic acid) [15].…”