Choosing Media for Separation

• Silica: Slightly acidic medium. Best for ordinary compounds, good separation is achieved.
• Florisil: Mild, neutral medium. 200 mesh can be effective for easy separations. Less than 200 mesh best for purification by filtration. Some compounds stick on florisil, test first.
• Alumina: Basic or neutral medium. Can be effective for easy separations, and purification of amines.
• Triethylamine-Deactivated Silica: A method for attenuating the acidity of silica gel, useful for purification of acid-sensitive compounds.
• Reverse phase silica: The most polar compounds elute fastest, the most nonpolar slowest. See
  • Reverse-Phase Flash Chromatography: Jeffrey J. Jackson, Zakarian Group. UC Santa Barbara.
  • Preparative Reverse-Phase Flash Chromatography, A Convenient Method for the Workup of Reaction Mixtures. Kuhler, T. C.; Lindsten, G. R. J. Org. Chem. 1983, 48 (20), 3589-3591.
  • Reverse Phase Flash Chromatography: A Convenient Method for the Large Scale Separation of Polar Compounds. O'Neil, I. A. Synlett 1991, 661-662.
• AgNO ₃-impregnated Silica Gel: For separating E/Z geometric isomers: see J. Med Chem. 2009, 52, 117.
• C2 Deactivated Silica Gel: Contributed by J. M. Fox, University of Delaware.
  This deactivated silica gel was developed for the handling of compounds that were prone to rearrangement on normal flash silica gel. It is also useful for chromatography of polar molecules (heterocycles; nitrogen-containing compounds) that tend to streak on normal silica gel. Compounds elute slightly faster on the C2 silica, but otherwise the selection of chromatography solvents is very similar to unmodified silica gel. Thus, the solvent system for chromatography can be chosen based on TLC analysis. A final merit is that the C2 silica does not significantly dissolve in MeOH.
  For preparation, see supporting information of P. Panne and J. M. Fox, J. Am. Chem. Soc., 2007, 129, 22–23; DOI: 10.1021/ja0660195
  Chuo Chen at UTSW found this silica gel to be important for the purification of sensitive intermediates in his studies on palau’amine (Z. Ma; J. Lu, X. Wang; C. Chen Chem. Commun., 2011, 47, 427-429; DOI: 10.1039/C0CC02214D). Chen describes a modified procedure for washing the silica in his supporting information.