Catalytic methods employing cheap, clean terminal oxidants in conjunction with catalytic amounts of chromium reagents produce only small amounts of metal byproducts.<ref>Muzart, J. ''Tetrahedron Lett.'', '''1987''', ''28'', 2133.</ref> However, undesired side reactions mediated by stoichiometric amounts of the terminal oxidant may occur.
==Experimental conditions and procedure==
===Typical conditions===
Reagent-grade pyridine is usually sufficient for the preparation of PDC and PCC. Although these reagents may darken over time, their loss in activity is minimal.{{Clarify|date=June 2011}} Isolated reagents should be stored in a desiccator in the dark. Care should be taken when adding chromium trioxide to pyridine, as ignition of pyridine has been known to occur. Celite or silica gel may be used to facilitate the removal of polymeric chromium byproducts from the reaction mixture; these adsorbents also serve as convenient buffer systems and [[desiccant]]s.
Reduced chromium residues can be removed from glassware with concentrated HCl or 10–15% aqueous HF. Solid chromium waste should never be thrown away, as residual CrO<sub>3</sub> may ignite. Chromium(VI) reagents are toxic and should be handled with care in a well-ventilated fume hood.
