一、琼斯试剂（Jones Reagent）: CrO3/H2SO4/H2O/Acetone
A 0.15–0.40volume of H2SO4(c) isadded over one volume of a 1.5–4.5 M solution of CrO3in water. A fraction of the resulting redsolution is dropped over a 0.01–0.5 M stirred solution of the alcohol inacetone. The alcohol causes the reduction of the red Cr (VI) cations tochromium species with a greenish look. A complete oxidation of the alcohol in ashort time requires normally between 1.2 and 5.0 equiv. of CrO3. Whenthe reaction is finished, the oxidant is quenched by the addition of 0.1–0.4volumes of 2-propanol. If so desired, the reaction mixture can be neutralizedby the addition of saturated aqueous NaHCO3 or diluted NaOH. The resulting mixture isextracted with an organic solvent, such as EtOAc, DCM or Et2O. Thecollected organic solutions are washed with brine, dried (Na2SO4 or MgSO4).
二、沙瑞特试剂和柯林斯试剂（Sarett and CollinsReagents:）:CrO3·2Py
Oneequivalent of CrO3 is slowly added over a 0.2–2.0 M solution of2–2.03 equivalents of dry pyridine in dry DCM. Very often, ca. 2–7 g ofdry Celite per g of CrO3 are added-normally before the preparationof the CrO3·2Py complex-in order to avoid loss of product on thechromium precipitates during the work-up.
Veryfrequently,ca. 2–5 equivalents of acetic anhydride are added-normally after thepreparation of the CrO3·2Py complex-in order to facilitate a milderreaction, particularly in sugars and nucleosides. It is not common to add bothCelite and acetic anhydride in the same reaction.
Afterca. 15–20 min, a 0.02–0.70 M solution of the alcohol in dry DCM isslowly added. Normally, between 4 and 10 equivalents of the CrO3·2Pycomplex are used per equivalent of alcohol. When most of the starting alcoholis consumed, two alternative work-ups can be carried out.
Thereaction mixture is filtered through a pad of silica, Florisil or Celite. Thefiltrate is washed with an organic solvent, like Et2O, EtOAc, orDCM. The collected organic phases may be optionally washed with diluted HCl,diluted aqueous base, brine or saturated CuSO4 solution. The resulting organic solutionis dried (Na2SO4 or MgSO4) and concentrated.
Thereaction mixture is sequentially washed with NaOH (5%), HCl (5%), NaHCO3(5%) and brine. Adding some ether can help the fractioning. Optionally, theorganic phase can be subsequently filtered through Florisil. The resultingorganic solution is dried (Na2SO4 or MgSO4)and concentrated.
Approximately,1.1–7 equivalents of solid PDC are added over a ca. 0.01–0.30 M solution of thealcohol in dry DCM. The resulting suspension is stirred at roomtemperature. Approximately, 0.5–4 g of activated MS-preferably finely ground 3ÅMS-per mmol of alcohol can be added in order to accelerate the oxidation. Thereaction can also be accelerated by the addition of ca. 0.9–4 equivalents of dryAcOH or 0.75–12 equivalents of acetic anhydride. The simultaneous use ofmolecular sieves and an organic acid has a synergistic accelerating effect. Theaddition of ca. 0.5–2.50 g of Celite or Florisil (magnesium silicate) per mmol of alcohol canfacilitate the work-up. Celite or Florisil can be added either at the beginningof the oxidation or ca. 30 min before the work-up. Two alternative work-ups canbe carried out.
The most common workup. Et2Ois added and the precipitate is decanted and washed with ether. The collectedorganic phases are filtered through a pad of Celite, silica or Florisil.Alternatively, decanting the precipitate can be avoided and the mixture,resulting from the addition of ether, can be directly filtered through a pad ofsilica, Celite or Florisil. When the reaction is carried out under diluteconditions, the addition of diethyl ether can be avoided. The organic phase isconcentrated giving a residue that may need chromatographic purification. Whenthe reaction is
carried out in the presence of addedCelite or Florisil, a similar work-up is made in which the Celite or Florisilis filtered.
Et2O is added and theresulting mixture is washed with aqueous phases. The aqueous phases used canbe: plain water, aqueous saturated NaHCO3 solution, diluted HCl or brine.The collected organic phases are dried (MgSO4 or Na2SO4)and concentrated, giving a residue that may need chromatographic purification.
- PCC（pyridinium chlorochromate）
Approximately, 1.1–7 equiv., typically1.5 equiv. of solid PCC are added over a ca. 0.01–0.25 M solution of thestarting alcohol in dry DCM. The resulting mixture is stirred at roomtemperature. Very often, ca. 0.2–1.2 g of activated MS per mmol of alcohol areadded in order to accelerate the reaction. In order to moderate the acidity ofPCC, it is very common to add ca. 0.3–1 equivalents of NaOAc. A solid support,such as silica gel, Celite, Florisil or magnesium sulfate, is added, very oftenin a proportion of ca. 0.3–2 g of solid support per mmol of alcohol, in orderto facilitate the work-up. Occasionally alumina, working both as a solidsupport-used to facilitate the work-up and as an accelerant, mixed with PCC isadded, in a
proportion of ca. 0.4–1.5 g of aluminaper mmol of alcohol. Normally, PCC is deposited over the alumina. Occasionally,ca. 10–20 equivalents of acetic acid are added in order to accelerate thereaction.
Sometimes, the reaction flask issonicated with ultrasound in order to fragment the surface of the PCC particlesand, therefore, accelerate the reaction.
Although in PCC oxidations, it is verycommon to add simultaneously to the reaction an accelerant, a buffer and awork-up-facilitator; it is not common to employ simultaneously two materialsbelonging to the same kind, with the exception of the combination of the twoaccelerants molecular sieve and acetic acid, which are very often usedtogether.
When a TLC analysis shows that most ofthe starting alcohol is consumed,
the solids suspended in the reaction andthe chromium species are removed by filtration through a pad of Florisil1,silica gel, alumina or Celite, and the pad is washed with an organic solvent,such as ether, DCM, or EtOAc. Sometimes, the solids can be removed bydecantation. Other times, it is advisable to add some diethyl ether to thereaction mixture before the filtration, in order to promote the separation ofreduced chromium species in a granular form. Occasionally, the reaction mixtureis concentrated before the addition of diethyl ether. Finally, the collectedorganic phases are concentrated at the rotary evaporator, giving a crudealdehyde or ketone that may need some further purification.
参考文献：common oxidation reagents, Yue Xu, Sundia Meditech