將吡啶加入到三氧化鉻的水溶液中有亮黃色的PDC固體生成，PDC溶于有機(jī)溶劑，在空氣中室溫下，易于儲存和操作。在二氯甲烷的懸浮溶液中可以將醇氧化為醛酮（ 與PCC氧化類似，惰性氣體保護(hù)避免接觸空氣中的水。）。PDC用DMF當(dāng)溶劑可以將伯醇氧化為酸。另外3?分子篩，HOAc，PPTS，PTFA，Ac2O可以加快PDC的氧化速度。反應(yīng)結(jié)束可以用亞硫酸鈉快速淬滅反應(yīng)。
PDC的氧化能力較PCC弱，其氧化作用一般在中性條件下進(jìn)行，而PCC則需在酸性中進(jìn)行。因此，對酸不穩(wěn)定的化合物用PCC氧化時，必須在醋酸鈉存在下進(jìn)行。
單單只是用PCC或PDC的話，伴隨著反應(yīng)的進(jìn)行，會生成出黑褐色油狀殘渣。生成物被這些殘渣所包裹，導(dǎo)致產(chǎn)率降低。像反應(yīng)溶液中加入適量硅藻土，硅膠或者是分子篩，能夠改善這種情況。
氧化的一般操作步驟：
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 3?MS-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.
Work-upA:
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.
Work-upB:
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.
反應(yīng)實例
【Terpstra, J. W.; Van Leusen, A. M. J. Org. Chem. 1986, 51, 230–208】
【J. Org. Chem. 1992, 57, 6173–6177】
中間先生成了半縮醛中間體，接著氧化得到內(nèi)酯。
【Tetrahedron: Asymmetry 2003, 2567–2571】
參考文獻(xiàn)
一、Name Reactions （A Collection of Detailed Reaction Mechanisms）, Jie Jack Li, PCC oxidation，page 337.
二、common oxidation reagents, Yue Xu, Sundia Meditech
