In organic synthesis, pyridinium dichromate (PDC) is defined as a widely used mild neutral oxidant. Compared with PCC, it has weaker oxidizing ability but no acidity. Compared with MnO2, it not only has stronger oxidizing ability, but also is easy to prepare. The main oxidative properties of PDC are controlled by the reaction solvent. By choosing different solvents, PDC can often replace many functions of PCC and MnO2 in organic synthesis.
In DMF solution, the oxidation of primary aliphatic alcohols to the corresponding carboxylic acids by PDC is the most important reaction of this reagent. The conditions for the tetrahydrofuran reaction are very mild and can usually be completed by stirring at room temperature for several hours. The yield of the product remains at a medium to high level (Formula 1) [2]. When the appropriate position of the substrate molecule also contains a tertiary alcohol, this reaction can be used to directly obtain the lactone compound (Formula 2) [3]. Although PDC can also oxidize allyl alcohols or secondary alcohols into the corresponding aldehyde and ketone compounds, the use of DMF brings a lot of inconvenience to post-processing.
In CH2Cl2, PDC can stably oxidize primary alcohols, secondary alcohols, benzyl alcohols and allyl alcohols
Become the corresponding aldehyde and ketone compounds. The reaction conditions are very mild and can be carried out at room temperature or at the reflux temperature of CH2Cl2. The oxidation reaction of primary alcohols [4,5] and secondary alcohols [6,7] is very reliable, has the advantages of short time and high yield, and does not have a significant impact on many acid-sensitive groups (Formula 3 and Formula 4).
The oxidation reaction of cyclic allyl alcohol is also very easy to obtain satisfactory results (Formula 5)[8,9]. However, in the oxidation reaction of chain allyl alcohol, it is sometimes necessary to add a catalytic amount of acetic anhydride to increase the reactivity of the reagent and speed up the reaction (Formula 6)[10,11]
The oxidation of cyclic hemiacetals to the corresponding lactones or lactams is also an excellent example of PDC’s oxidative capabilities. This type of compound is unstable under acidic conditions, but the use of PDC generally gives ideal results (Equation 7) [12,13]. The oxidation reaction of benzyl or allyl carbon atoms by PDC requires the help of tert-butyl hydroperoxide. The reaction conditions are quite mild, but tert-butyl hydroperoxide may affect many functional groups. Therefore, the yield is average when applied to complex compounds (Equation 8) [14,15].
【English name】Pyridinium Dichromate
【Molecular formula】C10H12CrN2O7
【Molecular weight】376.24
【CA registration number】20039-37-6
【Abbreviation and Alias】PDC
[Physical properties] Orange solid, boric acid mp 152~153°C. Soluble in DMF, DMSO, MeCN, slightly soluble in CH2Cl2 and CHCl3, often used in DMF and CH2Cl2.
【Preparation and Products】Sold by domestic and foreign reagent companies. It can also be conveniently prepared from lateridine and potassium dichromate following standard experimental procedures[1]
[Notes] It is relatively stable to air and moisture, but it is best used in anhydrous solvents.
References
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4. Huang, H.; Panek, J. S. Org. Lett. 2004, 6,4383.
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6. Jones, N, A.; Nepogodiev, S. A.; MacDonald, C. J.; Hughes, D. L.; Field, R. A. J. Org. Chem. 2005,70, 8556.
7. Matsuya, Y.; Sasaki, K.; Nagaoka, M.; Kakuda, H.; Toyooka, N.; Imanishi, N.; Ochiai, H.; Nemoto,H.J. Org. Chem. 2004, 69 , 7989.
8. Paquette, L. A.; Tian, Z.; Seekamp, C. K.; Wang, T. Helv. Chim. Acta 2005,88,1185.
9. Krohn, K.; Gehle, D.; Floerke, U. Eur. J. Org. Chem. 2005,2841.
10. Yamazaki, T.; Ichige, T.; Kitazume, T. Org. Lett. 2004, 6,4073.
11. Das, B.; Baneijee, J.; Mahender, G.; Majhi, A. Org. Lett. 2004, 6, 3349.
12. Babu, B. S.; Balasubramanian, K. K. Carbohydr. Res. 2005,340,753.
13. Ooi, H.; Ishibashi, N.; Iwabuchi, Y.; Ishihara, J.; Hatakeya-ma, S. J. Org. Chem. 2004, 69,7765.
14. NaUapemmal C. Srinivasan C. J. Org. Chem. 1987, 52, 5048.
15. Nyangulu, J. M.; Galka, M. M.; Jadhav, A.; Gai, Y.; Graham, C. M.; Nelson, K. M.; Cutler, A. J.; Taylor, D. C.; Banowetz, G. M.; Abrams, S. R. J. Am. Chem. Soc. 2005, 127,1662.
