Pyridinium Chlorochromate (PCC)
Chlorochromic acid can by prepared by the dissolution of chromium trioxide in 6 M aq. hydrochloric acid. Addition of pyridine gives pyridinium chlorochromate as orange crystals.
The properties of PCC can be compared with those of PDC: it is not particularly hygroscopic, is stable, commercially available and can be stored. PCC is soluble in many organic solvents, and especially dichloromethane at room temperature has been used in most cases, whereas DMF promotes the over-oxidation of primary alcohols into carboxylic acids.
PCC is more acidic than PDC, but acid-labile compounds can be oxidized in the presence of sodium acetate or other buffers such as carbonates. Another drawback is the formation of viscous materials that complicate product isolation. Addition of Celite, powdered molecular sieves or magnesium sulfate to PCC oxidation reaction mixtures can simplify the work-up, because the reduced chromium salts and other reagent-derived byproducts are deposited onto these solids, which can then be readily removed by filtration.
A full review of chromium-based reagents can be found in the book written by Tojo and Fernández (Oxidation of Alcohols to Aldehydes and Ketones, Springer Berlin, 2006, 1-97.).
Attention: Chromium (VI) compounds are toxic and must be handled with care.
Pyridinium chlorochromate is a readily available, stable reagent, that oxidizes a wide variety of alcohols to carbonyl compounds with high efficiency.
E. J. Corey, J. W. Suggs, Tetrahedron Lett., 1975, 16, 2647-2650.
A facile and quantitative preparation of carboxylic acids by a pyridinium chlorochromate (PCC) catalyzed (2 mol%) oxidation of primary alcohols and aldehydes using 2.2 equivalents and 1.1 equivalents of H5IO6, respectively, in acetonitrile is described here.
M. Hunsen, Synthesis, 2005, 2487-2490.
Isatins can be synthesized from α-formyl amides in good yields via one-pot intramolecular cyclization-oxidation reaction in the presence of pyridinium chlorochromate (PCC). The reaction proceeded smoothly under air, offers a broad substrate scope, and is operationally simple.
Q. Yue, Y. Wang, L. Hai, L. Guo, H. Yin, Y. Wu, Synlett, 2016, 27, 1292-1296.
A multifunctional modular organocatalysis enables a simple and efficient approach to enantioenriched α,β-disubstituted γ-butyrolactones via a one-pot sequential Michael-hemiacetalization-oxidation reaction. The catalytic process offers good substrate compatibility, and the products can be transformed to synthetically useful molecules.
P. Mahto, N. K. Rana, K. Shukla, B. G. Das, H. Joshi, V. K. Singh, Org. Lett., 2019, 21, 5962-5966.