Examples:
A. Ates, A. Gauthier, B. Leroy, J.-M. Planncher, Y. Quesnel, I. E. Marko, Tetrahedron Lett. 1999 , 40 , 1799.
S. J. Clark, C. P. Dell, J. M. McDonagh, J. Geden, P. Mawdsley, Org. Lett. 2003 , 5 , 2063.
K. Pitchamuthu, Y. D. Vankar, J. Org. Chem. 2001 , 66 , 7511.
4.1.3 Cerium(IV) Ammonium Sulfate (Ce(NH4)4 (SO4 )4ยท2H2O)
CAN is the most extensively utilized cerium(IV) oxidizing agent, but cerium(IV) ammonium sulfate (CAS) is a versatile substitute when complications occur due to the involventment of nitrate ligands, resulting in side products such as nitrate esters.
| M. Periasamy, U. Radhakrishnan, Encyclopedia of Reagents for Organic Synthesis, John Wiley and Sons, Inc., L. A. Paquette, Ed., New York, 1995, 2 , 1029. |
Oxidation of Aromatic Rings
The most important use of CAS is the oxidation of aromatic rings to quinones. CAN oxidizes polyaromatic rings only in moderate yields. Furthermore, these reactions often give nitrate esters as by-products. In contrast, CAS usually oxidizes aromatic rings to quinones in good yields. For example, naphthalene is oxidized to 1,4-naphthaquinone by CAS in a mixture of H2SO4 and MeCN (Scheme 10). A similar result is observed with polycyclic aromatic compounds such as
Scheme 10
Scheme 11
phenanthrene and anthracene. Whereas the oxidation of 1-phenyl and 1,4-diphenylnaphthalene react to form some substituted naphthaquinones through rearrangement depending on the reaction conditions (Scheme 11).