Nitro compounds Cerium ammonium nitrate

Cerium(IV) ammonium nitrate, 67 Grignard reagents, 138 Other nitro compounds Alumina, 14 Nitrones... 

Catechols and hydroquinones can be converted (91-98%) into quinones by cerium(IV) salts coated onto silica as free-flowing yellow powder from impregnation with cerium(IV) ammonium nitrate. This reaction is usually performed in the presence of magnesium sulfate. The same (NH4)2Ce(N03)6 SiQ2 reagent in the dry state effects oxidative nitrations of arenes. For example a-mq>hthol is converted to the Orth) (42%) and the para (38%) nitro compounds, while its metiiyl or ethyl ethers give exclusively the para nitration product (equation 4). In solution, the products are cmtaminated with the products of dinitration and of oxidation into quinones. ... 

The advantage of mild reaction conditions is obvious, if enolates are oxidized at low temperatures in methanol. Thus, Narasaka et al. demonstrated that cerium(IV) ammonium nitrate smoothly generates radicals 12 after deprotonation of nitro compounds Id [8], The electrophilic radicals can be added to electron-rich double bonds like silyl enol ethers 13. Ketones 14 are formed as intermediates, which after elimination of HNO2 under the basic reaction conditions alford enones 15 in high yields as final products (Scheme 4). 

Cerium(lll) ammonium nitrate (CAN) in acetic anhydride is also an efficient nitrating reagent for aromatic compounds [135]. The nitration of thiophene by CAN gave a mixture of 2-nitro- (58%) and 3-nitrothiophene (12%) (Scheme 86) [134]. 

Mononitration of 1-hydroxynaphthalene could be obtained by use of ammonium hexanitra-tocerate(IV) supported on silica gel in acetonitrile (Chawla and Mittal, 1985) (scheme 39). The same reaction with CAN in acetic acid give the 2,4- and 4,6-dinitro derivatives. By the same method, 2-hydroxy naphthalene is converted into l-nitro-2-hydroxy naphthalene and 4-nitro-2-hydroxynaphthalene (scheme 40). The 1-alkoxynaphthalenes can be mononitrated regioselectively in the 4-position (scheme 41). The lower reactivity of CAN supported on silica gel is also evident from the fact that naphthalene derivatives are not oxidized into 1,4-naphthoquinones. The authors noticed that no reaction could be observed when ammonium hexanitratocerate(IV) was replaced by a mixture of ammonium nitrate and ammonium cerium(IV) nitrate. Silica supported CAN has also been used for the nitration of methoxyben-zenes (Grenier et al., 1999) and less electron rich aromatic compounds like benzene, toluene, chlorobenzene and bromobenzene (Mellor et al., 2000) (scheme 42). For the less electron rich aromatics, dichloromethane is used as solvent instead of acetonitrile. In most cases, the yields are good to excellent. 

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