Ammonium hexanitratocerate method

Colorimetric methods have been successfully used for determining trace amounts of ethanol. Ammonium hexanitratocerate(IV) has been used as a reagent (262) and for continuous automatic analysis. Alcohols form colored complexes with 8-hydroxyquinoline and vanadic compounds. The absorbance of these complexes, measured at 390 p.m has been used to provide an analytical procedure (263). 

The most frequently used method to destroy unused or unwanted azides requires ammonium hexanitratocerate(IV), (NH4)2Ce(NO3)6 (common name. 

Nair et al. (2001) describe the bromination of alkenes using a mixture of ammonium hexanitratocerate(IV) and potassium bromide in a two-phase system consisting of water and dichloromethane. For instance, styrene is transformed by this reaction system in excellent yield at room temperature into 1,2-dibromo-phenyl ethane (scheme 28). It is assumed that the bromide ion is first oxidized by CAN to the bromine radical, which subsequently undergoes addition to the double bond to produce a benzylic radical. Trapping of another bromine radical results in the formation of the 1,2-dibromide. The method is not only applicable to substituted styrenes, but also to alkenes and o, 5-unsubstituted carbonyl compounds. However, the choice of the solvent is of prime importance the reaction only occurs in the water/dichloromethane two-phase system. In other solvents, like aqueous solutions of methanol or acetonitrile, a variety of products such as phenacyl bromides and nitratobromides are formed (scheme 29). The nitrato bromides are formed exclusively when the reaction is carried out in a deoxygenated atmosphere. In the two-phase system water/dichloromethane, side reactions are avoided be-... 

Ammonium hexanitratocerate(IV) is an efficient catalyst for fast esterification of carboxylic acids and alcohols under mild conditions (Goswami and Chowdhury, 2000). The reaction can be carried out under solventless conditions, or in chloroform. The reaction works with primary and secondary alcohols, and with aliphatic carboxylic acids. No reaction was observed for tertiary alcohols or for aromatic acids. The method is of interest because it is also applicable to the esterification of alcohols based on steroids and on other natural products (scheme 37). Pan and coworkers described the esterification of phenylacetic acids and cis-o cic acid with simple primary and secondary alcohols in presence of an excess of CAN at room temperature (Pan et al., 2003). The alcohol acted as solvent. Ammonium hexanitratocerate(IV) does catalyze not only the esterification of carboxylic acid, but also the transesterification with another alcohol (Stefane et al., 2002). 

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. 

Inspired by the Belousov-Zhabotinskii reaction, where cerium(III) is reoxidized by bromate ions. Ho developed a dual oxidant system consisting of ammonium hexanitratocerate(IV) and sodium bromate for the oxidation of arylmethanols (benzylic alcohols) to the corresponding aldehydes (Ho, 1978). The method has also been successfully used for the oxidation of hydroquinones to quinones (scheme 59) and for the oxidation of sulfides to sulfoxides (Ho, 1979). 

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