Cerium trifluoroacetates

Cerium phthalocyanine, 7 64 Cerium tetrafluoride, 20 63-67 lattice parameters, 20 64 Cerium trifluoroacetates, 17 5, 26 Cermets, nitrides in, 9 81-82 Cerous ion, reaction with hydroxyl ions, 3 187 Ceruloplasmin, 40 123, see also Blue copper oxidases... 

Cerium(IV) ammonium nitrate, 67 Thallium(III) trifluoroacetate, 295 Allylic iodides... 

Yamashiro et al. 1972), boron trifluoride etherate in acetic acid (Schnabel et al. 1971), trimethylsylil triflate (Schmidt et al. 1987), trimethylsilyl perchlorate (Vorbrueggen Krolikiewicz 1975), and, most frequently, trifluoroacetic acid (Farowicki Kocienski 1995 and references therein). Deprotection of the /-HOC group under neutral conditions was not described until recently, yet it is highly desirable. Now it has been found that the tert-butoxycarbonyl protecting group for amines, alcohols, or thiols is removed efficiently (90-99% yield) with use of 0.2 equivalent of cerium ammonium nitrate in acetonitrile at 80°C (Hwu et al. 1996) ... 

Enhancement by strong acids such as TFA is a general feature of oxidations with metal acetates. Metal trifluoroacetates in TFA are much more powerful oxidants (electrophiles) than the corresponding acetates in acetic acid. Activation of the metal oxidant in TFA has been observed with co-balt(III)217 249,259,27S 276 manganese(III),237,275 lead(IV),277-281 thallium-(III),282-287 cerium(IV),288 289 and copper(II).290 Similarly, the electrophilic properties of copper(I)291 and mercury(II)292 acetates are strongly enhanced by replacement of acetate by trifluoroacetate. It has been proposed217,276 that the potent oxidizing properties of Co(III) trifluoroacetate are due to ionization to the cationic Co(III) species,... 

The use of electricity in reactions is clean and, at least in some cases, can produce no waste. Toxic heavy metal ions need not be involved in the reaction. Hazardous or expensive reagents, if needed, can be generated in situ where contact with them will not occur. The actual oxidant is used in catalytic amounts, with its reduced form being reoxidized continuously by the electricity. In this way, 1 mol% of ruthenium(III) chloride can be used in aqueous sodium chloride to oxidize benzyl alcohol to benzaldehyde at 25°C in 80% yield. The benzaldehyde can, in turn, be oxidized to benzoic acid by the same system in 90% yield.289 The actual oxidant is ruthenium tetroxide. Naphthalene can be oxidized to naphthoquinone with 98% selectivity using a small amount of cerium salt in aqueous methanesulfonic acid when the cerium(III) that forms is reoxidized to cerium(IV) electrically.290 Substituted aromatic compounds can be oxidized to the corresponding phenols electrically with a platinum electrode in trifluoroacetic acid, tri-ethylamine, and methylene chloride.291 With ethyl benzoate, the product is a mixture of 44 34 22 o/m/fhhy-... 

In a solid-phase synthesis (Wang or Sasrin resin), cyclocondensation of immobilized 2-alkyli-dene- or 2-arylidene-/ -oxo esters with 6-aminouracils in dimethylformamide, after aromatiza-tion by ammonium cerium(lV) nitrate and cleavage by trifluoroacetic acid, furnishes the corresponding pyrido[2,3-rf]pyrimidines in 90 100%.568... 

Cerium(iv) trifluoroacetate is readily prepared by treatment of the hydroxide with hot trifiuoroacetic acid, followed by further treatment of the basic trifluoroacetate with a mixture of trifiuoroacetic acid and trifiuoroacetic anl dride (equation 1). Ce(OH)4 Ce(0H)2(02C-CF3)2 Ce(02C-CFs)4 (1)... 

Cerium (III) chloride s. under Mg Trifluoroacetic acid s. under Al Lead(II) bromide s. under Al... 

Phenols (e.g., phenol itself [CeHs-OH or Ar-OH], Table 6.10, item 2) and their esters (e.g., the trifluoroacetate ester of phenol [C6H5-O2CCF3 or Ar02CCH3], Table 6.10, item 3) have been oxidized with air and oxygen (O2), in neutral and alkaUne solutions, with and without ionic and/or radical catalysts and/or irradiation and in a variety of solvents. Enzymes (this chapter and Chapter 12) from a wide variety of sources have also been used. Frequently, oxidation of aromatic systems to phenols cannot be stopped before quinones and products of ring fragmentation occur and numerous, sometimes ill-defined, products result. Thus, as shown in Equation 6.80, oxidation of the polynuclear hydrocarbon chrysene with anunonium cerium(IV) sulfate [ceric ammonium sulfate, Ce(NH,)4(S04)4] is reported to produce 6H-benzo[d]naphtho[l,2-/>]pyran-6-one (8% yield) and a quinone (23% yield). The remainder of the product(s) (69%) was unidentified. 

To a reaction tube charged with cerium ammonium nitrate (68 mg, 0.125 mmol, 0.25 mmol of NH4, 1 equiv.) and copper trifluoroacetate hydrate (14.5 mg, 0.05 mmol, 20 mol%) was added a solution of acetaldehyde (1 mmol) and H2O (135 iL, 7.5 mmol, 30 equiv.) in DMF (3 mL) imder argon (1 atm). The reaction mixture was then stirred at 80°C for 12 h. After cooling to room temperature, the mixture was diluted with ethyl acetate, washed with saturated sodium bicarbonate, water and brine, dried over anhydrous sodium sulfate, and concentrated in vacuo to give dark residue, which was purified by flash chromatography (using petroleum ether and ethyl acetate as the effluent) on silica gel to afford the 5-diarylpyridine product. 

Cerium(IV) trifluoroacetate was applied to the oxidation of certain arenes, but the reaction suffered from poor yields and complex product mixtures (Norman et al., 1973). As with the acetate, reagent preparation was an involved procedure. 

The nitration of aromatics is an important chemical reaction, and new reagents include iV-nitropyrazole in the presence of a Lewis acid, metal nitrates in trifluoroacetic anhydride, and silver nitrate-boron trifluoride in acetonitrile. Metal salts, especially cerium(iv) acetate, also promote aromatic nitromethyl-... 

Benzene and monosubstituted benzene derivatives could be radiolabeled with iodide-131 by reaction of the substrate with iodine-131 in presence of cerium(IV) triflate (Mennicke et al., 2000). The reaction was carried out in trifluoroacetic acid as solvent. Cerium(IV) is however not soluble in this solvent. 

---