Trifluoroacetate ions

The active acylating agent may be the protonated mixed anhydride, or, alternatively, the anhydride m dissociate to the acylium and trifluoroacetate ions ... 

The effect of the addition of sulphate and fluoride ions were found by these workers to increase the rate of exchange addition of acetate and trifluoroacetate ions produced relatively minor changes. For the addition of sulphate ions, a rate law... 

Nitric acid-trifluoroacetic anhydride mixtures are used extensively for nitrolysis and N-nitration reactions (see Chapters 5 and 6). The same is not true for aromatic nitrations. This reagent contains trifluoroacetyl nitrate, which can ionize to nitronium and trifluoroacetate ions in the presence of strong acid. 

Brown, I. D. (1980). A structural model for Lewis acids and bases. An analysis of the structural chemistry of acetate and trifluoroacetate ions. /. Chem. Soc., Dalton Trans. pp. 1118-1123. 

The acidic nature of the reagent is important the trifluoroacetic acid liberated in the reaction catalyzes hydrolysis of the intermediate isocyanate, and also ensures that the amine which is formed is protonated and cannot react with the isocyanate to give urea by-products. The reaction can be accelerated by addition of pyridine to an observed pH of about 3.5, and is retarded by added acid or trifluoroacetate ion. In the present procedure pyridine was not employed, since the reaction in its absence proceeds with a satisfactory rate. 

Since chloride and trifluoroacetate ions affect neither the efficiency nor the Co(II)/Co(III) stoichiometry of photoreduction of 1-p or 2-p, kinetic analysis is possible of the reactions of the cobalt(III) intermediate produced in the photoreduction with water or added anions as shown by reaction (34). Calculation of the ratio, R = kx-jkH20, has... 

The trifluoroacetate ion CF3CO2 (Fig. 3.5(a)) is similar (Brown 1980 ). F and are both anions so the two C atoms are both formally cations, each with a valence of +4. As before, we treat the C-C unit as a single pseudocation, reserving one electron pair for the C-C bond. It is instructive to compare this with the closely related acetate ion, [H C" — whose... 

The bonding in the hydrazinium and trifluoroacetate ions can also be described in a similar way. Since each atom of the N-N or C-C bond contributes a different number of electrons (valence) to the bond, one can show the net valence transfer by means of an arrow as shown in Fig. 3.3(b). The valence sum rule is obeyed by this graph but at the expense of ignoring the electron pairs that provide the primary bond between the two N atoms. As in the case of dmso, the bond valence of the N-N bond in Fig. 3.3(b) shows only the net electron transfer, not the total number of electron pairs that contribute to the bond. The bond valence does not, therefore, correlate with the bond length. 

In most of these cases the homoionic bond can be assigned a valence, but this does not always correlate with bond length as the examples of the trifluoroacetate ion and S-bonded dmso show. However, a correlation is expected for Cu(N02)g and has been found for Hg-Hg bonds. In addition to the well-known mercurous ion (Hg ), cations such as ngj" ", Hg4+, (Hg +) (infinite chains), and (Hg ) (infinite sheets) are also known. The Hg-Hg bonds in these cations show a considerable variation in length which correlates well with the bond valence, as shown in Fig. 3.8 (Brown et al. 1984). 

Fig. 9.1. Structures of the acetate ion showing bond valences (above the bond) and bond lengths (in pm below the bond) (a) the ideal structure of the isolated ion (b) the structure normally observed in the solid state (c) the structure observed when bonded to a strong cation (Si) (d) the structure observed for the diprotonated acetate ion (e) the structure of the trifluoroacetate ion normally observed in the solid state.

In a recently reported synthesis of pyridines, lithiated methoxyallenes react with nitriles in the presence of trifluoroacetic acid (Scheme 107) <2004CEJ4283>. The mechanism is postulated to proceed via initial protonation followed by nucleophilic addition of the trifluoroacetate ion with subsequent intramolecular acyl transfer and aldol condensation to give the pyridine. An additional pyridine formation starting from azaenyne allenes forms a-5-didehydro-3-picoline diradicals, which can be trapped by 1,4-cyclohexadiene, chloroform, and methanol to produce various pyridines <20040L2059>. 

A solution of Os3H2(CO)10 in CF3C02H gives H-nmr hydride signals in intensity ratio 2 1, and the species formed is believed to be [Os3H3(CO)10]+ (67), although the trifluoroacetate ion may be coordinated and the unsatu-... 

Ketones and nitriles are rather soft bases their coordination onto electron-deficient sites on oxides is, therefore, relatively weak. One may, however, expect an improved specificity of chemisorption due to their softness. Unfortunately, however, these substances very easily undergo chemical transformations at oxide surfaces. Thus, carboxylate structures are formed on adsorption of acetone on alumina (194, 245-247), titanium dioxide (194), and magnesium oxide (219, 248, 249). Besides, acetone is also coordinated onto Lewis acid sites. A surface enolate species has been suggested as an intermediate of the carboxylate formation (248, 249). However, hexafluoroacetone also leads to the formation of trifluoroacetate ions (219). The attack of a basic surface OH ion may, therefore, be envisaged as an alternative or competing reaction path ... 

The reaction of phenyl vinyl sulfoxide 234 with isobutene, in the presence of trifluoroacetic anhydride, yielded the to-alkylated product 238 (Scheme 59).128 It was suggested that this reaction proceeded by a different mechanism than the usual additive Pummerer mechanism. The alkene reacts with the electrophilic sulfur atom of intermediate 235, giving, after loss of a trifluoroacetate ion and a proton, the sulfonium ion 236. Thio-Claisen rearrangement of the ion then gives the thonium ion 237 which reacts with a further molecule of isobutene to give the product 238. 

The second mechanism which cannot always be strictly differentiated from the first one 41) should be considered as a typical electrophilic substitution of the arene by the iiigh valent metal compound. The latter is still more electrophilic with tri-fluoroacetate than with acetate anions. The organometallic arene intermediates were isolable in some cases 43). In the second step, the metallic residue is substituted by the acetate or trifluoroacetate ion. 

The utility of perfluoroacetic anhydride as a medium for promoting esterifications is well known [54] and, again, is based on the stability of the trifluoroacetate ion (Figure 8.6). 

The elimination of the trifluoroacetate ion has been used synthetically in ligand substitution reactions of the [M(C0)6(02CCF3)] (where M = Cr, Mo, or W) anions Eq. (20) is typical of these reactions. 

A base (the trifluoroacetate ion) abstracts a proton from one of the methyl groups of the oxysulfonium ion, and a bond shift through a five-membered transition state gives the ketone and dimethyl sulfide [1016 (equation 261). 

There have been recent attempts to apply the same type of argument to the broadening of Raman lines as a result of chemical reaction. Thus, for example, the 1435 cm band of the trifluoroacetate ion, CF3CO2, is broadened considerably in acid as compared with neutral solution. This has been interpreted in terms of the shortness of the lifetime of the species on account of the exchange reaction... 

The first example of this fragmentation reaction to be described is the conversion of the /V-oxide (63) to the 17-oxa-D-homoandrostane derivative (65 Scheme 12). The crucial step in this transformation involves the participation of the lone pair of electrons on oxygen in the departure of trifluoroacetate ion from the 0-acylimonium salt interm ate (64). 

Many types of palladacyclic complexes have been used as precursors to catalysts for a variety of coupling processes146,147. Mixtures of dimeric palladacycles containing bridging halide, acetate or trifluoroacetate ions and a phosphine or carbene ligand have been studied as catalysts for the animation of aryl halides. The isolated phosphine adducts can also be applied in catalysis. 

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