Activation of molecular oxygen in trifluoroacetic acid

The interaction of molecular oxygen with aqueous trifluoroacetic acid (TFA) led to an increase in pH. This effect was explained by a decrease in the concentration of the protonated CF₃CO₂H₂⁺ and H₃O⁺ species after oxygen was fed in the reactor. Quantum-chemical calculations show that a radical pair can be formed in an activation-free exothermal reaction involving the radical residue of the acid, the CF₃CO₂H₂⁺...³O₂...CF₃CO₂⁻ peroxide radical, and the acid molecule in the CF₃C₂^·...HOO^· collision complex. It was assumed that the activation of molecular oxygen in aqueous TFA solutions, providing the activity of the system in oxidations of various organic and inorganic substrates, is related to the formation of peroxide radicals in them.     

Chemical transformations of methane in trifluoroacetic acid

The reaction of methane conversion in anhydrous trifluoroacetic acid (TFA) is shown to take place at room temperature and atmospheric pressure and to result in the formation of a resinous product. Signals of ions with molecular weights of 684 and 700 are observed in MALDI-TOF spectra of the dry residue of methane conversion products.     

Activation of molecular oxygen in trifluoroacetic acid

The possibility of the formation of the H₂O₂^+· cation-radical was determined according to the data from nonempirical calculations for liquid trifluoroacetic acid, which forms a hydroperoxide radical after deprotonation. A catalytic cycle was obtained in which CF₃COOH serves as a catalyst in the oxidation of a substrate by dissolved molecular oxygen.     

Reaction of indoles with trifluoroacetic acid

3-Trifluoroacetyl indoles are formed by the action of trifluoroacetic acid on indole-2-carboxylic acid and its benzo-substituted derivatives. When unsubstituted indole is refluxed with trifluoroacetic acid, it gives 3-trifluoroacetylindole in 30% yield.Deceased.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1233–1235, September, 1981.     

Transformation of organic and inorganic compounds in trifluoroacetic acid

It is established that the effectiveness of fluorine-containing acids in the transformation of organic and inorganic substrates is due to the ability of the acid to perform several functions: to accumulate relatively high concentrations of molecular oxygen, to activate it, and to serve as a hydrogen-containing medium.     

Adamantylation of N-aryl and N-arylalkyl acetamides in trifluoroacetic acid

Russian Chemical Bulletin - Alkylation of N-aryl and N-arylalkyl acetamides with hydroxy adamantane derivatives in trifluoroacetic acid was studied. The differentiating effect of trifluoroacetic...     

AgOAc-mediated rearrangement of gem-dibromospiropentanes in trifluoroacetic acid

AgOAc-mediated intramolecular skeleton rearrangement reaction of gem-dibromospiropentanes produced the corresponding naphthalene and indene derivatives in moderate to good yields under mild conditions.     

Chemical transformations of CO2 in trifluoroacetic acid solutions

It is established that a conversion reaction of carbon dioxide takes place at room temperature and atmospheric pressure in aqueous solutions of trifluoroacetic acid (TFA), which leads to the formation of oxalic acid and heavier polymerized products.     

Inverse temperature-dependent pathway of cellulose decrystallization in trifluoroacetic acid

An unusual inverse temperature-dependent pathway was observed during cellulose decrystallization in trifluoroacetic acid (TFA). Decreasing the TFA treatment temperature accelerated the cellulose decrystallization process. It took only 100 min to completely decrystallize cellulose at 0 degrees C in TFA, a result not achieved in 48 h at 25 degrees C in the same medium. There was neither cellulose esterification nor a change of cellulose macrofibril morphology by TFA treatment at 0 degrees C. Our IR data suggest that TFA molecules are present as cyclic dimers when they penetrate into crystalline cellulose regions, transforming crystalline cellulose to amorphous cellulose. On the other hand, the rate of TFA penetration into the cellulose matrix was greatly retarded at higher temperatures where monomeric TFA prevails. At elevated temperatures, esterification of TFA monomers on the external surface of crystalline cellulose, agglomeration of cellulose macrofibrils, as well as water released from the esterification reaction, inhibit the diffusion rate of TFA into the cellulose crystalline region and decrease the TFA swelling capability.     

Kinetics of heptene-I interaction with formaldehyde in trifluoroacetic acid

A mechanism for formation of hydrogenated furans in the reaction of α-olefins with formaldehyde is suggested. Based on kinetic data, it involves the equilibrium addition of protonated formaldehyde to the olefin.     

Studies of transnitrilation mechanism in the presence of trifluoroacetic acid

A non-cyclic imide, an intermediate of transnitrilation, is shown to be formed through the step of unstable isoimide isomerization. The addition of a carboxy group of the acid to the cyano group has been studied. Interaction of acetonitrile with aliphatic carboxylic acids is suggested to follow a concerted but not a synchronous mechanism with prior formation of the N–H bond.

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, — — . . , , N–H.

     

Scalar dynamic nuclear polarization of protons in trifluoroacetic acid solutions

Strongly scalar ¹H intermolecular dynamic nuclear polarization (DNP) of solvent ¹H nuclei in solutions of organic free radicals has now been observed at room temperature. Transient protonation of the CF₃COOH/pyridyl imidazoline-1-oxyl radical system accounts for the observed effects.     

Proton exchange and protonation of substituted oxadiazoles in trifluoroacetic acid

The rates of NH? COOH proton exchange between 5-amino-( 1a ) and 5-N-methylamino-( 1b )3-[2-(5′-nitro-2′-furyl)vinyl]-1,2,4-oxadiazoles and trifluoroacetic acid (TFA) have been measured by NMR spectroscopy. The values of the first-order rate constant and thermodynamic parameters for 1a and 1b , respectively, are: k_app (sec^?1) = 820 and 40 (50°C), ΔF (kcal/mole) = 14·7 and 16·5, ΔH^# (kcal/mole) = 17·3 and 24·3 and ΔS^# (e.u.) = 17 and 34. The comparison of rate constants indicates that after correction for proton equivalency proton exchange in 1a is faster than in 1b by a factor of ten. The presence of an NH₂ proton resonance ( 1a ) and an N-methyl doublet (J = 5·0 Hz) between 0 and 30° ( 1b ) suggests that 1a and 1b are present as amines and not as imines in TFA.     

Electrophoretic deposition of phthalocyanine in organic solutions containing trifluoroacetic acid

The absorption spectra of copper phthalocyanine (CuPc) 1,2-dichloroethane (DCE) solutions containing trifluoroacetic acid (TFAA) shows that the number of protons coordinating to the CuPc molecule was 1 and 2 for the first and second proton adducts, respectively, which indicates the formations of CuPcH(+) and CuPcH(2)(2+). This CuPc molecule may act as a catalyst to dissociate TFAA into trifluoroacetate anion (A(-)) and H(+) and form the proton adducts. The electrical conductivity dependence of the solution on CuPc concentration also supports this mechanism. A dense film of CuPc was deposited on an indium tin oxide cathode plate by electrophoresis of the solution. Similar dense films of a wide variety of phthalocyanines (MPc; M = Cu, H(2), Fe, Ni, Zn, Pb, VO) were also deposited using this method. Similar films of CuPc were also formed using dichloromethane (DCM) and 1,1,1-trichloroethane (TCE) in place of DCE. Depositions are ascribed to the migration of positively charged monomers (i.e., protonated MPc). Scanning electron microscopy revealed that these films are composed of fibrous crystallites, size of which was found to increase with the electrophoresis time, the strength of the applied electrical field and the concentration of CuPc in the bath. The influence of the dielectric constant of the organic solvent on the film growth is discussed.     

The behaviour of unsaturated 1,2-hydroxyiminoketones with trifluoroacetic acid

(E)-1,2-Hydroxyiminoketones containing an appropriately positioned and substituted olefinic group afford high yields of various 5- and 6-membered heterocyclic systems when reacted with trifluoroacetic acid. Under the same conditions inappropriately substituted unsaturated 1,2-hydroxyiminoketones fragment by means of the second order Beckmann process.     

Stabilization and induction of discotic mesophases by trifluoroacetic acid

It is shown that trifluoroacetic acid (TFA) can form 1 1 molar complexes with alkyloxy discotic compounds, thereby enhancing their mesomorphic properties. In particular, when hexaalkyloxytriphenylenes (THEn) (n being the number of carbons per side chain) are crystallized from, or mixed with, TFA, complexes are formed which exhibit the Dho(Colho) mesophase, as do the neat THEn's, but with a broader range of thermal stability and a higher degree of order. The mesophases of these complexes are completely miscible with those of the neat compounds. Likewise, 1 1 mixtures of hexa-alkyloxytribenzocyclononene (TBCEn) and TFA yield complexes showing enhanced mesomorphic properties for the mesogenic homologues of this series and induced mesomorphism for the lower homologues, which in the neat form are not mesogenic. The mesomorphic properties of these TFA complexes with THEn (n=3-6) and with TBCEn (n=4-6) are investigated by means of optical microscopy, differential scanning calorimetry, X-ray diffraction and NMR spectroscopy. It is suggested that the enhancement of the mesomorphic properties is due to formation of oxonium ion complexes.