Trifluoroacetic Acid Medium Research Articles

Heterogeneously Catalyzed Aerobic Oxidation of Methane to a Methyl Derivative

AbstractA promising strategy to break through the selectivity‐conversion limit of direct methane conversion to achieve high yields is the protection of methanol via esterification to a more stable methyl ester. We present an aerobic methane‐to‐methyl‐ester approach that utilizes a highly dispersed, cobalt‐containing solid catalyst, along with significantly more favorable reaction conditions compared to existing homogeneously‐catalyzed approaches (e.g. diluted acid, O2 oxidant, moderate temperature and pressure). The trifluoroacetic acid medium is diluted (<25 wt %) with an inert fluorous co‐solvent that can be recovered after the separation of the methyl trifluoroacetate via liquid–liquid extraction at ambient conditions. Silica‐supported cobalt catalysts are highly active in this system, with competitive yields and turnovers in comparison to known aerobic transition metal‐based catalytic systems.

One-Pot Fabrication of Hierarchical Nanosheet-Based TiO2 -Carbon Hollow Microspheres for Anode Materials of High-Rate Lithium-Ion Batteries.

Hierarchical and hollow nanostructures have recently attracted considerable attention because of their fantastic architectures and tunable property for facile lithium ion insertion and good cycling stability. In this study, a one-pot and unusual carving protocol is demonstrated for engineering hollow structures with a porous shell. Hierarchical TiO2 hollow spheres with nanosheet-assembled shells (TiO2 NHS) were synthesized by the sequestration between the titanium source and 2,2'-bipyridine-5,5'-dicarboxylic acid, and kinetically controlled etching in trifluoroacetic acid medium. In addition, annealing such porous nanostructures presents the advantage of imparting carbon-doped functional performance to its counterpart under different atmospheres. Such highly porous structures endow very large specifics surface area of 404 m(2) g(-1) and 336 m(2) g(-1) for the as-prepared and calcination under nitrogen gas. C/TiO2 NHS has high capacity of 204 mA h g(-1) at 1 C and a reversible capacity of 105 mA h g(-1) at a high rate of 20 C, and exhibits good cycling stability and superior rate capability as an anode material for lithium-ion batteries.

Molecular design of cage iron(II) and cobalt(II,III) complexes with a second fluorine-enriched superhydrophobic shell.

Pentafluorophenylboron-capped iron and cobalt(II) hexachloroclathrochelate precursors were obtained by the one-pot template condensation of dichloroglyoxime with pentafluorophenylboronic acid on iron and cobalt(II) ions under vigorous reaction conditions in trifluoroacetic acid media. These reactive precursors easily undergo nucleophilic substitution with (per)fluoroarylthiolate anions, giving (per)fluoroarylsulfide macrobicyclic complexes with encapsulated iron and cobalt(II) ions; nucleophilic substitution of the cobalt(II) hexachloroclathrochelate precursor with a pentafluorophenylsulfide anion gave the target hexasulfide monoclathrochelate and the mixed-valence Co(III)Co(II)Co(III) bis-clathrochelate as a side product. The complexes obtained were characterized using elemental analysis, MALDI-TOF mass spectrometry, IR, UV-Vis, (57)Fe Mössbauer (for the X-rayed iron complexes), (1)H, (11)B, (13)C and (19)F NMR spectroscopies and by X-ray diffraction; their redox and electrocatalytic behaviors were studied using cyclic voltammetry and gas chromatography. As can be seen from the single-crystal X-ray diffraction data, the second superhydrophobic shell of such caged metal ions is formed by fluorine atoms of both the apical and ribbed (per)fluoroaryl peripheral groups. The main bond distances and chelate N=C-C=N angles in their molecules are similar, but rotational elongation (contraction) along the molecular C3-pseudoaxes, accompanied by changes in the geometry of the corresponding MN6-coordination polyhedra from a trigonal prism to a trigonal antiprism, allowed encapsulating Fe(2+), Co(2+) and Co(3+) ions. The nature of an encapsulated metal ion and its oxidation state affect the M-N bond lengths, and, for cobalt(ii) clathrochelate with an electronic configuration d(7) the Jahn-Teller structural effect is observed as an alternation of the Co-N distances. Pentafluorophenylboron-capped hexachloroclathrochelate precursors, giving stable catalytically active metal(I)-containing intermediates due to the electron-withdrawing effect of their six ribbed chlorine substituents, were found to show moderate electrocatalytic activity in a 2H(+)/H2 hydrogen-forming reaction. In the case of their ribbed-functionalized sulfide derivatives, the strong electron-withdrawing (per)fluoroaryl groups do not stabilize the reduced electrocatalytically active metal(i)-containing species as their mesomeric effect is absent or substantially decreased by steric hindrances between them.

A theoretical investigation of the reaction mechanism for hydrogenated furan formation under Prins reaction conditions in trifluoroacetic acid medium

The formation mechanism of hydrogenated furans by coupling between terminal alkenes and aldehydes in trifluoroacetic acid medium were investigated by ab initio calculations, the main attention was focused on the study of the rate controlling step. Two possible mechanisms for this reaction involving unsaturated alkoxycarbenium ions or dioxolenium ions as a key intermediate were considered. It was shown that the mechanism of formation of 3-alkylsubstituted hydrogenated furans in trifluoroacetic acid under Prins reaction conditions preferably includes recyclization of 3-(2-hydroxyethyl)-1-trifluoromethyl-2,5-dioxolenium ions.

Studies of acylation kinetics of aspen wood with aromatic carboxylic acids

With the help of Erofeev-Kolmogorov and Eiring equations kinetic characteristics of acylation of the aspen wood with the aromatic carboxylic acids in presence of thionyl chloride in the trifluoroacetic acid medium were calculated and thermodynamic parameters of this process were established.

ChemInform Abstract: An Influence of a Basic Side Chain Moiety on the Tautomer Ratio Between the Enamine and Methylene Imine Forms in Azole Condensed Quinoxalines.

The reaction of 7-chloro-4-(2-cyano-2-hydroxyvinyl)tetrazolo[1,5-α]quinoxaline 2a with 4-aminopyridine, p-toluidine or p-aminophenol gave 7-chloro-4-(4-pyridylcarbamoylmethylene)-4,5-dihydrotetrazolo[1,5-α]-quinoxaline 7a, 7-chloro-4-(p-tolylcarbamoylmethylene)4, 5-dihydrotetrazolo[1,5-α]quinoxaline 8a or 7-chloro-4-(p-hydroxyphenylcarbamoylmethylene)-4,5-dihydrotetrazolo[1,5-α]quinoxaline 9a, respectively. The reaction of 7-chloro-4-(2-cyano-2-hydroxyvinyl)-1,2,4-triazolo[4,3-α]quinoxaline 2b with 4-aminopyridine, p-toluidine or p-aminophenol afforded 7-chloro4-(4-pyridylcarbamoylmethylene)-4,5-dihydro-1,2,4-triazolo-[4,3-α]quinoxaline 7b, 7-chloro-4-(p-tolylcarbamoylmethylene)-4,5-dihydro-1,2,4-triazolo[4,3-α]quinoxaline 8b or 7-chloro-4-(p-hydroxyphenylcarbamoylmethylene)-4,5-dihydro-1,2,4-triazolo[4,3-α]quinoxaline 9b, respectively. The reaction of compound 2a with 2-aminopyridine or 3-aminopyridine provided 7-chloro-4-(2-pyridyl-carbamoylmethylene)-4,5-dihydrotetrazolo[1,5-α]quinoxaline 10 or 7-chloro-4-(3-pyridyl-carbamoylmethylene)-4,5-dihydrotetrazolo[1,5-α]quinoxaline 11, respectively. Compounds 7a,b(4-pyridylcarbamoyl) predominated as the enamine tautomer A in a trifluoroacetic acid solution, while compounds 8a,b (p-tolylcarbamoyl) and compounds 9a,b (p-hydroxyphenylcarbamoyl) coexisted as the enamine A and methylene imine B tautomers in a trifluoroacetic acid solution. Moreover, the ratio of the enamine tautomer A elevated in an order of compound 11 (3-pyridylcarbamoyl), compound 10 (2-pyridylcarbamoyl) and compound 7a (4-pyridylcarbamoyl), reflecting an order of the increase in the pKa values of the aminopyridine side chain moieties. In general, the ratio of the enamine tautomer A was higher in the basic carbamoyl derivatives 7–11 than in the neutral ester derivatives 3a,b. From these results, the basic side chain moiety of the tetrazolo[1,5-α]quinoxalines 7a-11 or 1,2,4-triazolo[4,3-α]quinoxalines 7b-9b was found to increase the ratio of the enamine tautomer A in trifluoroacetic acid media.

Acid base interactions of octaphenyltetrapyrazinoporphyrazine and its complex with lutetium(III) in proton-donor media

Acid base interactions of octaphenyltetrapyrazinoporphyrazine and its complex with lutetium(III) in acetic and trifluoroacetic acid media were studied, and parameters characterizing equilibria between the acid and base forms were determined. Acid-base interactions of octaphenyltetrapyrazinoporphyrazine involve primarily nitrogen atoms in the pyrazine fragments, while its lutetium(III) complex undergoes protonation at the meso-nitrogen atoms.

Synthesis and antiviral activity of N- and O-substituted amino acids

As was shown in a previous publication [I], both the Nacyl and O-acyl derivatives ofthreo-DL-phenylserine possess antiviral activity in vitro and are capable, in the maximum tolerable dose, of completely inhibiting reproduction of the A2 influenza virus. The present article, which continues a series of communications devoted to the search for new antiv;ral compounds, reports on the synthesis and biological characterization of the derivatives of nonproteinogenic amino acids. The new compounds were obtained on the basis of DL-serine, threo-DLphenylserine, threo-DL-m-nitrophenylserine, 2-methoxy-5nitro-DL-phenylalanine, 4-methoxy-3-nitro-DL-phenylalanine, and e-aminocaproic acid. The structures of these acids and their alkyl esters were modified by introducing alkylcarboxylic and arylsulfonic acid residues and fluorenylidene radicals. The N-acyl derivatives (I-III) of threo-DL-m-nitrophenylserine ethyl ester were obtained by condensation of myristic, palmitic, and stearic acid chlorides with threo-DLm-nitrophenylserine ethyl ester hydrochloride [2] in chloroform in the presence of triethylamine. Condensation of lauryl chloride with DL-serine, phenylacetyl chloride with threoDL-phenylserine, and phenylacetyl chloride with threo-DLphenylserine ethyl ester hydrochloride [3] in an anhydrous trifluoroacetic acid medium was used to obtain O-lauroylDL-serine hydrochloride (IV. HCI), O-phenylacetyl-threoDL-phenylserine hydrochloride (V - HCI), and O-phenylacetyl-threo-DL-phenylserine (V. HCI) ethyl ester (VI. HCI), respectively. Upon crystallization of IV �9 HCI from an ethanol - water medium, and V - HCI from a methanol - water medium, these hydrochlorides lose HCI and convert into compounds IV and V, respectively. N-Propionyl-4-methoxy-" 3-nitro-DL-phenylalanine octyl ester (VII) was synthesized by condensation of 4-methoxy-3-nitro-DL-phenylalanine octyl toluenesulfonate [4] with propionyl chloride in chloroform in the presence of triethylamine. Compounds VIII and IX were obtained as described previously [5]. N-Arylsulfonyl derivatives of threo-DL-phenylserine ethyl, octyl, and

Selective adamantylation of p-H-calix[4]arene in trifluoroacetic acid

It is shown for the first time that unsubstituted p-H-calix[4]arene can be selectively adamantylated at the upper rim by reaction with functionally substituted 1-hydroxyadamantanes in trifluoroacetic acid medium.

Tautomeric behavior of 3‐(arylhydrazono)methyl‐2‐oxo‐1,2‐dihydroquinoxalines between the hydrazone imine and diazenyl enamine forms in acidic media. Solvent and substituent effects

AbstractThe 3‐(arylhydrazono)methyl‐2‐oxo‐1,2‐dihydroquinoxalines 1a‐h and 2a‐e showed tautomeric equilibria between the hydrazone imine A and diazenyl enamine B forms in a series of mixed trifluoroacetic acid/dimethyl sulfoxide media. The substituent and solvent effects on the tautomer ratios of A to B in a series of mixed media were studied for compounds 1a‐h and 2a‐e by the nmr spectroscopy. In compounds 1a‐h and 2a‐e, the ratios of the tautomer B gradually increased with elevation of acid concentration, and the tautomer B exclusively existed in trifluoroacetic acid media. The various acid concentrations (C v/v%, C' mol/1) giving the 1:1 tautomer ratios [C(A:B = 1:1), C'(A:B = 1:1)] were obtained from all compounds (Figures 1–13), and the linear correlation of the Hammett σp values with the log C'(A:B = 1:1) values were observed for compounds 1a‐h. The larger Hammett σp values brought about the larger acid concentrations C(A:B = 1:1) in compounds 1a‐h and 2a‐e, indicating that the higher acid concentration was required for the stabilization of tautomer B possessing the electron‐withdrawing p‐substituents R1, which weakened the basicity of the azo nitrogen atom. Moreover, the ester group R2 of compounds 2a‐e was found to decrease the electron density of the azo nitrogen atom, since the acid concentration C(A:B = 1:1) of compound 2c (R1 = H, R2 = COOMe, σp = O) was 52%, whose value was larger than that of compound 1b (R1 = CN, R2 = H, σp = 0.66) [C(A:B = 1:1) = 42%].

An influence of a basic side chain moiety on the tautomer ratio between the enamine and methylene imine forms in azole condensed quinoxalines

AbstractThe reaction of 7‐chloro‐4‐(2‐cyano‐2‐hydroxyvinyl)tetrazolo[1,5‐α]quinoxaline 2a with 4‐aminopyridine, p‐toluidine or p‐aminophenol gave 7‐chloro‐4‐(4‐pyridylcarbamoylmethylene)‐4,5‐dihydrotetrazolo[1,5‐α]‐quinoxaline 7a, 7‐chloro‐4‐(p‐tolylcarbamoylmethylene)4, 5‐dihydrotetrazolo[1,5‐α]quinoxaline 8a or 7‐chloro‐4‐(p‐hydroxyphenylcarbamoylmethylene)‐4,5‐dihydrotetrazolo[1,5‐α]quinoxaline 9a, respectively. The reaction of 7‐chloro‐4‐(2‐cyano‐2‐hydroxyvinyl)‐1,2,4‐triazolo[4,3‐α]quinoxaline 2b with 4‐aminopyridine, p‐toluidine or p‐aminophenol afforded 7‐chloro4‐(4‐pyridylcarbamoylmethylene)‐4,5‐dihydro‐1,2,4‐triazolo‐[4,3‐α]quinoxaline 7b, 7‐chloro‐4‐(p‐tolylcarbamoylmethylene)‐4,5‐dihydro‐1,2,4‐triazolo[4,3‐α]quinoxaline 8b or 7‐chloro‐4‐(p‐hydroxyphenylcarbamoylmethylene)‐4,5‐dihydro‐1,2,4‐triazolo[4,3‐α]quinoxaline 9b, respectively. The reaction of compound 2a with 2‐aminopyridine or 3‐aminopyridine provided 7‐chloro‐4‐(2‐pyridyl‐carbamoylmethylene)‐4,5‐dihydrotetrazolo[1,5‐α]quinoxaline 10 or 7‐chloro‐4‐(3‐pyridyl‐carbamoylmethylene)‐4,5‐dihydrotetrazolo[1,5‐α]quinoxaline 11, respectively. Compounds 7a,b(4‐pyridylcarbamoyl) predominated as the enamine tautomer A in a trifluoroacetic acid solution, while compounds 8a,b (p‐tolylcarbamoyl) and compounds 9a,b (p‐hydroxyphenylcarbamoyl) coexisted as the enamine A and methylene imine B tautomers in a trifluoroacetic acid solution. Moreover, the ratio of the enamine tautomer A elevated in an order of compound 11 (3‐pyridylcarbamoyl), compound 10 (2‐pyridylcarbamoyl) and compound 7a (4‐pyridylcarbamoyl), reflecting an order of the increase in the pKa values of the aminopyridine side chain moieties. In general, the ratio of the enamine tautomer A was higher in the basic carbamoyl derivatives 7–11 than in the neutral ester derivatives 3a,b. From these results, the basic side chain moiety of the tetrazolo[1,5‐α]quinoxalines 7a‐11 or 1,2,4‐triazolo[4,3‐α]quinoxalines 7b‐9b was found to increase the ratio of the enamine tautomer A in trifluoroacetic acid media.

Nature of the transformations of oleanolic acid in an acid medium

3-Trifluoroacetoxyoleanolic acid and 3-trifluoroacetoxyolean-13(18)-en-28-oic acid have been isolated from the mixture of the products of the transformation of oleanolic acid in a trifluoroacetic acid medium, and their structures have been established with the aid of IR, PMR and mass spectra. The formation of these products indicates an unambiguous route of the stabilization of the intermediate carbocation with the charge on the C-13 atom. The hydroxy group at C-3 is esterified by the trifluoroacetic acid.

Modified bovine serum albumin. IV. Characterization and immunochemical studies of the O-acetylated derivative

1. 1. The reaction of bovine serum albumin (BSA) with acetic anhydride in trifluoroacetic acid medium resulted in a product in which about eight tyrosines and five aliphatic hydroxyls were esterified. There was evidence of other side reactions and some irreversible structural changes. 2. 2. Studies on the reaction of the derivative with antibodies produced against native BSA suggest that phenolic groups of BSA may not be necessary for the BSA-anti-BSA interaction. 3. 3. Studies with antibodies produced against O-acetyl BSA reveal that the ester group was not a major determinant in the antibody synthesis. The specificity of the antibodies progressively became broadened with prolonged immunization. 4. 4. The difficulties in evaluating data from immunochemical studies of chemically modified proteins and the bearing of the above findings on the mechanism of interaction of protein antigens with their antibodies are discussed.