Presence Of Trifluoroacetic Acid Research Articles

Nanocrystalline cerium-doped Y-type barium hexaferrite; a useful catalyst for selective oxidation of styrene

The cerium-doped Y-type barium hexaferrites Ba2−xCexCo2Fe12O22 (x = 0.0, 0.1, 0.2, and 0.3) were synthesized using the sol–gel auto combustion method. The synthesized nanocrystalline hexaferrite powders were characterized; especially it’s structural, morphological, and magnetic properties, through X-ray diffractometer, FTIR spectroscopy, scanning electron microscopy and vibrating sample magnetometer, respectively. The effects of catalyst amount, reaction temperature and time, solvent and oxidizing agent required for the entire conversion of styrene to benzaldehyde were also examined with pure Y-type barium hexaferrite (BrM). The catalytic performance of the BrM powder was measured for its suitability in the oxidation of styrene using various oxidants, and the isolated yield of the benzaldehyde was calculated using the column chromatography separation. The as-prepared 20 mg BrM samples showed total conversion of styrene and 66% isolated yield for benzaldehyde at 120 °C for 24 h in the presence of trifluoroacetic acid as an oxidant. The effect of cerium doping on the benzaldehyde selectivity was also analyzed at optimized conditions and found that cerium-doped samples showed excellent catalytic performance. Paralleled with the pristine barium hexaferrite, the catalytic efficiency was significantly enriched and exhibited its maximum performance with Ba1.8Ce0.2Co2Fe12O22 ferrite, almost 71% selectivity was achieved with the same reaction conditions. This enhanced performance was correlated with the XPS studies for x = 0.2 sample. The as-prepared catalyst was magnetically separable to reprocess. There was no remarkable loss of catalytic activity when it was reprocessed for five consecutive trials.

Correction to: Synthesis of novel macrocyclic and heterocyclic taurine derivatives based on the reaction of sodium 2-[(4,4-diethoxybutyl)amino]ethanesulfonate with phenols

An approach to the synthesis of novel macrocyclic and heterocyclic taurine derivatives based on the reaction of sodium 2-[(4,4-diethoxybutyl)amino]ethanesulfonate with phenols in the presence of trifluoroacetic acid has been developed. The structures of the obtained products are confirmed by spectral data.

Self-Catalyzed Rapid Synthesis of N-Acylated/N-Formylated α-Aminoketones and N-Hydroxymethylated Formamides from 3-Aryl-2H-Azirines and 2-Me/Ph-3-Aryl-2H-Azirines.

A rapid and effective method has been established for the synthesis of N-acylated α-aminoketone derivatives by the reaction of 3-aryl-2H-azirines and highly substituted 2-Me/Ph-3-aryl-2H-azirines with various carboxylic acids under ambient air within 10 min at room temperature. N-Trifluoroacetylated α-aminoketones with different substituents have been reported in the presence of trifluoroacetic acid. This protocol is equally effective to synthesize N-formylated α-aminoketone and N-hydroxymethylated formamide derivatives.

Synthesis and Aromaticity of Benzene-Fused Doubly N-Confused Porphyrins.

A bicyclo[2.2.2]octadiene(BCOD)-fused bis(dipyrromethane) derivative was reacted with methylal in the presence of trifluoroacetic acid followed by oxidation with chloranil to give a doubly N-confused phlorin derivative, which did not undergo the retro-Diels-Alder reaction extruding an ethylene molecule on heating. In contrast, a 7-tert-butoxybicyclo[2.2.1]heptadiene(7-BuOBCHD)-fused bis(dipyrromethane) yielded benzene-ring-fused doubly N-confused porphyrins by following similar reaction sequences.

N-Trifluoroacetylated pyrazolines: Synthesis, characterization and antimicrobial studies.

A series of N-trifluoroacetyl-2-pyrazolines have been synthesized via cyclization of chalcones in the presence of trifluoroacetic acid and hydrazine as a base. The method used for the preparation of pyrazolines was found to be an efficient one as all of the compounds were obtained in good yield (up to 79%). Various spectroscopic techniques established the structures and additionally corroborated the compounds 2a and 2e by single crystal X-ray. Newly synthesized pyrazolines were investigated for their potential as antimicrobial agents. Compound 2a displayed promising antimicrobial activity against pathogenic Escherichia coli and Pseudomonas aeruginosa. Furthermore, the mechanism of the antimicrobial activity of 2a was demonstrated with the help of scanning electron microscopy (SEM), which revealed complete damage of the bacterial cell membrane, providing dead cell debris in the milieu. The minimum inhibitory concentration (MIC) observed was 79 and 90µM against E. coli and P. aeruginosa, respectively. Hence, these compounds might be significantly useful in antimicrobial drug development.

Neutral heteroleptic nickel complexes incorporating maleonitriledithiolate and bis(diphenylphosphanyl)amine as robust molecular electrocatalysts for hydrogen evolution

Five neutral heteroleptic maleonitriledithiolate nickel complexes [RN(PPh2)2Ni(mnt)] bearing bis(diphenylphosphanyl)amine ligands (where mnt2− = maleonitriledithiolate; R = CH3O(CH2)3 (1), CH3S(CH2)3 (2), (S)-CH3CHPh (3), (CH3)2CH(CH2)2 (4), and p-CH3C6H4 (5)) have been synthesized and fully characterized by elemental analysis, FTIR, NMR (1H, 13C, and 31P) spectroscopy, UV–Vis spectrum, single crystal X-ray diffraction, thermogravimetric analysis, and density functional theory (DFT) calculation. The nickel atom in 1, 2, 4, and 5⋅1.5CH2Cl2 adopts a slightly distorted square-planar coordination environment with two phosphorus atoms of RN(PPh2)2 and two sulfur atoms of mnt2−, respectively, while the nickel atom in 3 exhibits a pseudo square pyramid with HP2S2 chromophore. Furthermore, the electrochemical properties for 1–5 were also investigated by cyclic voltammetry. With the addition of 120 mM trifluoroacetic acid (TFA) to 1–5 in MeCN, the turnover frequency (TOF) values are estimated to be 368.59–585.17 s−1 with the corresponding overpotential (η) values of 0.59–0.73 V. The electrochemical studies indicate that all complexes can be used as low-cost robust molecular eletrocatalysts for the reduction protons to hydrogen in the presence of TFA and a possible ECEC mechanism for electrocatalytic hydrogen evolution has been also proposed.

A Trimetallic Cu(II) Derivative as an Efficient and Stable Electrocatalyst for Reduction of Proton to Molecular Hydrogen

A trinuclear copper(II) complex, namely [Cu3(L)2(CF3COO)2] (1) is afforded integrating a ‘compartmental’ Schiff base, H2L [where H2L = N,N′-bis(salicylidene)-1,3-propanediamine] and fully characterized. Complex 1 is implemented for electrocatalytic proton reduction to originate molecular hydrogen in a homogenous system. The electrochemical study involving CV (cyclic voltammetry), CPE (controlled potential electrolysis) and GC (gas chromatography) reveals that in homogeneous system, 1 is highly active towards proton reduction in presence of trifluoro acetic acid as a proton source. Following CPE at − 1.8 V vs Ag/AgCl, the headspace gas is sampled and gas chromatography is carried out to quantify the amount of hydrogen discharged. The ratio of theoretical H2 production from charge aggregation during electrolysis to the practical amount of H2 resolved on GC is yielded a Faradaic efficiency value of 87%. Moreover, an extended bulk electrolysis experiment carried out for 35 h illustrates the presence of a stable catalytic system in which 230 C of charge is accumulated. As a consequence, this efficient and stable H2 evolution obtained using a Cu(II) derivative (CuII is cheap and earth abundant) has shown that the synthesis of judiciously designed copper complex is a promising strategy towards potential catalysts from proton reduction. Electrochemical and catalytic study of a trimetallic Cu(II) derivative in DMSO with the presence of trifluoroacetic acid as weak proton source shows the hydrogen evolution Faradaic efficiency as 87%. A continuous increment of the charge accumulation through time is observed, indicating the high stability of our catalyst under electrochemical H2 generation.

Acid mediated synthesis of thiazolines, thiazoles and enamide derivatives from methyl enol ethers: Application towards synthesis of wilsoniamine B

An efficient metal-free synthesis of thiazolines, dihydrothiazole and enureas or thioureas from methyl enol ether with urea or thiourea derivatives in the presence of TFA (trifluoroacetic acid) are reported here. This synthetic protocol involves the formation of two bonds, C–N as well as C–S, in one step for the synthesis of thiazoline derivatives, dihydrothiazoles and a direct C–N bond for the synthesis of enamides with good to excellent yields. Further, this method was employed for the synthesis of wilsoniamine B alkaloid.

Synthesis, structures, and electrocatalytic properties of phosphine‐monodentate, −chelate, and ‐bridge diiron 2,2‐dimethylpropanedithiolate complexes related to [FeFe]‐hydrogenases

To further extend diiron subsite models of [FeFe]‐hydrogenases, the various substitutions of all‐carbonyl diiron complex Fe2(μ‐Me2pdt)(CO)6 (A, Me2pdt = (SCH2)2CMe2) with monophosphines or small bite‐angle diphosphines are studied as follows. Firstly, the monodentate complexes Fe2(μ‐Me2pdt)(CO)5{κ1‐P(C6H4R‐p)3} [R = Me (1a) and Cl (1b)] and Fe2(μ‐Me2pdt)(CO)5{κ1‐Ph2PX'} [X' = NHPh (2a) and CH2PPh2 (2b)] are readily afforded through the Me3NO‐assisted reactions of A with monophosphines P(C6H4R‐p)3 (R = Me, Cl) and diphosphines (Ph2P)2X (X = NPh, CH2 (dppm)) in MeCN at room temperature, respectively. Secondly, the chelate complexes Fe2(μ‐Me2pdt)(CO)4(κ2‐(Ph2P)2X) [X = NPh (3a) and NBun (3b)] can be efficiently prepared by the UV‐irradiated reactions of A with small bite‐angle diphosphines (Ph2P)2X (X = NPh, NBun) in toluene. Thirdly, the bridge complexes Fe2(μ‐Me2pdt)(CO)4(μ‐(Ph2P)2X) [X = NPh (4a) and CH2 (4b)] are well obtained from the refluxing solutions of A and diphosphines (Ph2P)2X (X = NPh, CH2) in xylene. Rarely, the diphosphine‐bridge complex 4b may be produced in low yield via the UV‐irradiated solutions of A and the dppm ligand in toluene emitting at 365 nm. Eight new complexes obtained above have been well characterized by using element analysis, FT‐IR, NMR (1H, 31P) spectroscopies, and particularly for 1a, 1b, 2a, 3b, 4a, 4b by X‐ray crystallography. Meanwhile, the electrochemical and electrocatalytic properties of three representative complexes 2a, 3a, and 4a with pendant N‐phenyl groups are investigated and compared by using cyclic voltammetry (CV) in the absence and presence of trifluoroacetic acid (TFA) as a proton source, indicating that they are all found to be active for electrocatalytic proton reduction to hydrogen (H2).

Chiral Discrimination of Varied Ammonium Compounds through 1H NMR Using a Binuclear Ti Complex Sensor.

A simple chiral binuclear titanium complex ((S)-Ti2L3Na4) was first prepared and served as an excellent chiral sensor for discriminating a variety of chiral ammoniums by 1H NMR. In the presence of trifluoroacetic acid, the in-situ-generated ammoniums of varied amines can be effectively resolved by (S)-Ti2L3Na4. The different binding forces between (S)-Ti2L3Na4 and two enantiomers of analytes generate different shielding effects on two enantiomers, resulting in a split in the distinguishable chemical shift.

Playing the blues, the greens and the reds with cellulose-based structural colours.

Structural vivid colours can arise from the interference of light reflected from structures exhibiting periodicity on scales in the range of visible wavelengths. This effect is observed with light reflected from cell-walls of some plants and exoskeletons of certain insects. Sometimes the colour sequence observed for these structures consists of nearly circular concentric rings that vary in colour from Red, Orange, Yellow, Green, Cyan to Blue, from the periphery to the centre, similarly to the colour scheme sequence observed for the rainbow (ROYGB). The sequence of colours has been found for solid films obtained from droplets of aqueous cellulose nanocrystals (CNCs) suspensions and attributed to a "coffee ring" effect. In this work, coloured lyotropic solutions and solid films obtained from a cellulose derivative in the presence of trifluoroacetic acid (TFA), which acts as a "reactive solvent", are revisited. The systems were investigated with spectroscopy, using circularly and linearly polarised light, coupled with a polarised optical microscope (POM) and scanning electron microscopy (SEM). The lyotropic cholesteric liquid crystalline solutions were confined in capillaries to simplify 1D molecular diffusion along the capillary where an unexpected sequence of the structural colours was observed. The development and reappearance of the sequence of vivid colours seem consistent with the reaction-diffusion of the "reactive solvent" in the presence of the cellulosic chains. The strong TFA acts as an auto-catalyst for the chemical reaction between TFA and the hydroxyl groups, existing along the cellulosic chain, and diffuses to the top and bottom along the capillaries, carrying dissolved cellulosic chains. Uncovering the precise mechanism of colour sequence and evolution over time in cellulosic lyotropic solutions has important implications for future optical/sensors applications and for the understanding of the development of cellulose-based structures in nature.

In Russian

The low-temperature 1H NMR spectroscopy was used to study the structure of hydrated water layers bound by brain tissue after ischemic stroke, as well as the effect of chloroform and trifluoroacetic acid on their structure. Almost all the water that is part of the brain tissue is bound, and its structure is close to the structure of bulk water, when each water molecule is involved in the formation of 2-3 hydrogen bonds. It is shown that chloroform, which is poorly soluble in water, can have a significant effect on the binding of water in the brain tissues and helps to reduce the energy of interaction of water with the internal phase boundaries. Additives of 20% trifluoroacetic acid (TFA) make it possible to differentiate intracellular water by its ability to dissolve strong acids. It was revealed that part of intracellular water does not dissolve TFAs well. In the presence of TFA, the contribution of domains and clusters of water of a smaller radius increases. Encapsulation of brain tissue with hydrophilic nanosilica leads to a significant increase in the value of interfacial energy of bound water, which occurs due to an increase in the contribution from strongly bound water. This is probably due to a significant decrease in the linear dimensions of tissue particles caused by the encapsulation process. Due to the large size of neurons, it can be assumed that tissue is divided into separate cells or small groups of adjacent cells. At the same time, significant changes in the characteristics of intercellular interactions are observed. Accordingly, the main maximum on the distribution curve DC(R) shifts to the region of smaller values and corresponds to clusters with a radius of R = 7 nm. The chloroform medium in the encapsulated sample stabilizes larger radius domains. This process is accompanied by a significant decrease in interfacial energy.

Tuning Flavin‐Based Photocatalytic Systems for Application in the Mild Chemoselective Aerobic Oxidation of Benzylic Substrates

New flavin‐based photocatalytic systems used for chemoselective aerobic visible‐light oxidations have been developed by tuning the flavin structure and reaction conditions. 1,3‐Dimethyl‐7‐trifluoromethylalloxazine (2) and 10‐butyl‐3‐methyl‐7‐trifluoromethylisoalloxazine (3) were shown to mediate the selective oxidation of benzyl alcohols to form aldehydes in the presence of Cs2CO3. Flavin 3 was superior in the oxidation of toluene derivatives to form aldehydes in the presence of trifluoroacetic acid. On the other hand, photooxidations provided by ethylene‐bridged quaternary flavinium salt 1 gave the corresponding carboxylic acids. The usefulness of the developed catalytic systems using 1–3 was also demonstrated in the oxidation of secondary benzylic and aliphatic alcohols, and benzylic methylene groups to form the corresponding ketones. The systems have the advantage of a broad substrate scope and metal‐free conditions, which distinguish them from the previously reported flavin photooxidation reactions.

Novel β-ketoenamines versus azomethines for organic electronics: characterization of optical and electrochemical properties supported by theoretical studies

A simple and rapid synthesis of six new, stable β-ketoenamines by coupling 3-amino-1,8-naphthalimide derivatives with 2-(4-pyrimidinyl)-malondialdehyde in the presence of trifluoroacetic acid was developed. Two of the synthesized 3-amino-1,8-naphthalimide derivatives were condensed with 9H-fluorene-2-carboxaldehyde, resulting in azomethine products. The structure of obtained compounds was confirmed by 1H and 13C NMR, COSY, HMQC, FTIR spectroscopy and elemental analysis. The photophysical, electrochemical and thermal properties of the compounds were investigated. Additionally, calculations using density functional theory were performed to obtain the optimized ground-state geometry and distribution of the HOMO and LUMO levels as well as UV–Vis and photoluminescence spectra of the synthesized compounds. DSC measurements revealed that the compounds form amorphous material with glass transition temperature in the range of 41–146 °C and are thermally stable up to 300 °C. β-Ketoenamines have higher glass transition temperature, smaller energy gap (2.11–2.47 eV), higher PL quantum efficiency in solution (5.25–12.97%) and ability to aggregation-induced emission than the azomethines.

O‐Alkyldithiophosphate Nickel Complexes with dcpf Ligand as Efficient Electrocatalysts for Hydrogen Evolution

Six new O‐alkyldithiophosphate nickel complexes with dcpf ligand, [(dcpf)Ni(S2P{O}OR)] (dcpf = 1,1′‐bis (dicyclohexylphosphino)ferrocene, R = CH3 (1), CH3CH2 (2), Ph (3), 4‐MeC6H4 (4), PhCH2 (5) and PhCH2CH2 (6)), have been synthesized by the treatment of dcpf with ((RO)2PS2)2Ni in satisfactory yields. These complexes were characterized by elemental analysis, spectroscopy (FTIR, UV–vis, 1H, 13C, and 31P NMR), thermogravimetric analysis and single crystal X‐ray diffraction. The nickel atom in 1, 2·CH2Cl2, 3·CH2Cl2, 4·2CH2Cl2·THF, and 2(5)·hexane adopts a slightly distorted square‐planar coordination environment finished by two phosphorus atoms of dcpf ligand and two sulfur atoms of O‐alkyldithiophosphate ligand. Furthermore, the electrochemical properties for complexes 1–6 were also investigated by cyclic voltammetry. With the addition of 120 mM trifluoroacetic acid (TFA), the turnover frequency (TOF) values for 1–6 are estimated to be 1243.83, 1046.54, 1331.71, 2545.29, 1899.03, and 1191.37 s−1, with the overpotential (η) values of 0.62, 0.58, 0.71, 0.67, 0.60, and 0.56 V, respectively. The result of electrochemical studies indicates that all complexes can be used as efficient molecular eletrocatalysts for the reduction of protons to hydrogen in the presence of TFA in MeCN.

Synthesis of Phthalic Aldehyde and Its Diacetals

Acyclic phthalaldehyde diacetal without cyclic 1,3-dihydro-1,3-dimethoxybenzo[c]furan impurity has been obtained via the reaction of 1,2-bis(dibromomethyl)benzene with trimethyl orthoformate (1:6) at 90°C in the presence of 10 mol% of ZnCl2. Hydrolysis of phthalaldehyde diacetal has led to the formation of phthalaldehyde without HBr evolution. The reaction of phthalaldehyde with trimethyl orthoformate in the presence of trifluoroacetic acid has proceeded abnormally, with the formation of the cyclic diacetal. The acyclic diacetal has been phosphorylated by chlorophosphines and the action of PCl3 and a P(III) acid ester in sequence.

New methods to synthesize phthalaldehyde and its diacetals

A new synthesis of phthalaldehyde that avoided formation of HBr involved treatment of 1,2-bis(dibromomethyl)benzene with trimethyl orthoformate (1: 6, 90 °C, 10 mol.% ZnCl2) to obtain acyclic diacetal without admixture of cyclic one (1,3-dimethoxy-1,3-dihydrobenzo-[c]furan) followed by hydrolysis to give the target dialdehyde. Phthalaldehyde reacted with CH(OMe)3 in the presence of trifluoroacetic acid to yield exclusively cyclic diacetal. Acyclic diacetal was phosphorylated by treatment with secondary chlorophosphines and by the reaction with PCl3 followed by treatment with PIII acid ester.

1-Methyl-1,4-cyclohexadiene as a Traceless Reducing Agent for the Synthesis of Catechols and Hydroquinones.

Pro-aromatic and volatile 1-methyl-1,4-cyclohexadiene (MeCHD) was used for the first time as a valid H-atom source in an innovative method to reduce ortho or para quinones to obtain the corresponding catechols and hydroquinones in good to excellent yields. Notably, the excess of MeCHD and the toluene formed as the oxidation product can be easily removed by evaporation. In some cases, trifluoroacetic acid as a catalyst was added to obtain the desired products. The reaction proceeds in air and under mild conditions, without metal catalysts and sulfur derivatives, resulting in an excellent and competitive method to reduce quinones. The mechanism is attributed to a radical reaction triggered by a hydrogen atom transfer from MeCHD to quinones, or, in the presence of trifluoroacetic acid, to a hydride transfer process.

Synthetic Transformations of Higher Terpenoids. 38.* Synthesis of Conjugates Containing β-Carboline and Tricyclic Diterpenoids

The synthesis and properties of tricyclic pimaranes containing a C-16 β-carboline are reported. A Pictet–Spengler reaction of methyl 15-oxo-16-formylisopimarate (prepared in situ from the 15-oxo-15,16-dihydroisopimarate) and tryptamine or tryptophan methyl ester in the presence of trifluoroacetic acid formed a mixture of terpenoid 1,2,3,4-tetrahydro-β-carbolines, 3,4-dihydro-β-carbolines, and β-carbolines. Tetrahydro- and dihydro-β-carbolines in CHCl3 were oxidized to the corresponding β-carbolines by treatment in air with basic Al2O3.

Synthesis and Investigation of Linker-Free BODIPY-Gly Conjugates Substituted at the Boron Atom.

An efficient synthesis of boron-functionalized cyclic BODIPY-Gly conjugates, using commercially available N-protected glycine amino acids and a BF2-BODIPY moiety as starting materials, is reported. The existence of two conformers (up and down) is revealed through comprehensive DFT calculations and 1H and 11B NMR analyses. The experimental and computational results indicate that all BODIPYs are stable in aqueous solutions at neutral pH and that Fmoc-BODIPY (4) is more stable than Ac-BODIPY (6) in the presence of trifluoroacetic acid (TFA). In part due to their enhanced rigidity, all BODIPY-Gly conjugates display increased fluorescence quantum yields (0.6 < Φ < 0.9) relative to the corresponding BF2-BODIPY, making them excellent candidates for fluorescence imaging applications.