Acids Of Different Strengths Research Articles

Diaryl(fluorinated)-mercury species as potential precursors of triaryl(fluorinated)-gallium to be used in the synthesis of cyclometallated Ga compounds and unexpected formation of aryl-Ga clusters

The first goal of this work was to explore the feasibility of diaryl-mercury species as the synthetic precursors of triaryl-gallium species GaAr*3 (where Ar*= pH, 4; Ar*= 3,5-difluorophenyl, 5; and Ar*= 3,5-trifluoromethylphenyl, 6). Expecting that 4–6 behave as Lewis acids of different strength, the second purpose was to use them for the synthesis of either rollover or classic cyclometallated Ga compounds. Three analogous diaryl-mercury HgAr*2 species, 1–3, were successfully synthesized. The structures of compounds 2 and 3 were confirmed by gas chromatography - mass spectrometry experiments. Additionally, compound 3 was analyzed through X-ray diffraction; in the crystal structure obtained, π-stacking interactions were observed. The only Ga compound synthesized was GaPh3, 4, because the presence of fluorine-containing groups in meta-position caused sublimation of the respective mercury diaryl compounds, impeding their reaction with gallium. The attempts toward the synthesis of the rollover or classic cyclometallated compounds in the reaction of 4 with bipyridine-, pyrazole- or benzo-imidazole- type ligands have failed. On the other hand, under the experimental conditions applied, water traces favored formation of the solid aryl-Ga cluster containing twelve Ga atoms [Ga12], whereas the above-mentioned ligands were quantitatively recovered in the solution. The identity of aryl-gallium cluster was confirmed by electrospray ionization - high resolution mass spectrometry. Although Ga cluster was not expected, it is considered an important finding of this work, owing to the variety of possible applications and still limited data available on the synthesis and structural characterization of such compounds.

Photochemical production of molecular hydrogen in the presence of substituted acridine salts

The photocatalytic properties of new representatives of the family of metal-free catalysts, 10-hydro-9-phenylacridine, 10-methyl-9-phenylacridinium chloride, and 10-phenyl-9-phenylacridinium chloride, were studied with respect to the reaction of molecular hydrogen generation in the presence of acids of different strength (HClO4, CH3SO3H, and CF3COOH) and reducing agents ([Bu4N]Cl, [Bu4N]Br, and [Bu4N]I). It was found that the strength of acids (p K a) and the nature of the reducing agent ( E 0) significantly affect the efficiency, i.e. turnover frequency (TOF), of the process under study. The amount of formed molecular hydrogen reaches its maximum in the case of the combination HClO4 and [Bu4N]I, characterized by minimal p K a and E0 values, respectively. The influence of the nature of substituents at the nitrogen atom in 9-phenylacridine on the efficiency of the molecular hydrogen production was analyzed. It was shown that the limiting stage of the process is the protonation of the formed radical.

Switchable cyclopalladation of substrates containing two directing groups: on the way to non-symmetrical [2.2]-dipalladaparacyclophanes.

Simple switching of the site-selectivity of C-H activation reactions of substrates containing multiple directing groups is particularly important for the so-called late stage functionalization synthetic approach. In this work, we verified the possibility of achieving this by adding acids of different strengths. Using a substrate containing two differently strong (and basic) directing groups, the influence of the addition of acids on the regioselectivity of the C-H activation step of the reaction with palladium acetate was thoroughly studied. The addition of no or weak acids results in cyclopalladation being controlled by a stronger directing group. However, the addition of a strong acid causes protonation of this group and the reaction is then controlled by a weaker directing group. Finally, this approach enables double C-H activation leading to a unique class of compounds: "non-symmetrical" [2.2]-dipalladaparacyclophanes.

Assessing the propensity toward ionization in nanosized clusters of protic ionic liquids by Ab-initio methods

Nanosized clusters of protic ionic liquids are investigated using ab-initio DFT methods to understand their propensity to remain ionic. Protic ionic liquids are based on acid/base pairs and are ionic because of proton transfer from the acid to the base. Two prototypical ionic liquids based on triethylamine and two acids of different strengths are used here to trace the tendency toward proton transfer when the system size is gradually increased from an isolated pair of molecules to cluster of several pairs. We have found that the compounds based on the weak acid shows the existence of a well-defined minimal size that represents the threshold for the onset of ionization phenomena.

Thioxanthone-based organic probe with aggregation enhanced emission and exceptional mineral acids sensing abilities

The development of fluorescent probe(s) for naked eye analyte detection is an emerging area of research. Such probes can be judiciously engineered to realize analyte specific response with high sensitivity and broad applicability. Herein, we report reversible acid-base sensing ability of a donor-acceptor-donor (D-A-D) type thioxanthone-based luminophore 3,6-bis(dimethylamino)-9H-thioxanthen-9-one 10,10-dioxide (3). Photo-physical features of 3 in both the solid and solution states have also been determined. Moreover, the reported probe exhibited aggregation-enhanced emission (AEE) characteristics and pH dependent emission colour. An intramolecular charge transfer (ICT) process was observed between donor (N,N-dimethylamino) and acceptor (thioxanthone) units. The fact that changes can be seen under both the UV and visible lights without any special aid, signifies a remarkable prospect of this organic probe in distinguishing the commonly used laboratory acids of different strength.

On the Use of a Protic Ionic Liquid with a Novel Cation To Study Anion Basicity.

The need for reliable means of ordering and quantifying the Lewis basicity of anions is discussed and the currently available methods are reviewed. Concluding that there is need for a simple impurity-insensitive tool, we have sought, and here describe, a new method using NMR spectroscopy of a weak base, a substituted urea, 1,3-dimethyl-2-imidazolidinone (DMI), as it is protonated by Brønsted acids of different strengths and characters. In all cases studied the product of protonation is a liquid (hence a protic ionic liquid). NMR spectroscopy detects changes in the electronic structure of the base upon interaction with the proton donors. As the proton-donating ability, that is, acidity, increases, there is a smooth but distinct transition from a hydrogen-bonded system (with no net proton transfer) to full ionicity. The liquid state of the samples and high concentration of nitrogen atoms, despite the very low natural abundance of its preferred NMR-active isotope ((15) N), make possible the acquisition of (15) N spectra in a relatively short time. These (15) N, along with (13) C, chemical shifts of the carbonyl atom, and their relative responses to protonation of the carbonyl oxygen, can be used as a means, sensitive to anion basicity and relatively insensitive to impurities, to sort anions in order of increasing hydrogen bond basicity. The order is found to be as follows: SbF6 (-) <BF4 (-) <NTf2 (-) >ClO4 (-) >FSO3 (-) <TfO(-) <HSO4 (-) <Cl(-) <MsO(-) .

Protonolysis of Fe–C bonds of a diiminopyridineiron(II) dialkyl complex by acids of different strengths: Influence of monoanionic ligands on the spectroscopic properties of diiminopyiridine-FeY2 complexes

The reaction of the dialkyliron complex [Fe(CH2SiMe3)2(MesBIP)] (MesBIP=2,6-bis((N-mesityl)acetimidoyl)pyridine) with protic acids (HY) of different strengths (Y=C6F5O, CF3CO2, Cl, CF3SO3) invariably leads to the cleavage of both Fe–C bonds, independent of the Fe/HY ratio used (either 1:2 or 1:1), affording the corresponding complexes [FeY2(MesBIP)]. Relevant spectroscopic features of these compounds, such as paramagnetic 1H NMR shifts and UV–Vis absorption bands, exhibit a marked dependence on the nature of Y.

Application of Pyrite and Chalcopyrite Electrodes for the Acid-Base Determinations in Nitriles

The natural minerals pyrite and chalcopyrite have been used as the indicator electrode sensors using acetonitrile and propionitrile as solvents. The results show the exceptional advantage of pyrite and chalcopyrite as electrochemical sensors and also the possibility of the application of these electrodes for the determination in nonaqueous solutions where glass electrode shows many defaults. The behaviour of the pyrite and chalcopyrite indicator electrodes in nitriles were checked by titrating several bases and acids of different strengths using protons and lyate ions generated by the oxidation of some gallic acid esters and dihydroxy phenols, as well as m-cresol and 3-metoxy phenol. The results obtained by using these electrodes were compared with those obtained by the application of a glass electrode under the same conditions, and good agreement, reproducibility and accuracy were obtained. The standard deviation of the determination of the investigated acids and bases was less than 0.9%. In the potentiometric titrations with pyrite and chalcopyrite indicator electrodes, the potential is instantaneously established throughout. Both electrodes can be used without any time limit or without considerable divergence in potentials.

Simultaneous evaluation of the dissociated and undissociated acid concentrations by square wave voltammetry using microelectrodes

The square wave voltammetric response of the reduction of acids of different strength namely, hydrochloric acid, phosphoric acid, lactic acid, acetic acid and sodium dihydrogenophosphate at a platinum microdisk electrode are presented. The voltammograms of HCl and H 2 PO 4 - display a single peak which height increased linearly with concentration. The acids of intermediary strength exhibit voltammograms resulting from the overlapping of two peaks that are assigned to the reduction of hydrogen ions (H +) and of the undissociated acid form (HA). Peaks separation depends on the acid strength and concentration. A numerical deconvolution of voltammograms was performed based on Gaussian peaks fitting. The deconvoluted peak current data for H + were validated towards calibration curves of HCl. The validation of the current data of HA was performed using buffer solutions. The methodology present herein allows to assess simultaneously the concentration of each acid form from a single square wave voltammogram.

Theoretical simulations of proton conductivity: Basic principles for improving the proton conductor

Classical molecular dynamics (MD) simulations of proton conduction have been performed, to get insight into basic principles of potential improvements of proton conductivity in polyelectrolyte membranes. For the simulations the reactive force field for water (RWFF) was used, which allows bond dissociation of water, acids and hydronium ions. The effects are shown to be fundamental relevance for the diffusion of protons in membranes. One and two-dimensional conductors, and a Nafion ™ membrane have been modeled in our simulations. The two-dimensional model imitates a metal phosphate; the one-dimensional model imitates an idealized pore of hydrated Nafion membranes. The MD simulations of proton conductivity of the metal phosphate show the dissociation of the acid POH groups and their participation in the proton transport. Several simulations are performed with acids of different strength and the effect of the acid’s strength on the diffusion and on the conductivity is analyzed. The importance of the ion coupling on the conductivity is firstly proved in tubes, which imitate an ideal pore inside a membrane. Afterwards, the coupling is investigated in a real hydrated Nafion membrane by a non-equilibrium MD simulation. The results suggest a soliton-like behavior for proton conductivity in membranes.

Standard Molar Volumes and Heat Capacities of Aqueous Solutions of Trifluoromethanesulfonic Acid at Temperatures up to 573 K and Pressures to 30 MPa

Densities and heat capacities of dilute aqueous solutions (0.025 to 0.4 mol⋅kg−1) of trifluoromethanesulfonic acid (triflic acid) were measured with original high-temperature, high-pressure instruments at temperatures and pressures up to 574 K and 31 MPa, respectively. Standard molar volumes and standard molar heat capacities were obtained via extrapolation of the apparent molar properties to infinite dilution. The evolution of these standard derivative properties of triflic acid with temperature and pressure is qualitatively compared with that of other acids of different strengths.

A widely varying range of products in reactions of C 6F 5BrF 2, C 6F 5IF 2, and C 6F 5IF 4 with Lewis acids of different strength

The relative fluoride donor ability: C 6F 5BrF 2 > C 6F 5IF 2 > C 6F 5IF 4 was outlined from reactions with Lewis acids of graduated strength in different solvents. Fluoride abstraction from C 6F 5HalF 2 with BF 3·NCCH 3 in acetonitrile (donor solvent) led to [C 6F 5HalF·(NCCH 3) n ][BF 4]. The attempted generation of [C 6F 5BrF] + from C 6F 5BrF 2 and anhydrous HF or BF 3 in weakly coordinating SO 2ClF gave C 6F 5Br besides bromoperfluorocycloalkenes C 6BrF 7 and 1-BrC 6F 9. In reactions of C 6F 5IF 2 with SbF 5 in SO 2ClF the primary observed intermediate ( 19F NMR, below 0 °C) was the 4-iodo-1,1,2,3,5,6-hexafluorobenzenium cation, which converted into C 6F 5I and 1-IC 6F 9 at 20 °C. The reaction of C 6F 5IF 4 with SbF 5 in SO 2ClF below −20 °C gave the cation [C 6F 5IF 3] + which decomposed at 20 °C to C 6F 5I, 1-iodoperfluorocyclohexene, and iodoperfluorocyclohexane. Principally, the related perfluoroalkyl compound C 6F 13IF 4 showed a different type of products in the fast reaction with AsF 5 in CCl 3F (−60 °C) which resulted in C 6F 14. Intermediate and final products of C 6F 5HalF n−1 ( n = 3, 5) with Lewis acids were characterized by NMR in solution. Stable solid products were isolated and analytically characterized.

Feasibility of the spontaneous gas‐phase proton transfer equilibria between neutral Brønsted acids and Brønsted bases

AbstractThe computational investigation of interactions of different acid–base pairs regarding the nature and extent of spontaneous proton transfer was carried out at B3LYP/6‐311 + G** level. The selected acid–base pairs include the interactions of strong base (K2O) with acids of different strength (HClO4, HCl, and HF), and strong acid (HClO4) with bases ranging from K2O (GB = 322.8 kcal/mol) to H2O (GB = 157.6 kcal/mol). It was shown that spontaneus, unassisted proton transfer can take place in the gas‐phase reactions of strong neutral Brønsted acids and bases. The reaction might be barrierless as in case of interactions between strong acids and bases, for example perchloric acid and alkali metal oxides or potassium oxide and halogen hydrides, or involve the encounter complex (hydrogen bonded acid–base cluster), which is separated from ion‐pair by the transition state. Copyright © 2008 John Wiley &amp; Sons, Ltd.

Kinetics of homopolycondensation of furfuryl alcohol

The kinetic features of the homopolycondensation of furfuryl alcohol in an aqueous medium in the presence of acids of different strengths have been studied. The second order of the reaction with respect to the monomer has been established. A kinetic scheme of the polycondensation reaction has been proposed, and the activation parameters of the process have been calculated.

Interaction of para-substituted meso-tetraphenylporphyrins and meso-tetra(n-propyl)porphyrin with weak and strong carboxylic acids: A UV–Vis spectroscopic study

N-protonation of H2t(n-Pr)p and a series of para-substituted meso-tetraphenylporphyrins (arylpor), using carboxylic acids of different strength and size, CF3COOH, HCOOH, H2C2O4, CH2ClCOOH, CH3COOH and CH3CH2COOH, has led to a shift of the Soret and Q(0,0) bands with respect to those of the corresponding free base porphyrins. The size of central acceptor as well as the strength of N–H⋯carboxylate hydrogen bonding are the main factors influencing the red shift of the Soret band; the Soret band of H2t(n-Pr)p(CH3CH2COOH)2 is red shifted in comparison to those of the other dications of H2t(n-Pr)p. It may be shown that the out-of-plane deformation of the porphyrin core, which decreases the antibonding interactions in the frontier orbitals of the porphyrin core, leads to greater stabilization of the eg orbitals relative to the a1u one and consequently causes the red shift of the Soret band. Although the Q(0,0) band is blue shifted with respect to the free base porphyrin, the blue shift may be shown to be due to the protonation of the pyrrolenine nitrogen atoms rather than the saddling of the macrocycle. A comparison of the spectral data of the dications of arylpor, bearing strong electron donating para-substituents, with those of the related H2t(n-Pr)p adducts clearly indicates the importance of the π-resonance interactions in the observed spectral shifts of the Q(0,0) bands and, to less an extent, the Soret bands. The unusually large red shift observed for the Soret band of the H2t(4-NO2)pp dications seems to be due to the stabilization of eg orbitals through overlap with the proper unoccupied π∗ orbital of the electron withdrawing (4-NO2)phenyl in the excited state, a1u1eg1.

Novel Poly(amido‐amine)‐Based Hydrogels as Scaffolds for Tissue Engineering

Biodegradable and biocompatible amphoteric poly(amido-amine) (PAA)-based hydrogels, containing carboxyl groups along with amino groups in their repeating unit, were considered as scaffolds for tissue engineering applications. These hydrogels were obtained by co-polymerising 2,2-bisacrylamidoacetic acid with 2-methylpiperazine with or without the addition of different mono-acrylamides as modifiers, and in the presence of primary bis-amines as crosslinking agents. Hybrid PAA/albumin hydrogels were also prepared. The polymerisation reaction was a Michael-type polyaddition carried out in aqueous media. The PAA hydrogels were soft and swellable materials. Cytotoxicity tests were carried out by the direct contact method with fibroblast cell lines on the hydrogels both in their native state (that is, as free bases) and as salts with acids of different strength, namely hydrochloric, sulfuric, acetic and lactic acid. This was done in order to ascertain whether counterion-specific differences in cytotoxicity existed. It was found that all the amphoteric PAA hydrogels considered were cytobiocompatible both as free bases and salts. Selected hydrogels samples underwent degradation tests under controlled conditions simulating biological environments, i.e. Dulbecco medium at pH 7.4 and 37 degrees C. All samples degraded completely and dissolved within 10 d, with the exception of hybrid PAA/albumin hydrogels that did not dissolve even after eight months. The degradation products of all samples turned to be non-cytotoxic. All these results led us to conclude that PAA-based hydrogels have a definite potential as degradable matrices for biomedical applications.

Synthesis and characterization of polyaniline prepared in formic acid medium

AbstractThe oxidative polymerization of aniline in formic acid (HCOOH) medium was investigated using formic acid of different strengths (5–25N). It was observed that a certain portion of the total polymer (∼ 10%) remains soluble in the reaction medium. The UV–visible absorption spectra of the reaction mixtures in dilute and concentrated HCOOH indicate different initial reaction pathways and intermediates occurring under the conditions employed. It was found that the reaction yield and intrinsic viscosity of the polymer were dependent on the synthesis parameters. By contrast, the electrical conductivity was not sensitive to most of these variables. Elemental analysis revealed that the chemical composition of polyaniline (PANI)–formic acid salt is 4 : 2.2, indicating two units of formate anions present per four‐unit polymer chain containing 3 : 1 ratio of benzenoid to quinonoid moieties. Spectroscopic results showed that PANI prepared in HCOOH exists in an emeraldine oxidation state. A transmission electron micrograph of the soluble portion showed a wide distribution of spherical particles of different diameters in the range 20–200 nm. The thermal stability and crystalline structure of PANI–formic acid salt and its base form were ascertained by thermogravimetric analysis and wide‐angle X‐ray diffraction (WAXD) study, respectively. The base form of the polymer was stable up to 400°C and the acid form showed evolution of formic acid dopant in the temperature range 200–300°C. WAXD study showed a pseudo‐orthorhombic crystal structure for PANI–formic acid salt. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 991–999, 2004

The Reactivity of Potassium Polyfluoroaryl-, Polyfluoroalkenyl-, and Perfluoroalkyltrifluoroborates and their Hydrocarbon Analogues towards Acids of Different Strength: A Systematic Study of the Hydrodeboration

The hydrodeboration of the (fluoroorgano)trifluoroborates K [RFBF3] [RF = C6F5, XCF=CF (X = F, cis- and trans-Cl, C3F7O, cis-C2F5, trans-C4F9, -C4H9) and C6F13] and of the organotrifluoroborates K [RBF3] (R = C6H5, cis- and trans-C4H9CH=CH, C4H9 and C8H17) with CH3CO2H (100 %), CF3CO2H (100 %), aqueous HF and anhydrous HF was investigated. In the alkenyltrifluoroborates K [R'CF=CFBF3] the formal replacement of BF3 by a proton occurred stereospecifically under retention of the configuration. The 19F NMR spectra of K [RFBF3] in acids indicate strong interactions of the BF3 group with protons or acid molecules. (Fluororgano)fluorborane und -fluoroborate. 6 [1] Die Reaktivitat von Kaliumpolyfluoraryl-, polyfluoralkenyl- und perfluoralkyltrifluoroboraten und deren Kohlenwasserstoff Analoga gegenuber Sauren unterschiedlicher Starke: Eine systematische Studie zur Hydrodeborierung Die Hydrodeborierung der (Fluororgano)trifluoroborate K [RFBF3] [RF = C6F5, XCF=CF (X = F, cis- and trans-Cl, -C3F7O, cis-C2F5, trans-C4F9, -C4H9) und C6F13] und der Organotrifluoroborate K [RBF3] (R = C6H5, cis- und trans-C4H9CH=CH, C4H9 und C8H17) mit CH3CO2H (100 %), CF3CO2H (100 %), wasseriger HF und wasserfreier HF wurde untersucht. In den Alkenyltrifluoroboratsalzen K [R'CF=CFBF3] erfolgte formal die stereospezifische Substitution von BF3 durch ein Proton. Die 19F-NMR Spektren der Losungen von K [RFBF3] Salzen in Sauren weisen auf starke Wechselwirkungen der BF3-Gruppe mit Protonen oder Sauremolekulen hin.

Stress Generated on Aluminum During Anodization as a Function of Current Density and pH

Anodic oxidation is accompanied by stressgeneration during the growth of the oxide. The presentstudy focuses on the stress-generation mechanism onaluminum as a function of the applied current density in acidic solutions of sulfuric acid ofdifferent strengths giving variable pH. Abeam-deflection technique was utilized for thedetermination of the magnitude and direction of stressesgenerated during the anodic oxidation process. Generally,thickness of the oxide determines whether the stress iscompressive or tensile in nature. The results have beeninterpreted in terms of the formation and annihilation of anion (O2-) and cation(Al3+) vacancies. A reduction in thealuminum-ion vacancy concentration (V Al 3 ) results in a compressive stressdeflection, whereas tensile-stress deflection isintroduced by an increase in the oxygen vacancy(Vo2+) concentration. The mechanism isfurther elucidated by current-density jump/dropexperiments. The results show that stress in this caseis affected by the dissolution of the oxide at the oxide-electrolyteinterface.

Electropolymerization of benzene in a two-phase strong proton acid-benzene system

Anodic polymerization of benzene can be carried out under two-phase conditions if the electrode is immersed in the interfacial layer between benzene and acids of different strength, such as methanesulfonic, sulfuric, 20% fuming sulfuric, fluorosulfonic and trifluoromethanesulfonic acids. In all these cases the benzene oxidation is in the vicinity of 1 V/SCE. For films grown in usual acid media cyclic voltammetries are characterized by wide, ill-defined redox peaks. By contrast, in the superacids another state of the film with sharp redox peaks is observed. It is supposed that linear structure, with narrow distribution of the chain length, is realized in the latter case.