Strong Carboxylic Acids Research Articles

Acid-induced improvement of photosensitizing efficiency of porphyrins under heterogeneous aqueous conditions: High photosensitizing activity, dissociative stability and photooxidative durability

Meso-tetrakis(N-methylpyridinium-3-yl)porphyrin (H2TMPyP), electrostatically supported on the sodium salt of amberlyst 15 nanoparticles (nanoAmbSO3Na) was protonated with very weak (CH3COOH), weak (CH2ClCOOH, CHCl2COOH) and strong (CF3COOH) carboxylic acids and H2SO4 to prepare a series of new photosensitizers. NanoAmbSO3@H2TMPyP(HA)2 compounds were quite stable after separation from the aqueous solution and drying, even in the case of nanoAmbSO3@H2TMPyP(CH3COOH)2. The diacids were characterized by DR-UV–vis, AFM, TGA and DLS and used as photosensitizers in aerobic photooxidation of 1,5-dihydroxynaphthalene (DHN) and methyl phenyl sulfide. Almost no catalyst degradation was observed for the diacids in the oxidation of DHN after five successive runs. Also, the catalyst degradation was in the range of 0–68% in the oxidation of methyl phenyl sulfide at the end of the 5th run. The catalyst stability decreased as nanoAmbSO3@H2TMPyP(CF3COOH)2 >> nanoAmbSO3@H2TMPyP(CHCl2COOH)2 > nanoAmbSO3@H2TMPyP(H2SO4)2 > nanoAmbSO3@H2TMPyP(CH3COOH)2 > nanoAmbSO3@H2TMPyP(CH2ClCOOH)2. It is noteworthy that under the same conditions, ca. 50% of the non-protonated porphyrin, nanoAmbSO3@H2TMPyP, was degraded after 2 h, at the end of the first run. In other words, the formation of nanoAmbSO3@H2TMPyP(HA)2 species was associated with a significant increase in both the photocatalytic activity and oxidative stability of nanoAmbSO3@H2TMPyP, regardless of the type and strength of the acid used for diprotonation of the porphyrin. In the oxidation of methyl phenyl sulfide, nanoAmbSO3@H2TMPyP(CF3COOH)2 and nanoAmbSO3@H2TMPyP(CH2ClCOOH)2 were the most efficient catalysts of the series. The singlet oxygen quantum yields (ϕΔ), determined chemically by using 1,3-diphenylisobenzofuran as a specific quencher of singlet oxygen showed ϕΔ in the range of 0.51–0.98 for nanoAmbSO3@H2TMPyP(HA)2 and 0.66 for nanoAmbSO3@H2TMPyP.

Standard-Free Quantification of Dicarboxylic Acids: Case Studies with Salt-Rich Effluents and Serum.

The present study evaluates the ionization efficiency (IE) of linear and branched C2-C14 dicarboxylic acids (DCAs) by electrospray ionization (ESI) under different conditions. The influence of the concentration of organic modifier (MeOH); mobile phase additive; and its concentration, pH, and DCA structure on IE values is studied using flow injection analysis. The IE values of DCAs increase with the increase of MeOH concentration but also decrease with an increase of pH. The former is due to the increase in solvent evaporation rates; the latter is caused by an ion-pairing between the diacid and the cation (ammonium), which is confirmed by the study with different amines. The investigation of DCA ionization in the presence of different acidic mobile phase additives showed that a significant improvement in the (-)ESI responses of analytes was achieved in the presence of weak hydrophobic carboxylic acids, such as butyric or propanoic acid. Conversely, the use of strong carboxylic acids, such as trichloroacetic acid, was found to cause signal suppression. The results of the IE studies were used to develop the liquid chromatography-high-resolution mass spectrometry (LC-HRMS) method that provided instrumental limits of detection in the range from 6 to 180 pg. Furthermore, upon applying the nonparametric Gaussian process, a model for the prediction of IE values was developed, which contains the number of carbons in the molecule and MeOH concentration as model parameters. As a case study, dicarboxylic acids are quantified in salt-rich effluent and blood serum samples using the developed LC-HRMS method.

Efficient mercury removal from aqueous solutions using carboxylated Ti3C2Tx MXene

Water supplies contaminated with heavy metals are a worldwide concern. MXenes have properties that make them attractive for the removal of metal ions from water. This work presents a simple one-step method of Ti3C2Tx carboxylation that involves the use of a chelating agent with a linear structure, providing strong carboxylic acid groups with high mobility. The carboxylation decreases the zeta-potential of Ti3C2Tx by ~16 to ~18 mV over a pH range of 2.0–8.5 and improves Ti3C2Tx stability in the presence of molecular oxygen. pH in the range of 2–6 has a negligible effect on the adsorption capacity of Ti3C2Tx and COOH–Ti3C2Tx. Compared to Ti3C2Tx, COOH–Ti3C2Tx has a slightly higher and much faster mercury uptake, and the concentration of mercury ions leached out from COOH-Ti3C2Tx is lower. For both Ti3C2Tx and COOH–Ti3C2Tx, the leached mercury ion concentration is far below the U.S.-EPA maximum level. At an initial Hg2+ concentration of 50 ppm and pH of 6, COOH–Ti3C2Tx has the equilibrium adsorption capacity of 499.7 mg/g and removes 95% of Hg2+ in less than 1 min. Moreover, it has an equilibrium time of 5 min, which is significantly shorter than that of Ti3C2Tx (~ 60 min). Finally, its mercury-ion uptake capacity is higher than commercially available adsorbents reported in the literature. Its mercury removal is mainly via chemisorption and monolayer adsorption.

Palladium Nitrosyl Carboxylate Complexes as Catalysts for C−H/C−H Oxidative Coupling of Arenes: An Experimental and DFT Study

AbstractOxidative C−H/C−H coupling of arenes were carried out on palladium nitrosyl carboxylates Pd3(NO)2(CX3CO2)4(ArH)2 (I: X=Cl, Ar=Ph; II: X=F, Ar=Tol) under relatively mild conditions (5 bars of O2, 110 °C, 24 h). Over trifluoroacetate complex II, we obtained higher yields in both homocoupling of benzene and heterocoupling of benzene and other arenes. The catalytic system showed high selectivity over 90 % for all the studied substrates. The DFT calculations on the activation of arene through the proton transfer showed that the activation energies for all possible intramolecular pathways are much higher than those for the proton transfer to free carboxylate ions, indicating that the presence of external base is required to increase the performance of the considered catalytic system. In the catalytic tests it was found that the preferable external bases are ions of strong carboxylic acids, while acetate provides almost negligible improvement and pyridine suppresses the reaction most likely due to binding to active sites on palladium.

Oxalic acid quantification in mouse urine and primary mouse hepatocyte cell culture samples by ion exclusion chromatography-mass spectrometry.

Due to medical relevance and a direct correlation with some diseases, accurate quantification of oxalic acid in different complex matrices is required. Effective chromatographic separation of this strong carboxylic acid was achieved by ion exclusion chromatography (IELC). Sensitive and selective detection was carried out by means of electrospray ionization-tandem mass spectrometry. Furthermore, it was shown that the isobaric interference of lactic acid is chromatographically resolved. Structurally similar compounds like glyoxylic acid and glycolic acid were baseline separated as well. The application of stable isotope dilution analysis with 13C2 oxalic acid facilitated precise quantification. The developed method was validated with a reference oxalate sample of human urine diluted to a range of 10-500μM. Finally, the applicability of this method was demonstrated on complex matrices, like mouse urine and supernatants of primary mouse hepatocyte cell cultures.

The spontaneous decarboxylation of strong carboxylic acid − carboxylate mixtures and the use of carbon surfaces to trap the released free radicals

The mechanism of the spontaneous decomposition of a mixture of 4-nitrophenylacetic acid (NO2BzCOOH) with its respective tetrabutylammonium carboxylate in acetonitrile (NO2BzCOO−) was analyzed using cyclic voltammetry, atomic force microscopy, nuclear magnetic resonance and electronic structure calculations. This reaction is favoured by the high acidity of the carboxylic acid and occurs following a decarboxylation loop where the carboxylate anion has the function of reductant whereas the acidic proton of the carboxylic acid acts as oxidant. This redox reaction allows the generation of hydrogen as well as an acyloxy radical, that after cleavage, yields 4-nitrobenzyl radicals that have the possibility to react either in solution to produce 4-nitrotoluene or react with a carbon surface to produce a covalently modified layer with 4-nitrobenzyl groups.

Decomposition of Strong Carboxylic Acids Redox Catalyzed By Carboxylate Ions; Chemical Grafting of Carbon Surfaces

In mixtures of trichloroacetate ion and trichloroacetic acid in acetonitrile, trichloromethyl radicals are produced as a result of the redox reaction between the acid and its conjugated base. The reaction follows a loop mechanism in which the trichloroacetic acid is slowly consumed by proton reduction while the trichloroacetate ion is oxidized like in an electrochemical Kolbe reaction [1]. The hydroquinone-trichloroacetate complex was a good sensor of this unexpected self-decarboxylation redox reaction [2]. According to the conceptual framework of this reaction, the acid-base mixture was also tested but using the compounds derived from 4-nitrophenylacetic acid. The reaction ocurrs also in this system, however, when a glassy carbon electrode was present in the reaction solution, the grafting of nitrobenzyl groups on the surface was detected, whereas 4-nitrotoluene was detected as the product of a paralel reaction in solution. Therefore, the reaction represent an alternative to the covalent modification of carbon substrates without electrochemical induction.[1] Drochss P. Valencia, Pablo D. Astudillo, Annia Galano, Felipe J. González, Org. & Biomol. Chem., 2013, 11, 318-325 [2] Pablo D. Astudillo, Annia Galano, Jorge Tiburcio, Felipe J. González, J. Electroanal. Chem., 2007, 604, 57-64 Figure 1

Solvent Tuning of the Optical Absorption and Fluorescence Properties of Meso-tetra(aryl)porphyrins and Their Dications With Weak and Strong Carboxylic Acids

Solvent Tuning of the Optical Absorption and Fluorescence Properties of Meso-tetra(aryl)porphyrins and Their Dications With Weak and Strong Carboxylic Acids

N-acylation of amino-9,10-anthraquinones by the system of strong carboxylic acid – ammonium thiocyanate

The significance of the acylation reaction of amines is presented in the literary reference information. The products of the reaction of the corresponding amides are important intermediates in obtaining practically useful compounds. It has been shown that the most common methods of acylfunctionalization of amines are acetylation, trifluoroacetylation and formylation, usually acid anhydrides or chlorides are used as acylating reagents in these reactions in the presence of highly toxic and expensive catalysts. The authors have developed an approach to the synthesis of a number of N-acylated amino-9,10-anthraquinones, which is based on the use of a new acylation system consisting of a strong organic acid and ammonium thiocyanate. It has been determined that 1-amino-9,10-anthraquinone and its derivatives in the presence of the two-fold excess of ammonium thiocyanate can be acetylated only by formic and trifluoroacetic acids. 2-Amino-9,10-anthraquinone additionally can be acetylated by mercaptoacetic and acetic acids. The scheme of the reaction discovered has been proposed, it involves in situ generation of ammonium acetate from carboxylic acid and ammonium thiocyanate, which serves as the acylating reagent.

The absorption and fluorescence emission spectra of meso-tetra(aryl)porphyrin dications with weak and strong carboxylic acids: a comparative study

The absorption and emission spectra, natural radiative lifetime, radiative rate constant (kr) and the non-radiative one (knr) of the dications of a series of meso-tetra(aryl)porphyrins with CF3COOH and HCOOH were studied and compared.

Chemical burns caused by trifluoroacetic acid

Trifluoroacetic acid is a very strong carboxylic acid. The acid has been suspected to have similar toxic effects as hydrofluoric acid on skin contact. Hydrofluoric acid is highly toxic, owing to skin penetration by fluoride ions. A spill of hydrofluoric acid on the skin may be fatal. As trifluoroacetic acid contains fluorine, patients with chemical burns caused by trifluoroacetic acid have been given particular attention when treated in the hospital. To gather the known cases of trifluoroacetic acid burns from our department to give an overview of how they were exposed, the clinical presentation, and treatment. Five patients with chemical skin burns caused by trifluoroacetic acid were reviewed with regard to the extent of the burn, treatment, blood samples taken, and systemic effects. The chemical burns reported were limited (<1% of the total body surface). The burns healed as expected for chemical burns caused by acids. None of the patients showed any symptoms or signs that are typical for hydrofluoric acid burns. Localized chemical burns caused by trifluoroacetic acid should be regarded as being similar to burns from other acids, with the exception of hydrofluoric acid. To our knowledge, there are no indications that trifluoroacetic acid causes the same toxic effects as hydrofluoric acid.

Electrochemical study of the dication of porphyrins with carboxylic acids: Shift of the absorption bands compared to that of the redox potentials

Abstract Core protonation of a series of meso -tetraarylporphyrins (aryl = phenyl, 4-chlorophenyl and 4-methoxyphenyl) with weak and strong carboxylic acids was studied by cyclic voltammetry and UV–vis absorption spectroscopy. Positive shifts of the first and second oxidation and reduction potentials, observed upon protonation of the porphyrins are in close agreement to the observed red shifts of the Q(0,0) bands in the UV–vis spectra and give evidence for the stabilization of the e g (LUMO) and a 2u (HOMO) orbitals. Significantly larger positive shifts of the reduction potentials (0.622–0.892 V and 0.527–0.913 V for ΔE 1 and ΔE 2 , respectively) compared to the oxidation ones (0.06–0.397 V and 0.085–0.166 V for ΔE 1 and ΔE 2 , respectively) indicate much greater stabilization of the LUMOs compared to the HOMOs upon diprotonation of the porphyrins. Also, larger red shifts of the Soret bands relative to the Q(0,0) bands (Δν Soret /Δν Q(0,0) = 1.61–6.32) for the used porphyrins are more in accordance with destabilization of the a 1u orbital upon the reaction.

Transformations of acetone in reactions with carboxylate complexes of palladium

Interaction of palladium carboxylates [Pd(RCO 2 ) 2 ] n with acetone was studied and two new types of palladium polynuclear compounds containing acetonyl and carboxylate groups were isolated. The compounds of the first type are resented by Pd 4 (μ-CF 3 CO 2 ) 4 (μ, k 2 -CH 2 C(O)CH 3 ) 2 (η 3 -CH 2 C(OH)CH 2 ) 2 ·2CH 3 C(O)CH 3 . This complex has been characterized by the X-ray diffraction analysis. The compound has been shown to contain bridging enolate-anions and η 3 -coordinated 2-hydroxoallyl ligands. Both ligands represent the result of acetone transformations. The compound is the first transition metal complex simultaneously containing coordinated acetonyl and η 3 -coordinated 2-hydroxoallyl. The compounds of the second type represent polymeric complexes of the common formula [Pd 2 (μ-RCO 2 ) 2 (μ, k 2 -CH 2 C(O)CH 3 ) 2 ] n (R = CF 3 , CCl 3 ) containing only bridging enolate-anions. The obtained result shows that, in the presence of strong carboxylic acids, acetone acts as a high-reactive moiety towards palladium carboxylates. Interaction of palladium carboxylates [Pd(RCO 2 ) 2 ] n with acetone was studied and two new types of palladium polynuclear compounds containing acetonyl and carboxylate groups were obtained. The complex Pd 4 (μ-CF 3 CO 2 ) 4 (μ, k 2 -CH 2 C(O)CH 3 ) 2 (η 3 -CH 2 C(OH)CH 2 ) 2 was characterized by X-ray analysis and shown to contain η 3 -coordinated 2-hydroxoallyl ligand which is a result of acetone transformation. ►Palladium carboxylates [Pd(RCO 2 ) 2 ] n reveal high reactivity towards acetone. ►The reactivity depends on the presence of strong carboxylic acid. ►Acetone transforms into coordinated enolate-anions and hydroxoallyls. ►The first carboxylate-enolate platinum metal complex was characterized by X-ray analysis.

IR spectra of cyclic hydrogen-bonded complexes of bifunctional nitrogen compounds in solution

We measured the IR absorption spectra of self-associates and complexes with carboxylic acids of 3,5-dimethylpyrazole (DMP), diphenylformamidine (DPFA), diphenyltriazene (DPT), and diphenylguanidine (DPG) in solutions in a wide range of concentrations and temperatures and calculated spectroscopic, geometric, and energy characteristics of complexes in the quantum-mechanical harmonic and anharmonic 1D and 2D approximations. Spectroscopic data show that, in the case of DMP, cyclic trimers are predominantly formed; DPFA and DPG form cyclic dimers with two NH...N bonds in inert solvents, whereas, upon the complexation of DPT, cyclic structures do not occur, and only open dimers are formed. Upon the interaction of DMP, DPFA, and DPT with weak carboxylic acids (HCOOH, CH3COOH, CH2ClCOOH) in CCl4 or in CH2Cl2, molecular cyclic structures with NH...O=C and OH...N H-bonds are formed, whereas cyclic dimer complexes with stronger acids (CHCl2COOH, CCl3COOH, CF3COOH) predominantly have the structure of hydrogen-bonded ion pairs with proton transfer from the hydroxyl group to the proton-acceptor nitrogen atom. The calculations of the structure and vibrational frequencies using various basis sets of atomic functions confirm the formation of cyclic complexes in accordance with experimental results and, in the case of interaction with strong carboxylic acids, the proton transfer along the OH...N hydrogen bridge.

Role of Gelling Soluble and Colloidal Microbial Products in Membrane Fouling

The mechanism underlying gel layer formation on membrane surfaces from soluble and colloidal microbial products (SCMPs) produced under unfavorable operational conditions for membrane bioreactors (MBRs) has been investigated using supernatants from a bench-scale MBR. SCMPs can be grossly classified into gelling and nongelling SCMPs with the gelling fraction associated mostly with the polysaccharide content. The significant role played by multivalent metals in gel formation through metal-ligand complexation has been confirmed. Functional groups of the gelling SCMPs were determined by pH titration and zeta potential measurement as amine/phenolic sites (pK(a) 9.3 and 8.0), carboxylic sites (pK(a) 6.6, 4.9, and ca. 4.0), and phosphoric sites (pK(a) ca. 2.5). The carboxylic sites were more directly involved with multivalent cation complexation; however, the gelling propensity of the SCMP dispersion was minimally affected by pH change in the circum-neutral pH range, suggesting that the strong carboxylic sites were principally responsible for gel formation. The SCMPs demonstrated a high potential for gel formation given the high density of the strong carboxylic acid groups of about 0.44 mmol/g-TOC and a moderate calcium binding stability constant of about 4.9 x 10(3) M(-1).

Brønsted Acidity of Substrates Influences the Outcome of Passerini Three-Component Reactions

Passerini three-component reactions of aldehydes, isocyanides, and strong carboxylic acids (i.e., pK(a) < 2) yield alpha-acyloxycarboxamides and/or alpha-acylaminocarboxamides, the characteristic products of Ugi four-component reactions. We propose that alpha-acylaminocarboxamide formation with these substrates is a consequence of in situ Brønsted acid-catalyzed reaction of the isocyanide and aldehyde to yield an imine that participates in an Ugi-type reaction. The apparent transfer of the isocyanide alpha-carbon to protic solvents as a formyl group during imine formation is indicative of new isocyanide reactivity.

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.

3,5-Dimethylpyrazole Complexes with Strong Carboxylic Acids

3,5-Dimethylpyrazole and halogen-containing carboxylic acids in solution give rise to equilibrium between the free molecules and 1 : 1 and 1 : 2 H-complexes. These complexes either have a ion pair-like structure with two equivalent hydrogen bonds O−⋯HN+ (1 : 1) or include homoconjugate anion with strong hydrogen bond C-O-H⋯O-C (1 : 2). At low temperatures, 2 : 1 complexes were detected. The structure and harmonic vibration frequencies of the complexes were calculated in terms of the density functional theory.

Hydrolysis and Solvolysis of Methyltriethoxysilane Catalyzed with HCl or Trifluoroacetic Acid: IR Spectroscopic and Surface Energy Studies

The aim of this study was, at first, to re-consider the IR spectra of methyltriethoxysilane (MTEOS) catalysed with HCl (hydrolysis) and to compare them with IR spectra of MTEOS catalysed with trifluoroacetic acid (TFAcOH). TFAcOH as a strong carboxylic acid performs non-hydrolytic sol-gel process based on the condensation between the alkoxide and the acid function, liberating ester molecules (solvolysis). We assessed from the time-dependent IR attenuated reflection spectroscopic (IR ATR) measurements the solvolysis and hydrolysis reactions, formation of the oligomeric species and final condensation products. Additional evidence for the formation of these species was obtained from the spectra of films dip-coated from sols aged to different extent. The results of the IR spectral analysis showed that the structure of both xerogels consisted of irregular T n (n = 8, 10, 12) cube-like species bridged via the ladder-like oligomers (in the case of MTEOS/TFAcOH) and open-chain trisiloxane species (for MTEOS/HCl). 29Si NMR spectra of MTEOS/TFAcOH showed only signals of T3 while MTEOS/HCl spectra showed beside T3 also T2 signals, in agreement with IR spectra results. From the XRD peaks at low Bragg angles (∼ 9–10°) we inferred that both xerogels consisted of nanocrystalline CH3-SiO3/2 species. In addition, the surface energy values of the films deposited from the corresponding sols were measured and the dispersive and polar portions correlated with the spectral features noted in the films.

Generation of an Active Intermediate(s) during the Storage of a Peroxyoxalate Chemiluminescence Reagent Solution under the Presence of Strong Carboxylic Acids

Catecholamines have been measured using a fully-automated HPLC-ethylenediamine condensation reaction-peroxy-oxalate chemiluminescence (CL) detection system with both high sensitivity and selectivity. When a CL solution containing trifluoroacetic acid was kept at room temperature, 4°C or − 20°C, and then used for the CL detection of catecholamines, the CL intensity was significantly increased. With the solutions stored at − 20°C, the maximum CL intensity was observed, even after being stored for one year. This increase in the CL intensity was observed with CL solutions prepared using either bis(2,4,6-trichlorophenyi)oxalate (TCPO) or bis[4-nitro-2-(3,6,9-trioxadecyloxycarbon-yl)phenyl]oxalate (TDPO) in either dioxane/ethyl acetate or acetonitrile. A certain strong carboxylic acid in the CL solution, such as trifluoroacetic acid, trichloroacetic acid or heptafluorobutyric acid, was necessary in order to increase the CL intensity. This increase in the CL intensity was also observed even after decomposition of all the oxalate in the CL solution, suggesting that an active intermediate(s) for generating CL is produced in a strongly acidic solution during storage.