Spectrophotometric determination of ionization constants of some organic compounds in aqueous solution

Ionization constants of some phenols and anilines in aqueous solution with a ionic strength of 0.01 were measured at 25°C by spectrophotometric method. The set of substrates was selected on the basis of the results of preliminary calculations of ionization constants in terms of an elemental linear empirical approach with account taken of the lack of the corresponding consistent published data.     

Medium effects on the ionization constants of some quinoline derivatives

Summary The deprotonation and acid ionization constants of some quinoline derivatives in aqueous organic solvents were determined. The organic solvents used include methanol and ethanol as amphiprotic solvents andDMF andDMSO as dipolar aprotic solvents. The obtainedpK ₁ andpK ₂ values are discussed with respect to the nature and the amount of the organic component. The high stabilization of the non-protonated form by dispersion forces and of the proton by its interaction with the solvent are the main factors responsible for the increase in the ionization constants of the protonated forms of the quinolines under investigation. On the other hand, H-bonding interactions (in addition to the electrostatic effect) seem to play the major role in determining the second acid-base equilibrium of 8-hydroxyquinoline. The deprotonation constants of the examined quinolines are correlated with their experimentally determined lone-pair ionization potential values.

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Lösungsmitteleffekte auf die Ionisationskonstanten einiger Chinolinderivate

Zusammenfassung Die Deprotonierungs- und Ionisationskonstanten einiger Chinolinderivate wurden in wäßrigen organischen Medien, darunter Methanol und Ethanol als amphiprotische undDMF undDMSO als dipolare aprotische Lösungsmittel, bestimmt. Die gemessenenpK ₁- undpK ₂-Werte werden im Hinblick auf die Art und Menge der organische Komponente diskutiert. Die hohe Stabilisierung der nichtprotonierten Form durch Dispersionskräfte und des Protons durch Wechselwirkungen mit dem Lösungsmittel sind die wesentlichen Faktoren, die für den Anstieg der Ionisationskonstanten der protonierten Formen der untersuchten Chinoline verantwortlich sind. Andererseits scheinen Wasserstoffbrückenbindungen — zusätzlich zum elektrostatischen Effekt — das zweite Säure-Basen-Gleichgewicht von 8-Hydroxychinolin entscheidend zu beeinflussen. Die Deprotonierungskonstanten aller untersuchten Chinoline werden mit ihren experimentell bestimmtenlone-pair-Ionisationspotentialen korreliert.

     

Studies on intrinsic ionization constants of Fe-Al-Mg hydrotalcite-like compounds

The theoretical analysis of the intrinsic ionization constant (K(a2)(int)) of Fe-Al-Mg hydrotalcite-like compounds (HTlc) possessing permanent charges was first performed using the double extrapolation method proposed by James et al. The theoretical permanent charge density (sigma(p,T)) of the HTlc sample was calculated from the crystal structure of HTlc, and the influence of sigma(p,T) on the K(a2)(int) was also examined. From the experimental results, these conclusions can be obtained: the zero point of the charge (pH(ZPC)) of Fe-Al-Mg HTlc increases with decreased Fe3+ content and increases with increased Mg2+ in the HTlc. The pK(a2)(int) of Fe-Al-Mg HTlc also increases with decreased Fe3+ and increased Mg2+ content in the sample; furthermore, the pK(a2)(int) of Fe-Al-Mg HTlc increases with decreased sigma(p,T).     

Medium effects on the ionization constants of some pyridinecarboxylic acid derivatives

Summary The dissociation constants of 3-hydroxy-2-carboxypyridine (3H2CP), 2-hydroxy-3-carboxypyridine (2H3CP), and 2-mercapto-3-carboxypyridine (2M3CP) were determined by potentiometric titration in 20 mole% ethanol/water, dimethylsulfoxide/water, N,N-dimethylformamide/water, and dioxane/water mixtures at 25±0.1°C applying an empiricalpH correction for mixed aqueous solvents. ThepK _n values obtained are discussed with respect to the nature of the solvent and the ionic strength of the medium as well as the molecular structure. Linearization of the titrimetric data for the second equivalence point of3H2CP,2H3CP, and2M3CP was carried out using theGran method.

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Einfluß des Mediums auf die Ionisationskonstanten einiger Pyridincarbonsäurederivate

Zusammenfassung Die Dissoziationskonstanten von 3-Hydroxy-2-carboxypyridine (3H2CP), 2-Hydroxy-3-carboxypyridin (2H3CP) und 2-Mercapto-3-carboxypyridin (2M3CP) wurden mittels potentiometrischer Titration in 20 mol% Ethanol/Wasser, Dimethylsulfoxid/Wasser, N,N-Dimethylformamid/Wasser und Dioxan/Wasser bei 25±0.1°C unter Verwendung einer empirischenpH-Korrektur für wässrige Lösungsmittelgemische bestimmt. Die erhaltenenpK _n-Werte werden im Zusammenhang mit Lösungsmitteleigenschaften, Ionenstärken und Molekülstruktur diskutiert. Die titrimetrischen Daten für die zweiten Äquivalenzpunkte von3H2CP,2H3CP und2M3CP wurden mit Hilfe derGranschen Methode linearisiert.

     

Medium and structural effects on the ionization constants of some pyrazole carboxylic acid derivatives

Abstract  Stoichiometric ionization constants of some pyrazole carboxylic acids [4-benzoyl-1-(3-nitrophenyl)-5-phenyl-1H-pyrazole-3-carboxylic acid, 4-benzoyl-1-(4-nitrophenyl)-5-phenyl-1H-pyrazole-3-carboxylic acid, 4-(ethoxycarbonyl)-1,5-diphenyl-1H-pyrazole-3-carboxylic acid, 4-(ethoxycarbonyl)-1-(3-nitrophenyl)-5-phenyl-1H-pyrazole-3-carboxylic acid, 4-(ethoxycarbonyl)-1-(4-nitrophenyl)-5-phenyl-1H-pyrazole-3-carboxylic acid] were determined in ethanol–water mixtures of 50, 60, 70% ethanol (v/v) by a potentiometric titration method. Titrations were performed in an ionic strength of 0.10 M NaCl at 25.0 ± 0.1 °C using an Orion 960 automatic titrator under a nitrogen atmosphere. Using the potentiometric titration data, ionization constants were calculated in three different ways. The effects of structure and solvent on the acidity of pyrazole carboxylic acids are also discussed. Graphical abstract        

Determination of acidic constants of some phenyl-hydroxyiminoethyl quinolinium compounds

Mixed acidic constants (pK _a ) of quinolinium oximes [1-(2-phenyl-2-hydroxyiminoethyl)-1-quinolinium chloride (F-1), 1-(2-phenyl-2-hydroxyiminoethyl)-1-isoquinolinium chloride (F-2), 1-(2-phenyl-2-hydroxyiminoethyl)-1-(4-methyl)-quinolinium chloride (F-3), and 1-(2-phenyl-2-hydroxyiminoethyl)-1-(6-methyl)-quinolinium chloride (F-4)] have been determined via their UV absorption spectra recorded in the series ofBritton-Robinson's buffer solutions in thepH region 8.74–11.28 (t=25±0.5°C, =0.2). The obtainedpK _a values are in good agreement with those achieved by applying graphical methods. The followingpK _a values have been obtained: 9.93 forF-1, 9.90 forF-2, and 10.02 forF-3 andF-4.On the basis of potentiometric titrations thermodynamic acidic constants (pK _a ) of compoundsF-1,F-2,F-3, andF-4 have been determined and they were found to be 9.82, 9.71, 9.91, and 9.86, respectively. The values obtained by transferringpK _a intopK _a are in good agreement with the values obtained spectrophotometrically.

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Bestimmung der Aciditätskonstanten einiger Phenyl-hydroxyiminoethylchinolin-Verbindungen

Zusammenfassung Die Mischaciditätskonstanten (pK _a ) der Chinolin-Oxime 1-(2-Phenyl-2-hydroxyiminoethyl)-1-chinolinium chlorid (F-1), 1-(2-Phenyl-2-hydroxyiminoethyl)-1-isochinolium chlorid (F-2), 1-(2-Phenyl-2-hydroxyiminoethyl)-1-(4-methyl)-chinolinium chlorid (F-3) und 1-(2-Phenyl-2-hydroxyiminoethyl)-1-(6-methyl)-chinolinium chlorid (F-4) wurden durch ihre UV-Absorptionspektren in einer Reihe vonBritton-Robinson-Pufferlösungen impH-Intervall 8.74–11.28 (t=25±0.5°C; =0.2) bestimmt. Die berechnetenpK _a -Werte stimmen mit den über graphische Methoden erhaltenen Ergebnissen überein. DerpK _a -Wert beträgt 9.93 für die VerbindungF-1 und 9.90 fürF-2, sowie 10.02 fürF-3 andF-4.Auf Grund der potentiometrischen Titration wurden auch die thermodynamischen Aciditätskonstanten (pK _a ) berechnet: 9.82 fürF-1, 9.71 fürF-2, 9.91 fürF-3 und 9.86 fürF-4. Wenn man diese Konstanten in Mischaciditätskonstanten überträgt, erhält man Werte, die mit den durch spektrophotometrischen Bestimmungen erhaltenen Werten gut übereinstimmen.

     

Modern methods for estimation of ionization constants of organic compounds in solution

The review considers main up-to-date approaches to the calculation of ionization constants of organic compounds in solutions. Methods based on quantum-chemical calculations, continuum solvent models, cluster models, and quantitative structure-property relationships are discussed. The results of calculations of pK _a values by different methods, obtained in the past decade, are compared.     

Studies on coordination compounds : Formation constants of some metal salts of the nitrosonaphthols

Formation constants of various metal derivatives of I-nitroso-2-naphthol and 2-nitroso-1-naphthol have been measured in 50 and 75 volume per cent dioxan. The anomalies of the nickel and cobalt compounds are considered and explanations offered.     

Acetone chemical ionization studies. VII-acetylation of some aromatic compounds

Acetone chemical ionization mass spectra of 14 monosubstituted aromatic compounds were studied. Benzene, toluene and halobenzenes give exclusively charge-exchange spectra with very little fragmentation. Protonation is characteristic of compounds with higher proton affinities than acetone, with the exception of benzonitrile. Acetylation reactions are observed mainly with benzonitrile, phenol, anisole and aniline. The acetylation of phenol and aniline mostly occurs at the substitutent.     

羟氨苄青霉素的微观电离常数

测知酸碱性物质的微观电离常数, 对全面深入地了解该物质的化学行为及生物活性均很重要, 本文报道了用电位滴定法和分光光度法, 测求羟氨苄青霉素在20℃时的微观电离常数.     

Effect of solvent on spin-spin coupling constants in pmr spectra of some organophosphorus compounds containing p=o groups

Theoretical and Experimental Chemistry -     

Combination of solid-phase extraction-hollow fiber for ultra-preconcentration of some triazole pesticides followed by gas chromatography-flame ionization detection

In this study, an extraction and preconcentration technique using solid-phase extraction (SPE) along with hollow fiber (HF) has been developed as an ultra-preconcentration technique for some triazole pesticides in aqueous samples. Triazole pesticides were employed as model compounds to assess the method and were monitored by gas chromatography-flame ionization detection (GC-FID). Initially, an aqueous solution of target analytes was passed through an RP-8 SPE cartridge and then the adsorbed analytes were eluted with μL amounts of toluene. The collected elute was slowly introduced into an HF that had one end blocked. This allowed precipitation inside the lumen and pores of the HF. Finally, the obtained HF was mounted on a home-made solid-phase microextraction syringe and entered into the GC injection port for thermal desorption-GC analysis. The effect of various experimental parameters including injection port temperature, desorption time, state of HF, washing solvent, elution solvent and its volume, sample volume, etc. were investigated for finding the optimum conditions. The calibration graphs were linear in the ranges of 2-1000 ng/mL (penconazole and hexaconazole), 5-1000 ng/mL (tebuconazole), 15-1000 ng/mL (triticonazole) and the detection limits (LODs) ranged from 0.6 to 4.5 ng/mL. The enhancement factors were in the range of 870-950. The relative standard deviations (RSD%) for five repeated experiments (C=250 ng/mL of each pesticide) varied from 4.5 to 8.7%. The relative recoveries obtained for analytes in grape juice samples, spiked with different levels of each pesticide, were in the range of 87-119%.     

Chemical ionization and electron impact mass spectrometry of some organophosphonate compounds

The application of gas chromatography chemical ionization mass spectrometry to the determination of a variety of alkyl alkylphosphonates, phosphonofluoridates, phosphonothiolates and an amidophosphorocyanidate is described. Comparison is made between the electron ionization and chemical ionization mass spectrometry of these compounds. Chemical ionization mass spectrometry is shown to enhance the capability for identification, especially when a limited sample is available. Results indicate that methane is highly useful for obtaining protonated molecular ions and association ions (formed by the transfer of a reactant ion to a sample molecule) as well as meaningful fragment ions. Ionizing ethylene and isobutane gives protonated molecular ions as base peaks for all of the compounds studied, including those where a lower abundance of the [MH]₊ ion is found via methane chemical ionization mass spectrometry. Ethylene is superior to isobutane on the basis of its effectiveness for serving as both a carrier and a reagent gas and gives better sensitivity. Although not an intrinsic part of this present study, analytical sensitivities in the subnanogram range were found.     

Investigation of correlation between impact sensitivities and bond dissociation energies in some triazole energetic compounds

In this article, density functional theory has been utilized to study on the correlation between impact sensitivities h _50% and the bond dissociation energies (BDEs) of nine triazole energetic explosives. By employing B3LYP and B3P86 method with the 6-311G** basis set, all the molecules have been fully optimized. The BDEs for removal of the NO₂ group in these compounds have also been calculated at the same level. Computed results show that BDEs calculated by B3LYP method are all less than those by B3P86 method. The relationship between the impact sensitivities and the weakest C–NO₂ bond dissociation energy (BDE) values have been investigated. The results indicate a good linear correlation between the impact sensitivity h _50% and the ratio (BDE/E) of the weakest BDE to the total energy E.     

Organomagnesium synthesis of some organophosphorus compounds in an ether-free medium

Summary Some dialkylphosphinic acids, dialkylphosphinous esters, and alkylenebis(dialkylphosphine) P,P'-dioxides were synthesized via organomagnesium compounds prepared in absence of ether and other catalysts for the Grignard reaction.This article is published in accordance with a resolution of the Conference of Chief Editors of Journals of the Academy of Sciences of the USSR of June 12, 1962, as a dissertation paper by B. N. Strunin.     

Empirical procedure for the calculation of ionization constants of organic compounds in water from their molecular volume

An empirical procedure was used to calculate 278 ionization constants of 271 organic compounds, including phenols, NH acids, benzoic acid derivatives, and mono- and dihydric carboxylic acids, in water. The examined compounds were divided into 11 structural groups. The ionization constants for compounds belonging to a single group were calculated from constant empirical coefficients, molecular volumes, and formulas with an average error of less than 3.5%, the maximal error not exceeding 9.9%.     

Spectrophotometric determination of the ionization constants of fluorodinitromethane

Summary Spectrophotometric methods determined the ionization constant of fluorodinitromethane in water and absolute alcohol.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2063–2065, November 1965     

Effect of protonation exothermicity on the chemical ionization mass spectra of some alkylbenzenes

The H₂, N₂/H₂, CO₂/H₂, N₂O/H₂, CO/H₂ and CH₄ chemical ionization mass spectra of thirteen C₈ to C₁₁ alkylbenzenes are reported. Characteristic hydride and alkide ion abstraction reactions are observed with all reagent gases. The major fragmentation reactions of [MH]⁺ are olefin elimination to form a protonated arene and arene elimination to form an alkyl ion. From the effect of structure and protonation exothermicity it is concluded that rearrangement of primary alkyl groups to the more stable secondary or tertiary structure occurs prior to alkyl ion formation. A detailed fragmentation mechanism for protonated arenes is proposed. The ‘effective’ proton affinity of the methane-derived reagent system is estimated to be ～556 kJ mol^?1.     

Estimation of microscopic, zwitterionic ionization constants, isoelectric point and molecular speciation of organic compounds

Mathematical models based on structure-activity relationships and perturbed molecular orbital theory have been developed to calculate the ionization pK(a)s for a large number of organic molecules. These models include resonance, direct and indirect electrostatic field effects, sigma induction, steric effects, differential solvation and hydrogen bonding. The thermodynamic microscopic ionization constants, pk(i), of molecules with multiple ionization sites and the corresponding complex speciation as a function of pH have been determined using these chemical reactivity models. For a molecule of interest SPARC (SPARC performs automated reasoning in chemistry) calculates all of the microscopic ionization constants and the fraction of each species as a function pH along with the titration (charge) curve. The system has been tested on several biologically and environmentally important compounds.