Determination of the Glass Electrode Parameters by Means of Potentiometric Titration of Acetic Acid in Aqueous Sodium or Potassium Chloride Solutions at 25°C

Single-ion activity coefficient equations are presented for the calculation of stoichiometric (molality scale) dissociation constants K _m for acetic acid in aqueous NaCl or KCl solutions at 25°C. These equations are of the Pitzer or Hückel type and apply to the case where the inert electrolyte alone determines the ionic strength of the acetic acid solution considered. K _m for a certain ionic strength can be calculated from the thermodynamic dissociation constant K _a by means of the equations for ionic activity coefficients. The data used in the estimation of the parameters for the activity coefficient equations were taken from the literature. In these data were included results of measurements on galvanic cells without a liquid junction (i.e., on cells of the Harned type). Despite the theoretical difficulties associated with the single-ion activity coefficients, K _m can be calculated for acetic acid in NaCl or KCl solutions by the Pitzer or Hückel method (the two methods give practically identical K _m values) almost within experimental error at least up to ionic strengths of about 1 mol-kg^–1. Potentiometric acetic acid titrations with base solutions (NaOH or KOH) were performed in a glass electrode cell at constant ionic strengths adjusted by NaCl or KCl. These titrations were analyzed by equation E = E _o + k(RT/F) ln[m(H⁺)], where m(H⁺) is the molality of protons, and E is the electromotive force measured. m(H⁺) was calculated for each titration point from the volume of the base solution added by using the stoichiometric dissociation constant K _m obtained by the Pitzer or Hückel method. During each base titration at a constant ionic strength, E _o and k in this equation were observed to be constants and were determined by linear regression analysis. The use of this equation in the analysis of potentiometric glass electrode data represents an improvement when compared to the common methods in use for two reasons. No activity coefficients are needed and problems associated with liquid junction potentials have been eliminated.     

o-phthalic acid as a standard substance for calibrations of hydrogen ion concentrations with a glass electrode

o-Phthalic acid is proposed as a standard substance for buffer solutions of known hydrogen ion concentration (I ? 0.2 M KCl, p[H⁺] = 3.0–5.4, 25°C). Its crystallinity, purity and slightly wide buffer range afford advantages over acetic acid. Empirical relationships between measured pH (pH_m) and calculated [H⁺] were derived for sequences of buffer solutions at several ionic strengths: pH_m - Mp[H⁺] + C. These calibration lines were parallel and of unit slope as required by theory. A table of p[H⁺] values for o-phthalic acid buffer solutions at I = 0.1 M (KCl) is presented and the method of calculation of p[H⁺] values for a buffer series generated by additions of potassium hydroxide is outlined.     

Dissociation Kinetics of Nickel (II), Zinc (II) and Cadmium (II) Complexes of 1,7-Diaza-4,10,13-trioxacyclopentadecane-N,N′-diacetic Acid and 1,10-Diaza-4,7,13,16-tetraoxacyclooctadecane-N,N′-diacetic Acid

The dissociation kinetics of the complexes of nickel(II), zinc(II) and cadmium(II) of 1,7-diaza-4,10,13-trioxacyclopentadecane-N,N′-diacetic acid (K21DA) and 1,10-diaza-4,7,13,16-tetraoxacyclooctadecane-N,N′-diacetic Acid (K22DA) were studied in constant ionic strength aqueous medium with various [H⁺]-range, i.e., (0.88?53.9) × 10^?5 M and (0.5?7.5) × 10^?3 M. Copper(II) was used as the scavenger of free ligand and the rates of dissociation of these complexes have been found to be independent of (Cu²⁺]. All the complexes exhibit acid-independent and acid-dependent pathways. For NiK21DA, CdK21DA and CdK22DA complexes, the acid-dependent rates are linear functions of [H⁺]. For NiK22DA and ZnK21DA complexes, a saturation kinetics is observed, i.e., [H⁺]-dependence at low [H⁺] and [H⁺]-independent at high [H⁺]. The rationalization of such different observations is proposed to be due to difference in complex solution structures rather than the thermodynamic stabilities. Influence of acetate content in the buffer, temperature, and total electrolyte concentration on the rate of dissociation has also been investigated and discussed.     

Kinetics of the bromate–bromide reaction at high bromide concentrations

At bromide concentrations higher than 0.1 M, a second term must be added to the classical rate law of the bromate–bromide reaction that becomes ?d[BrO₃^?]/dt = [BrO₃^?][H⁺]²(k₁[Br^?] + k₂[Br^?]²). In perchloric solutions at 25°C, k₁ = 2.18 dm³ mol^?3 s^?1 and k₂ = 0.65 dm⁴ mol^?4 s^?1 at 1 M ionic strength and k₁ = 2.60 dm³ mol³ s^?1and k₂ = 1.05 dm⁴ mol^?4 s^?1 at 2 M ionic strength. A mechanism explaining this rate law, with Br₂O₂ as key intermediate species, is proposed. Errors that may occur when using the Guggenheim method are discussed. © 2006 Wiley Periodicals, Inc. Int J Chem Kinet 39: 17–21, 2007     

Zum Mechanismus Massenspektrometrischer Fragmentierungsreaktionen—IV: Zur Bildung von Phenonium-Ionen bei der Elektronenstoß-Fragmentierung von ß-Phenyläthylbromiden

The apparently equal binding of all 9 H-atoms, demonstrated with the aid of deuterium labeling by N. M. M. Nibbering et al.,³ in [C₈H₉]⁺-ions generated from β-phenylethyl bromides has been confirmed. This result has been explained by a cyclooctatrienyl structure (a) of the ions. A comparison of the heats of formation of [C₈H₉]⁺-ions of different origin reveals, however, that this is not true for [C₈H₉]⁺-ions of β-phenylethyl bromide in the ground state. As a result of a study of the influence of substituents at the phenylring of β-phenylethyl bromide on the intensities of the [M ? Br]⁺-ions, R. H. Shapiro et al.⁴ proposed a phenonium structure (c) for the [C₈H₉]⁺-ions. The substituent effect on intensities and AP of [M ? CH₂Br]⁺- and [M ? Br]⁺-ions of β-phenylethyl bromides is quite different and can be explained much better by a ‘classical’ structure of the [C₈H₉]⁺- ions. This structure can also be deduced by a comparison of the IP and AP of [M ? Br]⁺-ions of benzyl-, β-phenylethyl- and γ-phenylpropyl-bromide.     

Kinetics of electron transfer reactions of manganese (III) complexes of trans-cyclohexane-1,2-diamine,-NNN′N′-tetraacetic acid and 2,2′-bipyridyl with ascorbic acid in aqueous acid media

The kinetics of the reactions of manganese(III) complexes of trans-cyclohexane-1,2-diamine-NNN′N′-tetraacetic acid (H₄cydta) and 2,2′-bipyridyl (bpy) have been investigated in the acid ranges [H⁺] = 1.00 ×10⁻⁵ − 3.16 × 10⁻³ M and [H⁺] = 0.10 − 1.00 M, respectively, at different temperatures and at a constant ionic strength. Both the molecular and mono-anionic forms of ascorbic acid have been found to be reactive in the experimental acid ranges. The monoanionic species has been found to be more reactive than the molecular form. Attempts have been made to correlate the kinetic results in terms of the Marcus relationship for outer-sphere electron transfer reaction. Differences between the calculated rates (k_0.8) and experimental rates (k) by approximately four and seven orders of magnitude (k_0.8≪ k) suggest an innersphere pathway for the reaction of Mn(cydta)(H₂O)⁻. Inner-sphere reaction is also believed to be operative for the other reaction. The activation parameters have been evaluated and compared with other reported systems.     

Inner-sphere oxidation of 2-aminomethylpyridinecobalt(II) complex by N-bromosuccinimide

The kinetics of the oxidation of the 2-aminomethylpyridineCo^II complex by N-bromosuccinimide (NBS), have been studied in aqueous solutions under various conditions, and obey the following rate law:Rate = [NBS][Co(L)(H₂O)₂]²⁺[k₂₊k₃/[H⁺]]An inner-sphere mechanism is proposed for the oxidation pathway for both protonated and deprotonated complex species, with the formation of an intermediate, which is slowly converted into the final oxidation products. The reaction rate is increased by increasing the pH, T, [complex], and decreased by increasing ionic strength over the range studied.     

Kinetics of cerium (IV) oxidation of mandelic acid. Ionic strength and specific cation effects

The kinetics of the redox reaction between mandelic acid (MA) and ceric sulfate have been studied in aqueous sulfuric acid solutions and in H₂SO₄? MClO₄ (M⁺ = H⁺, Li⁺, Na⁺) and H₂SO₄? MHSO₄ (M⁺ = Li⁺, Na⁺, K⁺) mixtures under various experimental conditions of total electrolyte concentration (that is, ionic strength) and temperature. The oxidation reaction has been found to occur via two paths according to the following rate law: rate = k[MA] [Ce(IV)], where k = k₁ + k₂/(1 + a)²[HSO₄^?]² = k₁ + k₂/(1 + 1/a)²[SO₄^2?]², a being a constant. The cations considered exhibit negative specific effects upon the overall oxidation rate following the order H⁺ ? Li⁺ < Na⁺ < K⁺. The observed negative cation effects on the rate constant k₁ are in the order Na⁺ < Li⁺ < H⁺, whereas the order is in reverse for k₂, namely, H⁺ ? Li⁺ < Na⁺. Lithium and hydrogen ions exhibit similar medium effects only when relatively small amounts of electrolytes are replaced. The type of the cation used does not affect significantly the activation parameters.     

Kinetics and mechanism of the aquation of pentaaqua (trichloroacetato-O)-chromium(2+) ion

The kinetics of the aquation of (H₂O)₅Cr(O₂CCCl₃)²⁺ have been examined at 35–55°C and 1.00M ionic strength with [H⁺] = 0.01?1.00M. The reaction follows the rate equation -d ln [Cr_total]/dt = (a[H⁺]^?1 + b + c[H⁺])/(1 + d[H⁺]), where [Cr_total] is the stoichiometric concentration of the complex. At 45°C a = (1.41 ± 0.03) × 10^?7M/s, b = (1.66 ± 0.02) × 10^?5 s^?1, c = (7.0 ± 0.8) × 10^?5M^?1·S^?1 and d = 2.3 ± 0.3M^?1. Two mechanisms consistent with this rate law are discussed, with evidence being presented in favor of an ester hydrolysis mechanism involving steady-state intermediates. Equilibrium and activation parameters were determined.     

Kinetics and mechanism of silver(I)-catalysed oxidation of malonic acid by peroxodiphosphate in acetate buffers

Summary The kinetics of the silver(I)-catalysed oxidation of malonic acid by peroxodiphosphate (pdp) was studied in acetate buffers. The rate law as represented by-d[pdp]/dt = {(k ₁ K _inf2 ^sup-1 [H⁺]² + k ₂[H⁺] + k ₃ K ₃)/ ([H⁺]²/K ₂ + [H⁺] + K ₃)}[pdp][Ag(I)] conforms to the proposed mechanism. The rate is independent of malonic acid concentrations. Acetate ions do not affect the rate; however, the rate decreases as the ionic strength increases. A probable portrait of reaction events is suggested. A comparative analysis of the reactivity pattern of malonic acid towards peroxodiphosphate and peroxodisulphate in presence of silver(I) has been made.     

离子液体中13-芳基-5,7,12,14-四氢二苯并[b, i]氧杂蒽5,7,12,14(13H)-四酮衍生物的绿色高效合成

在离子液体[bmim+][BF4-]中高产率的合成了一系列13-芳基-5,7,12,14-四氢二苯并[b, i]氧杂蒽-5,7,12,14(13H)-四酮类化合物。该反应操作步骤简单,离子液体易于与产物分离,并且离子液体可以循环使用。     

Inner-sphere oxidation of iron(II) by tris(malonato)cobaltate(III)

The kinetics of oxidation of Fe²⁺ by [Co(C₃H₂O₄)₃]^3? in acidic solutions at 605 nm showed a simple first-order dependence in each reactant concentration. The second-order rate constant dependence on [H⁺] is in accordance with eqn (i) k₂ = k′₂ + k₃[H⁺] (i) where k′₂ and k₃ have values of 73.4 ± 14.0 M ^?1 s^?1 and 353 ± 41 M^?2 s^?1, respectively, at 1.0 M ionic strength (NaClO₄) and 25°C. At 310 nm the formation and decomposition of an intermediate, believed to be [FeC₃H₂O₄]⁺, was observed. The increase in the rate of oxidation with increasing [H⁺] was interpreted in terms of a “one-ended” dissociation mechanism which facilitates chelation of Fe₂₊ by the carbonyl oxygens of malonate in the transition state.     

A kinetic study on the iron(III)-promoted aquation of [Cr(C2O4)2(picolinato)]2− and [Cr(C2O4)2(2-pyridineacetato)]2− complexes

Two [Cr(C₂O₄)₂(AB)]^2– type complexes, obtained from the reaction of cis-[Cr(C₂O₄)₂(H₂O)₂]^– with the AB ligand, [AB = picolinic (pyac) or 2-pyridine-ethanoic acid (pyeac) anions], were converted into [Cr(C₂O₄)(pyac)(H₂O)₂]⁰ and [Cr(C₂O₄)(pyeac)(H₂O)₂]⁰ compounds, respectively via Fe^III-induced substitution of the oxalato ligand. The aquation products were separated chromatographically and their spectral characteristics and acid dissociation constants determined. The kinetics of the oxalato ligand substitution were studied with a 10–40 fold excess of Fe^III over [Cr^III] at [H⁺] = 0.2 M and at constant ionic strength 1.0 M (Na⁺, H⁺, Fe³⁺, ClO^– ₄). The reaction rate law is of the form: r = k _obs[Cr^III], where k _obs = kQ[Fe^III]/(1 + Q[Fe^III]). The first-order rate constants (k), preequilibria quotients (Q) and activation parameters derived from the k values have been determined. The reaction mechanism is discussed in terms of a Lewis acid catalyzed (induced) ligand substitution.     

The Protonation of Acetamide and Thioacetamide in Super­acidic Solutions: Crystal Structures of [H3CC(OH)NH2]+AsF6– and [H3CC(SH)NH2]+AsF6–

Acetamide and thioacetamide react with the superacid solutions HF/MF₅ (M = As, Sb) under formation of the corresponding salts [H₃CC(OH)NH₂]⁺MF₆^– and [H₃CC(SH)NH₂]⁺MF₆^– (M = As, Sb), respectively. The reaction of DF/AsF₅ with acetamide and thioacetamide lead to the corresponding deuterated salts [H₃CC(OD)ND₂]⁺AsF₆^– and [H₃CC(SD)ND₂]⁺AsF₆^–, respectively_. The salts are characterized by vibrational and NMR spectroscopy, and in the case of [H₃CC(OH)NH₂]⁺AsF₆^– and [H₃CC(SH)NH₂]⁺AsF₆^– also by single‐crystal X‐ray analyses. The [H₃CC(OH)NH₂]⁺AsF₆^– ( 1 ) salt crystallizes in the triclinic space group P$\bar{1}$ with two formula units per unit cell, and the [H₃CC(SH)NH₂]⁺AsF₆^– ( 2 ) salt crystallizes in the monoclinic space group P2₁/c with four formula units per unit cell. In both crystal structures three‐dimensional networks are observed which are formed by intra‐ and intermolecular N–H ··· F and O–H ··· F or S–H ··· F hydrogen bonds, respectively. For the vibrational analyses, quantum chemically calculated spectra of the cations [H₃CC(OH)NH₂ · 3HF]⁺ and [H₃CC(SH)NH₂ · 2HF]⁺ are considered.     

Collisional activation study of cyclic polysulfides

Cyclic polysulfides isolated from higher plants, model compounds and their electron impact induced fragment ions have been investigated by various mass spectrometric methods. These species represent three sets of sulfur compounds: C₃H₆S_x (x=1?6), C₂H₄S_x (x=1?5) and CH₂S_x (x=1?4). Three general fragmentation mechanisms are discussed using metastable transitions: (1) the unimolecular loss of structural parts (CH₂S, CH₂ and S_x); (2) fragmentations which involve ring opening reactions, hydrogen migrations and recyclizations of the product ions ([M? CH₃]⁺, [M? CH₃S]⁺, [M? SH]⁺ and [M? CS₂]^+˙); and (3) complete rearrangements preceding the fragmentations ([M? S₂H]⁺ and [M? C₂H₄]^+˙). The cyclic structures of [M]^+˙ and of specific fragment ions have been investigated by comparing the collisional activation spectra of model ions. On the basis of these results the cyclic ions decompose via linear intermediates and then recyclizations of the product ions occur. The stabilities of the fragment ions have been determined by electron efficiency vs electron energy curves.     

Metastable ion studies. IV—thermochemistry and ion structures among fragmenting [C3H6]+· ions

Metastable ion peak shapes, dimensions and relative abundances have been measured for the three fragmentations [C₃H₆]⁺· → [C₃H₄]⁺· + H₂, [C₃H₆]⁺· → [C₃H₅]⁺ + H· and [C₃H₆]⁺· → [C₃H₃]⁺ + H₂ + H·. [C₃H₆]⁺· ions were derived from propene, cyclopropane, tetrahydrofuran, cyclohexanone, 2-methyl but-1-ene and cis-pent-2-ene. Activation energies for these fragmentations have been evaluated. Three daughter ion dissociations ([C₃H₅]⁺ → [C₃H₃]⁺ + H₂, [C₃H₅]⁺ → [C₃H₄]⁺· + H· and [C₃H₄]⁺· → [C₃H₃]⁺ + H·) have been similarly examined. Ion structures have been determined and the metastable energy releases have been correlated with the thermochemical data. It is concluded that the molecular ions of propene and cyclopropane become structurally indistinguishable prior to fragmentation and that differences in their metastable ion characteristics can be ascribed wholly to internal energy differences; the latter can be correlated with the photoelectron spectra of the isomers. The pathway for the consecutive fragmentation which generates the metastable ion peak (m/e 42 → m/e.39) has been shown to be It is likewise concluded that fragmentating [C₃H₆]⁺· ions generated from the various precursor molecules are also structurally indistinguishable and cannot be classified with either molecular ion of the isomeric C₃H₆ hydrocarbons.     

Thermal Activation of CH4 and H2 as Mediated by the Ruthenium Oxide Cluster Ions [RuOx]+ (x=1–3): On the Influence of Oxidation States

Thermal gas-phase reactions of the ruthenium-oxide clusters [RuO_x]⁺ (x=1–3) with methane and dihydrogen have been explored by using FT-ICR mass spectrometry complemented by high-level quantum chemical calculations. For methane activation, as compared to the previously studied [RuO]⁺/CH₄ couple, the higher oxidized Ru systems give rise to completely different product distributions. [RuO₂]⁺ brings about the generations of [Ru,O,C,H₂]⁺/H₂O, [Ru,O,C]⁺/H₂/H₂O, and [Ru,O,H₂]⁺/CH₂O, whereas [RuO₃]⁺ exhibits a higher selectivity and efficiency in producing formaldehyde and syngas (CO+H₂). Regarding the reactions with H₂, as compared to CH₄, both [RuO]⁺ and [RuO₂]⁺ react similarly inefficiently with oxygen-atom transfer being the main reaction channel; in contrast, [RuO₃]⁺ is inert toward dihydrogen. Theoretical analysis reveals that the reduction of the metal center drives the overall oxidation of methane, whereas the back-bonding orbital interactions between the cluster ions and dihydrogen control the H−H bond activation. Furthermore, the reactivity patterns of [RuO_x]⁺ (x=1–3) with CH₄ and H₂ have been compared with the previously reported results of Group 8 analogues [OsO_x]⁺/CH₄/H₂ (x=1–3) and the [FeO]⁺/H₂ system. The electronic origins for their distinctly different reaction behaviors have been addressed.     

Ion–molecule reaction in the gas phase 3—nucleophilic substitution of 17ξ-R-5α,14β-androstane-14,17ξ-diols under [NH4]+ chemical ionization conditions1

Under Ammonia chemical Ionization conditions the source decompositions of [M + NH₄]⁺ ions formed from epimeric tertiary steroid alchols 14 OH_β, 17OH_α or 17 OH_β substituted at position 17 have been studied. They give rise to formation of [M + NH₄? H₂O]⁺ dentoed as [MH_sH]⁺, [M_sH? H₂O]⁺, [M_sH? NH₃]⁺ and [M_sH? NH₃? H₂O]⁺ ions. Stereochemical effects are observed in the ratios [M_sH? H₂O]⁺/[M_sH? NH₃]⁺. These effects are significant among metastable ions. In particular, only the [M_sH]⁺ ions produced from trans-diol isomers lose a water molecule. The favoured loss of water can be accounted for by an S_N2 mechanism in which the insertion of NH₃ gives [M_sH]⁺ with Walden inversion occurring during the ion-molecule reaction between [M + NH₄]⁺ + NH₃. The S_N1 and S_Ni pathways have been rejected.     

Stability of crown-ether complexes with alkali-metal ions in ionic liquid-water mixed solvents

Stability constants of sodium and cesium ion complexes with 18-crown-6 (18C6) and dibenzo-18-crown-6 (DB18C6) in N-butyl-4-methyl-pyridinium tetrafluoroborate [BMP][BF₄] aqueous solutions were measured using the ²³Na and ¹³³Cs NMR technique at 23 °C. To the best of our knowledge, the estimated values of stability constants reported in this study are the first such values given for ionic liquid solutions. The cationic exchange between the free and complexed species is rapid, and only formation of the 1:1 complexes [M(18C6)]⁺ and [M(DB18C6)]⁺ (M = Na⁺, Cs⁺) were observed. The complex formation constants demonstrated a strong dependence on the [BMP][BF₄] concentration. For [M(18C6)]⁺, in solutions with a 0.33–0.70 mole fraction of water in [BMP][BF₄], lg K values are found to be more than one unit higher than the lg K values measured in pure aqueous solutions, although no information concerning the influence of [BMP][BF₄] on the complex formation selectivity could be observed. DB18C6 complexes revealed significantly lower stability under the same conditions. An extrapolation to zero water content gave the lg K = 2.42 for [Cs(18C6)]⁺ in [BMP][BF₄]. It was discovered that when added to water, [BMP][BF₄] increases the solubility of crown ethers and decreases the solubility of alkali metal nitrates. Complex formation with crown ethers enhances the solubility of alkali metal salts in [BMP][BF₄].     

Positive chemical ionization triple‐quadrupole mass spectrometry and ab initio computational studies of the multi‐pathway fragmentation of phthalates

We report the first positive chemical ionization (PCI) fragmentation mechanisms of phthalates using triple‐quadrupole mass spectrometry and ab initio computational studies using density functional theories (DFT). Methane PCI spectra showed abundant [M + H]⁺, together with [M + C₂H₅]⁺ and [M + C₃H₅]⁺. Fragmentation of [M + H]⁺, [M + C₂H₅]⁺ and [M + C₃H₅]⁺ involved characteristic ions at m/z 149, 177 and 189, assigned as protonated phthalic anhydride and an adduct of phthalic anhydride with C₂H₅⁺ and C₃H₅⁺, respectively. Fragmentation of these ions provided more structural information from the PCI spectra. A multi‐pathway fragmentation was proposed for these ions leading to the protonated phthalic anhydride. DFT methods were used to calculate relative free energies and to determine structures of intermediate ions for these pathways. The first step of the fragmentation of [M + C₂H₅]⁺ and [M + C₃H₅]⁺ is the elimination of [R? H] from an ester group. The second ester group undergoes either a McLafferty rearrangement route or a neutral loss elimination of ROH. DFT calculations (B3LYP, B3PW91 and BPW91) using 6‐311G(d,p) basis sets showed that McLafferty rearrangement of dibutyl, di(‐n‐octyl) and di(2‐ethyl‐n‐hexyl) phthalates is an energetically more favorable pathway than loss of an alcohol moiety. Prominent ions in these pathways were confirmed with deuterium labeled phthalates. Copyright © 2010 John Wiley & Sons, Ltd.