Diffusion kinetics of the ion exchange of benzocaine on sulfocationites

The theory of the ion exchange kinetics on strong acid cationites with the participation of weak electrolytes is discussed. The kinetics of desorption of benzocaine in the protonated and molecular forms from strong acid cationites, sulfonated polycalixarene, and KU-23 30/100 sulfocationite, is studied experimentally. It is shown that the flow of protonated benzocaine from cationite upon desorption proceeding by the ion-exchange mechanism is more intense than upon desorption of nonionized benzocaine molecules. It is established that the diffusion coefficient of benzocaine cations is (1.21 ± 0.23) × 10^?12 m²/s in KU-23 30/100 sulfocation and (0.65 ± 0.06) × 10^?13 m²/s in sulfonated polycalixarene, while the diffusion coefficient of benzocaine molecules is (0.65 ± 0.15) × 10^?14 m²/s in sulfonated polycalixarene.     

The Mechanism of Acid-Catalyzed Nucleophilic Substitution in Decahydro-closo-Decaborate(2–) Anions

The reactions of salts formed by the B₁₀H^2– ₁₀anion with carboxylic acids were studied. From the model systems Cat₂B₁₀H₁₀+ HCOOH (Cat = Et₄N⁺, Bu₄N⁺, Ph₄P⁺, Ph₄As⁺), several intermediates were isolated and characterized. A mechanism was proposed for the replacement of the exo-polyhedral hydrogen atoms in B₁₀H^2– ₁₀by carboxylate groups in the reactions of Cat₂B₁₀H₁₀with carboxylic acids.     

Kinetics and mechanism of autocatalyzed reaction between Phenyl Hydrazine and Toluidine blue in aqueous solution

The kinetics and mechanism of reduction of aqueous toluidine blue (TB⁺) by phenyl hydrazine (Pz), which exhibits nonlinear behavior, is studied spectrophotometrically at 630 nm. Typical kinetic curves exhibited autocatalytic characteristics. The role of H⁺ as an autocatalyst is established. Rate constants for the uncatalyzed and acid catalyzed reactions are determined. The forward rate constants for the uncatalyzed and acid catalyzed reactions were 1.4 × 10⁻² M⁻¹ s⁻¹ and 60 M⁻¹ s⁻¹. Reaction products are toluidine white, phenol, and an azo dye. From the stoichiometric ratios, the major reaction is Pz + 2 TB⁺ + H₂O = PhOH + 2 TBH + 2 H⁺ + N₂. The rate expression and a detailed 12‐step reaction mechanism supported by simulations are proposed. ©1999 John Wiley & Sons, Inc. Int J Chem Kinet: 31: 83–88, 1999     

Electrochemical reduction of 5,5′-dichlorohydurilic acid. mechanism and analytical applications

The electrochemical reduction of 5,5′-dichlorohydurilic acid has been studied at the dropping mercury electrode (DME) and the pyrolytic graphite electrode (PGE). At the DME the single polarographic reduction wave observed at pH 6–11 involves a direct 4e—2H⁺ reduction of the carbon-halogen bond to give hydurilic acid and chloride. The state of hydration or ionization of the 5,5′-dichlorohydurilic acid has no effect on the electrochemical reaction. At the PGE, 5,5′-dichlorohydurilic acid shows two voltammetric peaks. Peak I_c, observed between pH 5 and 7, arises from an overall 4e—2H⁺ reduction of 5,5′-dichlorohydurilic acid via a mechanism that involves initial electron attack at a carbonyl group alpha to a carbon-halogen bond with simultaneous elimination of chloride ion. The peak II_c process involves an initial 2e—1H⁺ reduction of a partially hydrated form of 5,5′-dichlorohydurilic acid with only one unhydrated halocarbonyl moiety available for reaction. Attack is again via the carbonyl group with simultaneous elimination of chloride and formation of 5-chlorohydurilic acid. A chemical dehydration step then occurs with a rate constant of ca. 0.24 s^?1 at pH 8.2, with formation of a further reducible halocarbonyl group. This is again reduced in an overall 2e—2H⁺ reaction to give hydurilic acid and chloride ion. The peak II_c process hence proceeds via an ECE mechanism. The different mechanisms observed for reduction of 5,5′-dichlorohydurilic acid at mercury and pyrolytic graphite electrodes are unusual. Analytical methods have been developed for the polarographic determination of 5,5′-dichlorohydurilic acid via its reduction wave at the DME, and for the voltammetric determination of hydurilic acid via its first oxidation peak at the PGE.     

Sorption and conducting properties of perfluorinated MF-4SC membranes in aqueous solutions containing phenylammonium ions

A comparative study of the sorption effect is performed for nitrogen-containing ammonium, phenylammonium (PhA⁺), and tetrabutylammonium (TBA⁺) cations on conducting and hydrophilic properties of protonic form of perfluorinated sulfocationite MF-4SC membrane. Conductometric method was used to study thermodynamic equilibria in the systems of perfluorinated MF-4SC membrane—aniline in the acid solutions of variable composition (PhA⁺/HCl and PhA⁺/H₂SO₄). Concentration constants of ion-exchange equilibrium are calculated for a MF-4SC membrane on the basis of these data. These constants in the solutions of aniline with HCl and H₂SO₄ are 10.3 and 27.0, accordingly. The choice of sulfuric acid as background electrolyte for matrix polyaniline synthesis is substantiated.     

[2,6(9)-B10H8>(O)2CCH3]− and [2,7(8)-B10H8(OC(O)CH3)2]2− derivatives in synthesis of position isomers of the [B10H8(OC(O)CH3)(OH)]2− anion with the 2,6(9)- and 2,7(8)-arrangement of functional groups

The interaction of Cat₂B₁₀H₁₀ (Cat = Ph₄P⁺, Ph₄As⁺) with acetic acid has been studied. Disubstituted closo-decaborate derivatives with a bidentately bound acetate group, Cat[2,6(9)-B₁₀H₈>(O)₂CCH₃], or two monodentate acetate groups, Cat₂[2,7(8)-B₁₀H₈(OC(O)CH₃)₂], have been isolated (Cat = Ph₄P⁺, Ph₄As⁺). Hydrolysis of these compounds has led to the position isomers of the [B₁₀H₈(OC(O)CH₃)(OH)]^2? anion with the hydroxo and acetate groups in the 2,6(9)- and 2,7(8)-positions. The structures of {Pb(Bipy)₂[2,6(9)-B₁₀H₈(OC(O)CH₃)(OH)]}₂ · 3H₂O, (Ph₄As)₂[2,6(9)-B₁₀H₈(OC(O)CH₃)(OH)] · 0.4C₂H₅OH · 0.25H₂O, and (Ph₄As)₂[2,7(8)-B₁₀H₈(OC(O)CH₃)(OH)], as well as of the product of the reaction of the B₁₀H ₁₀ ^2? anion with formic acid (Ph₄P)₂[2-B₁₀H₉OC(O)H] · CH₃CN, have been determined by X-ray crystallography.     

One‐dimensional hydrogen‐bonded structures in the 1:1 proton‐transfer compounds of 4,5‐dichlorophthalic acid with 8‐hydroxyquinoline, 8‐aminoquinoline and quinoline‐2‐carboxylic acid (quinaldic acid)

The structures of the 1:1 proton‐transfer compounds of 4,5‐dichlorophthalic acid with 8‐hydroxyquinoline, 8‐aminoquinoline and quinoline‐2‐carboxylic acid (quinaldic acid), namely anhydrous 8‐hydroxyquinolinium 2‐carboxy‐4,5‐dichlorobenzoate, C₉H₈NO⁺·C₈H₃Cl₂O₄⁻, (I), 8‐aminoquinolinium 2‐carboxy‐4,5‐dichlorobenzoate, C₉H₉N₂⁺·C₈H₃Cl₂O₄⁻, (II), and the adduct hydrate 2‐carboxyquinolinium 2‐carboxy‐4,5‐dichlorobenzoate quinolinium‐2‐carboxylate monohydrate, C₁₀H₈NO₂⁺·C₈H₃Cl₂O₄⁻·C₁₀H₇NO₂·H₂O, (III), have been determined at 130 K. Compounds (I) and (II) are isomorphous and all three compounds have one‐dimensional hydrogen‐bonded chain structures, formed in (I) through O—H...O_carboxyl extensions and in (II) through N⁺—H...O_carboxyl extensions of cation–anion pairs. In (III), a hydrogen‐bonded cyclic R₂²(10) pseudo‐dimer unit comprising a protonated quinaldic acid cation and a zwitterionic quinaldic acid adduct molecule is found and is propagated through carboxylic acid O—H...O_carboxyl and water O—H...O_carboxyl interactions. In both (I) and (II), there are also cation–anion aromatic ring π–π associations. This work further illustrates the utility of both hydrogen phthalate anions and interactive‐group‐substituted quinoline cations in the formation of low‐dimensional hydrogen‐bonded structures.     

Inorganic reactions of iodine(+1) in acidic solutions

We present a thorough analysis of the former works concerning the hydrolysis of iodine and its mechanism in acidic or neutral solutions and recommend values of equilibrium and kinetic constants. Since the literature value for the reaction H₂OI⁺ ? HOI + H⁺ appeared questionable, we have measured it by titration of acidic iodine solutions with AgNO₃. Our new value, K(H₂OI⁺ ? HOI + H⁺) ～ 2 M at 25°C, is much larger than accepted before. It decreases slowly with the temperature. We have also measured the rate of the reaction 3HOI → IO₃^? + 2I^? + 3H⁺ in perchloric acid solutions from 5 × 10^?2 M to 0.5 M. It is a second order reaction with a rate constant nearly independent on the acidity. Its value is 25 M^?1 s^?1 at 25°C and decreases slightly when the temperature increases, indicating that the disproportionation mechanism is more complicated than believed before. An analysis of the studies of this disproportionation in acidic and slightly basic solutions strongly supports the importance of a dimeric intermediate 2HOI ? I₂O·H₂O in the mechanism. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36:480–493, 2004     

Formation of H3O+ from alcohols and ethers induced by intense laser fields

The processes of H₃O⁺ production from alcohols (ethanol, 2‐propanol, 1‐propanol, 2‐butanol) and ethers (diethyl ether and ethyl methyl ether), and their deuterium‐substituted species, by intense laser fields (800 nm, 100 fs, ～1 × 10¹⁴ W/cm) were investigated through time‐of‐flight (TOF) mass spectrometry. H₃O⁺ formation was observed for all these compounds except for ethyl methyl ether. From the analysis of TOF signals of H_(3?n)D_nO⁺ (n = 0, 1, 2, and 3) that have expanding tails with increasing flight time, it has been confirmed that the reaction proceeds through metastable dissociation from the intermediate species C₂H_(5?m)D_mO⁺(m = 0–5). The common shape of the H_(3?n)D_nO⁺ signal profiles contains two major distributions in the time constant, i.e., fast and slow components of <50 ns and ～500 ns, respectively. The H_(3?n)D_nO⁺ branching ratio is interpreted to be the result of complete scrambling of four hydrogen atoms at the C? C site in C₂H₄‐OH⁺, and partial exchange (18–38%) of a hydrogen atom in the OH group with four other hydrogen atoms within 1 ns prior to H_(3?n)D_nO⁺ production. Ab initio calculations for the isomers and transition states of C₂H₅O⁺ were also performed, and the observed H_(3?n)D_nO⁺ production mechanism has been discussed. In addition, a stable isomer having a complex structure and two isomerization pathways were discovered to contribute to the H₃O⁺ formation process. Copyright © 2010 John Wiley & Sons, Ltd.     

Six two‐ and three‐component ammonium carboxylate salt structures with a ladder‐type hydrogen‐bonding motif,three incorporating neutral carboxylic acid molecules

Six ammonium carboxylate salts are synthesized and reported, namely 2‐propylammonium benzoate, C₃H₁₀N⁺·C₇H₅O₂⁻, (I), benzylammonium (R)‐2‐phenylpropionate, C₆H₁₀N⁺·C₉H₉O₂⁻, (II), (RS)‐1‐phenylethylammonium naphthalene‐1‐carboxylate, C₈H₁₂N⁺·C₁₁H₇O₂⁻, (III), benzylammonium–benzoate–benzoic acid (1/1/1), C₆H₁₀N⁺·C₇H₅O₂⁻·C₇H₆O₂, (IV), cyclopropylammonium–benzoate–benzoic acid (1/1/1), C₃H₈N⁺·C₇H₅O₂⁻·C₇H₆O₂, (V), and cyclopropylammonium–ea‐cis‐cyclohexane‐1,4‐dicarboxylate–ee‐trans‐cyclohexane‐1,4‐dicarboxylic acid (2/1/1), 2C₃H₈N⁺·C₈H₁₀O₄²⁻·C₈H₁₂O₄, (VI). Salts (I)–(III) all have a 1:1 ratio of cation to anion and feature three N⁺—H...O⁻ hydrogen bonds which form one‐dimensional hydrogen‐bonded ladders. Salts (I) and (II) have type II ladders, consisting of repeating R₄³(10) rings, while (III) has type III ladders, in this case consisting of alternating R₄²(8) and R₄⁴(12) rings. Salts (IV) and (V) have a 1:1:1 ratio of cation to anion to benzoic acid. They have type III ladders formed by three N⁺—H...O⁻ hydrogen bonds, while the benzoic acid molecules are pendant to the ladders and hydrogen bond to them via O—H...O⁻ hydrogen bonds. Salt (VI) has a 2:1:1 ratio of cation to anion to acid and does not feature any hydrogen‐bonded ladders; instead, the ionized and un‐ionized components form a three‐dimensional network of hydrogen‐bonded rings. The two‐component 1:1 salts are formed from a 1:1 ratio of amine to acid. To create the three‐component salts (IV)–(VI), the ratio of amine to acid was reduced so as to deprotonate only half of the acid molecules, and then to observe how the un‐ionized acid molecules are incorporated into the ladder motif. For (IV) and (V), the ratio of amine to acid was reduced to 1:2, while for (VI) the ratio of amine to acid required to deprotonate only half the diacid molecules was 1:1.     

Kinetics and mechanism of reduction of 2,8-dimethyl-1,9-diphenyl-3,7-diaza-2,7-nonadiene-1,9-dione dioximatocopper(III) ([CuIII A]+) and 4,6,9-trimethyl-5,8-diaza-4,8-dodecadiene-2,3,10,11-tetraone 3,10-dioximatocopper(III) ([CuIIIB]+) by p-methoxyphenol, 1,2-dihydroxybenzene, 1,4-dihydroxybenzene and some of its derivatives

The kinetics of reduction of two copper(III)-imine-oxime complexes, [Cu^IIIA]⁺ and [Cu^IIIB]⁺, (H₂A and H₂B=2,8-dimethyl-1,9-diphenyl-3,7-nonadiene-1,9-dione dioxime and 4,6,9-trimethyl-5,8-diaza-4,8-dodecadiene-2,3,10,11-tetraone 3,10-dioxime respectively) by hydroquinone (H₂Q), 2-methylhydroquinone (MH₂Q), 2-chlorohydroquinone (ClH₂Q), catechol (H₂Cat) and p-methoxyphenol (pMHP) have been examined in aqueous acidic solution. Under fixed reaction conditions, the kinetics display first-order dependence on each oxidant and reductant. The pH-dependence is complex for the reduction of [Cu^IIIA]⁺, since both the copper(III) complex and the reductants undergo protonation–deprotonation equilibria. In the lower pH range, the second-order rate constant, k ₂, decreases with increasing pH. In the higher pH range, k ₂ increases with increasing pH. In the lower pH range the most important oxidant is [Cu^IIIHA]²⁺, whereas, in the higher pH range the most important reactants are deprotonated reductants. However for H₂Cat, as was observed before, two reaction pathways seem to operate in the high pH range. In one pathway, HCat^? seems to be involved; whereas, in the other pathway Cat^2? seems to be the reactive species. Doubly deprotonated catechol, Cat^2?, is very unlikely to be formed at pH ≤ 5. It was therefore necessary to invoke a strong interaction between [Cu^IIIA]⁺ and HCat^? followed by loss of the second proton. The pH dependence for the reduction of [Cu^IIIB]⁺ is less complex. Thus H₂Q and MH₂Q showed no pH dependence up to pH ～ 4.60, whereas ClH₂Q, pMHP and H₂Cat displayed an inverse first-order dependence on [H⁺]. Observed rate constants showing first-order dependence and inverse first-order dependence on [H⁺] correlate reasonably well with those calculated using the Marcus equation. The reaction path involving Cat^2? is believed to proceed by an inner-sphere mechanism. The agreement between the calculated and observed values for the [Cu^IIIA]⁺ complex is lower than was found for the [Cu^IIIA₁]⁺(A₁=3,9-diethyl-4,8-diaza-3,8-undeca-2,10-dionedioxime). It seems that the replacement of methyl groups in the latter complex by phenyl groups in the former complex causes both electronic and steric effects, and both effects seem to retard electron transfer. The electronic effect is readily seen in the decrease of the reduction potential of [Cu^IIIA]⁺ (E ⁰=1.09 V) compared to the reduction potential of [Cu^IIIA₁]⁺(E ⁰=1.16 V) and thus making the former a weaker oxidant. The self-exchange rate constant (5 × 10⁵ M ^?1 s^?1) estimated for complexes with type H₂A ligands seem to work well for complexes with type H₂B ligands. This situation is supported by the findings of a fairly constant value for the self-exchange rate constant for Cu ^III/II –peptide complexes with varying substituents.     

Inorganic reactions of iodine(III) in acidic solutions and free energy of iodous acid formation

An analysis of the former works devoted to the reactions of I(III) in acidic nonbuffered solutions gives new thermodynamic and kinetic information. At low iodide concentrations, the rate law of the reaction IO + I^? + 2H⁺ ? IO₂H + IOH is k_+B [IO][I^?][H⁺]² – k_?B [IO₂H][IOH] with k_+B = 4.5 × 10³ M^?3s^?1 and k_?B = 240 M^?1s^?1 at 25°C and zero ionic strength. The rate law of the reaction IO₂H + I^? + H⁺ ? 2IOH is k_+C [IO₂H][I^?][H⁺] – k_?C [IOH]² with k_+C = 1.9 × 10¹⁰ M^?2s^?1 and k_?C = 25 M^?1s^?1. These values lead to a Gibbs free energy of IO₂H formation of ?95 kJ mol^?1. The pK_a of iodous acid should be about 6, leading to a Gibbs free energy of IO formation of about ?61 kJ mol^?1. Estimations of the four rate constants at 50°C give, respectively, 1.2 × 10⁴ M^?3s^?1, 590 M^?1s^?1, 2 × 10⁹ M^?2s^?1, and 20 M^?1 s^?1. Mechanisms of these reactions involving the protonation IO₂H + H⁺ ? IO₂H and an explanation of the decrease of the last two rate constants when the temperature increases, are proposed. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 40: 647–652, 2008     

Ion-neutral complex-mediated hydrogen exchange in ionized n-butanol: A mechanism for ‘non-specific’ hydrogen migrations

Water elimination from ionized n-butanol reflects near randomization of all hydrogens in ions decomposing after ～10^?5s. This probably takes place in ion-neutral complexes by formation of a cyclobutane ion–H₂O complex and/or rearrangement within [C₄H₈]⁺˙ in open-chain [C₄H₈⁺˙? H₂O] complexes, in either case accompanied by hydrogen exchange between water and open-chain hydrocarbon moieties. Extensive hydrogen rearrangements in which restraints on conventional transition-state ring size have little apparent influence may generally be ion–neutral complex-mediated processes.     

Untersuchungen im System Al3+?WO42−?H2O?H3O+

Investigations in the System Al³⁺? WO₄^2?? H₂O? H₃O⁺ The composition of the tungstoaluminate anion [AlW₁₂O₄₀]^5? was determined by means of the molar ratio and JOB 's method of continuous variations modified by us. The optimum conditions for the complex formation in the system Al³⁺? WO₄^2?? H₂O? H₃O⁺ were determined: 1.33 ≤ acid degree Z ≤ 2.5; 105°C; 2–6h (c = 7.15 · 10^?2–6 · 10^?3 moles · l^?1). The complex formation in dependence on the acid degree Z is complete at Z = 16 H₃O⁺/12 WO₄^2? = 1.33.     

Mechanism of electron transfer reaction of ternary nitrilotriacetatocobalt(II) complexes involving succinate and malonate as secondary ligands

The mechanism of oxidation of ternary complexes, [Co^II(nta)(S)(H₂O)₂]^3? and [Co^II(nta)(M)(H₂O)]^3? (nta = nitrilotriacetate acid, S = succinate dianion, and M = malonate dianion), by periodate in aqueous medium has been studied spectrophotometrically over the (20.0–40.0) ± 0.1°C range. The reaction is first order with respect to both [IO₄^?] and the complex, and the rate decreases over the [H⁺] range (2.69–56.20) × 10^?6 mol dm^?3 in both cases. The experimental rate law is consistent with a mechanism in which both the hydroxy complexes [Co^II(nta)(S)(H₂O)(OH)]^4? and [Co^II(nta)(M)(OH)]^4? are significantly more reactive than their conjugate acids. The value of the intramolecular electron transfer rate constant for the oxidation of the [Co^II(nta)(S)(H₂O)₂]^3?, k₁ (3.60 × 10^?3 s^?1), is greater than the value of k₆ (1.54 × 10^?3 s^?1) for the oxidation of [Co^II(nta)(M)(H₂O)]^3? at 30.0 ± 0.1°C and I = 0.20 mol dm^?3. The thermodynamic activation parameters have been calculated. It is assumed that electron transfer takes place via an inner‐sphere mechanism. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 40: 103–113, 2008     

The oxidation of thiosulphate ions by octacyanotungstate(V) in weak acidic medium

The kinetics of the oxidation of thiosulphate ions by octacyanotungstate(V) ions has been studied in the pH range 3.9–5.0. The reaction showed zero-order kinetics with respect to [W(CN)₈^3?] and is consistent with the rate law R = k[H⁺][S₂O₃^2?]². A reaction mechanism is proposed for the reaction with a third-order rate constant of 0.26 M^?2 s^?1 at 25°C.     

Infrared Spectrum of the Si3H8+ Cation: Evidence for a Bridged Isomer with an Asymmetric Three‐Center Two‐Electron Si?H?Si Bond

The IR spectrum of Si₃H₈⁺ ions produced in a supersonic plasma molecular beam expansion of SiH₄, He, and Ar is inferred from photodissociation of cold Si₃H₈⁺–Ar complexes. Vibrational analysis of the spectrum is consistent with a Si₃H₈⁺ structure ( 2⁺ ) obtained by a barrierless addition reaction of SiH₄ to the disilene ion (H₂Si?SiH₂⁺) in the silane plasma. In this structure, one of the electronegative H atoms of SiH₄ donates electron density into the partially filled electrophilic π orbital of the disilene cation. The resulting asymmetric Si? H? Si bridge of the 2⁺ isomer with a bond energy of approximately 60 kJ mol^?1 is characteristic for a weak three‐center two‐electron bond, which is identified by its strongly IR active asymmetric Si? H? Si stretching fundamental at about 1765 cm^?1. The observed 2⁺ isomer is calculated to be only a few kJ mol^?1 less stable than the global minimum structure of Si₃H₈⁺ ( 1⁺ ), which is derived from vertical ionization of trisilane. Although more stable, 1⁺ is not detected in the measured IR spectrum of Si₃H₈⁺–Ar, and its lower abundance in the supersonic plasma is rationalized by the production mechanism of Si₃H₈⁺ in the silane plasma, in which a high barrier between 2⁺ and 1⁺ prevents the efficient formation of 1⁺ . The potential energy surface of Si₃H₈⁺ is characterized in some detail by quantum chemical calculations. The structural, vibrational, electronic and energetic properties as well as the chemical bonding mechanism are investigated for a variety of low‐energy Si₃H₈⁺ isomers and their fragments. The weak intermolecular bonds of the Ar ligands in the Si₃H₈⁺–Ar isomers arise from dispersion and induction forces and induce only a minor perturbation of the bare Si₃H₈⁺ ions. Comparison with the potential energy surface of C₃H₈⁺ reveals the differences between the silicon and carbon species.     

Small-angle neutron-scattering study of bis(quaternaryammonium bromide) surfactant micelles in water. Effect of the long spacer chain on micellar structure

The microstructure of the normal micelles formed by dimeric surfactants with long spacers, [Br⁻(CH₃)₂N⁺(C _m H_{2 m +1})-(CH₂) _S  -(C _m H_{2 m +1})N⁺(CH₃)₂Br⁻, m = 10 and s = 8, 10 and 12], has been investigated by small-angle neutron scattering and compared with previously reported results for micelles of the same dimeric surfactants with shorter spacers (m = 10 and s = 2, 3, 4 and 6). It was found that for dimeric surfactants with long spacers (s = 8 and 10), both micellar growth and variation in shape occur to only a small extent, if at all, compared with dimeric surfactants with short spacers. However, for the dimeric surfactant with the longest spacer, s = 12, the extent of micellar growth and shape variation is also large. These results are due to the differences in conformation of dimeric surfactants with short spacers (s = 2–6) compared with that of the surfactants with long spacers (s = 8–12). Received: 15 June 1998 Accepted: 22 July 1998     

Contribution from the ion-exchange factor to the potential of a copper-containing electron-ion exchanger

The process of formation of the electrode potential of EI-21 electron-ion exchanger, composed of ultrafine copper particles and KU-23 sulfocationite, was studied. The potentials of a EI-21 powdery electrode with a platinum lead in copper(II) sulfate solutions of various concentrations (0.005–1.0 M) were measured using currentless-mode potentiometry. The potential of this electrode first shifted by 0.02–0.15 V in the negative direction with respect to a compact copper electrode, after which the shift eventually decreased to ?0.010 ± 0.003 V. It was demonstrated that the time evolution of the potential is determined by the interplay of electron and ion exchange. When EI-21 is placed onto a platinum lead, the role of the potential-determining reaction passes from Cu²⁺ + e^? ? Cu⁺ to Cu²⁺ + 2e^? ? Cu. At the same time, H⁺-Cu²⁺ ion exchange gives rise to a change in the ratio of the concentration of copper(II) ions in the internal and external solutions. The Donnan potential, which arises at the boundary between the electron-ion exchanger and the external solution, maintains a high concentration of copper(II) ions in the internal solution, a factor that facilitates the recrystallization of the particle distributed over the bulk of the exchanger. The process of recrystallization slows down with time to such an extent that the electrode potential stops changing, remaining at a level close to the equilibrium potential of the Cu²⁺/Cu pair. It was concluded that the internal stability of the system makes the potential of the EI-21 electrode sensitive to the dispersity of the metal component and the concentration of potential-determining metal ions in the external solution.     

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.