Synthesis,Characterization and Evaluation of the Surface Active Properties of Novel Cationic Imidazolium Gemini Surfactants

New imidazolium gemini surfactants were synthesized by reaction of epichlorohydrin with long chain fatty alcohols furnishing products 2-(alkoxymethyl)oxirane followed by their subsequent treatment with imidazole resulting in the formation of 1-(1H-imidazol-1-yl-3 alkoxy)propane-2-ol which on subsequent treatment with 1,2-dibromoethane and 1,3-dibromopropane resulted in the formation of title gemini surfactants:1,2-bis(1(3-alkoxy-2-hydroxypropyl)-1H-imidazol-3-ium)ethane bromide (7), 1,3-bis(1(3-alkoxy-2-hydroxypropyl)-1H-imidazol-3-ium)propane bromide (8), 1,2-bis(1(3-alkoxy-2-hydroxypropyl)-1H-imidazol-3-ium)ethane bromide (9), 1,3-bis(1(3-alkoxy-2-hydroxypropyl)-1H-imidazol-3-ium)propane bromide (10), 1,2-bis (1(3-alkoxy-2-hydroxypropyl)-1H-imidazol-3-ium)ethane bromide (11) and 1,3-bis (1(3-alkoxy-2-hydroxypropyl)-1H-imidazol-3-ium)propane bromide (12). Their identification was based on IR, ¹H-, ¹³C-NMR, DEPT, COSY and mass spectral studies. Their surface active properties were also evaluated on the basis of surface tension and conductivity measurements.     

New mononuclear CuII and ZnII complexes capable of stabilizing phenoxyl radicals as models for the active form of galactose oxidase

Herein, we describe the synthesis and crystal structure of mononuclear Cu^II and Zn^II complexes containing the new pentadentate H₂L ligand (H₂L = N-(methyl)-N^′-(2-pyridylmethyl)-N,N^′-bis(3,5-di-tert-butyl-2-hydroxybenzyl)-1,3-propanediamine. The [Cu^II(L)] and [Zn^II(L)] complexes and their one-electron oxidized [Cu^II]⁺ ([1]⁺) and [Zn^II]⁺ ([2]⁺) compounds exhibit electrochemical and spectroscopic (UV–Vis and EPR) features with relevant insight into the oxidizing half-reaction of the metalloenzyme galactose oxidase.     

(R,R)-salen/salan-based polymer fluorescence sensors for Zn detection

(R,R)-salen-based polymer fluorescence sensor P-1 could be synthesized by the polymerization of 5,5′-(isoquinoline-5,8-diylbis(ethyne-2,1-diyl))-bis(3-tert-butyl-2-hydroxybenzaldehyde) (M-1) with (R,R)-1,2-diaminocyclohexane (M-2) via nucleophilic addition-elimination reaction, and (R,R)-salan-based polymer sensor P-2 could be obtained by the reduction reaction of P-1 with NaBH₄. The fluorescence response behaviors of two chiral polymers P-1 and P-2 on Zn²⁺ were investigated by fluorescence spectra. The fluorescence intensities of P-1 and P-2 can exhibit gradual enhancement upon addition of Zn²⁺. Compared with other cations, such as Na⁺, K⁺, Mg²⁺, Ca²⁺, Fe³⁺, Co²⁺, Ni²⁺, Cu²⁺, Ag⁺, Cd²⁺, Cr³⁺ and Pb²⁺, Zn²⁺ can lead to the pronounced fluorescence enhancement as high as 22.8-fold for P-1 and 3.75-fold for P-2, respectively. The results show that P-1 and P-2 incorporating (R,R)-salen/salan moieties as receptors in the polymer main chain backbone can exhibit high sensitivity and selectivity for Zn²⁺ detection.     

Tris(acrylato)uranylates as a scaffold for NLO materials

Novel uranyl acrylate complexes with general formula R[UO₂(CH₂CHCOO)₃] (RK⁺, NH₄⁺, Rb⁺, or Cs⁺) were synthesized and characterized by X-ray diffraction, IR spectroscopy and second harmonic generation (SHG) measurements. All four compounds are isostructural and crystallize in the non-centrosymmetric P2₁3 space group. Acrylate anions act as bidentate chelating ligands forming [UO₂(CH₂CHCOO)₃]⁻ complexes which are connected through electrostatic interactions with counter ions. SHG measurements revealed the inverted correlation between the Q = I_2ω/I_2ω SiO₂ values and the radii of counter ions.     

Synthesis and properties of chiral helical polymers based on optically active polybinaphthyls

The chiral polymer P-1 was synthesized by the polymerization of (R)-6,6′-dibutyl-3,3′-diiodo-2,2′-bisoctoxy-1,1′-binaphthyl (R-M-1) with 5,5′-divinyl-2,2′-bipyridine (M-1)via Pd-catalyzed Heck reaction. P-2 and P-2′ were prepared by Wittig-Horner reaction of (R)-6,6′-dibutyl-2,2′-bisoctoxy-1,1′-binaphthyl-3,3′-dicarbaldehyde (R-M-2) with 5,5′-bis (diethylphosphonomethyl)-2,2′-bipyridine (M-2) in the presence of EtONa or NaH, respectively. P-3 was synthesized by Wittig-Horner reaction of (R)-6,6′-di(4-trifluoromethylphenyl)-2,2′-bisoctoxy-1,1′-binaphthyl-3,3′-dicarbaldehyde (R-M-3) with M-2 using NaH as a base. The four polymers have strong blue-green fluorescence due to the extended π-electronic structure between the chiral model compounds (R)-6,6′-dibutyl-/di(4-trifluoromethylphenyl)-2,2′-bisoctoxy-1,1′-binaphthyl (R-1 or R-2) and the conjugated linker 2,2′-bipyridyl group via vinylene bridge. Both monomers and polymers were analyzed by NMR, MS, FT-IR, UV-vis spectroscopy, DSC-TGA, fluorescence spectroscopy, GPC and circular dichroism (CD) spectroscopy. Based on the great differences of specific rotation values and CD spectra, P-1 and P-2 may adopt a zigzag chain configuration, while P-2′ and P-3 may adopt a helical configuration. The responsive optical properties of the two chiral helical polymers P-2′ and P-3 on transition metal ions were investigated by fluorescence, UV-vis and CD spectra. The results show that Ag⁺ and Ni²⁺ lead to nearly complete fluorescence quenching of P-2′ and P-3, Cu²⁺ and Fe²⁺ can cause obvious fluorescence quenching, but Zn²⁺ and Cd²⁺ can only produce slight fluorescence quenching. Ag⁺, Ni²⁺, Cu²⁺ and Fe²⁺ can also lead to the obvious changes of UV-vis spectra of P-2′ and P-3. On the contrary, Zn²⁺ and Cd²⁺ cause little changes. Most importantly, the CD intensities and wavelengths of the chiral helical polymers P-2′ and P-3 exhibit the pronounced changes upon addition of Ag⁺ and Ni²⁺.     

A polymer based fluorescent sensor for Zn detection and its application for constructing logic gates

A polymer-based fluorescent sensor was synthesized by polymerization of (S)-6,6′-dibutyl-3,3′-(di-5-salicylde-ethynyl)-2,2′-binaphthol (M-1) with (R,R)-1,2-diaminocyclohexane (M-2) via nucleophilic addition-elimination reaction. The responsive optical properties of the polymer on transition metal ions were investigated by fluorescence and UV-vis spectra. The polymer (1.0 × 10⁻⁵ mol/L in THF) could emit fluorescence at 550 nm and exhibit high selectivity for sensing Zn²⁺ with 36.1-fold fluorescence enhancement. Three logic gates were designed according to the different fluorescence responses of this polymer sensor to Zn²⁺ and Cu²⁺.     

Estimation of standard reduction potentials of alkyl radicals involved in atom transfer radical polymerization

The redox properties of some alkyl radicals, which are important in atom transfer radical polymerization both as initiators and mimics of the propagating radical chains, have been investigated in CH₃CN by an indirect electrochemical method based on homogeneous redox catalysis involving alkyl halides (RX) and electrogenerated aromatic or heteroaromatic radical anions (D⁻). Dissociative electron transfer between RX and D⁻ yields an intermediate radical (R), which further reacts with D⁻ either by radical coupling or by electron transfer. Examination of the competition between these reactions, which depends on ED/D−°, allows determination of the standard reduction potential of R as well as the self-exchange reorganization energy λR/R⁻. The standard reduction potentials obtained for the radicals CH₂CN, CH₂CO₂Et and CH(CH₃)CO₂Me are −0.72 ± 0.06, −0.63 ± 0.07 and −0.66 ± 0.07 V vs. SCE, respectively. Quite high values of λR/R⁻ (from 122 to 164 kJ mol⁻¹) were found for all radicals, indicating that a significant change of structure accompanies electron transfer to R.     

Voltammetric characterization of selective potassium ion transfer across micro-water/1,2-dichloroethane interface facilitated by a novel calix[4]arene derivative

In this study, transfer reactions of alkali and alkaline-earth metal ions across a micro-water/1,2-dichloroethane (1,2-DCE) interface facilitated by a novel calix[4]arene derivative, 5,11,17,23-tetra-tert-butyl-25,27-bis(2′amino-methylpyridine)-26,28-dihydroxy calix[4]arene (APHC4), were investigated by cyclic and differential pulse voltammetry techniques. Well-defined voltammetric behavior was obtained only for K⁺ ion among the used metal ions. The electrochemical data were used to determine the stoichiometry and the appropriate association constant of the occurring complex between K⁺ ion and APHC4. The obtained steady-state voltammograms indicated that the facilitated transfer process occurs with a TIC/TID mechanism according to 1:1 stoichiometry. The logarithm of the association constant () of K(APHC4)⁺ complex in the DCE phase was calculated to be 6.32. Also, the availability of the facilitated transfer for the design of an amperometric screening sensor for K⁺ ion was evaluated in the range of 50–500 μmol dm⁻³.     

Structure-resonance theory and electrochemical oxidation potentials of π-electron hydrocarbons

The polarographic half-wave oxidation potentials of 51 benzenoid hydrocarbons are correlated with the logarithms of the structure counts of the neutral molecule and the radical cation, ln SC_R and ln SC_R⁺, respectively. For example, for 25 unsubstituted hydrocarbons and 26 methylsubstituted hydrocarbons, the following relationship was obtained: E_{$\text{1}\text{2}$}(ox) = 4.018 + 1.607 ln SC_R ?1.027 ln SC_R⁺; r = 0.955, s = ± 0.07. Such an excellent correlation indicates that effects associated with delocalization of π-electrons and the π-electron charge distribution in the neutral and charged molecular species, respectively, are significant in electrochemical oxidation, contrary to an earlier literature report which claimed that they are not. The results also show that the structure counts provide a simple working method for correlations of the electrochemical reactivities of polynuclear aromatic hydrocarbons and their derivatives.     

Study of Fe/Fe ratio in thin films of carbonate or sulphate green rusts obtained by potentiostatic electrosynthesis

Thin films of carbonate or sulphate green rusts were synthesised from potentiostatic oxidation of solutions containing ferrous species and bicarbonate or sulphate ions at slightly alkaline pHs and ambient temperature. The thin films were characterised by means of electrochemical quartz crystal microbalance, scanning electron microscopy, X-ray diffraction and infrared reflection-absorption spectroscopy. The composition of carbonate or sulphate green rusts was studied through chemical titration, inductively coupled plasma-optical emission spectroscopy (ICP-OES) and gravimetry and is as follows:

[Fe^II_(2R)Fe^III₂(OH)_{(4R−2R′+6)}(H₂O)_(2R′−2)]^2R′+·[R′CO₃,(2R-{3 or 4}R′ + 2)·H₂O]^2R′− and [Fe^II_(2R)Fe^III₂(OH)_{(4R−2R″+6)}(H₂O)_(2R″−2)]^2R″+·[R″SO₄,(4R − 4R′ + 4)·H₂O]^2R″−     

Electroreductive dimerization of acetyl compounds in dimethylformamide

Seven acetyl compounds were cathodically electrolyzed in dimethylformamide containing TBAI and LiI to give corresponding hydrodimers in good yields respectively. On the basis of the rate constant of dimerization determined by use of digital simulation, it was found that the dimerization proceeded through anion radical (R⁻)/ion-pair (R⁻Li⁺) coupling in all the cases that a linear relationship existed between the logarithm of the rate constant and electron spin density at the carbonyl carbon.     

Interdiffusion of thallous ion in molten lithium nitrate studied by optical interferometry

The interdiffusion coefficient of thallous ion in molten lithium nitrate has been measured by wave-front-shearing interferometry. The results are obtained in a region of low Tl⁺ concentration and can be summarized with an Arrhenius equation

where D is the interdiffusion coefficient in cm²/s, R the gas constant in cal/mole/deg and T the temperature in °K. The interdiffusion coefficient of Tl⁺ in LiNO₃ is lower than that of Rb⁺, which may be interpreted in terms of differences in the Van der Waals interaction with the solvent lithium ion.     

A highly selective and sensitive fluorescence chemosensor based on optically active polybinaphthyls for Hg

The chiral polymer was synthesized by the polymerization of 4,7-diethynylbenzo[2,1,3]-thiadiazole (M-1) with (R)-6,6′-dibutyl-3,3′-diiodo-2,2′-bis(diethylaminoethoxy)-1,1′-binaphthyl (R-M-1) via Pd-catalyzed Sonogashira reaction. The chiral polymer has orange fluorescence due to the extended π-electronic structure between binaphthyl unit and benzo[2,1,3]thiadiazole (BT) group via ethynyl bridge. The responsive optical properties of the polymer on various metal ions were investigated by fluorescence spectra. The fluorescence of the chiral polymer can produce the pronounced enhancement as high as 1.8-fold upon addition of 1:2 molar ratio of Hg²⁺. Compared with other cations, such as K⁺, Mg²⁺, Pb²⁺, Co²⁺, Ni²⁺, Ag⁺, Cd²⁺, Cu²⁺, Zn²⁺, Mn²⁺ and Fe³⁺, Hg²⁺ can produce the pronounced fluorescence response of the polymer. The result indicates this kind of chiral polybinaphthyls incorporating diethylamino and benzo[2,1,3]thiadiazole (BT) moieties as receptors exhibits highly sensitive and selective behavior for Hg²⁺ detection.     

Electro-Fenton degradation of antimicrobials triclosan and triclocarban

The antimicrobials triclosan (2,4,4′-trichloro-2′-hydroxydiphenyl ether) and triclocarban (N-(4-chlorophenyl)-N′-(3,4-dichlorophenyl)urea) have been degraded by four electro-Fenton systems using undivided electrolytic cells with a Pt or boron-doped diamond (BDD) anode and a carbon felt or O₂ diffusion cathode. The main oxidant is hydroxyl radical (OH) produced both on the anode surface from water oxidation and in the medium by Fenton's reaction, which takes place between electrogenerated H₂O₂ and Fe²⁺ coming from cathodic reduction of O₂ and Fe³⁺, respectively. Triclosan from saturated aqueous solutions of pH 3.0 is completely removed in all cells, decreasing its decay rate in the order: Pt/carbon felt > BDD/carbon felt > Pt/O₂ diffusion > BDD/O₂ diffusion, in agreement with their OH generation ability from Fenton's reaction. Glyoxylic, maleic and oxalic acids are identified as aliphatic intermediates. Complexes between oxalic acid and iron ions persist largely in solution, although Fe²⁺-oxalato complexes are mineralized by OH in the medium and Fe³⁺-oxalato complexes are destroyed by OH on BDD. Analogous treatments of more concentrated triclosan solutions using a 20:80 (v/v) acetonitrile/water mixture as solvent evidence the role of hydroxyl radicals along the degradation. In this hydroorganic medium hydroxylated derivatives such as 2,4-dichlorophenol, 4-chlorocatechol, chlorohydroquinone and chloro-p-benzoquinone, and carboxylic acids such as maleic, oxalic, formic and acetic acids are detected as products. Complete destruction of iron-oxalato complexes and released Cl⁻ ion involves some oxidizing species coming from parallel acetonitrile oxidation. The same electro-Fenton systems also yield the overall removal of triclocarban in acetonitrile/water mixtures, giving rise to urea, hydroquinone, chlorohydroquinone, 1-chloro-4-nitrobenzene and 1,2-dichloro-4-nitrobenzene as primary intermediates.     

Study on physical and electrostatic interactions of counterions in poly(perfluorosulfonic) acid matrix: Characterization of diffusion properties of membrane using radiotracers

The self-diffusion coefficients of water and ions were used to study the physical (tortuosity) and electrostatic interactions of counterions in poly(perfluorosulfonic) acid membrane (Nafion-117) matrix. The self-diffusion coefficients of water were measured in the water swollen Nafion-117 membrane with Zn²⁺, Ca²⁺, Sr²⁺, and Fe²⁺ counterions by analyzing the experimental exchange rates between tritium tagged water (HTO) in membrane and equilibrating water. In order to study the effects of equilibrating solution, the HTO-desorption rate profiles between the membrane samples in H⁺ or Cs⁺ forms and equilibrating solution containing CsCl or HCl (0.25 mol/L) were measured. It was observed that the HTO-exchange rate profile was slower in case of membrane sample in Cs⁺-from equilibrated with salt/acid solution than that equilibrated with deionized water in same ionic form. However, HTO-exchange rate profile did not alter in case of H⁺-form of membrane on equilibration with salt or acid solution. The variation of ln  with polymer volume function V_p/(1 − V_p), where V_p is polymer volume fraction, indicated that: (i) in the membrane with multivalent counterions was lower than that reported for membrane with monovalent counterions at same V_p, and (ii) the linear trends observed in variation of ln  with V_p/(1 − V_p) for multivalent and monovalent counterions were significantly different. The values of in membrane normalized with at V_p = 0 were taken as an estimate of the tortuosity factor for self-diffusion of ions in the membrane matrix. The self-diffusion coefficients of ions reported in the literature along with tortuosity factor obtained from in the corresponding ionic forms of the membrane were analyzed to obtain the charge (Z_i) independent electrostatic interaction parameter g(φ) of monovalent and divalent ions in the membrane. This analysis indicated that g(φ) also vary exponentially as a function of V_p/(1 − V_p) irrespective of charge on counterions. In order to study the influence of V_p on diffusional transport rates of Na⁺ and Cs⁺ ions in membrane, a permeation experiment was carried out using H⁺-form of membrane having high water volume fraction. The diffusional transport rates of Cs⁺ and Na⁺ in H⁺-form of membrane were found to be similar indicating that the water volume fraction in membrane has strong influence on the parameters that govern the diffusion across the Nafion-117 membrane.     

The aerobic and peroxide-induced coupling of aqueous thiols—II. Reaction mechanisms,model analysis,and a comparison of the model and experimental results

Kinetic results of the preceeding paper are used to formulate the most probable reaction mechanisms for the peroxide-induced and aerobic coupling of aqueous thiols. Parameters in the proposed mechanisms are evaluated for n-propylthiol using the results of independent measurements. A remarkably good agreement is achieved between the model and experimental results.The peroxide reaction, which is not affected by either copper ion or radical scavengers, is shown to be a nucleophilic substitution (S_N 2) reaction which proceeds by a two-step mechanism as follows: RS⁻ + H₂O₂

RSOH + OH⁻ rate-determining RS⁻ + RSOH → RSSR + OH⁻ In the reaction the thiolate anion acts as the nucleophile while hydrogen peroxide and the transient sulfenic acid, RSOH, function as electrophiles.The most plausible mechanism for the copper-catalyzed, aerobic coupling reaction is as follows: Cu⁺ (RSSR)₂⁺ + RS⁻

(RSSR)Cu⁺ (RS⁻) + RSSR (RSSR)Cu⁺ (RS⁻) + RS⁻

(RSSR)Cu⁺ (RS⁻)₂⁻ (RSSR)Cu⁺ (RS⁻)₂⁻ + O₂

Cu⁺(RSSR)₂⁺ + HO₂⁻ rate-determining RS⁻ + H₂O₂

RSOH + OH⁻ rate-determining RS⁻ + RSOH → RSSR + OH⁻ For the n-propylthiol substrate, the pertinent parameters in the mechanism are 1n (K₁) = −11,000 K/T + 33.6, where K₁ is dimensionless, 1n (K₂) = 4270 K/T −10.5, where K₂ is in 1/mol, 1n (k₂) = 30.0 − 5260 K/T, and 1n (k₂) = 26.8 − 6190 K/T, where k₁ and k₂ are in 1/(mol min).     

Behavior of cesium cation in zeolite Y (FAU,Si/Al = 1.56) and their single-crystal structures, |Cs<Subscript>75−x</Subscript>Na<Subscript>x</Subscript>|[Si<Subscript>117</Subscript>Al<Subscript>75</Subscript>O<Subscript>384</Subscript>]-FAU (x = 35 and 54)

To study the tendency of Cs⁺ exchange into zeolite Y (Si/Al = 1.56) dependence on Cs⁺ and Na⁺ concentration of aqueous solution during exchange, two single-crystals of fully dehydrated, Cs⁺-and Na⁺-exchanged zeolites Y were prepared by the flow method using a mixed ion-exchange solution whose CsNO₃:NaNO₃ mol ratios were 1:1 (crystal 1) and 1:100 (crystal 2), respectively, with a total concentration of 0.1 M, followed by vacuum dehydration at 723 K. Their crystals were determined by single-crystal synchrotron X-ray diffraction techniques in the cubic space group Fd \(\overline{ 3}\) m, respectively, and were refined to the final error indices R ₁/wR ₂ = 0.084/0.248 and 0.088/0.274 for crystals 1 and 2, respectively. In the structure of |Cs₄₀Na₃₅|[Si₁₁₇Al₇₅O₃₈₄]-FAU (crystal 1), 40 Cs⁺ ions per unit cell occupy five different equipoints; 3, 3, 14, 9, and 11 are at sites I, II′, II, IIIa and IIIb, respectively, whereas, the remaining 35 Na⁺ ions occupy three different sites: 9, 11, and 15 are at sites I, I′, and II, respectively. In the structure of |Cs₂₁Na₅₄|[Si₁₁₇Al₇₅O₃₈₄]-FAU (crystal 2), 21 Cs ⁺ ions per unit cell occupy three equipoints; 4, 6, and 11 are at sites II, IIIa, and IIIb, respectively. The residual 54 Na⁺ ions per unit cell are found at three different sites; 6, 20 and 28 are at sites I, I′, and II, respectively. The degrees of ion exchange are 53 and 28 % for crystals 1and 2, respectively. This result shows that the degree of Cs⁺ exchange decreased sharply by decreasing the initial Cs⁺ concentration and increasing the initial Na⁺ concentration in given ion-exchange solution.     

Homo- and R/S-copolymerizations of chiral methylpropargyl esters carrying pyrene moieties, and optical properties of the formed polymers

Pyrene-functionalized chiral methylpropargyl esters, (R)-3-butyn-2-yl-1-pyrenebutyrate [(R)-1], (S)-3-butyn-2-yl-1-pyrenebutyrate [(S)-1], (R)-3-butyn-2-yl-1-pyrenecarboxylate [(R)-2], and 3-butyn-2-yl-1-pyrenecarboxylate [(R,S)-2] were polymerized with (nbd)Rh⁺[η⁶-C₆H₅B⁻(C₆H₅)₃] to obtain the corresponding polymers with moderate molecular weights (M_n: 10?500-66?500) in good yields (82-97%). All the polymers were soluble in CHCl₃, CH₂Cl₂, and THF. The polarimetric and CD spectroscopic data indicated that poly[(R)-1], poly[(S)-1], and poly[(R)-2] existed in a helical structure with predominantly one-handed screw sense in these solvents. The helical structure of poly[(R)-1] and poly[(S)-1] was stable upon heating and addition of MeOH, while that of poly[(R)-2] changed upon MeOH addition. The copolymerization of (R)-1 with (S)-1 was also conducted to obtain the copolymers satisfactorily. Poly[(R)-1], poly[(S)-1], and poly[(R)-2] emitted fluorescence smaller than the corresponding racemic copolymers. The fluorescence intensity was tuned by the addition of MeOH to THF solutions of the polymers.     

Dissolution kinetics of periclase in dilute hydrochloric acid

Kinetics of the reaction between particulate sintered polycrystalline MgO and dilute hydrochloric acid were studied. The effects of process parameters, i.e., concentrations of H⁺ and Mg²⁺ ions, temperature and particle size were investigated. It was observed that the rate of chemical dissolution of MgO: (a) increased with increase in both HCl concentration (from 10^-4 to ) and temperature (from 25 to ); (b) decreased with increase in particle size (from 63 to ); (c) was not affected by Mg²⁺ ion concentration. Thorough comparison of our results with those published by other authors revealed that the “initial” stage of MgO dissolution has never been observed under the conditions of the experiments in the present work. It was concluded that the initial stage of MgO dissolution was probably too short to be detected and just the “advanced” kinetic regime was investigated. Values of the kinetic parameters were calculated, and apparent activation energy between 93 and and the reaction order for H⁺ ions from 0.41 to 0.76 were obtained. The presented values of the reaction order for H⁺ ions are consistent, allowing for experimental error, with current kinetic theories and most of other experiments. However, the rate-controlling step could not be assigned unambiguously, because the same value of the reaction order for H⁺ ions can be predicted by various theories for different rate-determining steps. The broad variety of likely rate-determining steps indicates some intrinsic diversity in current kinetic models.