Voltammetric study of the reduction process of ethylenediaminetetraacetatovanadium(IV): oxidation-state-dependent speciation

Cyclic voltammetry, differential-pulse polarography (d.p.p.), and direct-current tast polarography (d.c.t.p.) were used to study the electrochemical reduction of ethylenediaminetetraacetatovanadium(IV) [V(IV)OEDTA^2?]. The two-electron reduction wave of V(IV)OEDTA^2? is gradually split into two one-electron waves when the concentration of the supporting electrolyte is increased. A detailed study of the electrochemistry of V(III)EDTA^? allowed the conclusion that the two one-electron waves of V(IV)OEDTA^2? reflect the reduction sequence V(IV)OEDTA^2?$\text{+e}{}^{\mathrm{?}}$ V(III)EDTA^?$\text{+e}{}^{\mathrm{?}}$|$\text{?e}{}^{\mathrm{?}}$ V(II)EDTA^2?. The process responsible for the observed “chemical” peak separation was found to be ion pairing, by which the reduction of V(IV)OEDTA^2? is facilitated. A method is presented by which the parallel determination of V(IV) and V(III) (when present as the appropriate EDTA complexes) is possible with d.p.p, or d.c.t.p.     

Demasking reactions of potassium hydroxotrifluoroborate with lanthanum(III) complexes of polyaminopolycarboxylic acids: Part 1. Equilibrium constants for the reactions with EDTA and NTA complexes

Equilibrium constants for the demasking reactions of potassium hydroxotrifluoroborate. (KBF₃OH) toward La(III) complexes of EDTA and NTA have been estimated by means of ¹H-n.m.r- measurement at 35°C. For the constants defined as K^BF_LaLm = [L]^m[La(BF₃OH)_n]/[LaL_m][BF₃OH]_n, the results were: for EDTA (m = 1,n = $\text{1}\text{3}$) K^BF_LaL = 10^2.7, and for NTA (m = 2, n = $\text{1}\text{3}$) K^BF_LaL2 = 1026. These values are much larger than the equilibrium constants for the well known demasking reaction of fluoride ion toward La(III) complexes of EDTA and NTA, which are —12.43 and —14.92, respectively.     

Oxygenation of 2,6-di-t-butylphenols with superoxo Co(III) complexes

Superoxo Co(III) complexes, [Co(CN)₅O₂][X]₃ where X = Et₃N⁺ and (Ph₃P)₂N⁺, mediate the dioxygen incorporation into 2,6-di-$\text{t}$-butylphenols ($\text{1}$) with the same regioselectivity as that in the base-catalyzed oxygenation of $\text{1}$. The superoxo species acts as a base but is not incorporated into the substrate.     

Polarographic determination of iron(II) and iron(III) complexes with edta

The iron(II) and iron(III) complexes with EDTA can be determined separately and in mixtures in acetate-buffered medium at pH 4.0. The E_{$\text{1}\text{2}$}values are in the range ?0.105 to ?0.112 V vs. SCE. Linear calibration plots are obtained over the range 0–1.0 mM for each oxidation state. A sample-handling procedure for avoiding oxidation of iron(II) species is described. It is shown that the acetate buffer system does not affect the stability of the iron-EDTA complexes.     

Analytical aspects of some organic acids

Summary Back titrimetric procedures for the estimation of aluminium, zirconium, and thorium have been developed, which involved the adjustment of the concentration of the metallic salts, concentration of EDTA,ph, and temperature, addition of indicator solution (namely, 2-hydroxy3-naphthoic acid and back titration with standard 0.1 M ferric chloride solution. This method is based on the fact that the excess EDTA, which is added to the metal solutions may be back titrated with iron(III), which forms a highly coloured complex with the indicator, when present in slight excess. Quantities of aluminium, zirconium and thorium as small as 10.8, 4.6, 11.6 mg respectively, can be back titrated with in experimental error, when present in a volume of 100 ml.Part IV: See Z. analyt. Chem. 172, 356 (1960).     

Kinetics of the reaction of aluminum EDTA and cobalt(II) EDTA with calmagite

The reaction of aluminum EDTA with calmagite was found to be first-order in calmagite, half-order in aluminum EDTA, and zero-order in excess EDTA. The three-halves-order apparent rate constant at pH 9.48 and 20°C with ionic strength 0.30 was 0.232 ± 0.0141^{$\text{1}\text{2}$} · mol^{$\text{1}\text{2}$} · s^?1. The activation energy was 3.2 ± 0.3 kcal/mol. The pH dependence was complex between 8 and 10. The mechanism proposed is a rapid dissociation of a dimer of aluminum EDTA to a monomer followed by a rate-determining displacement of the EDTA by calmagite. The reaction of Co(II) EDTA with calmagite was confirmed to be first-order in Co(II) EDTA and first-order in calmagite with an activation energy of 7.5 ± 0.6 kcal/mol.     

Extraction of indium(III) from chloride medium with 1-phenyl-3-methyl-4-acylpyrazol-5-ones. Synergic effect with high molecular weight ammonium salts.

The extraction of In(III) from 1M (Na,H)(Cl,ClO₄) media with 4-acylpyrazol-5-ones (HL) in toluene at 25°C is described by equilibria In ³⁺ + 3 $\text{HL}$ ? $\text{InL}{}_3$ + 3 H⁺ (log K = 1.48, 1.03, 0.87 with acyl = benzoyl, lauroyl, 2-thenoyl), InCl ²⁺ + 2 $\text{HL}$ ? $\text{InClL}{}_2$ + 2 H⁺ (log K = 0.26, ?0.45, ?0.35 respectively) and In³⁺ + m Cl^? ? InCl_m^(3-m)+ (log β_m available from literature). The extraction from 1M (Na,H)(Cl,NO₃) medium is enhanced by addition of aliquat (TOMA⁺,Cl^?) and the following synergic equilibrium takes place : $\text{InCl}{}_2$ + $\text{(TOMA}{}^{\mathrm{+}}$,Cl^?) ? $\text{(TOMA}{}^{\mathrm{+}}$, InCl₂L₂^? (log K = 5.49, 5.25, 5.21 respectively). Cl^? of (TOMA⁺,Cl^?) is exchanged by NO₃^? with the equilibrium constant log K = 1.50. If (TOMA⁺,Cl^?) is replaced by tri-n-octylammonium chloride, the synergic effect is largely reduced (log K = 4.17 with acyl = benzoyl). The extraction from chloride solutions containing ClO₄^? remains unchanged by addition of ammonium salts.     

Reduction of olefinic bond under ammonia chemical ionization

The unsaturated $\text{trans}$dicarboxylates (III and IV) form stable (M+N₂H₇)⁺ adducts in addition to the (M+NH₄)⁺ adduct. At high ammonia pressure in the ion source, bimolecular reactions between (M+NH₄)⁺ (M+N₂H₇) adducts and NH₃ result in the reduction of olefinic bonds in unsaturated $\text{cis}$ and $\text{trans}$ dicarboxylates. Evidence was obtained from MIKE/CAD data on the possible structure of the product ion.     

Synthesis of “capped porphyrins”

The synthesis of “capped porphyrins” ($\text{10}$), ($\text{18}$), and ($\text{28}$), and their (chloro)iron(III), iron(II), cobalt (II), and zinc(II) complexes is reported. These complexes serve as models for the active site of the oxygen binding haemoproteins. In addition to reversible binding of dioxygen by each of the iron (II) porphyrin complexes, the 1-methyl-imidazole-(“C₃-capped porphyrin”) iron (II) complex ($\text{23}$) reacts reversibly with carbon monoxide, in solution at 25°C.     

Extraction-polarographic determination of cobalt(II) and nickel(II) as 2,2′-bipyridine complexes in acetonitrile

The tris(2,2′-bipyridine)cobalt(II) complex gives a reversible d.c. wave with E$\text{1}\text{2}$ = ?1.02 V vs. SCE and a sharp differential pulse peak at E_p = ?1.03 V in a salted-out acetonitrile phase. A simple selective method is described for the determination of cobalt(II); down to 0.25 μg of cobalt(II) can be determined in presence of large amounts of Ni, Zn, Cd, Pb, and Cu; iron(III) can be masked with sodium fluoride. The method is applicable to the determination of >0.0l% cobalt in nickel salts and >5 × 10^?5% cobalt in iron salts. Nickel(II) can also be extracted from aqueous solution and determined by differential pulse polarography, even in presence of a 20-fold amount of cobalt(II) by masking with EDTA; >0.01% of nickel in cobalt salts can be determined reproducibly.     

Effect of inorganic aqueous anions on the synergic extraction of cadmium and zinc with 1-phenyl-3-methyl-4-benzoyl-pyrazol-5-one (HPMBP) and lipophilic ammonium salts

As a part of a systematic study of the synergic extractions of metals with mixtures of acidic chelating extractants and lipophilic anion-exchangers (B, X with X^?6 inorganic anion), the extractions of M  Cd and Zn from perchlorate, nitrate and sulphate media with 1-phenyl-3-methyl-4-benzoyl-pyrazol-5- one (HL) and tri-n-octylammonium salts (TOAH.X) or aliquat 336 (TOMA.X) in toluene have been investigated. Three key equilibria describe the extractions: (a) M²⁺+2$\text{HL}$?$\text{ML}{}_2$+2H⁺. (b) $\text{B.X}$ +$\text{HL}$?$\text{B.L}$+H⁺+X^? with B efficiency TOMA < TOAH and X efficiency ClO₄ < NO₃ < SO₄. (c) $\text{ML}{}_2$+$\text{B.L}$?$\text{B.ML}{}_3$ with B efficiency toma > TOAH and Ni ～ Co > Cd > ZN.As a consequence of the conflicting orders of efficiencies of TOMA and TOAH in equilibria b and c, TOAH.X is a better synergic extractant from perchlorate medium than TOMA.X whereas the inverse is observed from nitrate and sulphate media. Equilibrium c is independent of the inorganic anions. Constants of equilibria a, b and c are given. B.ML₃ species are not extracted in 1-octanol.     

X-ray molecular structure of the 1:1 adduct of [FeH(CO)4]− and dimethyl acetylenedicarboxylate. η3-[trans-2,3-bis(methoxycarbonyl)acryloyl]tricarbonylferrate

The crystal structure of a bis(triphenylphosphine)iminium salt of the 1:1 adduct of [FeH(CO)₄]^? and dimethyl acetylenecarboxylate has been determined from three-dimensional X-ray data collected by the counter method. Single crystals belong to the triclinic space space group P$\text{1}$, with two units of [C₃₆H₃₀NP₂]⁺[C₁₀H₇FeO₈]^? in a cell of dimensions: $\text{a}$ = 13.918(2), $\text{b}$ = 15.669(5), $\text{c}$ = 9.909(2) Å, $\text{α}$ = 91.22(3), $\text{β}$ = 94.83(2), and $\text{γ}$ = 77.62(2)°. The structure was refined to a conventional $\text{R}$ of 0.068 for 5373 observed

reflections. The resulting structure indicates that the complex anion is η³-[$\text{trans}$-2,3-bis(methoxycarbonyl)acryloyl]tricarbonylferrate, the coordination around the iron atom being described as a considerably distorted trigonal bipyramid. A comparison of the present structure with the structures of related complexes suggests that the η³-acryloyl portion is best represented as an intermediate of (η³-allyl) with the oxygen atom and (η²-olefin + η¹-acyl). The short Fe-C(acyl) length of 1.897(5) Å implies an enhanced back-donation of electrons from the iron atom to the acyl group.     

Electron transfer reactions of excited ruthenium(II) complexes in monolayer assemblies at the SnO2-water interface

Monolayers of several surfactant analougues of Ru(bipy)$\text{2}\text{3}$⁺ ha ve been deposited on SnO₂ electrodes. Anodic photocurrents were observed when these electrodes were illuminated in (Ru-free) aqueous solutions. The photocurrents are interpreted by an electron transfer from the Ru(II) complex, excited to its triplet state, to the conduction band of SnO₂. The Ru(III) complex formed in this reaction is efficiently reduced by water.     

Preparation and synthetic utility of fluorinated phosphonium salts,bisphosphonium salts and phosphoranium salts

The synthesis and mechanism of formation of phosphonium salts of the type [R₃$\text{P}\text{+}$CFXY]Z^? (where X = F, Cl, Br; Y = Br, Cl; Z = Br, Cl), $\text{bis}$-phosphonium salts of the type [R₃$\text{P}\text{+}$CF₂$\text{P}\text{+}$R₃]2Br^?, and phosphoranium salts of the type [R₃$\text{P}\text{+}$$\text{C}\text{?}$F$\text{P}\text{+}$R₃]X^? (X = Br, Cl) will be presented. The applicability of these substrates in the generation of useful nucleophilic or electrophilic synthetic intermediates will be discussed.     

An unusual example of a rapid spin-equilibrium iron complex

Bis(N-(1-benzoyl-2-propylidene)-2-pyridylmethylaminato)iron(III) hexafluorophosphate (Fe(bzpa)₂PF₆ is shown to be a spin-equilibrium compound between low- (S = $\text{1}\text{2}$) and high- (S = $\text{5}\text{2}$) spin states depending on temperature, and to have the unusual property that the relaxation time of the spin change is shorter than the Mössbauer lifetime (1 × 10^?7s) of iron- 57 (l = $\text{3}\text{2}$) in the solid state.     

A practical synthesis of fluoromethyltriphenylphosphonium salts

A practical synthesis of [Ph₃$\text{P}\text{+}$CH₂F]BF₄^? is reported $\text{via}$ two routes, $\text{via}$ fluorination of [Ph₃$\text{P}\text{+}$CH₂OH]BF₄^? with DAST or $\text{via}$ hydrolysis of the phosphoranium salt, [Ph₃$\text{P}\text{+}$$\text{C}$F$\text{P}\text{+}$Ph₃]Br^?.     

Use of nitrosochromotropic acid as a metal indicator

Summary Nitrosochromotropic acid and copper give a purple coloured complex in the pH range 5.8–6.5, which is less stable than Cu(II)-EDTA complex. When milligramme quantities of copper solution containing few drops of nitrosochromotropic acid were titrated with EDTA the colour changes to light green or colourless. Copper can be titrated from 15–30° C, but at higher temperature low results are obtained due to dissociation of copper complex. Alkaline earths do not interfere in the titration of copper, but zinc, cadmium, nickel, cobalt, aluminium and iron(III) interfere. The interference of aluminium and iron(III) is masked by sodium fluoride. Microtitration can be carried out using nitrosochromotropic acid screened with xylene cyanol FF as metal indicator.     

Direct observation of the spinorbit splitting in the Ar+ ion with a diode laser

The ²P_{$\text{1}\text{2}$}-²P_{$\text{3}\text{2}$} fine structure transition in the ground (3p⁵) state of the argon atomic ion. Ar⁺, has been detected in absorption using a tunable diode laser. The transition was calibrated against water vapour lines and measured to be 1431.644 ± 0.001 cm^?1 in ⁴⁰Ar⁺ and 3.0 × 10^?3 cm^?1 (91 MHz) smaller in ³⁶Ar⁺.     

Photochemistry of phenyl alkyl ketones adsorbed on zeolite molecular sieves. Observation of pronounced effects on Type I/Type II photochemistry

The photolysis of phenyl alkyl ketones adsorbed on a number of commonly available zeolites (molecular sieves) can result in dramatic changes in Type I/Type II photochemistry.The photochemistry of ketones in ordered environments is a topic of current interest^2–4. Environmental effects can have important influence on the conformational flexibility of organic molecules, which in turn can affect the outcome of photochemical reactions⁵. Two recent reports^2,3 on the Norrish Type II reaction in ordered media prompts us to report our initial studies of the photochemistry of a number of phenyl alkyl ketones adsorbed in zeolites.Zeolites are crystalline aluminosilicates of usually well-defined structure⁶. Within the zeolite framework are a system channels and cavities of varying dimensions(2 – 13Å)⁶, some of which are capable of adsorption of large organic molecules (e.g., substituted benzenes). Thus the possibility that the internal spaces (or void volumes) of zeolites can exert topological control on organic photochemical reactions warrants investigation, since it is well-known that zeolites display shape-selective catalytic and adsorptive properties in important industrial chemical processes¹⁰. However, only a handful of reports of photochemical reactions on zeolites are known^4,7–9; the majority of these concern the catalytic splitting of water⁹. In this study, several commonly available zeolites were studied, and the results are compared to those obtained in homogeneous solution.Phenyl alkyl ketones $\text{1}$ - $\text{3}$ were employed in this study. The photochemistry of valerophenone $\text{1}$, octanophenone $\text{2}$, and α,α-dimethylvalerophenone $\text{3}$ is relatively well-understood in solution^11–13. For $\text{1}$ and $\text{2}$, the photobehaviour is characterized by Type II reaction, to give a triplet 1,4-biradical, which can either fragment, to give acetophenone, or cyclize, to give $\text{cis}$ and $\text{trans}$ cyclobutanols (eqn.1). Type I reaction in not observed. In solution, the ratio of fragmentation of cyclization (F/C) products is ～ 4 for $\text{1}$ and $\text{2}$. In general, the $\text{trans}$ isomer dominates, with t/c = 3 – 5 in benzene, and decreasing to a limit of 1 in more polar solvents (MeOH or micelles)^11-–13. For $\text{3}$. Type I reaction is observed in addition to Type II. The ratio of Type I/Type II product has been reported to be 0.3 in benzene without added thiol, and 0.6 with added thiol¹¹.Ketones $\text{1}$ and $\text{3}$ were deposited on Zeolites Na⁺-A, Na⁺-X, Na⁺-Y, Na⁺-Mordenite and resembling $\text{C}$ is also possible, from which cyclization is prohibited. For $\text{3}$, Type I reaction is known to compete with the Type II process¹¹. Adsorption of this ketone on Silicalite results in reaction via the least-motion pathway, namely Type I reaction, to give benzaldehyde as the aromatic product. Thus the behaviour of this ketone on Silicalite is quite consistent with the explanation offered for $\text{1}$ and $\text{2}$.Na⁺-Y is a large pore zeolite, with a pore diameter of ～8 Å and an internal cavity (supercage) of ～13 Å⁶. Additionally, we have found from related studies¹⁶ that of the zeolites capable of adsorbing benzene-type molecules studied in this work, Na⁺-Y allows the greatest degree of molecular mobility for photogenerated benzyl radical. Thus the observed F/C ratios of less than unity for this zeolite probably reflects the increased mobility of the photogenerated 1,4-biradical, allowing it to undergo ring closure readily. Interestingly, this zeolite also gave an $\text{inverse}$ t/c ratio for cyclobutanols of $\text{2}$.The results for the other zeolites are not readily distinguishable from those observed in solution, although two of these (Na⁺-X and Na⁺-Mordenite) are capable of adsorbing $\text{1}$ - $\text{3}$⁶. In any event, these two zeolites offer a medium for Type I/Type II reaction which essentially duplicate the behaviour in solution without the presence of solvent. Additional studies are in progress to further study the use of zeolites as a medium for photochemical reactions.     

Extraction of cobalt(II) and nickel(II) with mixtures of 1-phenyl-3-methyl-4-benzoyl-pyrazol-5-one (HPMBP) and tri-n-octylamine (TOA)

The extraction of Co(II) with mixtures of 1-phenyl-3-methyl-4-benzoyl-pyrazol-5-one ((H)PMBP) and tri-n-octylamine (TOA) is investigated in order to explore the influence of diluents and inorganic anions with synergistic acidic extractant + liquid anion exchanger systems. Although it is proved that the same species [HTOA]⁺ [Co(PMBP)₃]^? is extracted from various inorganic media, with toluene as the diluent, the presence of ClO₄^? SO₄^2? or Cl^? anion modifies the distribution of the anions which are associated to (HTOA)⁺ in the organic phase, leading to different synergistic equilibria; with Cl^? or SO₄^2?: $\text{CO(PMBP)}{}_2$ + $\text{(HTOA}{}^{\mathrm{+}}$,PMBP^?) ?$\text{(HTOA}{}^{\mathrm{+}}$,Co(PMBP)₃^? (log K = 6.10) and with ClO₄^? : $\text{Co(PMBP)}{}_2$ + $\text{HPMBP}$ + $\text{(HTOA}{}^{\mathrm{+}}$,ClO₄^? ? $\text{(HTOA}{}^{\mathrm{+}}$,Co(PMBP)₃^? + H⁺ + ClO₄^? (log K = 2.34) The same synergistic equilibrium is observed for the extraction of Ni(II) from ClO₄^? medium, with a comparable value of the constant (log K = 2.45). The synergistic effect is cancelled in n-octanol.