Electrochemical behaviour of zinc gluconate complexes

Voltammetric studies revealed that under transient conditions in the pH range 3.7 to 5.0, the deposition of zinc from ZnSO₄ solutions involves the formation of adsorbed monovalent zinc. The conversion of divalent zinc to monovalent is a slow step. In the presence of gluconate, the reduction of divalent complex involves the monovalent zinc complex and the second electron transfer is slow. In the pH range 10 to 12.5, the zinc complex may be [(Zn(GH₄)₄]2^- and is found to vary with gluconate and OH^- ions. The conversion of [Zn(GH₄)(OH)_abs ^-] to Zn(OH)₂ or Zn(GH₄)₂ is the slow step in the reduction of the complexes. In strong alkali solutions sodium gluconate forms zinc hydroxy gluconate complexes. [Zn(OH)₃(GH₄)]^2- to adsorbed [Zn(OH)(GH₄)]^- is the slow step in the reduction.     

Adamanthylazoles: VII. Acid-catalyzed Adamanthylation of C-C- and C-N-Linked Azopyrazoles

Acid-catalyzed N-adamanthylation of C-C-linked pyrazolyl- and tetrazolylpyrazoles in H₃PO₄- AcOH (4:1) or H₂SO₄ involves, depending on conditions, one or both rings. The mutual effect of the rings is weak. C-N-Linked azolylpyrazoles are a conjugated system, and the formation of N-adamanthyl derivatives is strongly affected by the second azolyl ring.     

gem-Dihalocyclopropane formation by iron/copper activation of tetrahalomethanes in the presence of nucleophilic olefins. Evidence for a carbene pathway

The activation of CBr₄ and CCl₄ by a bimetallic iron/copper couple in acetonitrile is a new, inexpensive, nontoxic and efficient procedure for gem-dibromo- and gem-dichloromethylenation of nucleophilic alkenes. This new route to gem-dihalocyclopropanes involves dihalocarbene species.     

Cyclo- and cyclized diene polymers. XVI. Nature of the active species and a proposed mechanism of cyclopolymerization of isoprene with catalysts containing ethylaluminum halides

The polymerization of isoprene with C₂H₅AlCl₂ to yield solid cyclopolyisoprene is markedly accelerated by the addition of TiCl₄. The polymer yield passes through a maximum on increasing the catalyst reaction time with or without monomer present. The active species are probably cations formed by dissociation of the reaction product of C₂H₅AlCl₂ and TiCl₄. The polymerization of isoprene with (C₂H₅)₂AlX–TiCl₄ (X = F, Br, Cl) has maximum activity at an Al/Ti mole ratio of 0.75 corresponding to conversion of R₂AlX to RAIX₂ which then reacts with remaining TiCl₄. A proposed mechanism of cyclopolymerization of conjugated dienes involves monomer activation, i.e., conversion to cation radical by one-electron transfer to catalyst cation which is itself neutralized, addition of cation end of monomer cation radical to terminal or internal unsaturation of fused cyclohexane polymer chain, one-electron transfer from “neutral” catalyst to cation on polymer chain which is then transformed to a diradical which undergoes coupling to form a cyclohexene ring. The mechanism of the “living” polymerization involves addition of catalyst-activated monomer to a “dead” polymer with a terminal cyclohexene ring and regeneration of the active catalyst.     

On the temperature dependence of proton magnetic resonance lineshapes of tunnelling ammonium in NH4ClO4 and NH4PF6

The proton magnetic resonance lineshapes of NH₄ClO₄ and NH₄PF₆ at liquid helium temperature are narrower than those usually expected for rapidly tunnelling ammonium ions. The narrowing is temperature-dependent, suggesting a kinetic process that involves a modulation of the tunnelling states. A possible “exchange-narrowing” mechanism involving fluctuating molecular torsional states brought about by external lattice perturbations is considered, and is seen to lead to a satisfactory simulation of the observed low-temperature lineshapes. Activation energies of 0.9 ± 0.1 K and 1.7 ± 0.5 K governing the exchange process are derived for the cases of NH₄ClO₄ and NH₄PF₆, respectively.     

Thermal studies on oxalate complexes. III. Complexes of cobalt(III) and cobalt(II)

The decomposition of K₂[Co(C₂O₄)₂] and K₃[Co(C₂O₄)₃] has been studied using TG. In the case of the latter compound, the first step involves the rupture of all the oxalates and one of the resultant carbonates to liberate CO₂ and three molecules of CO. Subsequent steps involve the loss of CO₂. In the case of K₂[Co(C₂O₄)₂], four decomposition reactions are observed. The first involves the loss of only CO. Subsequent steps involve loss of CO₂, CO₂ and CO, and CO₂, respectively. Basic carbonates appear to be the intermediate products. Kinetic parameters are presented for most of the reactions.     

New synthesis of hexamethyltungsten(VI); hexamethylrhenium(VI) and dioxotrimethylrh enium(VII)

A new synthesis of hexamethyltungsten involves the reaction of WCl₆ and AlMe₃, while interaction of AlMe₃ and ReOMe₄ gives ReMe₆; a dioxorhenium(VII) methyl, ReO₂ Me₃, is reported.     

Studies in sesquiterpenes—LV: Isolongifolene(part 6): Mechanism of rearrangement of longifolene to isolongifolene-I

The gross mechanism of rearrangement of longifolene to isolongifolene has been elucidated by using site-specifically labelled longifolene-4, 4, 5, 5-d₄ and shown to follow the pathway proposed by Berson et al., which involves an exo, exo Me shift, in preference to the endo, endo Me migration route proposed earlier. An efficient synthesis of longifolene-4, 4, 5, 5-d₄, the key compound in the present investigation, is described.     

Fluctuating Storage of the Active Phase in a Mn-Na2WO4/SiO2 Catalyst for the Oxidative Coupling of Methane

Structural dynamics of a Mn-Na₂WO₄/SiO₂ catalyst were detected directly under reaction conditions during the oxidative coupling of methane via in situ XRD and operando Raman spectroscopy. A new concept of fluctuating storage and release of an active phase in heterogeneous catalysis is proposed that involves the transient generation of active sodium oxide species via a reversible reaction of Na₂WO₄ with Mn₇SiO₁₂. The process is enabled by phase transitions and melting at the high reaction temperatures that are typically applied.     

The stoichiometric hydrogenation of 1,1-diphenylethylene with hydridocobalt tetracarbonyl; differences from the hydroformylation reaction

The kinetics of the stoichiometric hydrogenation of 1,1-diphenylethylene with HCo(CO)₄ is cleanly second order, permitting a determination of the activation parameters. The rate is unaffected by the atmosphere over the reaction and is enhanced by substituting DCo(CO)₄ for HCo(CO)₄. These results contrast sharply with those secured in the hydroformylation of 1-alkenes and thus dual mechanistic pathways are available for the reaction of HCo(CO)₄ with unsaturated systems. It is very possible that the stoichiometric hydrogenation of 1,1-diphenylethylene involves a geminate free radical pair but definitive proof is still lacking.     

Polymerization of isoprene initiated by the reaction products of zirconium allylic complexes and titanium chlorides

Reaction of (all)₄Zr with TiCl₄ involves the migration of the allyl ligands to titanium which is accompanied by the reduction of titanium to a tri- and divalent state and the formation of diallyl. The reaction products are found to initiate polymerization and oligomerization of isoprene. The course of the isoprene reactions and the properties of the resulting polymers are determined by the nature of the complexes formed. The reaction products of TiCl₄ or TiCl₃ with (all)₂ZrCl₂ initiate cationic polymerization of isoprene. Complexes resulting from the reaction of TiCl₃ with (all)₄Zr or (all)₃ZrCl lead to cis-1,4-polyisoprene.     

Activation and transformation of white phosphorus by palladium(<Emphasis Type="SmallCaps">ii</Emphasis>) complexes

A reaction of bis(triphenylphosphine)palladium dibromide with white phosphorus in the presence of NaBPh₄ selectively gives phosphorous acid H₃PO₃. The mechanism of the formation involves coordination of a white phosphorus molecule, ligand exchange, and hydrolysis of the coordinated P₄ molecule in the coordination sphere of palladium.     

Coexistence of Three Ferroic Orders in the Multiferroic Compound [(CH3)4N][Mn(N3)3] with Perovskite‐Like Structure

The perovskite azido compound [(CH₃)₄N][Mn(N₃)₃], which undergoes a first‐order phase change at T_t=310 K with an associated magnetic bistability, was revisited in the search for additional ferroic orders. The driving force for such structural transition is multifold and involves a peculiar cooperative rotation of the [MnN₆] octahedral as well as order/disorder and off‐center shifts of the [(CH₃)₄N]⁺ cations and bridging azide ligands, which also bend and change their coordination mode. According to DFT calculations the latter two give rise to the appearance of electric dipoles in the low‐temperature (LT) polymorph, the polarization of which nevertheless cancels out due to their antiparallel alignment in the crystal. The conversion of this antiferroelectric phase to the paraelectric phase could be responsible for the experimental dielectric anomaly detected at 310 K. Additionally, the structural change involves a ferroelastic phase transition, whereby the LT polymorph exhibits an unusual and anisotropic thermal behavior. Hence, [(CH₃)₄N][Mn(N₃)₃] is a singular material in which three ferroic orders coexist even above room temperature.     

Spectral-luminescence properties and acid-base properties of luminophores obtained from 3-iodo-7-dialkylaminocoumarins

The absorption and fluorescence spectra of the conjugate acids of 7-dialkylaminocoumarins were studied, and their pK_a ^I, pK_a ^II, and pK_a ^* values were determined. It was established with the aid of PMR data that the primary protonation generally involves the nitrogen-containing substituent in the 3 or 4 position, while the secondary protonation involves the nitrogen atom in the 7 position.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1170–1175, September, 1991.     

Hydrogen‐bonded two‐ and three‐dimensional polymeric structures in the ammonium salts of 3,5‐dinitrobenzoic acid, 4‐nitrobenzoic acid and 2,4‐dichlorobenzoic acid

The structures of ammonium 3,5‐dinitrobenzoate, NH₄⁺·C₇H₃N₂O₆⁻, (I), ammonium 4‐nitrobenzoate dihydrate, NH₄⁺·C₇H₄NO₄⁻·2H₂O, (II), and ammonium 2,4‐dichlorobenzoate hemihydrate, NH₄⁺·C₇H₃Cl₂O₂⁻·0.5H₂O, (III), have been determined and their hydrogen‐bonded structures are described. All three salts form hydrogen‐bonded polymeric structures, viz. three‐dimensional in (I) and two‐dimensional in (II) and (III). With (I), a primary cation–anion cyclic association is formed [graph set R₄³(10)] through N—H...O hydrogen bonds, involving a carboxylate group with both O atoms contributing to the hydrogen bonds (denoted O,O′‐carboxylate) on one side and a carboxylate group with one O atom involved in two hydrogen bonds (denoted O‐carboxylate) on the other. Structure extension involves N—H...O hydrogen bonds to both carboxylate and nitro O‐atom acceptors. With structure (II), the primary inter‐species interactions and structure extension into layers lying parallel to (001) are through conjoined cyclic hydrogen‐bonding motifs, viz.R₄³(10) (one cation, an O,O′‐carboxylate group and two water molecules) and centrosymmetric R₄²(8) (two cations and two water molecules). The structure of (III) also has conjoined R₄³(10) and centrosymmetric R₄²(8) motifs in the layered structure but these differ in that the first motif involves one cation, an O,O′‐carboxylate group, an O‐carboxylate group and one water molecule, and the second motif involves two cations and two O‐carboxylate groups. The layers lie parallel to (100). The structures of salt hydrates (II) and (III), displaying two‐dimensional layered arrays through conjoined hydrogen‐bonded nets, provide further illustration of a previously indicated trend among ammonium salts of carboxylic acids, but the anhydrous three‐dimensional structure of (I) is inconsistent with that trend.     

Mass spectral fragmentation pattern of 2,2′-bipyridyls Part IV. Di-2-pyridly ketone

The fragmentation of di-2-pyridyl ketone on electron impact involves elimination of neutral CO from the molecular ion and rearrangement to the 2,2′-l>ipyridyl molecular ion in addition to rupture of the central bonds to form C₅H₄N⁺ and C₆H₄NO⁺ ions.     

C−C Coupling of Benzyl Fluorides Catalyzed by an Electrophilic Phosphonium Cation

The activation and cleavage of benzyl fluorides by the electrophilic organofluorophosphonium catalyst, [(C₆F₅)₃PF][B(C₆F₅)₄], is reported and used for the preparation of 1,1‐diarylalkanes (37 examples) and substituted aryl homoallylic alkenes (14 examples). This procedure involves mild conditions, avoids harmful waste, and is compatible with a range of substituted arenes and allylic silanes.     

Fluctuating Storage of the Active Phase in a Mn‐Na2WO4/SiO2 Catalyst for the Oxidative Coupling of Methane

Structural dynamics of a Mn‐Na₂WO₄/SiO₂ catalyst were detected directly under reaction conditions during the oxidative coupling of methane via in situ XRD and operando Raman spectroscopy. A new concept of fluctuating storage and release of an active phase in heterogeneous catalysis is proposed that involves the transient generation of active sodium oxide species via a reversible reaction of Na₂WO₄ with Mn₇SiO₁₂. The process is enabled by phase transitions and melting at the high reaction temperatures that are typically applied.     

Silica-supported HgSO4/H2SO4: a convenient reagent for the hydration of alkynes under mild conditions

The silica-supported aqueous-phase catalyst (SAPC) approach has proven convenient for efficiently performing the hydration of alkynes with HgSO₄/H₂SO₄ to give the corresponding carbonyl compounds in dichloromethane under mild conditions. The use of this solid reagent significantly improves the reaction work-up as it merely involves filtering and evaporating the solvent.     

Destruction reactions of some σ-derivatives of vanadium

The interactions of (Me₃SiCH₂)₄V and (Me₃SiCH₂)₃V·THF with cyclopentadiene have been studied. Me₄Si and Cp₂V were isolated. A scheme of the reactions was proposed which involves formation of unstable monocyclopentadienyl derivatives of vanadium. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1542–1544, August, 1997.