Theoretical studies on the interaction of anionic collectors with Cu+, Cu2+, Zn2+ and Pb2+ ions

 The influence of collector structure on interaction with metal cations was modelled by computational ab initio methods. The interaction energies were calculated between metal ions (Cu⁺, Cu²⁺, Zn²⁺ and Pb²⁺) and selected collector anions: ethyl xanthate, ethyl trithiocarbonate, dithiobutyric acid, ethyl dithiocarbamate, diethyl dithiocarbamate, diethylphosphinecarbodithioic acid and diethoxyphosphinecar bodithioic acid. The strongest interaction was found with diethyl dithiocarbamate. The results give qualitative information on the effect of the collector structure on the initial adsorption steps on sulphide mineral flotation. Received: 25 September / Accepted: 11 October 2001 / Published online: 22 March 2002     

Volumetric Properties of Ternary–Pseudobinary Mixtures [(Styrene + Ethyl Acetate or Benzene) + (<Emphasis Type="Italic">N</Emphasis>-Methyl-2-pyrrolidone + Ethyl Acetate or Benzene)]

The densities of the ternary-pseudobinary mixtures [(styrene + ethyl acetate or benzene) + (N-methyl-2-pyrrolidone + ethyl acetate or benzene)], formed by adding the third component (ethyl acetate or benzene) to the binary system (styrene + ethyl acetate), have been measured as a function of composition by means of a vibrating-tube densimeter at atmospheric pressure at 298.15 K. The excess molar volumes V _m ^E were calculated from the densities and correlated using the Redlich–Kister equation to estimate the coefficients and standard errors. The experimental and calculated quantities are used to discuss the mixing behavior of the components. The results show that the third component, ethyl acetate or benzene, have quite different influences on the interaction between styrene and N-methyl-2-pyrrolidone.     

Synthesis and unusual [2+2]-cycloaddition reactions of ethyl 4-chloro-2-oxobut-3-ynoate with unactivated alkenes

The highly activated acetylenes, ethyl 4-chloro-2-oxobut-3-ynoate and ethyl 4-bromo-2-oxobut-3-ynoate, were prepared from readily available bis(trimethylstannyl)acetylene in two steps with high overall yield. An unusual ability of the former to furnish [2+2]-cycloadducts with 1,1-disubstituted alkenes in the absence of irradiation and catalysts was discovered. The cycloaddition of ethyl 4-chloro-2-oxobut-3-ynoate to the 1,2-disubstituted alkenes was shown to be effectively catalyzed with stannic chloride.     

Octaalkyl tetracene-1,2,3,4,7,8,9,10-octacarboxylates: synthesis by twofold [2+2+2] cocyclization and crystallochromy

Tetracene octaesters, which were prepared by twofold [2+2+2] cocyclization, were isolated as red, orange, and orange-yellow solids for the methyl, ethyl, and propyl ester derivatives, respectively. X-Ray crystallographic analysis reveals that the difference in solid-state color arises owing to differences in molecular packing.     

Isobaric Vapor-Liquid Equilibria and Densities for the Binary Systems Oxolane + Ethyl 1,1-Dimethylethyl Ether,Oxolane + 2-Propanol and Propan-2-One + Trichloromethane

Vapor-liquid equilibrium data have been determined at 50 kPa for the binary systems oxolane (THF) + ethyl 1,1-dimethylethyl ether (ETBE) and oxolane + 2-propanol, and at 94 kPa for the system propan-2-one + trichloromethane. Excess volumes have also been determined from density measurements at 298.15 K. The systems oxolane + ethyl 1,1-dimethylethyl ether and oxolane + 2-propanol exhibit slight to moderate positive deviations from ideal behavior and no azeotrope is present. The system propan-2-one + trichloromethane exhibits negative deviations from ideal behavior and presents an azeotrope. The excess volumes of the system oxolane + ethyl 1,1-dimethylethyl ether are negative over the whole mole fraction range while those of the system oxolane + 2-propanol are positive. Excess volumes of the system propan-2-one + trichloromethane, change from negative to positive as the concentration of propan-2-one increases. The activity coefficients and boiling points of the solutions were correlated with the mole fraction by the Wohl, Wilson, UNIQUAC, and NRTL equations, and predicted by the UNIFAC group contribution method. Excess volume data were correlated using the Redlich-Kister expansion. The chemical association theory was applied for explaining the equilibrium behavior of the systems oxolane + 2-propanol and propan-2-one + trichloromethane.     

Vapour–liquid equilibrium for the ethyl ethanoate + 1-butene, +cis-2-butene, +trans-2-butene, +2-methylpropene, +n-butane and +2-methylpropane

Isothermal vapour–liquid equilibrium was measured for ethyl ethanoate + 1-butene, +cis-2-butene, +trans-2-butene, +2-methylpropene, +n-butane and +2-methylpropane at 318.4 K with an automated static total pressure measurement apparatus. The experimental data was correlated with the Wilson activity coefficient model. A good agreement between the experiments and the model was achieved. All six binary systems exhibited positive deviation from Raoult's law.     

Nickel-catalyzed intermolecular [3 + 2 + 2] cocyclization of ethyl cyclopropylideneacetate and alkynes

The [3 + 2 + 2] cocyclization of ethyl cyclopropylideneacetate (1a) and terminal alkynes (2) proceeded smoothly in the presence of 10 mol % "Ni(PPh3)2", which was prepared in situ from Ni(cod)2 and PPh3. The high reactivity of 1a, which was induced by the introduction of an electron-withdrawing group, is very important for the progress of this reaction. The cycloheptadiene derivatives were synthesized in highly selective manner in good yields.     

Gas-phase reactivity of the O=P(OCH3)2 + phosphonium ion towards alpha,beta-unsaturated esters in a quadrupole ion trap

Ion-molecule reactions between the O=P(OCH3)2 + phosphonium ions and eight alpha,beta-unsaturated esters (methyl acrylate, ethyl acrylate, methyl crotonate, ethyl crotonate, methyl 3,3-dimethylacrylate, ethyl 3,3-dimethylacrylate, methyl methacrylate and ethyl methacrylate) were performed in a quadrupole ion trap mass spectrometer. The O=P(OCH3)2 + phosphonium ions, formed by electron ionization from neutral trimethyl phosphite, were found to react with alpha,beta-unsaturated esters to give an adduct [RR'C=CR'COOR', O=P(OCH3)2]+, which lose spontaneously a molecule of trimethyl phosphate (R'=CH3) or dimethyl ethyl phosphate (R'=C2H5). An ion corresponding to a protonated trialkyl phosphate is also observed when substituent R'=H. To confirm the experimental results, and to elucidate the mechanism for the formation of the ionic species, a theoretical study using the density functional theory (DFT) approach was carried out. The potential energy surface obtained from B3LYP/6-31G(d,p) calculations for the reaction between O=P(OCH3)2 + and methyl acrylate is described.     

An expedient phosphine-catalyzed [4 + 2] annulation: synthesis of highly functionalized tetrahydropyridines

Ethyl 2-methyl-2,3-butadienoate acts as a 1,4-dipole synthon and undergoes [4 + 2] annulation with N-tosylimines in the presence of an organic phosphine catalyst. The resulting adducts, ethyl 6-substituted-1-(4-tosyl)-1,2,5,6-tetrahydro-pyridine-3-carboxylates, are formed in excellent yields with complete regioselectivity. Mechanistic reasoning for this new annulation has led to an expansion of the reaction scope by employing ethyl 2-(substituted-methyl)-2,3-butadienoates to give ethyl 2,6-cis-disubstituted-1-(4-tosyl)-1,2,5,6-tetrahydro-pyridine-3-carboxylates with high diastereoselectivities.     

Tautomeric equilibrium of ethyl acetoacetate in compressed CO2 + ethanol and CO2 + methanol mixtures

Tautomerism equilibrium of ethyl acetoacetate (EAA) in compressed CO2 + methanol and CO2 + ethanol mixtures was studied by UV-Vis spectroscopy at 308.15 K and different pressures. The volume expansion coefficient (alpha) of the solvents at different pressures was also determined. The relative permittivity (epsilon) of CO2 + methanol and CO2 + ethanol mixtures at different conditions was calculated using the Kc and Onsager solvent parameter. The equilibrium constant (Kc) of EAA in the binary mixtures increases considerably with increasing pressure or volume expansion coefficient. The relative permittivity or the polarity of the binary mixtures decreases sharply with increasing volume expansion coefficient in the range of 0 < alpha < 1.5. However, as the volume expansion coefficient exceeds 1.5, the relative permittivity decreases slowly. In other words, the dissolution of CO2 in the polar solvents can reduce the polarity of the solvents significantly in the low volume expansion coefficient range, and the polarity of the solution is not sensitive to the volume expansion coefficient as its value is large enough. The difference in polarity of the two solvents reduces with increasing pressure and becomes negligible after volume expansion coefficient exceeds about 2.5.     

Nickel-catalyzed intermolecular [3 + 2 + 2] cocyclization of ethyl cyclopropylideneacetate and alkynes. Synthesis of seven-membered carbocycles

The [3 + 2 + 2] cocyclization of ethyl cyclopropylideneacetate (1a) and various alkynes proceeded smoothly in the presence of Ni(cod)2-PPh3. The cycloheptadiene derivatives were synthesized in highly selective manners. The unique reactivity of 1a was essential for the progress of the reaction. The observed regioselectivity of the product formation and the mechanism of the reaction are discussed.     

Palladium-catalyzed [3 + 2] cycloaddition reaction using 2-(sulfonylmethyl)- or 2-(cyanomethyl)allyl carbonate

Reaction of ethyl 2-(sulfonylmethyl)- or 2-(cyanomethyl)allyl carbonate with α,β-unsaturated esters or ketones in the presence of PD₂(dba)₃·.CHCl₃-dppe catalyst gave highly functionalized cyclopentanes regio-selectively in good yields.     

Synthesis of Indole Derivatives by [2 + 2] Photocycloaddition of Indoline-2-thiones with alkenes and photodesulfurization of indoline-2-thiones

The photochemical synthesis of indole derivatives starting from the indoline-2-thiones 1 is described. Irradiation of indoline-2-thiones 1 in the presence of alkenes 3 gave 2-alkyl-3H-indoles 4 – 7 or 2-alkylindoles 8 – 22 through the ring cleavage of the intermediates, spirocyclic amino-thietanes, initially derived by [2 + 2] cycloaddition of the C?S bond of 1 and the C?C bond of 3 . Irradiation of 1 in the presence of trialkylamines 26 gave desulfurization products 27 – 32 and unexpected 3-alkylindoles 33 – 40 . N-Acylindoline-2-thiones 11 - p yielded the deacylated products, indoline-2-thiones 1a - b , and ethyl esters 43 through γ-H abstraction by the excited thioamide S-atom when irradiated in CDC1₃/EtOH or benzene/EtOH. Oxygen analogues 2a - d also underwent intramolecular H abstraction to give the indolin-2-ones 2e – f and ethyl esters 43 in a similar way.     

Substrate-controlled and site-selective [3+2] cycloadditions of N-heterocyclic carbene derived ambident dipoles

2-aryl thiocarbamoyl benzimidazolium and imidazolinium inner salts derived from benzimidazole and imidazoline carbenes are unique ambident C-C-S and C-C-N 1,3-dipolar systems, which undergo highly efficient and site-selective cycloaddition reactions with dimethyl acetylenedicarboxylate or dibenzoylacetylene to furnish spiro(imidazole-2,3'-thiophene) derivatives in excellent yields. When treated with ethyl propiolate, methyl acrylate or acrylonitrile, spiro(imidazole-2,3'-pyrrole) derivatives were formed in good yields. Theoretical studies revealed an asynchronous concerted mechanism for both the C-C-S and C-C-N 1,3-dipolar cycloaddition reactions. The site selectivity in the [3+2] cycloaddition reaction of ambident 1,3-dipoles was predictably regulated by both the electronic and steric effects of dipolarophiles.     

Gas-phase polar [4+ + 2] cycloaddition with ethyl vinyl ether: a structurally diagnostic ion-molecule reaction for 2-azabutadienyl cations

The intrinsic reactivity of eight gaseous, mass-selected 2-azabutadienyl cations toward polar [4(+) + 2] cycloaddition with ethyl vinyl ether has been investigated by pentaquadrupole mass spectrometric experiments. Cycloaddition occurs readily for all the ions and, with the only exception of those from the N-acyl 2-azabutadienyl cations (N-acyliminium ions), the cycloadducts are found to dissociate readily upon collision activation (CID) both by retro-Diels-Alder reaction and by a characteristic loss of an ethanol (46u) neutral molecule. Ethanol loss from the intact polar [4(+) + 2] cycloadduct functions therefore as a structurally diagnostic test: 72 u neutral gain followed by 46 u neutral loss, i.e., as a combined ion-molecule reaction plus CID 'signature' for N-H, N-alkyl and N-aryl 2-azabutadienyl cations. The two N-acyliminium ions tested are exceptional as they form intact cycloadducts with ethyl vinyl ether which dissociate exclusively by the retro-Diels-Alder pathway.     

Nickel-catalyzed [3+2+2] cycloaddition of ethyl cyclopropylideneacetate and diynes. Synthesis of 7,6- and 7,5-fused bicyclic compounds

The [3+2+2] cycloaddition reaction of ethyl cyclopropylideneacetate (1) and diynes proceeded in the presence of Ni(0) catalysts, and bicyclic compounds were isolated in good yields. The reaction provided a new approach to 7,6- and 7,5-fused bicyclic compounds.     

Comparative study of TmI2, SmI2, and SmI2/HMPA in the cross-coupling reactions of 2-acetylthiophene and thiophene-2-carboxylate with carbonyl compounds

The cross-coupling reactions of acetylthiophene or ethyl thiophene-2-carboxylate with aldehydes or ketones were achieved in a regioselective manner by using thulium diiodide in THF solution. Similar coupling reactions were also realized by using samarium diiodide together with excess amounts of hexamethylphosphoramide (HMPA). However, ethyl thiophene-2-carboxylate was inert in SmI₂/THF solution, and acetylthiophene was simply reduced to thienylethanol by SmI₂ in the absence of HMPA.     

McLafferty-type rearrangement in the collision-induced dissociation of Li+, Na+ and Ag+ cationized esters of N-acetylated peptides

In this study we investigated the multi-stage collision-induced dissociation (CID) of N-terminally acetylated di-, tri- and tetrapeptides in the form of C-terminal ethyl, n-propyl, isopropyl, n-butyl and tert-butyl esters and cationized by the attachment of Li(+), Na(+) and Ag(+). While methyl ester versions of the metal cationized peptides primarily eliminate H(2)O following collisional activation and dissociation, the ethyl, propyl and butyl ester versions of the peptides exhibit a dissociation pathway consistent with gamma-hydrogen transfer to the C-terminal carbonyl group, with associated elimination of an alkene, in a McLafferty-type rearrangement. The rearrangement leaves a metal cationized, free-acid form of the peptide, as confirmed by comparing the multi-stage CID of rearrangement products generated from peptide esters with the CID of corresponding metal cationized free-acid peptides. The transfer of a gamma-hydrogen in the rearrangement reaction was confirmed by investigating the CID of ethyl esters for which the terminal methyl group was labeled with deuterium. We found that the rearrangement product was significantly more abundant, relative to other product ions, when derived from isopropyl and tert-butyl esters than from ethyl, n-propyl or n-butyl ester analogues.     

[3+2] Dipolar cycloadditions of an unstabilised azomethine ylide under continuous flow conditions

The [3+2] dipolar cycloaddition reactions of the unstabilised azomethine ylide precursor benzyl(methoxymethyl)(trimethylsilylmethyl)amine with 12 electron-deficient alkenes in the presence of catalytic trifluoroacetic acid are examined under continuous flow conditions (20-100 °C, 10-60 min residence time). The more reactive and hazardous alkenes such as ethyl acrylate, N-methylmaleimide and (E)-2-nitrostyrene afford substituted N-benzylpyrrolidine products in 77-83% yields, whereas less reactive dipolarophiles such as (E)-crotononitrile and ethyl methacrylate give lower yields (59-63%). Under optimised conditions, the reaction with ethyl acrylate is scaled up to afford ethyl N-benzylpyrrolidine-3-carboxylate (30 g, 87%) in 1 h.     

Density and Volumes of Mixing of the Ternary System Ethylbenzene + Styrene + Ethyl Acrylate and its Binaries at 298.15 K

Densities of the ternary system, ethylbenzene + styrene + ethyl acrylate, and its three binaries have been measured in the whole composition range at 298.15 K and atmospheric pressure using an Anton Paar DMA 5000 oscillating U-tube densimeter. The calculated excess molar volumes are positive for the binary system, ethylbenzene + ethyl acrylate, and negative for the systems ethylbenzene + styrene and styrene + ethyl acrylate. The corresponding data were correlated with the Redlich-Kister equation and with a series of Legendre polynomials. Several models were used to correlate the ternary behavior from the excess molar volume data of their constituent binaries and were found to fit the data equally well. The best fit was based on a direct approach, without information on the component binary systems.