Polarography of some sulphur-containing compounds: Part XIV.Anodic waves of ethylene-1,2-bisdithiocarbamate and reactions with heavy metals

The presence of two 2-electron anodic steps on polarographic curves of ethylene-1,2-bisdithiocarbamates together with the shifts of the half-wave potentials with pH and the adsorption phenomena, indicate a simultaneous reaction of both dithiocarbamate groupings at the electrode surface. In the homogeneous alkaline solutions, cadmium(II), copper(II) and lead(II) ions form an intermediate 1:1 compound with ethylene-1,2-bisdithiocarbamate in which only one dithiocarbamate group reacts. A 1 M sodium hydroxide solution is most suitable for the determination of the ethylene 1, 2-bisdithiocarbamate anion liberated from zinc or manganese derivatives in the analysis of pesticides ZINEB and MANEB. Waves of disodium ethylene-bisdithio-carbamates (NABAM) allow 1 · 10^-5M solutions to be analysed.     

Novel approach towards 2-substituted aminobenzimidazoles on imidazolium ion tag under focused microwave irradiation

We have developed an efficient, parallel synthesis of 2-substituted aminobenzimidazoles via intramolecular ring closing reactions of imidazolium ion tag immobilized o-phenylenediamine with various isothiocyanates. The methodology is based on the attachment of 4-fluoro-3-nitro benzoic acid into the imidazolium ion tag, which enables the S_NAr reactions with different amines followed by neutral reduction to furnish o-phenylenediamines under microwave irradiation. The substituted isothiocyanates are reacted with o-phenylenediamines to form monothiourea, which is further activated by methyl iodide to undergo desulfurization in one pot manner. The ionic liquid bound 2-substituted aminobenzimidazoles were finally cleaved from the support with sodium methoxide to generate target compounds in good yields and high purities with two points of structural diversity. This synthetic protocol has promising features of extremely short reaction time, operational simplicity, good yields, as well as widespread applications, leading to a facile and straightforward admittance to structurally diverse 2-substituted aminobenzimidazole analogues with potential bioactivities.     

Influence of self-assembly of amphiphilic imidazolium ionic liquids on their host–guest complexes with cucurbit[n]urils

Two symmetric amphiphilic imidazolium ionic liquids having ω-undecenyl chains form supramolecular complexes with CB[7] and CB[8] in water as revealed by ¹H NMR spectroscopy and MALDI-MS. Binding constants in the range 10⁴ to 10⁵ M^?1 were estimated from the conductivity measurements for the 1:1 complexes of these imidazolium ionic liquids with CB[7] and CB[8]. Radical initiated polymerization of these host–guest complexes at concentrations above the critical self-assembly concentration of imidazolium ionic liquids to form liposomes, destroys completely (CB[7]) or partially (CB[8]) the host–guest ionic liquid@CB[n] complex; this behaviour was proved by titration with acridine orange tricyclic dye, of CB[n]s in the colloidal solutions of the liposomes before and after performing dialysis to remove free CB[n]s. Thus, the increase in the fluorescence emission of acridine orange by CB[7] is not observed if the polymerized ionic liquid@CB[7] complex is submitted to dialysis to remove uncomplexed CB[7]. Analogous study by titration of absorbance change of acridine orange solutions caused by CB[8], reveals only a partial destruction of the host–guest complex by self-assembly of amphiphilic ionic liquid above the critical self-assembly concentration. The results obtained have been rationalized considering that the driving force for the formation of supramolecular ionic liquid@CB[n] complexes is a hydrophobic interaction between the apolar alkenyl chain and the cucurbituril interior cavity and that these hydrophobic interactions are disturbed when self-assembly leading to liposomes occurs.     

Polarographic reduction of aldehydes and ketones: Part 19. Hydration-Dehydration Equilibria and their Effect on Reduction of α,α,α-Trifluoroacetophenone

In acidic media, at pH <5, the carbonyl group of α,α,α-trifluoroacetophenone (I) is reduced in the protonated form to give alcohol and pinacol, whereas at pH > 7 the first reduction step involves hydrogenolysis of the trifluoromethyl group of the unprotonated form of I to yield acetophenone, which can undergo further reduction at more negative potentials. Reduction of both the carbonyl group at lower pH and of the C—F bonds in the unprotonated form are accompanied by hydration-dehydration equilibria. At pH > 7 these reactions involve addition of water and of hydroxide ions. The increase of current at pH > 8 is due to a shift of the equilibria in favor of the geminal diol anion of I; the decrease at pH > 10 is due to an increase in the rate of the addition of hydroxide ions with increasing pH. Spectrophotometric measurements at μ = 0.1 gave the following values for the acid dissociation constant of the geminal diol of I: K₂ = 6.4 × 10^-11 in 2% ethanol and 5 × 10^-12 in 40% ethanol. Formation of the hemiketal results in an increase of the absorbance of the free carbonyl form with increasing ethanol concentration. Formation of the hydrate and hemiketal of I in dimethylformamide is compared.     

Complexing of Cu(II) with N,N'-Diphenylthiooxamide and N,N'-Diphenyldithiooxamide in a Gelatin-Immobilized Cu2[Fe(CN)6] Matrix

A study was made of complexing in Cu(II)-N'N'-diphenylthiooxamide, Cu(II)-N'N'-di-phenyldithiooxamide systems in gelatin-immobilized Cu₂[Fe(CN)₆] matrices brought into contact withaqueous alkaline (pH 12.0±0.1) solutions of these ligands. In both cases, complexing is preceded by alkaline breakdown of copper(II) hexacyanoferrate(II) into Cu(II) hydroxide or oxohydroxide which is the species reacting with the ligands. In each system, complexing yields a Cu(HL)2 chelate (HL^- is the single-deprotonated form of N,N'-diphenylthiooxamide or N,N'-diphenyldithiooxamide).     

Intercalation behavior of amino acids into Zn-Al-layered double hydroxide by calcination-rehydration reaction

The intercalation of amino acids for the Zn-Al-layered double hydroxide (LDH) has been investigated by the calcination-rehydration reaction at 298 K using mainly phenylalanine (Phe) as a guest amino acid. The Zn-Al oxide precursor prepared by the calcination of Zn-Al-carbonated LDH at 773 K for 2 h was used as the host material. The amount of Phe intercalated by the rehydration was remarkably influenced by the initial solution pH and reached ca. 2.7 times for anion exchange capacity (AEC) of the LDH at neutral and weak alkaline solutions, suggesting that Phe was intercalated as amphoteric ion form into the LDH interlayer. As Phe is intercalated for the LDH as monovalent anion in alkaline solution, the amount of Phe intercalated at pH 10.5 corresponded with AEC of the LDH. The solid products were found to have the expanded LDH structure, which confirmed that Phe was intercalated into the LDH interlayer as amphoteric ion or anion form. The basal spacing, d₀₀₃, of the Phe/LDH was 1.58 nm at pH 7.0 and 0.80 nm at pH 10.5; two kinds of expansion suggested for Phe in the interlayer space as vertical (pH 7.0) and horizontal (pH 10.5) orientations. The intercalation behavior of various amino acids for the LDH was also found to be greatly influenced by the feature of the amino acid side-chain, namely, its carbon-chain length, structure and physicochemical property. In particular, α-amino acids possessing a hydrophobic or negative-charged side-chain were preferentially intercalated for the LDH.     

Electrodimerization of the pyridiniumcarboxylic acids homarine and trigonelline

Homarine (1-methyl-2-carboxypyridinium ion) and trigonelline (1-methyl-3-carboxy-pyridinium ion) are reduced at mercury electrodes in alkaline solutions by a one-electron transfer to the pyridinium ring. Analysis of polarographic wave shapes using deviation-pattern recognition, peak widths of cyclic voltammograms, analysis of the products of bulk electrolyses and dependences of E_1/2 and E_p on scan rate, pH and concentration indicated that these reductions proceed by an EC² mechanism, where the second-order chemical reaction is a homogeneous dimerization. The zwitterionic form of the pyridiniumcarboxylic acid, which predominates in alkaline solutions, undergoes reduction to form a pyridinyl anion radical. Two radicals then couple to yield a dimer dianion which is subject to protonation. The dimer can be oxidized at mercury electrodes.     

Etude cinétique de l'ouverture du cycle Δ2 imidazoline par hydrolyse basique

The kinetics of base hydrolysis of two Δ₂ imidazolines were followed by uv spectroscopy in sodium hydroxide and in carbonate buffers. In the most basic medium the rate of hydrolysis is independant of pH. This is explained if the rate determining step is attack of hydroxide ion on the protonated form of the substrate. In less basic medium there is a change in the slow step, the breaking of the intermediate becomes rate determining.     

Improving the Alkaline Stability of Imidazolium Cations by Substitution

Imidazolium cations are promising candidates for preparing anion‐exchange membranes because of their good alkaline stability. Substitution of imidazolium cations is an efficient way to improve their alkaline stability. By combining density functional theory calculations with experimental results, it is found that the LUMO energy correlates with the alkaline stability of imidazolium cations. The results indicate that alkyl groups are the most suitable substituents for the N3 position of imidazolium cations, and the LUMO energies of alkyl‐substituted imidazolium cations depend on the electron‐donating effect and the hyperconjugation effect. Comparing 1,2‐dimethylimidazolium cations (1,2‐DMIm⁺) and 1,3‐dimethylimidazolium cations (1,3‐DMIm⁺) with the same substituents reveals that the hyperconjugation effect is more significant in influencing the LUMO energy of 1,3‐DMIms. This investigation reveals that LUMO energy is a helpful aid in predicting the alkaline stability of imidazolium cations.     

Mechanism of Alkaline Hydrolysis of Diazepam

Diazepam (1) is a frequently prescribed hypnotic/anxiolytic drug in worldwide use. Compound 1 is hydrolyzed in alkaline medium to form 2-methylamino-5-chlorobenzophenone imine (2) and 2-methylamino-5-chlorobenzophenone (3) ; the ratio of 2:3 increases with increasing NaOH concentration (J. Pharm. Sci. 85, 745–748, 1996). The mechanism in the conversion of 1 to 2 and 3 via various intermediates is the subject of this report. Results of hydrolysis kinetics and structural identification of some intermediate products indicated an initial hydroxide attack at the C2-carbonyl carbon of 1 , resulting in the formation of a dioxide ( 7 , 7-chloro-1,3-dihydro-1-methyl-5-phenyl-2H-1,4-benzodiazepin-2,2-dioxide). Compound 7 was characterized by proton NMR spectroscopy and via its monomethyl ether ( 8 , 7-chloro-1,3-dihydro-2-hydroxy-2-methoxy-l-methyl-5-pheny]-2H-1,4-benzodiazepine). The seven-member diazepine ring of 7 opened at the N1-C2 bond to form a glycinate [ 5 , 2-methylamino-5-chloro-α-(phenylhenzylidene)glycinate]. Compound 7 (and/or 5 ) underwent an additional hydroxide attack at the C5-N4 imine bond to form a tetrahedral intermediate, which decomposed to form 2 and 3 .     

A polarographic study of the complexes formed in alkaline solution by the cadmium(II) ion with ethylenediamine,N-(2-hydroxyethyl)ethylenediamine,and N,N′-bis(2-hydroxyethyl)ethylenediamine

A multiple regression analysis of polarographic data has been used to determine the formulas and formation constants of complexes formed in alkaline solution by reaction of cadmium(II) ion and hydroxide ion with ethylenediamine (en), N-(2-hydroxyethyl)-ethylenediamine (hn) and N,N′-bis(2-hydroxyethyl)ethylenediamine (2hn). The complexes formed are designated by the general formula Cd(A)_p(OH)_p^2?q and the formation constants are given as log β_pq. The complexes found and their formation constants are: for en, 1 : 2 (10.3), 1 : 3 (12.3), and 1 : 2 : 1 (12.2); for hn, 1 : 2 (9.5), 1 : 2 : 1 (12.2), and 1 : 2 : 2 (12.6); and for 2hn, 1 : 2 (8.9), 1 : 1 : 2 (11.1), 1 : 2 : 1 (11.2), and 1 : 2 : 2 (12.6). It is concluded that in each case for which the hydroxide ion is reacted, a proton is removed from an alcoholic hydroxyl group which is coordinated to form a five-membered chelate ring linking a nitrogen atom and oxygen atom to the cadmium(II) ion.     

Expeditious synthesis of aromatic-free piperidinium-functionalized polyethylene as alkaline anion exchange membranes

Alkaline anion exchange membranes (AAEMs) with high hydroxide conductivity and good alkaline stability are essential for the development of anion exchange membrane fuel cells to generate clean energy by converting renewable fuels to electricity. Polyethylene-based AAEMs with excellent properties can be prepared via sequential ring-opening metathesis polymerization (ROMP) and hydrogenation of cyclooctene derivatives. However, one of the major limitations of this approach is the complicated multi-step synthesis of functionalized cyclooctene monomers. Herein, we report that piperidinium-functionalized cyclooctene monomers can be easily prepared via the photocatalytic hydroamination of cyclooctadiene with piperidine in a one-pot, two-step process to produce high-performance AAEMs. Possible alkaline-degradation pathways of the resultant polymers were analyzed using spectroscopic analysis and dispersion-inclusive hybrid density functional theory (DFT) calculations. Quite interestingly, our theoretical calculations indicate that local backbone morphology—which can potentially change the Hofmann elimination reaction rate constant by more than four orders of magnitude—is another important consideration in the rational design of stable high-performance AAEMs.

Piperidinium-functionalized polyethylene-based alkaline anion exchange membranes that show high hydroxide conductivities and good alkaline stabilities are easily prepared using photocatalytic hydroamination reactions.     

Studies on optimization of conditions for separating rhodium and platinum by cation-exchange

It has been established that, owing to the amphoteric properties of rhodium(III) hydroxide, by making a rhodium chloride solution alkaline (pH approximately 13) with sodium hydroxide and then acidifying to pH 2 with nitric acid it is possible to convert at least 99% of the rhodium into cationic forms. This fact is utilized for separation of rhodium(III) and platinum(IV) from chloride solutions on a sulphonic acid cation-exchanger in hydrogen form. Loss of rhodium in the separation process is < 1%. Platinum elution is complete. This method is suitable for separation of mixtures of rhodium and platinum (present in molar ratio between 1:200 and 20:1).     

Vibrational and electronic spectral studies of substituted 1,3-dihydro-1,3-diphenyl-2-thioxo-2H,5H-pyrimidine-4,6-diones

The vibrational spectra of 1,3-diphenyl-; 1,3-di (4′-chlorophenyl)-; 1,3-di(3′-methoxyphenyl)-1,3-dihydro-2-thioxo-2H,5H-pyrimidine-4,6-diones in solid state (KBr pellet) and in solution (CHCl₃ and CCl₄) have been studied and assignments made. Tautomeric and hydrogen bonding behaviour are discussed. Electronic spectra in various solvents at different pH values are recorded. The effect of substituents, change of solvent on the π—π* and n—π* transitions of all the compounds is explained. The bathochromic and hypsochromic shifts observed when the neutral form changes to the cationic or anionic form depending on the pH of solution, are also discussed.     

Bromures et ethers ortho- et para-acetoxybenzyliques: Hydrolyse alcaline et étude cinétique de leur réaction avec l'imidazole

A kinetic study of the alkaline hydrolysis and the imidazole-catalysed hydrolysis of a series of o - or p-acetoxybenzyl bromides and p-nitrophenyl ethers has been determined as a function of pH and temperature. The reactions were followed by disappearance of ester and by release of bromide or p-nitrophenolate anions. In both cases, the rates obtained were equal, and proportional to the ester and nucleophile concentrations. The formation of N- acetyl-imidazole intermediate, followed at 245 nm, as well as the observed deuterium isotope effect, correspond to a nucleophilic attack on the carbonyl group. When the acetoxy group is hindered, the reaction with hydroxide ion is slower, no catalysis can occur, and imidazole may react directly at the benzylic site of the molecule.     

Polarographic reduction of benzylidenemalononitrile

The mechanism of reduction of benzylidenemalononitrile (1), C₆H₅CH=C(CN)₂, at the dropping mercury electrode in aqueous solutions containing 50% methanol changes with pH. In acidic solutions the reduction proceeds by a four-electron transfer to the monoprotonated species, yielding an aminomethyl derivative. In alkaline solutions two one-electron steps involving the vinyl double bond reduction are observed. Hydrolysis of dinitrile 1 to form benzaldehyde complicates the study at high pH values. The system is unique in that at pH 5–6 the unprotonated form is reduced at more positive potentials than the protonated form, reflecting a change in the mechanism of the reduction process.     

Vibrational spectra, structure, and proton conduction in hydrous tin dioxide

SnO₂ · nH₂O (hydrous tin dioxide, HTD, n = 1.5) and SnO₂ · nD₂O (deuterated hydrous tin dioxide, DHTD) samples were studied by IR and Raman spectroscopy. The using of these spectroscopic methods elucidated some structural features of the hydrogen-bond network in HTD, where two types of water molecules and two types of hydroxide groups are present. Type 1 water molecules and hydroxide groups are found to be linked to one another by weak hydrogen bonds, as in liquid water. Type 2 water molecules and hydroxide groups are linked to type 1 water molecules and hydroxide groups by rather strong hydrogen bonds. The existence of these strong hydrogen bonds is interpreted as arising from the effect of tin ions on some water molecules and hydroxide groups. Proton conductivity in HTD was found by the impedance method to be a nearly linear function of n. The break of the line at n = 1.3 corresponds to the percolation threshold. The roles of type 1 and type 2 water molecules and hydroxide groups in the generation of proton conduction in HTD are discussed.     

Deposition of zinc hydroxide films using weak organic bases

Chemical deposition of zinc hydroxide (obtained by deposition with N,N′-dimethylformamide from alkaline solutions) on glass substrates is studied. The morphology and structure of the films are investigated. The films are shown to consist of zinc hydroxide and zinc oxide that are formed at different steps of the deposition process.     

Synthesis of Lithiophorite in High Alkaline Conditions

Lithiophorite consists of alternatively stacked MnO₆ octahedral sheets and LiAl₂(OH)₆ octahedral sheets. Its applications in laboratories and industries have been hindered by sophisticated operation procedures, long reaction time, or impurities existing in the final product. We proposed a fast and simple method, mixing birnessite, aluminate and lithium hydroxide together (designated it as the BAL method) in high alkaline conditions (pH > 13), and treating it hydrothermally at 423 K for 6 hours to prepare pure lithiophorite. A specific reaction between lithium cations and aluminate anions plays as a key role in the BAL method. Due to this specific reaction, Li_xAl_n(OH)_m^+z complexed cations can form and penetrate into interlayers of birnessite to replace sodium cations. In high alkaline conditions (pH > 12), Li_xAl_n(OH)_m^+z complexed cations become smaller and are soluble. Thus, the higher alkaline Li_xAl_n(OH)_m^+z complexed cations can penetrate into interlayers of birnessite at a higher rate. Furthermore, impurities, such as lithium intercalated gibbsite (LIG), aluminum oxyhydroxides and aluminum hydroxides are not stable in high alkaline conditions. Consequently, pure lithiophorite can be easily obtained within 6 hours in high alkaline conditions.     

Cyanosilylation of aldehydes catalyzed by N-heterocyclic carbenes

N-Heterocyclic carbenes produced in situ from salts of imidazolium, benzimidazolium, pyrido[1,2-c]imidazolium, imidazolinium, thiazolium, and triazolium catalyze the addition of trimethylsilylcyanide to aldehydes to yield cyanohydrin trimethylsilyl ethers. The use of C₂-symmetric imidazolidenyl carbene derived from (R,R)-1,3-bis[(1-naphthyl)ethyl]imidazolium chloride led to enantioselective cyanosilylation.