Effect of carboxylic acids on the cathodic reduction of benzophenone in N,N-dimethyl-formamide. Polarographic and CNDO/2 studies

Effect of eight carboxylic acids on the polarographic reduction of benzophenone in N,N-dimethylformamide has been studied. In the presence of these acids, a new cathodic wave (“pre-wave”) appears at more positive potentials than the original wave of benzophenone. Linear correlation has been found between ΔE_{$\text{1}\text{2}$} and the pK^DMF_a values of acids, where ΔE_{$\text{1}\text{2}$}  (E^pre-wave_{$\text{1}\text{2}$}  E^{original wave}_{$\text{1}\text{2}$}). It is suggested that in all the cases investigated the reduction proceeds via a hydrogen-bonded complex formed between the carbonyl compound and the acid in the double-layer. The structural aspects of the benzophenoneformic acid adduct have been solved using CNDO/2 method.     

Thermodynamic studies on thallium halides formation in N,N-dimethylformamide

The differences of the order of stability among halide ions for metal halogeno-complexes in nonaqueous solvents and water are examined by the thermodynamic constants for formation of thallium halides of transfer from water to N, N-dimethylformamide (DMF). The thermodynamic constants for formation of thallium halides were calculated from solubility products of thallium halides. The differences of the order of stability for thallium halides were found to be dependent mainly on the enthalpy changes for formation of thallium halides of transfer from water to DMF.     

Dissolution potential of alkali halides in N,N-dimethyl formamide

Phase potential, diffusion potential, observed and true dissolution potentials of alkali halides in N,N-dimethyl formamide have been determined. True dissolution potentials are found to be positive in DMF. The sign and magnitude of these potentials have been explained on the basis of difference between the ionic mobilities of cations and anions.     

Electrochemistry of the biliverdin—bilirubin system in N,N-dimethylformamide

The electrochemical behaviour of biliverdin and bilirubin on platinum electrodes in N, N-dimethylformamide has been investigated by means of voltammetric as well as controlled-potential electrolysis techniques.Bilirubin can be oxidized to biliverdin and the latter, in turn, to further oxidation products; conversely, biliverdin can be reduced to bilirubin, and the latter to further reduction products: however, the potential for the anodic oxidation of bilirubin to biliverdin and that for the cathodic reduction of biliverdin to bilirubin are about 1.6 V apart from each other. The reduction of biliverdin to bilirubin is shown to be amenable to preparative electrochemistry.     

Conductimetric investigations on salts in N,N-dimethylthioformamide at 25° C

Conductimetric measurements have been performed on solutions of the following salts in N,N-dimethylthioformamide (DMTF) at 25°C:- triisoamyl-n-butylammonium tetraphenylborate, triisoamyl-n-butylammonium iodide, triisoamyl-n-butylammonium perchlorate, tetra-n-butylammonium tetraphenylborate, tetra-n-butylammonium iodide, tetra-n-butylammonium perchlorate, bis(DMTF)copper(I)chloride, bis(DMTF)copper(I) bromide, bis(DMTF)copper(I) iodide, tetrakis(DMTF)copper(I) perchlorate, bis(DMTF)silver(I) chloride, bis(DMTF)silver(I) bromide and (DMTF)silver(I) iodide. The data have been analysed with the Pitts and the Fuoss—Justice conductivity equations and single ion conductivities have been calculated based on the assumption of equal limiting anion and cation conductivities for triisoamyl-n-butylammonium tetraphenylborate.     

Solubility parameter-based analysis of polyacrylonitrile solutions in N,N-dimethyl formamide and dimethyl sulfoxide

The physical properties of the solutions of polyacrylonitrile (PAN) in N,N-dimethyl formamide (DMF) and dimethyl sulfoxide (DMSO) were characterized in terms of solubility parameter. The physical properties were largely determined by individual solubility parameters, particularly the polar term, rather than overall solubility parameter. With increasing temperature, the intrinsic viscosity and hydrodynamic diameter of dilute solutions were decreased but the dynamic viscosity (η′) of concentrated solutions was increased. Of the two solvents, these phenomena were more pronounced with DMF; DMF gave greater η′ and yield stress than DMSO. When the polymer solutions were dried at 25 °C DMSO generated a cocontinuous structure whereas DMF produced a dispersed morphology. In addition, DMF dissolved PAN faster than DMSO, and the dissolution process followed a mechanism analogous to S_N2 reaction.     

The effects of substitution on the eletrochemical reduction of dihydroxynaphtacenequinone in N,N-dimethylformamide

The electrochemical reduction of 6,11-dihydroxy-5,12-naphthacenequinone (DHNQ) in N,N- dimethylformamide was investigated. Under polarographic conditions, DHNQ behaves like a simple aromatic quinone with reduction occuring in two successive one-electron steps followed by protonation in the aprotic system and a single two-electron irreversible in the protic medium. The substituent inductive effects in several DHNQ derivatives were noted. The electron withdrawing groups, chloro and phenylsulfonyl, enhance the oxidation potentials, and the eletron-releasing groups, methyl and methoxy, make the reduction more difficult. The strength of the substituents follows the order: C₆H₅SO₂ ? Cl ? CH₃ ? CH₃O. A linear Hammett relationship exists in this series when the averaged value of σ_meta and σ_para are used as substitution constants.     

Multi-element determinations of N,N-dimethylformamide (DMF) coal slurries using ICP-OES

A slurry nebulisation technique was applied for elemental analysis of bituminous coals SARM 18, SARM 19 and four coals from three different seams in Witbank, South Africa, by inductively coupled plasma optical emission spectroscopy (ICP-OES). Major elements (Al, Ca, Fe, Mg, S, Si and Ti) and trace elements (Ba, Cr, Mn, Ni, Sr, V, Zn and Zr) in coal were determined. Various slurry preparations were evaluated using two dispersants (glycerol and Triton X-100) and by varying the concentration of dispersants, between 0.1% and 1.0% (v/v). The effect of initially solubilising the ground coal in N,N-dimethylformamide (DMF) was investigated by varying the volume of DMF added. The effect of wet grinding with DMF was investigated. Wet grinding with DMF was shown to drastically reduce particle sizes (50.0% < 0.28 μm and 90.0% < 6.17 μm) as compared to dry grinding (50.0% < 5.25 μm and 90.0% < 11.1 μm). The reduced particle sizes and increased transport efficiency of the coal slurries led to improved analytical recoveries of elements in the reference coal, SARM 18. The best analytical recoveries for all elements were achieved using 0.1% Triton X-100 with 10.0% DMF. Results obtained by ICP-OES after wet grinding of the coal with DMF, using 0.1% Triton X-100, also gave excellent recoveries (Al, 100%; Ca, 103%; Cr, 106%; Fe, 102%; Mg, 100%; Mn, 104%; Ni, 109%; Si, 102%; Ti, 95.0%; and V, 108%). The results obtained with 10.0% DMF and 0.1% Triton X-100 were in agreement with certified values for all selected elements according to paired t-test at the 95.0% confidence level. Selected elements (Al, Ca, Fe, Mg, Mn, Si, Ti and V) were also analysed with X-ray fluorescence for comparison with results obtained from ICP-OES. Analysis by ICP-OES of microwave digested coal was also carried out. It is suggested that the DMF slurry technique could be used for routine analysis of bituminous coals.     

N,N-dicyclohexylcarbodiimide assisted synthesis and characterization of poly(vinyl alcohol-co-vinyl levulinate)

Poly(vinyl alcohol-co-vinyl levulinate) was synthesized by N,N-dicyclohexylcarbodiimide assisted esterification of poly(vinyl alcohol) with free levulinic acid using 4-pyrrolidino pyridine as a catalyst in N,N-dimethyl acetamide/lithium chloride solvent system in order to optimize the reaction condition. The vinyl levulinate content in the copolymer was attained up to 0.95. The ¹³C NMR dyad compositional analysis indicated the block character of the copolymer was 0.92, suggesting almost random poly(vinyl alcohol-co-vinyl levulinate) was formed. Glass transition temperature dependence on vinyl levulinate content of the copolymers fitted better into Gordon-Taylor equation as compared with Fox equation and the glass transition temperature of poly(vinyl levulinate) was given as 2.3 °C by the least regression method.     

Double stimuli-responsive behavior of linear and star-shaped poly(N,N-diethylaminoethyl methacrylate) in aqueous solution

We report on the synthesis and characterization of linear and star-shaped poly(N,N-diethylaminoethyl methacrylate) (PDEA). The synthesis was accomplished by Atom Transfer Radical Polymerization (ATRP) via a core-first approach using sugar-based multifunctional initiators. The investigation of the solution properties in water shows that PDEA is both pH- and temperature-responsive, analogous to the behavior of poly(N,N-dimethylaminoethyl methacrylate) (PDMA). In literature, PDEA is frequently referred to as being only pH-sensitive. The critical pH values for the aggregation are close to the apparent pK_a values in all cases, i.e. a high charge density is necessary to keep the polymers soluble. The cloud points show a strong dependence on the pH value of the solution but no dependence on either molecular weight or architecture. Thus, the two polymers differ only quantitatively, as PDEA has cloud points about 40 K lower than PDMA and critical pH values which are 1.5-2 units lower than PDMA.     

Conductance measurements of some electrolytes in N,N-dimethyformamide and its binary mixtures witth other organic solvents—II

Equivalent conductances of Bu₄NBPh₄, Bu₄NNO₃, Bu₄NI,KClO₄, Kl, NaI, NaBPh₄, Ph₄PCl, LiCl, AgNO₃ and CuClO₄. 4AN have been measured at 25°C in binary mixtures of N,N-dimethylformamide (DMF) containing 1 mol % of 1, 1, 3, 3-tetramethylurea (TMU), dimethylsulphoxide (DMSO) and hexamethylphosphotriamide (HMPT). Such measurements for LiCl, NaI, KClO₄ and CuClO₄. 4AN have also been carried out in DMF and in binary mixtures of DMF containing 1 mol % pyridine (Py), α-picoline (α-Pic), β-picoline (β-Pic), γ-picoline (γ-Pic) and acetonitrile (AN). The conductance data in all the cases have been analyzed by the Shedlovsky equation. Limiting ion conductances have been obtained by the method of Fuoss et al. The actual solvated radii of ions, evaluated using limiting ion conductances show that Ag⁺ and Cu₊ have strong preferential solvation by all solvents which have been used to prepare the binary mixtures with DMF and the preferential solvation for both Ag⁺ and Cu⁺ with HMPT, DMSO and TMU is relatively stronger than with AN and is practically of similar magnitude as with the organic bases.     

Synthesis and properties of N,N'-unsymmetrical dialkyl-3,4:9,10-perylenebis(dicarboximide)s

N,N'- Unsymmetrical dialkyl-3,4:9,10-perylenebis(dicarboximide)s (in which alkyl = methyl, ethyl, propyl, butyl, isobutyl, pentyl, hexyl and octyl) were prepared by the condensation of N-alkyl-3,4:9,10-perylene-tetracarboxylic monoanhydride monoimide with the appropriate alkyl-amines. The properties of these derivatives as pigments were tested and their thermal stability measured.     

Studies on ion—solvent interactions through viscosity measurements—potassium iodide in N,N-dimethylformamide—water mixtures

The viscosities of DMF—water mixtures and of KI solutions in these mixed solvents have been measured at 25°, 30°, 35° and 40° C, covering the whole range of solvent composition. The Jones—Dole B-Coefficient, after passing through a minimum in water-rich solvent composition region, increases with the increase in DMF content in the solvent mixture. The variation of viscosity of the solvent mixture and of B-coefficient with solvent composition and temperature have been discussed in terms of solvent—solvent and ion—solvent interactions.     

Anodic chlorination of substituted benzenes - the choice of the chlorination reagents

Some substituted benzenes ArH were anodically chlorinated in acetonitrile LiClO₄ on a platinum electrode in the presence of either Cl^? anion or a chlorinated Lewis acid (such as AlCl₃). The overvoltage on the oxidation of Cl^? caused by a strong complexation by some Lewis acid allows consideration that the anodic reaction passes through the radical cation of the aromatic substrate. In such conditions, polychlorinations are possible and in the specific case of toluene, it is shown that the reaction favors the parachlorotoluene formation. The influence of different parameters (for example, the ratio of the concentrations AlCl₃/ArH, the nature of the Lewis acid) in such a reaction are discussed.     

Conductance studies in amide—water mixtures—III. Tetraethylammonium iodide in N,N-dimethylacetamide-water mixtures at 35°C

Conductance data of tetraethylammonium iodide in N,N-dimethylacetamide (DMA)—water mixtures (44.01 ? D ? 66.96) in the concentration range 0.001–0.06N and densities, viscosities and dielectric constants of the solvent mixtures (DMA—water) at 35°C are reported. Limiting equivalent conductance A_o, association constant K_A and pairing radius R are derived from Fuoss (1978) equation. Most structuredness of the solvent mixture indicated by the maximum viscosity is obtained at 1(DMA):3(H₂O) mole ratio. Walden product passes through a maximum with change of DMA content in the solvent mixture. Ionic association is found negligible (K_A < 10) in all the solvent compositions studied.     

Anodic oxidation of aniline for waste water treatment

The electro-oxidation of dilute aqueous solutions of aniline was studied on a lead dioxide packed bed anode. The anolyte consisted of 400 ml of 5.5 mM aniline in dilute sulphuric acid. The anolyte was recirculated through a packed bed electrochemical reactor with an anode compartment volume of 5.0, at various flowrates. The concentrations of aniline, benzoquinone, maleic acid and carbon dioxide were measured against time for experiments ranging from 0.5 to 5.0h in duration. The effects of applied current, pH, flowrate and initial aniline concentration on the percentage of aniline oxidized and carbon dioxide produced are discussed. Aniline in the solution oxidized readily, but further oxidation of intermediates to carbon dioxide was more difficult. The percentage of aniline oxidized increased with increasing current density, while it decreased with increasing initial aniline concentration and pH. Current efficiencies ranged from 15 to 40% for complete oxidation of aniline to CO₂.     

The behaviour of high polar organic solvents at platinum electrode—III. the study of adsorption and electrode reactions of N,N-dimethylformamide

The adsorption of N,N-dimethylformamide and oxidation of adsorbed species at platinized platinum electrode in 0.5 M aq H₂SO₄ were studied by potentiodynamic, potentiostatic and radiometric techniques. It was shown, that adsorption occurs with decomposition of DMF molecule. Below 0.15 V the adsorbed species are desorbed from the electrode surface.The kinetics of adsorption and oxidation of DMF are described by Langmuire type relation. The mechanism of adsorption of DMF as well as oxidation of adsorbed products has been considered.     

Influence of pressure on the state of poly(N-isopropylacrylamide) and poly(N,N-diethylacrylamide) derived polymers in aqueous solution as probed by FTIR-spectroscopy

We investigated the hydration and swelling properties of poly(N-isopropylacrylamide) and poly(N-isopropylacrylamide)-poly(N,N-diethylacrylamide) derived microgels by Fourier transform infrared- (FTIR-) spectroscopy in a wide region of the temperature-pressure plane. These systems are known to show a swollen-to-collapsed-transition upon temperature elevation. Our data reveal that pressure favours the swollen, hydrated state over the collapsed state in all systems investigated. A detailed analysis of the fractions of the respective IR sensitive amide-I′-subbands allowed the calculation of ΔG^o and ΔV^o for the pressure-induced swelling process as well as evaluation of various intra- and intermolecular hydrogen bonding connectivities in the different systems. In fact, considerable differences exist between different polymer or microgel types with regards to their hydrogen bonding pattern as a function of temperature and pressure, and the microgels may even exhibit a biphasic swelling behavior. Notably, the thermodynamic parameters derived reveal to be in the same order of magnitude as measured for the pressure and cold denaturation of proteins.     

N,N-dialkylimidazolium dialkylphosphate ionic liquids: Their extractive performance for thiophene series compounds from fuel oils versus the length of alkyl group

N-butylimidazole-derived dialkylphosphate ionic liquids (ILs) are demonstrated to be effective for extractive removal of aromatic sulfur compounds (S-compounds) from fuel oils, and show strong preferential extraction for aromatic S-compound versus toluene. Sulfur partition coefficients (K_N) between IL and fuel oil at 298.15 K are determined experimentally over a wide range of sulfur content. The results show that the sulfur removal selectivity for a specific IL is dependent on the molecular structure of the S-compounds and follows the order dibenzothiophene > benzothiophene > thiophene > 3-methylthiophene, and the efficiency of the ILs for removal of aromatic S-compounds is dependent on the size and structure of both cations and anions of the ILs. For the dialkylphosphate ILs studied with the same anion, the longer the alkyl substitute to the imidazolium ring is the higher the K_N value for that IL, and a similar trend is found for the ILs with same cation.     

Viscosity of tetraethylammonium bromide solutions in N,N-dimethylformamide-water mixtures

The viscosity of tetraethylammonium bromide solutions in dimethylformamide-water mixtures have been determined at 25, 30 and 35°C. From this data, the B-coefficient of Jones-Dole equation have been calculated and are analysed in terms of structure making or structure breaking ability of the ions. Further, the activation parameters of viscous flow were obtained by means of the application of the transition-state theory. These values are studied in function of solvation and volume effects, in order to estimate the mechanism of the viscous flow.