2-methoxyethanol as a solvent for conductometric acid-base titrations

Conductometric titrations of a series of organic acids in 2-methoxyethanol were performed with 1,3-diphenylguanidine (DPG) as titrant. For benzoic, p-chlorobenzoic and picric acids, phenylphenol and barbital, excellent recoveries were obtained from well-defined conductance vs. volume plots. Results for the dicarboxylic phthalic and adipic acids were also good. However, the titration curves for the difunctional salicylic and p-hydroxybenzoic acids were not clearly defined. The results are discussed and compared with cnductometric titrations of acids in other non-aqueous solvents. Several determinations of electrolyte conductance as a function of concentration revealed that, as expected, the selected substances are weak electrolytes in methoxyethanol.     

Ion solvation in 3-methyl-2-oxazolidone

In continuing previous studies of the solvation behavior of electrolytes in nonaqueous media, a series of tetraalkylammonium tetraphenylborates, cesium and rubidium tetraphenylborates, tetraalkylammonium perchlorates, and tetraphenylarsonium chloride were investigated by proton magnetic resonance spectroscopy in 3-methyl-2-oxazolidone, a solvent with high dielectric constant, high polarity, and wide liquid range. In this study, as in a previous investigation, it was found that salt solutions containing the tetraphenylborate anion were found to shift the proton peaks upfield, indicating an increase in electron density around solvent protons. In this study the same effect has been noted for tetraphenylborate as well as tetraphenylarsonium ion and is attributed to the large diamagnetic anisotropy of the aromatic solute molecules which results in circulation of electrons induced by the magnetic field. This ring current causes shielding of the solvent protons, and the shielding increases as the concentration of aromatic solute increases, resulting in upfield morement of chemical shift irrespective of whether the aromatic moiety is the cation or anion.     

The use of 2,6-dichlorophenolindophenol as indicator in acid-base titrations

2,6-Dichlorophenolindophenol shows acid-base indicator properties. Its colour is red in acidicmedia and blue in alkaline media. 'Ihe transitional pH value is 5.7 and the colour change is sharp and easy to observe. The use of the indicator in various acid-base titrations, as well as the effects of neutral salts, alcohol and temperatures, were checked. The absorption spectra of the acidic and basic forms of the indicator are presented.     

Conductance behavior of 1:1 electrolytes in 3-methyl-2-oxazolidone at 25°C

The conductance behavior of twenty-five 1∶1 electrolytes has been investigated in 3-methyl-2-oxazolidone (3Me20x) at 25°C. Conductance data were analyzed by the Lee-Wheaton equation, and all salts studied were found to be only slightly associated. Ionic limiting equivalent conductances were obtained using tris(iso-pentyl)butylammonium tetraphenylborate as a reference electrolyte. The relative values of the ionic limiting molar conductance are generally similar to those for other dipolar aprotic solvents. However, the order $$\lambda _0 (i - Pent_3 BuN^ + ) > \lambda _0 (Pent_4 N^ + )and\lambda _0 (Br^ - ) > \lambda _0 (ClO_4^ - )$$ is opposite to that found previously in the similar solvent 3-tert-bytyl-2-oxazolidone.     

Synthesis of acid-base transformations of 3-aroyl-6-methyl-2-oxopyridines

In hydrolysis of 3-aroyl-6-methyl-2-methoxypyridines, 3-aroyl-6-methyl-2-oxopyridines are formed, which with methyl iodide in an alkaline medium give the corresponding 1-methyl derivatives.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1354–1356, October, 1986.     

A twinned mercury-filled glass electrode system for acid-base titrations in a number of non-aqueous solvents

A pair of mercury-filled glass electrodes is proposed for acid-base titrations in non-aqueous solvents or their mixtures with each other or with water.     

Eriochrome black a as an indicator for chelatometric titrations

The use of Eriochrome Black A for the EDTA titrations of Zn, Mn, Ni, Pb and Cu ions is described. Spot tests for the determination of the sensitivity limits of detection have been made     

Microemulsions with CO2 as a solvent

Supercritical CO₂ is considered as a promising alternative for volatile organic solvents currently used in certain industrial processes and products, however, the poor solubilizing power of CO₂ towards polar substances remains a significant barrier to applications. Employing effective surfactants which generate stable dispersions and water/CO₂ microemulsions is accepted as one way to improve the physico-chemical properties of CO₂. This article reviews recent studies on microemulsions in liquid CO₂, as well as the development of CO₂-philic surfactants.     

Aromatisation of 3-carbomethoxy-3-methyl-3h-pyrazol solvent effect and catalysis through acid

At 60° the title compound isomerises quantitatively to aromatic products $\text{3}$ and $\text{4}$. A kinetic study reveals the influence of solvent polarity and of acid on the rate and direction of this reaction.     

On the use of bis(1,5-dimethyl-2-phenyl-3-pyrazolone)perchlorate as a standard for non-aqueous titrations

Summary Titration curves and data are presented for the standardization of perchloric acid in glacial acetic acid and for tetrabutylammonium hydroxide solutions vs. antipyrine perchlorate. In the standardization of the basic titrant this compound yields a single potentiometric break only in the highly basic solvent 1,1,3,3-tetramethylguanidine. In methanol, pyridine, acetonitrile, N,N-dimethylformamide, and dimethylsulfoxide two breaks are obtained. Only the second break is analytically useful and corresponds to a monobasic acid.Work performed under the auspices of the U.S. Energy Research & Development Administration, contract No. W-7405-Eng-48     

Proposed molecular structures for 3-butenenitrile, 2-methyl-3-butenenitrile,and 3-methyl-3-butenenitrile

Molecular structures are proposed for the two conformers, s-cis and gauche, existing for 3-butenenitrile and 3-methyl-3-butenenitrile, and for the three predicted conformers of 2-methyl-3-butenenitrile, using structural parameters transferred from related molecules. The proposed structures for the two conformers of 3-butenenitrile have principal moments of inertia which agree well with experimental values obtained by microwave spectroscopy, except for the gauche I_A moment. The experimental value of I_A for the gauche conformer of 3-butenenitrile could only be determined at the time with a low degree of precision, hence the microwave spectrum of this conformer should probably be reexamined.     

Dehydration-dehydrogenation of 2-propanol as a model reaction for acid-base characterization of catalysts

The relationship between the acid-base properties of various solids, as determined by a spectrophotometric procedure and the apparent dehydrogenation (K₁) and dehydration rate constant (K₂) of 2-propanol have been studied by using a continuous-flow reactor.     

Transition metal complexes with 2-methyl-, 3-methyl-, and 4-methyl-piperidine dithiocarbamate as ligands

Summary A new series of manganese(III), cobalt(II), nickel(II), zinc(II), cadmium(II) and mercury(II) complexes with monomethylsubstituted dithiocarbamates as ligands has been synthesized and studied. Their structures are discussed in relation to their spectroscopic, magnetic and thermal properties. The dithio-ligands exhibit bidentate behaviour acting as S,Sdonors in all the complexes. In the far i.r. region particular attention is paid to a comparison of the spectra of the octahedral complexes with those of the other metal derivatives (12 metal to ligand molar ratio). The e.s.r. spectra are indicative of aD _2h symmetry in the cobalt(II) complexes.     

Development of an impedimetric immunosensor for the determination of 3-amino-2-oxazolidone residue in food samples

The use of furazolidone in food animals has been banned in European Union (EU) because of its carcinogenicity and mutagenicity on human health, but its continued misuse is widespread. Therefore, there is an urgent need for a simple, reliable, and rapid method for the detection of its marker residue, 3-amino-2-oxazolidinone (AOZ), in food products. In this regard, a sensitive and reliable electrochemical method was presented to detect AOZ based on a novel label-free electrochemical impedimetric immunosensor to address this need. The immobilization of monoclonal antibody against AOZ (denoted as AOZ-McAb) on the gold electrode was carried out through a stable acyl amino ester intermediate generated by 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC) and N-hydrosuccinimide (NHS), which could condense antibodies on the self-assembled monolayer (SAM). The detection of AOZ was performed by measuring the relative change in charge transfer resistance before and after AOZ and AOZ-McAb immunoreaction by electrochemical impedance spectroscopy (EIS). Under the optimized conditions, the relative change in charge transfer resistance was proportional to the logarithmic value of AOZ concentrations in the range of 20.0 to 1.0 × 10⁴ ng mL⁻¹ (r = 0.9987). Moreover, the proposed immunosensor has a high selectivity to AOZ alone with no significant response to the metabolites of other nitrofuran antibiotics, such as 3-amino-5-morpholinomethyl-2-oxazolidinone (AMOZ), semicarbazide (SEM), and 1-aminohydantoin hydrochloride (AHD). This protocol has been applied to detect AOZ in food samples with satisfactory results.     

Electrogenerated iodine as a reagent for coulometric titrations in alcoholic media

Conditins are established for the generation of iodine with high current efficiency (>99%) in solutions of potassium acetate in methanol or ethanol, in the presence of potassium iodide or tetraethylammonium iodide at platinum or glassy carbon working electrodes, respectively. Iodine solutions in methanol are stable, but solutions in ethanol are less so. Procedures are given for coulometric titration of various thiols with anodically generated iodine in these solvents; biamperometric or potentiometric end-point detection can be used. The error of the titrations did not exceed ± 2.0% for ca. 1-mg samples.     

Evaluation of 2-methyl-3-hydroxy-4-pyridinecarboxylic acid as a possible chelating agent for iron and aluminium

In view of a possible application to Fe and Al chelation therapy, 2-methyl-3-hydroxy-4-pyridinecarboxylic acid (DT2) was synthesised, and its complex formation, electrochemical and cytotoxic properties were studied. The complexing properties of DT2 towards Fe(III) and Al(III) were investigated in aqueous 0.6 m (Na)Cl at 25 degrees C by means of potentiometric titrations, UV-vis spectrophotometry, and 1H NMR spectroscopy. DT2 is a triprotic acid (H3L+) having pKa1 = 0.47, pKa2 = 5.64 and pKa3 = 11.18. The metal-ligand complexes observed in solution and their corresponding stability constants (log beta values) are the following: FeLH (19.38), FeL (16.01), FeLH(-1) (12.28), FeL2H2 (37.29), FeL3H3 (53.41), FeL3H2 (47.99), FeL3H (41.21) and FeL3 (34.1); AlLH (17.43), AlL2H2 (33.74), AlL2H (27.6), AlL3H3 (48.72), AlL3H2 (42.67), AlL3H (35.8) and AlL3 (27.92). The complex formation between DT2 and Fe(II) was studied by UV-vis: the weak complex FeLH (log beta = 15.8) was detected. DT2 shows a lower complexation efficiency with Fe(III) and Al(III) than that of other available chelators, but higher than that of its non-methylated analogue 3-hydroxy-4-pyridinecarboxylic acid (DT0). The electrochemical behaviour of DT2 was investigated by means of cyclic voltammetry, indicating that the oxidation of the ligand proceeds through a two electron process with a CECE mechanism. Voltammetric curves suggest that the oxidation or the reduction of DT2 in vivo is unlikely. According to the thermodynamic data, also the Fe(III)-DT2 complexes do not undergo redox cycling at physiological pH. Amperometric titrations of solutions containing Fe(III) and DT2 at pH = 5 indicated the same Fe(III) : ligand stoichiometric ratio as calculated from potentiometric data. The toxicity of DT2 and of other simple hydroxypyridinecarboxylic acids was investigated in vitro and no cytotoxic activity was observed (IC50 > 0.1 mM) on cancer cell lines and also on primary human cells, following a three day exposure.     

Luminol as a fluorescent acid-base indicator

The acid and base dissociation constants of luminol are determined at various ionic strengths. The transition interval occurs at pH 7.7-9.0, therefore luminol is a fluorescent indicator for the titration of strong and weak acids and strong bases. Its value as an indicator is established by titrating milk, red wine and cherry juice.     

Phthalhydrazidylazoacetylacetone as a chemiluminescent acid-base indicator

Phthalhydrazidylazoacetylacetone, an azo derivative of luminol, has been shown to be superior to luminol as a chemiluminescent indicator for acid-base titrations.     

An arbitrary correction function for CO(2) evolution in acid-base titrations and its use in multiparametric refinement of data

A great number of acid-base titrations are performed under an inert gas flow: in the procedure, a variable amount of CO(2)-from carbonated reactants-is carried away and thus prevents strict application of mass-balance equations. A function for the CO(2) evolution is proposed and introduced into the general expression for the volume of titrant. Use of this expression in multiparametric refinement yields, besides the usual values (concentrations, acidity constants...), a parameter characteristic of this departure of CO(2). Furthermore, a modified weighting factor is introduced to take into account the departure from equilibrium caused by the slow CO(2) evolution. The validity of these functions was successfully tested on three typical examples: neutralization of strong acid by sodium carbonate, of sodium carbonate by strong acid, and of a mixture of hydrochloric acid, 4-nitrophenol and phenol by carbonated potassium hydroxide.     

NMR isotope shifts as a probe of a rapid nondegenerate equilibrium in 2-aryl-3-methyl-2-butyl cations

Equilibrium NMR isotope shifts can be detected for nondegenerate equilibria by comparison with intrinsic shifts in static model compounds. Such equilibrium shifts are smaller than in similar nondegenerate equilibria.