Microtitrations of organic bases in nonaqueous solvents

Summary The use of acetic acid as a solvent for the microtitration of organic bases has been investigated. Bases, whose pK_b, in water are 12 or below have been found titrable both visually and potentiometrically.Acetic anhydride permits extending the scope to bases whose pK_b in water are no greater than about 13.5. Visual and potentiometric titrations have been performed at room temperature and at 0° C.The possibilities of using formic acid and propionic acid have been investigated. Whereas both these solvents exert a greater levelling effect on bases than acetic acid or acetic anhydride, they also have some undesirable features. Formic acid is not stable and commercial propionic acid cannot be obtained with a sufficiently low water content to permit titrations without the addition of acetic anhydride.

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Zusammenfassung Die Eignung der Essigsäure als Lösungsmittel für die Mikrotitration organischer Basen wurde untersucht. Basen, deren pK_b in wäßriger Lösung unter 12 ist, konnten potentiometrisch sowohl, als auch mit Farbindikatoren titriert werden.Mit Essigsäureanhydrid als Lösungsmittel kann der Titrationsbereich erweitert werden, so daß noch Basen mit pK_b 13,5 eingeschlossen sind. Potentiometrische Titrationen und Titrationen mit Farbindikatoren wurden bei Zimmertemperatur und bei 0° C ausgeführt.Auch die Eignung von Ameisensäure und Propionsäure als Lösungsmittel wurde untersucht. Beide erhöhen die Titrierbarkeit schwacher Basen mehr als Essigsäure und Essigsäureanhydrid, besitzen aber auch unerwünschte Eigenschaften. Ameisensäure zersetzt sich langsam und die Propionsäure des Handels enthält zu viel Wasser, um für Titrationen ohne Zusatz von Essigsäureanhydrid geeignet zu sein.

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Résumé L'emploi de l'acide acétique comme solvant pour le microtitrage des bases organiques a été l'objet des recherches des auteurs. Les bases dont les pK_b dans l'eau sont égaux ou inférieurs à 12 peuvent être titrées soit visuellement soit potentiométriquement. L'anhydride acétique permet d'étendre le domaine de titrage à des bases dont les pK_b dans l'eau ne sont pas supérieurs à environ 13,5. Il a été possible d'effectuer des titrages visuels et potentiométriques à la température ambiante ainsi qu'à 0° C. Les possibilités d'emploi de l'acide formique et de l'acide propionique ont été également étudiées. Non seulement ces deux solvants exercent sur les bases un effet de nivellement plus élevé que l'acide acétique ou l'anhydride acétique, mais ils présentent en outre certaines caractéristiques défavorables. L'acide formique n'est pas stable tandis qu'il n'est pas possible d'obtenir l'acide propionique avec une teneur en eau suffisamment basse pour permettre des titrages sans addition d'anhydride acétique.

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This paper is abstracted from the Master's Thesis ofM. Gutterson, June, 1956.     

Microtitration of weak organic acids in nonaqueous solvents

Summary The applicability of nonaqueous titrimetry to the microdetermination of weak organic acids has been established.Phenols have been found to be titrable in dimethylformamide. Those containing one or more chlorine, hydroxyl, or carbonyl groups can be titrated to a thymol blue endpoint and those containing amino or alkyl groups to an azo-violet endpoint.Sulfonamides, barbiturates, enols, imides, and some hydrazides have also been titrated in dimethylformamide. The scope extends to compounds with a pK_a of about 9 for visual titrations and 10.5 for potentiometric titrations in dimethylformamide.Pyridine may be used as a solvent for the visual titration of weak acids with pK_a of up to about 10.5. Methyl-isobutanone may be used for the visual titration of acidic compounds with a pK_a of about 9 and lower by using thymol blue as the indicator.The hydrazides give better results in potentiometric titrations; the visual endpoints are poorly defined for practical purposes.

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Zusammenfassung Die Maßanalyse in nichtwäßrigem Milieu wurde für die Mikrobestimmung schwacher organischer Säuren herangezogen.Phenole lassen sich in Dimethylformamid titrieren. Enthalten sie ein oder mehr Chloratome bzw. Hydroxyl- oder Carbonylgruppen, so können sie gegen Thymolblau als Indikator titriert werden; Amino- oder Alkylgruppen tragende Phenole werden gegen Azoviolett titriert.Sulfonamide, Barbiturate, Enole, Imide und einige Hydrazide werden gleichfalls in Dimethylformamid titriert: Verbindungen mit einem pK_s bis etwa 9 durch visuelle Endpunktbestimmung, bis 10,5 auf potentiometrischem Weg.Pyridin eignet sich als Lösungsmittel für die visuelle Titration schwacher Säuren mit einem pK_s bis etwa 10,5, Methylisobutanon hingegen für saure Verbindungen mit einem pK_s von etwa 9 und weniger, wobei Thymolblau als Indikator dient.Hydrazide werden besser potentiometrisch titriert; die visuelle Endpunktbestimmung eignet sich für praktische Zwecke nur wenig.

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Rèsumè La possibilité d'application de la titrimétrie non aqueuse au microdosage des acides organiques faibles a été établie par les auteurs. Ils ont trouvé que les phénols étaient susceptibles d'être titrés dans la diméthylformamide. Ceux qui contiennent un ou plus d'un groupement chlore, hydroxyle ou carbonyle peuvent être titrés en présence de bleu de thymol comme indicateur de point final, et ceux qui contiennent des groupements amines ou des groupements alcoyles à l'aide de l'indicateur violet azoïque. Les sulfamides, les barbiturates, les énols, les imides et quelques hydrazides ont été également titrés dans la diméthylformamide. Le domaine de dosage s'étend à des composés dont le pK_a est voisin de 9 pour les titrages visuels et de 10,5 pour les titrages potentiométriques dans la diméthylformamide. Il est également possible d'utiliser la pyridine pour les titrages visuels d'acides faibles dont le pK_a est voisin de 10,5. On peut employer la méthylisobutanone pour des titrages visuels de composés acides dont le pK_a est inférieur à 9 ou voisin de cette valeur; on utilise alors le bleu de thymol comme indicateur.Il est préférable d'utiliser les titrages potentiométriques dans le cas des hydrazides car les points finaux de titrages sont mal définis dans la pratique courante lorsqu'on les détermine visuellement.

     

The oxidation of cytochrome c in nonaqueous solvents

Cytochrome c was adsorbed readily and remained electroactive, with a redox potential of 32 mV, on TiO2 films placed on SnO2; similar behaviour was observed in glycerol, whereas in acetonitrile, irreversible oxidation occurred at a potential of 800 mV.     

Acid-base titrations in nonaqueous solvents Analysis of dimethyl sulphate

A nonaqueous titrimetric procedure was developed for the determination of the dimethyl sulphate, methyl hydrogen sulphate and sulphuric acid content of dimethyl sulphate samples. Methyl hydrogen sulphate and sulphuric acid are determined by a differentiating potentiometric titration in pyridine with tributylethylammonium hydroxide. Pyridine converts the dimethyl sulphate into the weakly acidic methylpyridinium methyl sulphate which does not interfere in the titration. Dimethyl sulphate is determined by reacting it with an excess of 2-dimethylaminoethanol and titrating the excess with perchloric acid. Precision and recovery data for commercial samples of dimethyl sulphate are presented.     

Ni–Cu bimetallic colloids prepared in nonaqueous solvents

Colloidal dispersions in nonaqueous media were obtained by simultaneous evaporation of Ni and Cu. The metals were cocondensed at 77 K in an organic matrix of 2-methoxyethanol, 2-propanol or acetone. The metallic dispersions were characterized by transmission electron microscopy, electron diffraction and UV–vis spectroscopy. The stability at room temperature was also measured. The stability of the Ni–Cu bimetallic dispersions is less than that of the Ni and Cu dispersions alone. The presence of more than one phase was observed. It is interesting to note that Ni/Cu ratio does not change the stability of the bimetallic dispersions dramatically. The polarity of the solvent should play a very important role in stabilizing the metal particles by solvatation effects. Transmission electron microscopy studies show the size control effect of Cu with small colloidal size in the bimetal. The electron diffraction studies reveal the presence of amorphous bimetallic particles and particles with crystallinity show typical particles formed for more than one phase (NiO, CuO, Cu, Ni and Cu–Ni). Cu and Ni, for example, are amorphous and crystalline particles, respectively. Differential scanning calorimetry and X-ray spectroscopy characterized the bimetallic solids of Ni–Cu/2-methoxyethanol obtained by evaporation of solvent. The differential scanning calorimetry studies of the solids show transition characteristics of crystalline growth; no glass transitions were observed. The X-ray diffractograms show that the crystallites are too small (less than 100 Å), giving rise to low intensity and wide peaks.     

Alternating current polarography of metal carbonyl complexes in nonaqueous solvents

Using commercially available instrumentation, a supporting electrolyte and electrode system was devised which permits ac polarography of organometallic compounds, transition metal complexes, and other substances in nonaqueous solvents such as methanol, N,N-dimethylformamide, or acetonitrile. The first two solvents mentioned were found to be far superior to the latter. Tetrabutylammonium perchlorate electrolyte (0.1 M or less) in methanol, for example, affords a fairly flat baseline in the applied dc potential range of 0 to ?3 V with well-shaped voltammetric peaks for most reducible substances. A unique feature of the method, which permits one to easily obtain replicable polarograms and peak potentials, is the use of a mercury pool auxiliary electrode rather than the usual platinum or tungsten electrodes.     

Ion-specific influence of electrolytes on bubble coalescence in nonaqueous solvents

We report the effects of electrolytes on bubble coalescence in nonaqueous solvents methanol, formamide, propylene carbonate, and dimethylsulfoxide (DMSO). Results in these solvents are compared to the ion-specific bubble coalescence inhibition observed in aqueous electrolyte solutions, which is predicted by simple, empirical ion combining rules. Coalescence inhibition by electrolytes is observed in all solvents, at a lower concentration range (0.01 M to 0.1M) to that observed in water. Formamide shows ion-specific salt effects dependent upon ion combinations in a way analogous to the combining rules observed in water. Bubble coalescence in propylene carbonate is also consistent with ion-combining rules, but the ion assignments differ to those for water. In both methanol and DMSO all salts used are found to inhibit bubble coalescence. Our results show that electrolytes influence bubble coalescence in a rich and complex way, but with notable similarities across all solvents tested. Coalescence is influenced by the drainage of fluid between two bubbles to form a film and then the rupture of the film and one might expect that these processes will vary dramatically between solvents. The similarities in behavior we observe show that coalescence inhibition is unlikely to be related to the surface forces present but is perhaps related to the dynamic thinning and rupture of the liquid film through the hydrodynamic boundary condition.     

Influence of tetraalkylammonium ions on structure of nonaqueous solvents

Summary The half-wave potentials of the redox system [Co(en)₃]³⁺/[Co(en)₃]²⁺ have been influenced by the tetraalkylamonium cation of the supporting electrolyte used. This was explained with the specific interactions (solvation) of the tetraalkylamonium ion with the nonaqueous solvent.

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Einfluß von Tetraalkylammoniumionen auf die Struktur nichtwäßriger Lösungsmittel (Kurze Mitt.)

Zusammenfassung Das Halbwellenpotential des Redoxsystems [Co(en)₃]³⁺/[Co(en)₃]²⁺ wird von Tetraalkylammonium-Ionen des Stützelektrolyten beeinflußt. Dies wird durch die spezifischen Wechselwirkungen (Solvatation) der Ionen mit dem nichtwäßrigen Lösungsmittel erklärt.

     

Complexing ability of some mixed sulfur-oxygen crown ethers in nonaqueous solvents

Complexes of the Li⁺, Na⁺, Cs⁺, Tl⁺ and Ag⁺ ion with macrocyclic ligands dithia-18-crown-6 and trithia-12-crown-4 were studied by multinuclear NMR in several nonaqueous solvents and their stabilities are compared with the complexes formed by the analogous polyethers, 18-crown-6 and 12-crown-4. In all cases the substitution of the sulfur atoms for the oxygens results in a substantial decrease in the stability of the complexes. While the stability of the macrocyclic complexes is strongly influenced by the solvents and varies inversely with the Gutmann's donicity scale for these solvents, the decrease in the stability of the thia-complexes is only marginally dependent on the solvent properties but varies significantly with the cation, being largest for the Cs⁺ ion.     

Capillary electrophoresis of boron cluster compounds in aqueous and nonaqueous solvents

The electrophoretic properties of boron cluster compounds were determined in water, methanol and ACN as solvents of the BGE and discussed based on the principles of ion migration. Two types of boron cluster compounds were investigated. One type consisted of derivatives of the nido-7,8-dicarbaundecaborate cluster, the other types are derivatized cobalt bis(dicarbollide) ions (COSANs) whose central cobalt atom is sandwiched by two 7,8-dicarbaundecaborate clusters. The BGE in all solvents was acetate/acetic acid buffer with pH 4.75 in water, 9.7 in methanol and 22.3 in ACN, respectively, at different ionic strength between 5 and 30 mM. The dependence of the mobility on ionic strength could not be explained by the theory of Debye, Hückel and Onsager, but good agreement was found upon considering an ion size parameter. Limiting mobilities were derived by curve fitting, and by the aid of the solvent viscosities the hydrodynamic radii of the analyte anions were calculated. They are between 0.25 and 0.48 nm, and were nearly independent of the solvent. Electrophoresis of the analytes in a BGE consisting of 6 mM perchloric acid in ACN allows the conclusion that the present boron cluster compounds behave as stronger acids than perchloric acid.     

Kinetics of oxidation of hydrogen peroxide at hemin-modified electrodes in nonaqueous solvents

Hemin adsorbed on graphite electrodes and used to catalyse the reduction of hydrogen peroxide in an aqueous buffer and in a range of nonaqueous solvents has been described. The immobilised hemin is stable in the solvents examined. The rate limiting step involves the reaction between hemin and hydrogen peroxide. Kinetic analysis of the response in nonaqueous solvents showed that I_max / K_m^app increased linearly with the solvent hydrophobicity (log P) in all solvents, a trend that is explained by preferable partitioning of hydrogen peroxide into the polar hemin layer.     

Sorption of amides by cationic exchange resins from nonaqueous solvents

Separation of weakly basic acetanilide, N-methylacetanilide, and N-n-propylacetanilide could not be accomplished using a conventional sulfonic acid resin and various mixed eluants containing methanol and acetonitrile. The chromatograms showed elution bands that were broad and tailed badly. However, with a new macroreticular resin, some separations were obtained with the same nonaqueous eluants that had been used with the conventional resin. Although separation of acctanilide from the two N-substitutcd acetanilides was almost complete, the separation of the two N-substituted compounds was not.Acetamides were separated from acetanilides because the former were not retained by the resin when a 1 :9 methanol-acetonitrile eluant was used.The two important parameters which render these separations possible are probably solvation and hydrogen bonding around tile sulfonic acid group of the resin and resin matrix attraction. Methanol is a better solvating liquid than acetonitrile. In acetonitrile the amide probably associates through the carbonyl with the sulfonic acid; in methanol this association does not occur.     

Magnesium-25 NMR studies of magnesium salts and complexes in nonaqueous solvents

Magnesium-25 NMR measurements were carried out on aqueous and non-aqueous solutions of magnesium salts. In the former case the²⁵Mg resonance frequency was independent of the concentration or of the counterion. In nonaqueous solvents, however, the resonance frequency was dependent on the solvent, the concentration, and on the nature of the counterion, indicating some cation-anion interactions. Measurements on Mg²⁺—phosphonoacetic acid mixtures in aqueous solutions gave strong indications of complexation. Only inconclusive evidence was obtained on the complexation of Mg²⁺ by macro-bicyclic cryptand C211 in methanol solutions, and no evidence of complexation was obtained with macrocycle 12-crown-4 in dimethylformamide solutions.     

Far-infrared and Raman study of lithium and sodium cryptates in nonaqueous solvents

Far-infrared spectra of sodium and lithium cryptates were observed in several nonaqueous solvents. The spectra are characterized by a broad band whose frequency is independent of the solvent or of the anion and which is assigned to the vibration of the cation in the cryptand cavity. The band frequencies were 234±2, 218±1, 243±3, and 348±1 cm^?1 for Na⁺-C222, Na⁺-C221, Li⁺-C221, and Li⁺-C211 cryptates, respectively. These bands were found to be Raman-inactive, indicating that the cation-ligand interaction is very largely electrostatic in nature.     

The principles of migration and dispersion in capillary zone electrophoresis in nonaqueous solvents

Nonaqueous solvents are interesting media for capillary zone electrophoresis as they can affect all relevant parameters governing the separation of sample zones. However, for a rational planning of the working conditions and an appropriate interpretation of the results obtained, the basic principles of ion migration and zone dispersion must be understood. Many solvent induced effects need to be carefully considered and recognized before full exploitation of nonaqueous solvents can take place. It is the goal of this overview to present the fundamental physicochemical aspects of capillary zone electrophoresis in nonaqueous solvent systems. Therefore, the detailed discussion is related to the effect of organic solvents on electrophoretic mobilities (based on the theory of conductance), acid-base dissociation behavior (based on the transfer activity coefficient and medium effect), pH, separation efficiency (with regard to mobility and diffusion coefficient in dilute solutions), resolution, and electroosmotic flow.