Elution and analysis of residual chloride from anion exchangers

Summary Strong anion exchangers can be transformed to the hydroxyl forms by elution with analytical grade sodium hydroxide. The residual chloride contents remain above the 0.1% level. Such chloride amounts can rapidly and easily be determined with a radiochemical method using ^110mAg as tracer. This method was compared with neutron activation and potentiometric titration methods.

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Zusammenfassung Starke Anionenaustauscher können durch Spülen mit Natronlauge in die Hydroxylform übergeführt werden. Der Rest-Chloridgehalt bleibt jedoch immer über 0.1%. Diese Chloridgehalte können unter Zuhilfenahme des Isotopes ^110mAg mit einer radiochemischen Methode bestimmt werden. Vergleiche mit potentiometrischen Titrationen und Neutronenaktivierungsanalysen werden gegeben.

     

On the influence of some inorganic salts on the partitioning of citric acid between water and organic solutions of tri-n-octylamine: Part I: Methyl isobutyl ketone as organic solvent

Reactive extraction is a commonly applied process to recover carboxylic acids from aqueous solutions. Such processes are nowadays designed using process simulation software. However, the essential prerequisite for such a simulation is the availability of a reliable thermodynamic model for the encountered phase equilibrium. Industrial experience revealed that even very small amounts of a strong electrolyte (e.g., sodium chloride) can considerably reduce the amount of carboxylic acid extracted from the aqueous into the organic phase. This contribution presents new experimental results for the influence of sodium nitrate, sodium chloride, sodium sulfate, sodium citrate and hydrochloric acid on the partitioning of citric acid to the coexisting aqueous/organic liquid phases of the system water + methyl isobutyl ketone (organic solvent) + tri-n-octylamine (chemical extractant) at 25 °C. A detailed discussion of the experimental results reveals that the dramatic decrease of the partition coefficient of carboxylic acid is caused by the chemical loading of the extractant by the inorganic acid, i.e. both acids (the weak carboxylic acid as well as the strong inorganic acid) compete for the sodium ions (in the aqueous phase) and for the amine (in the organic phase). In phase equilibrium the amine is predominantly loaded with the inorganic acid while the sodium salt of the carboxylic acid remains in the aqueous phase. That behavior is described by a thermodynamic framework that is able to predict the complex liquid–liquid equilibrium from information determined exclusively from investigations on subsystems.     

Potentiometric titration of hydroxide,aluminate and carbonate in sodium aluminate solutions

An automated potentiometric titration of hydroxide, aluminate and carbonate in sodium aluminate solutions is described. The addition of barium chloride before titration with hydrochloric acid enables the three components to be determined in one run, involving neutralization of hydroxide, protonation of aluminate and dissolution of barium carbonate. The accuracy and precision of the method are satisfactory for a rapid method used for control of aluminum oxide production.     

Acid-base strengths in 1,2-dichloroethane

The pK_a value of hydriodic acid in 1,2-dichloroethane was determined from conductivity measurements. A glass electrode was calibrated for dichloroethane in the potentiometric titration of hydriodic acid with tetramethylguanidine. From potentiometric titrations, the pK_a values in dichloroethane of hydrobromic acid, hydrochloric acid, picric acid and some sulfonphthaleins as well as some protonated nitrogen bases were determined. In the curves of the titrations of the carboxylic acids and the hydrogen halides with TMG, evidence was found for the formation of the complex B(HX)₂.     

Acid—base equilibria in the mixed solvent 80% dimethyl sulfoxide—20% water : Determination of pK Values and Investigation of the Conditions for Titration of some Aromatic Carboxylic Acids and their Conjugated Bases

The acid—base properties of some aromatic carboxylic acids of zero charge type HA have been investigated in the mixed solvent, 80% DMSO—20% water, by means of potentiometric measurements with a glass electrode. The pK_a values of the following aromatic carboxylic acids have been determined: benzoic, o-chlorobenzoic,p-chlorobenzoic, m-bromobenzoic, 2,4-dichlorobenzoic, 2,5-dichlorobenzoic, 2,6-dichlorobenzoic, 2,3,5-triiodobenzoic, 3,5-dinitrobenzoic,p-methylbenzoic, m-aminobenzoic, o-hydroxybenzoic 3,4-dihydroxybenzoic, 3,4,5-trihydroxybenzoic, o-methoxybenzoic, 2,3-dimethoxybenzoic, 5-amino-2-hydroxybenzoic, pyridine-2-carboxylic, thiophene-2-carboxylic, 1-naphthylacetic, diphenylglycolic. The mixed solvent investigated offers better titration conditions for the determination of these acids than water and some other non-aqueous solvents.     

Transition metal free one pot synthesis of aryl carboxylic acids via dehomologative oxidation of styrenes

Iodine/NaOH-catalyzed one-pot dehomologative oxidation of styrenes to aryl carboxylic acids has been reported. A wide range of carboxylic acids are obtained using iodine (I₂) as a catalyst, tert-butyl hydroperoxide (TBHP) as an oxidant and sodium hydroxide (NaOH) as a base. This reliable conversion involves dehomologation of styrene to aromatic aldehyde which on subsequent oxidation affords aryl carboxylic acid. This protocol was used for gram-scale synthesis as it is free from chromatographic purification. This is the first report for the oxidative transformation of styrenes into aryl carboxylic acids under transition metal-free conditions.     

Potentiometric studies on organic compounds containing sulphur with a sulphide ion-selective membrane electrode

Phenylthiourea and N,N-diphenylthiourea can be determined in the concentration range 10¹–10^?3M by potentiometric titration with silver nitrate solution with a sulphide ion-selective membrane electrode. The influence of the alkali and acid concentration on the course of the reactions with the silver nitrate titrant was studied. When phenylthiourea is titrated in the presence of 0.1 M sodium hydroxide, silver sulphide is precipitated, and the phenylcyanamide formed simultaneously reacts further with silver nitrate to form a silver phenylcyanamide precipitate. When N,N-diphenylthiourea is titrated under similar conditions, silver sulphide is again formed, but no cyanamide-type compound can be formed owing to the presence of the second phenyl group. In 1 M sodium hydroxide both compounds studied react with two equivalents of silver to give silver sulphide and phenylurea or diphenylurea, respectively. In the presence of nitric acid both compounds react similarly with silver nitrate. Two molecules of the compounds react with one molecule of silver nitrate to give a white precipitate.     

Trimerization of aldehydes with one α-hydrogen catalyzed by sodium hydroxide

Trimerization of 2-methylpropanal (isobutyraldehyde) is a simple and effective method to synthesize 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate and 2,2,4-trimethyl-1,3-pentanediol-3-monoisobutyrate which are often used as film forming auxiliaries in paints. The use of solid sodium hydroxide as a catalyst provides an excellent yield of above 85 % after the optimization of the reaction time and the catalyst dosage. Furthermore, trimerization of four other aldehydes with one α-hydrogen catalyzed by solid sodium hydroxide can also take place and the yield of 1,3-diol monoesters reaches 50–70 %. Trimerization of aldehydes with one α-hydrogen can be explained by a three-step reaction mechanism: (i) aldol condensation of aldehyde; (ii) crossed Cannizzaro reaction; and (iii) esterification of carboxylic acid and alcohol.     

Epoxidation of syndiotactic 1,2-polybutadiene with peracids

The epoxidation of syndiotactic 1,2-polybutadiene (84 and 16% 1,2 and 1,4 units, respectively) with carboxylic peracids prepared in situ and m-chloroperbenzoic acid was studied. In the course of epoxidation in the presence of carboxylic peracids, oxirane groups are formed only through epoxidation of double bonds in the macromolecular backbone, whereas m-chloroperbenzoic acid is responsible for the chemical modification of 1,2 and 1,4 units of polybutadiene. The basic kinetic parameters of 1,2-polybutadiene epoxidation with peracids of various chemical structures were determined.     

Bestimmung der Oberfl?che von hochdisperser Kiesels?ure durch automatische potentiometrische Titration mit Natronlauge

Zusammenfassung Die Bestimmung der spezifischen Oberfläche von hochdisperser Kieselsäure kann durch Titration von pH 4 auf pH 9 mit 0,1 N Natronlauge erfolgen. Es wird eine Titrationseinrichtung beschrieben, die diese Bestimmung automatisch durchführt und den erhaltenen Oberflächenwert (Quadratmeter/Gramm) auf einem Papierstreifen ausdruckt.

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Determination of the surface area of highly dispersed silica by automatic potentiometric titration with sodium hydroxide solution

The specific surface area of finely divided silica can be determined by titration from pH 4 to pH 9 using aqueous 0.1 N sodium hydroxide solution. An apparatus is described performing this titration automatically with direct print-out of the resulting surface area (m²/g).

     

Analytik der polyacrylnitrilfasern : V über fine abgewandete reduktionsmethode zur bestimmung geringer schwefelmengen in acrylnitrilpolymerisaten

Sulphur contents (0.01–0.2% S) in polyacrylonitriles (50–100 mg samples) can be estimated by decomposition of the polymer by heating with KOH, reduction of the sulphate formed (with acetic acid, hydriodie acid, and hypophosphite) and absorption of hydrogen sulphide in 1 N sodium hydroxide. Sulphide is then determined polarographically utilizing the anodic sulphide wave, or potentiometrically with 0.001 M mercuric chloride as titrant and amalgamated silver wire and stainless steel wire as electrodes. The whole procedure is done easily in a stream of nitrogen and can therefore be applied even when the atmosphere is contaminated with sulphur-containing substances.     

Oxidation and chlorination reactions of perfluoroketene-N,S-acetals

The paper presents the results of the investigation of oxidation and chlorination reactions of perfluoroketene-N,S-acetals. Oxidation reactions of perfluoroketene-N,S-acetals proved to be dependent on the nature of oxidizing agent and led to the formation of corresponding sulfone in the case of m-chloroperbenzoic acid or amides of α-H-perfluoroalkane carboxylic acids in the case of tert-butyl hydroperoxide or hydrogen peroxide. Reaction of 1-tert-butylsulfanyl-2,3,3,4,4,4-hexafluoro-1-[N-methyl,N-((S)-α-methylbenzyl)amino]-but-1-ene with sulfuryl chloride demonstrated the chlorination of perfluoroketene-N,S-acetals as a new approach in the synthesis of chiral α-chloro perfluoroalkane carboxylic acid amides.     

The apparent molal volumes of mixtures of 1:1 electrolytes in aqueous urea solutions: A test of Young's rule

The apparent molal volumes of sodium chloride, sodium bromide, potassium chloride, and potassium bromide were determined for each salt at 2.000m in 8.000m urea-in-water solvent systems at 25°C. In each instance, the volumes were larger than those observed for the same salts in pure water. The volume changes on mixing the six pairs of these salts were measured at a constant ionic strength of 2m in the same urea-water solvent. The results of this test suggest that Young's rule applies equally well in urea-water solvent systems as it does in pure water.     

On the influence of some strong electrolytes on the partitioning of acetic acid to aqueous/organic two-phase systems in the presence of tri-n-octylamine: Part I: Methyl isobutyl ketone as organic solvent

The recovery of carboxylic acids from aqueous phases is often achieved by reactive extraction with water-insoluble amines which are dissolved in an organic solvent. The basic design of such downstream processes requires a thermodynamic framework for the encountered liquid–liquid equilibrium. The thermodynamic framework should be able to describe the rather uncommon and surprising effects that comparatively small amounts of strong electrolytes might have. Such strong electrolytes can either reduce or increase the affinity of a carboxylic acid for the organic phase in particular at low aqueous phase concentrations of the carboxylic acids. That behavior was explained in previous investigations with citric acid as a model compound for a carboxylic acid and modeled by combining the dissociation/protonation equilibrium in the aqueous phase with the formation of organic phase complexes of (amine + acid(s) + water). In the present investigation this work is extended to acetic acid as another example for a carboxylic acid. New experimental results are reported for the influence of sodium chloride, sodium nitrate, sodium sulfate, sodium citrate and hydrochloric acid on the partitioning of acetic acid to coexisting aqueous/organic liquid phases of the system (water + methyl isobutyl ketone (organic solvent) + tri-n-octylamine (chemical extractant)) at 25 °C. The phase behavior is described by an extension of the previously published thermodynamic framework that is able to describe/predict the influence of a strong electrolyte on the partitioning of acetic acid.     

Electronic emission and absorption spectra and the effect of hydrogen bonding on the ground and excited electronic states of some anilines

From electronic absorption and emission spectra in solutions it appears that intramolecular hydrogen bonding, strong enough to resist rupture by dioxane, exists in o-chloroaniline in the excited state only. Fluorescence quenching behaviour in the presence of dioxane indicates that intermolecular hydrogen bonding significantly increases intersystem crossing rate in m-chloroaniline only. This and other emission spectral characteristics in this hydrogen bonding solvent at 77 K show that the first excited singlet electronic state S₁ of m-chloroaniline is ππ*, whereas the states S₁ of aniline, toluidines and p-chloroanilines have some nπ* character. On formation of intermolecular hydrogen bond in dioxane, the corresponding triplet states of the molecules acquire pronounced nπ* character. An examination of phosphorescence decay curves reveals triplet complex formation in m- and p-chloroaniline but there is no evidence of triplet complex in the other aromatic amines studied.     

Application of flow-injection potentiometric system for determination of total concentration of aliphatic carboxylic acids

In this work, flow-injection system with potentiometric detection was tested for determination of total carboxylic acid concentration. Detection part of the examined system consists of ion-selective electrodes (ISEs) with polymer membranes of different compositions. First electrode is based on Zr(IV)-tetraphenylporphyrin as ionophore selective towards carboxylic acid anions, the membrane of second one contains only liphophilic anion exchanger - tridodecylmethylammonium chloride. Final response of the system is a result of combination of EMF signals from both electrodes. Combination of two detectors enables significant decrease of differences between potentiometric signals induced by mixtures of studied anions of various concentrations as compared to results obtained only with metalloporphyrin-based ISE. The use of anion-exchanger based detector allows for elimination of the influence of aliphatic carboxylic acids lipophilicity.Proposed potentiometric flow-injection system was employed for determination of short-chain aliphatic carboxylic acids (so-called VFA - volatile fatty acids) in samples originating from an anaerobic digester. Results obtained for these relatively complicated samples are in good agreement with results obtained with the use of reference colorimetric method.Linear response towards carboxylic acids was observed in the concentration range of 10⁻⁴ to 10⁻² mol dm⁻³, with the slopes in the range of −110 to −150 mV dec⁻¹ (for acetate⁻ and butyrate⁻, respectively). System enables for determination of about 6 samples per hour. Life time of ISEs average about 2 months.     

Potentiometric Titration of Weak Acids

Abstract

A desk-calculator program has been developed for determination of the equivalence point when a weak acid is titrated with a strong base. The stability constant (K^H _HA) of the acid can be computed simultaneously. When data from a potentiometric titration of boric acid with sodium hydroxide have been processed with the program the equivalence point has been determined with an accuracy of 0.3–0.4 per cent. The computed value of the stability constant of boric acid (log K^H _HA = 9.11) is in good agreement with the values given in literature.     

An ion-exchange scheme for the determination of the major cations in sea water

A cation-exchange scheme is described for the determination of the principal cations in sea water. The cations are adsorbed onto a column of Amberlite CG 120. Sodium and potassium are eluted together using 0.15 M ammonium chloride and determined gravimetrically as sulphates; potassium is then determined gravimetrically as potassium tetraphenylboron and sodium is determined by difference. Magnesium and calcium are eluted by means of 0.35 M ammonium chloride and 1 M ammonium acetylacetonate (pH 9.6) respectively, and titrated with EDTA. Finally, strontium is eluted with 2 M nitric acid and determined by flame photometry. Tests made using an artificial sea water showed that the method had coefficients of variation of 0.02, o.22, 0.04, 0.08 and 0.8% for sodium, potassium, magnesium, calcium and strontium respectively.     

Determination of carbonate in the presence of hydroxide: Part 2. Evidence for the existence of a novel species from first-derivative potentiometric titration curves

An additional maximum has been detected in the differential potentiometric titration of mixtures of sodium hydroxide and sodium carbonate with hydrochloric acid using pH-responsive glass electrodes. This maximum is not detected under the following conditions: if ethanol (mol fraction >0.2) or t-butanol (mol fraction >0.1) is added; when the temperature is raised above 55°C; when hydrogen gas is bubbled through the solution; if a hydrogen gas electrode is used instead of the glass electrode; when carbonic anhydrase is added. The additional feature is ascribed to a new species HCO₃·H₂CO₃^- formed in solutions by a slow reaction.     

Determination of Surface Silanols of Silica Gels and HPLC Bonded Phases

Abstract

A rapid method determining the surface silanols of silica gels and HPLC bonded phases involves a titration of silica gel with sodium hydroxide, in a medium of any of the following 10% aqueous salts: sodium chloride, sodium nitrate, sodium sulfate, potassium chloride, potassium nitrate and potassium sulfate. The silanols are quantified as m eg/g. It is possible to determine cation exchange capacity of a cation-exchanger due to an acid as an end group and surface silanols separately.