Ion-selective electrodes in titrations involving azo-coupling reactions

An organic cation-selective indicator electrode based on a PVC membrane plasticized with 2-nitrophenyl 2-ethylhexyl ether can be used in potentiometric titrations of aromatic hydroxy compounds, amines, and compounds containing active methylene groups, with 4-methyl-, 4-bromo-, or 4-nitro-benzenediazonium chloride solutions as titrants. Useful results were obtained in determinations of 16 passive components, including 2-naphthol, some 2-naphthol sulfonic acids, 8-quinolinol and its 5-sulfonic acid, ammo-1-naphthol-3-sulfonic acids, 1-naphthylamine sulfonic acids, resorcinol, 2,4-toluylenediamine, two acetanilide derivatives, and two substituted sulfophenyl pyrazolone derivatives. 4-Bromobenzenediazonium chloride proved to be the best titrant of the diazonium salts tested.     

Ion-selective electrodes in titrations involving azo-coupling reactions

Compounds that react slowly with arenediazonium salts can be determined by back-titration. When 1-naphthalene- or 4-bromo-1-naphthalenendiazonium chloride is used, the excess is back-titrated with sodium tetraphenlborate or 2,4-diaminotoluene, the titration being monitored with a PVC membrane electrode plasticized with 2-nitrophenyl 2-ethylhexyl ether. Disodium 2-naphthol-3,6-disulfonate (r-salt), 2-naphthol-7-sulfonic acid, acetylacetone, and 1-(2′,5′-dichloro-4′-sulfophenyl)-3-carboxy-5-pyrazolone were determined without xyxtematic errors in times shorter than needed for direct titration.     

Ion-selective electrodes in titrations involving azo-coupling reactions: Part 5. Determination of arenediazonium salts of ampholytic character

Determination of arenediazonium salts (0.3–0.7 g) of ampholytic character is based on their reaction with 1-phenyl-3-methyl-5-pyrazolone, the excess of which is titrated with a 4-bromo-1-naphthalenediazonium chloride solution. The titration is monitored potentiometrically with a PVC membrane electrode plasticized with 2,4-dinitrophenyl n-octyl ether. Eight arenediazonium salts containing hydrophilic groups (e.g., carboxylic and sulfonic acids) were determined without systematic errors.     

Ion-selective electrodes in titrations involving azo-coupling reactions: Part 4. Determination of Secondary Amines

The determination of secondary amines (1–10 mg) is based on their reaction with arenediazonium ions to form triazenes. The sample is mixed with 4-bromo-1-naphthalenediazonium chloride and, when the coupling reaction is complete, the excess of diazonium salt is back-titrated with sodium tetraphenylborate. The end-point is easily evaluated from the sigmoidal potentiometric titration curves recorded with a PVC membrane indicating electrode plasticized with 2,4-dinitrophenyl n-octyl ether. Diethylamine, diethanolamine, piperidine, N-ethylaniline and 1-(N-methyl)amino-9,10-anthraquinone were used as test compounds.     

Dual reactivity of diazonium salts derived from 1-amino-2-ethynyl-9,10-anthraquinones

Diazotization of vicinal 1-amino-2-ethynyl-4-R-9,10-anthraquinones followed by a reaction with NaN₃ gave 5-hydroxy-3-R-1H-naphtho[2,3-g]indazole-6,11-diones or 3-ethynyl-5-R-6H-anthra[1,9-cd]isoxazol-6-ones, depending on the substituents at the triply bonded C atom and in position 4 of the anthraquinone framework.     

Titrations with piezoelectric monitoring : Part 2. Compleximetric titrations and precipitation titrations

A piezoelectric detector is used to monitor titration reactions involving complex formation or precipitation. Analytes at concentrations down to 10^?4 mol 1^?1 can be determined. The frequency shift in the compleximetric titrations is affected by the composition of the solution, the buffer and competing ligands present in the solution. Factors influencing the frequency shift in the precipitation titration are also investigated.     

A generalized approach for the calculation and automation of potentiometric titrations Part 2. Redox Titrations

The very fast calculation procedure described earlier is applied to calculate the titration curves of complicated redox systems. The theory is extended slightly to cover inhomogeneous redox systems. Titrations of iodine or 2,6-dichloroindophenol with ascorbic acid are described. It is shown that correspondence between theory and practice is good as long as the relevant stability constants and redox potentials are known with sufficient accuracy.     

A generalized approach for the calculation and automation of potentiometric titrations Part 1. Acid-Base Titrations

Fast and accurate calculation procedures for pH and redox potentials are required for optimum control of automatic titrations. The procedure suggested is based on a three-dimensional titration curve V = f(pH, redox potential). All possible interactions between species in the solution, e.g., changes in activity coefficients and influences of redox potential on pH variations, are taken into account. The number of titrant additions can be reduced considerably without loss of precision, by using the fact that the pH of a protolyte or mixture of protolytes at some fraction titrated does not depend strongly on the actual concentration.     

Potentiometric titrations with ion-exchanging membrane electrodes: Part II. Theoretical aspects of simple precipitation titrations

Titration curves were derived for potentiometric titrations with zero electric current, utilizing a membrane electrode as indicating electrode, the membrane consisting of permselective, ion-exchanging material. As a first example, calculations were made for simple precipitation titrations with only +1 or -1 charged ions present in the solution to be titrated and in the reagent. For the calculations of the membrane potentials the theory of TEORELL and MEYER and SIEVERS was used. The influence of several parameters, such as the diffusion coefficients of the ions, the capacity of the membrane and the concentration of the solutions, was examined.     

The reactions of some pyranylideneiminium salts with amines. Part 1

The iminium salt, N,N-dimethyl-N-[2-(2,6-diphenyl-4H-pyran-4-ylidene)ethylidene]iminium perolilorate ( 1 ), reacts with secondary amines, such as piperidine, by exchanging the dimethyl-amino function for a piperidine. Primary amines react with 1 to give 1-alkyl-2-phenyl-4-phenacylidene-1,4-dihydropyridines. The bisiminium salt, N,N,N',N' -tetramethyI-N,N'-[2-(2,6-diphenyl-4H-pyran-4-ylidene)-1,3-propanediylidene]bis(iminium perchlorate) ( 2 ), reacts with ammonia to give 3,6-diphenylcopyrine and with primary amines to give the corresponding N,N' -dialkyl quaternary copyrines. The salt 2 reacts with secondary amines with exchange of the dimethylamino groups of 2 by the secondary arnine and addition of the amine at the 2-position of the pyran ring.     

Germylenes derived from pyridine-containing diols: reactions with diphenylphosphoryl azide and 9,10-phenanthrenequinone*

A study was carried out on the behavior of monomeric germylenes derived from pyridine-containing diols in reactions with diphenylphosphoryl azide and 9,10-phenanthrenequinone. It was found that the germanium atom increases its oxidation state to 4+ in these reactions. The structure of the product of the reaction with 9,10-phenanthrenequinone was confirmed by X-ray structural analysis, which showed a transannular germanium-nitrogen interaction in this product.     

Tautomerism of anthraquinones: IV. 1-Hydroxy-9,10-anthraquinone and its substituted derivatives

1-Hydroxyanthraquinone and its substituted derivatives exist as equilibrium mixtures of four tautomers and rotational isomers. Their anions have 9,10-and 1,10-quinoid structures. Each tautomer or conformer is characterized by a single π₁,π* band in the electronic absorption spectrum.     

Pd-catalyzed arylation reactions with phenol diazonium salts: application in the synthesis of diarylheptanoids

The first total synthesis of the natural product (3S,7R)-5,6-dehydro-de-O-methyl centrolobine and various analogues is reported, using a highly regio- and diastereoselective Mizoroki-Heck reaction of phenol diazonium salts and enantiopure dihydropyrans. The assigned relative configuration was confirmed by single-crystal X-ray structure analysis, but a revision of the absolute configuration is proposed based on polarimetric measurement.     

Coated-wire organic ion-selective electrodes in titrations based on ion-pair formation: Part 2. Determination of ionic surfactants

Both cationic and anionic surfactants can be determined titrimetrically using a coated-wire electrode with a PVC membrane plasticized with 2-nitrophenyl 2-ethylhexyl ether. Cationic surfactants and other organic compounds of cationic character are titrated with sodium tetraphenylborate; for the titration of anionic compounds, cetylpyridinium bromide or 1-(ethoxycarbonyl)pentadecyl-trimethylammonium bromide (Septonex) is recommended. Characteristics of titration curves together with statistical evaluation of results are described for determinations of 15 specimens, involving pure substances as well as technical samples.     

Titrations with piezoelectric monitoring : Part 1. Fundamental theory and titration of acids and bases

The use of a piezoelectric quartz crystal detector is proposed for monitoring the course of a titration reaction by observation of the frequency shift of the oscillating crystal. Satisfactory titrations can often be obtained using the acid-base technique, which is much more sensitive than the classical conductimetric titration and oscillometric titrration, with a lowest titratable concentration that is much lower but which can still be applied in the presence of a large amount of unreacting electrolyte.