The anodic oxidation of bases in the solvent m-cresol

The oxidation of bases in the solvent m-cresol was investigated by polarography, voltammetry at the rotating platinum disc electrode and by chronopotentiometry. It was shown that the m-cresolate ion is the electroactive species in this reaction. The oxidation is a one-electron process giving a phenoxy radical. This phenoxy radical is converted in a chemical reaction of higher than first order, most likely to the dimer

Acid-base strengths in 1,2-dichloroethane

The pKa 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 pKa 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

Application of ion-selective electrodes for the microdetermination of chlorine and bromine in volatile organic compounds

A method is described for the determination of chlorine and bromine in mg samples of highly halogenated volatile organic compounds. The samples are introduced into the combustion system by injection and burnt in a stream of oxygen at 1000° over platinum and quartz. The combustion gases are absorbed in a solution of 80% acetic acid containing some hydrogen peroxide, nitric acid and mercuric chloride or bromide. The halide is then titrated with mercury. The end-point is determined by an ion-specific electrode. One determination takes approximately 15 minutes. The relative standard deviation of the determination is about 1%. The reversibility and durability of the silver sulphide electrode are unaffected as long as the mercury ion concentration is less than 10−3M

Acid-base titrations in solvents of relatively low dielectric constant

From a comparison of the pKa values of various compounds in the solvent 1,2-dichloroethane, m-cresol, acetic acid and pyridine, the differences in basicity of these solvents could be determined. If the basicity of 1,2-dichloroethane is taken as 0 pK units, the basicities of m-cresol, acetic acid and pyridine were found to be 3, 7 and 11 pK units, respectively. It is shown how these differences in basicity can serve to predict pKa values in solvents belonging to the Brønsted classes 5–8

Acid-base strengths in m-cresol

For various acids and bases dissociation constants were determined conductimetrically in m-cresol. A glass electrode was calibrated by means of some compounds with dissociation constants known from conductivity measurements. Potentiometric titrations with this calibrated glass electrode gave dissociation constants of some other acids and bases in m-cresol. The value 2·10−19 was found for the self-dissociation constant of m-cresol. From the difference pKa (cresol) - pKa (pyridine) for those compounds having acid or base strengths which are not levelled either in pyridine or m-cresol, it was found that the solvent m-cresol has a basicity about 8 pK units less than that of pyridine

The coulometric titration of acids and bases in m-cresol medium

A method is described for the coulometric titration of acids and bases in the solvent m-cresol. The method is suitable for bases with pKa values greater than 11 in m-cresol, or for acids with pKa values below 13 in m-cresol. Amounts of 5–50 μeq of acid or base can be determined with a relative accuracy of ±1%

Ion-selective carbon-paste electrodes for halides and silver(I) ions

The behaviour of a simple type of ion-selective electrode for halogens and silver has been studied. The electrode consists of a plastic body filled with carbon paste, the surface of which can be easily renewed. The paste composition is based on carbon-nujol (5:1, w/v) or carbon-paraffin wax (3:1,w/w) containing a prepared mixture of silver halide-silver sulphide (1–30%). The electrodes have low ohmic resistance and show a rapid Nernstian response (within 2–5 mV) for halide and silver ions down to 5·10-5 M chloride, 1·10-5 M bromide and 5·10-7 M iodide with the respective electrodes. Ions forming very stable complexes with halide or silver and those having strong oxidizing or reducing action interfere

The coulometric titration of acids and bases in dimethylsulfoxide media

The coulometric titration of 20–200 μeq of acids and bases in DMSO media is described. In the titration of bases, the electro-oxidation of hydrogen at a platinized platinum electrode is used as the source of protons. The conditions for 100 % current efficiency at this electrode are low current density to avoid passivity and regular treatment of the electrode with potassium dichromate—sulfuric acid to remove a poisoning sulfide layer. The accuracy of the titrations is better than ±1 %. Very weak acids like phenols (pKa (DMSO) ≈16) can be titrated successfully. Tris(hydroxymethyl)aminomethane is the weakest base titrated

Acid-base strengths in pyridine

Although pyridine is a solvent with a low dielectric constant, spectrophotometric determinations show simple dissociation without ion pairs as intermediates for some sulfonphthaleins and polynitrophenols in pyridine.\ud \ud The salts of a number of amines and hydrochloric acid, perchloric acid and picric acid are not completely dissociated in pyridine. Dissociation constants of these salts were determined from differential vapour pressure measurements. For the titrations in pyridine of an acid with an amine, calculations were based on the following reactions : HXH+ + X−; B + H+ BH+; BH+ +X−BH+X−. With this reaction scheme it was possible to determine pKa values for protonated amines in pyridine from the curves of titrations carried out with a calibrated glass electrode. Evidence for the occurrence of homoconjugation of some polynitrophenols in pyridine was found in the titration of these compounds with tetramethylguanidine. Homconjugation constants were estimated from the titration curves

The determination of major and some minor constituents in lead zirconate-titanate compositions by x-ray fluorescence and atomic absorption spectrometry

An accurate X-ray fluorescence spectrometric method is described for the determination of lead, zirconium and titanium in lead zirconate-titanate ceramics. Careful matching of samples and standards by a borax fusion method resulted in a relative standard deviation of about 0.2% for the major constituents. The determination, after separation, of the unreacted oxide of lead by atomic absorption spectrometry, and of the unreacted oxides of zirconium and titanium by X-ray fluorescence spectrometry is also described. An X-ray fluorescence spectrometric method is proposed for the determination of dope elements (K, La, Sm, Yb) with internal standards (Ca, Ce, Cr, Ni respectively). The magnesium dope is determined by atomic-absorption spectrometry with standard addition