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

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

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 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

A borax fusion technique for quantitative X-ray fluorescence analysis

A borax fusion technique to cast glass discs for quantitative X-ray analysis is described in detail. The method is based on the “nonwetting” properties of a Pt/Au alloy towards molten borax, on the favourable composition of the flux and finally on the favourable form of the casting mould. The critical points of the technique are stressed, resulting in a method which could be carried out successfully by inexperienced workers. In general the method compares favourably in speed and accuracy with wet-chemical methods

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