Daniel Rosales

Solvent effects on the dissociation of aliphatic carboxylic acids in water—N,N-dimethylformamide mixtures

Abstract The autoprotolysis constants of several water- N,N -dimethylformamide mixtures were determined. The acid dissociation constants of formic, acetic, propionic, n-butyric, isobutyric, n-valeric, isovaleric, 2-methylbutyric and trimethylacetic acids were evaluated in the same media by potentiometric titration. Empirical equations for the calculation of autoprotolysis constants and acid dissociation constants at 25° C in the mixed solvents are proposed. Approximate solvation numbers were obtained by multiple linear regression analyses of p K a values.

Asymmetric derivatives of carbohydrazide and thiocarbohydrazide as analytical reagents.

The synthesis and analytical properties of two asymmetric derivatives of carbohydrazide and thiocarbohydrazide with pyridine and phenol have been studied. The compounds tested are 1-(2-pyridylmethylideneamino)-3-(salicylideneamino)urea and 1-(2-pyridylmethylideneamino)-3-(salicylideneamino) thiourea. The analytical utility of these reagents is outlined. A spectrophotometric method for determining the formation constants of the complexes is described.

Spectrophotometric determination of palladium in catalysts and carbenicillin with 1-(2-pyridylmethylidene)-5-(salicylidene)-thiocarbohydrazone

A selective and sensitive method is described for the spectrophotometric determination of palladium using 1-(2-pyridylmethylidene)-5-(salicylidene)thiocarbohydrazone reagent. The orange complex is formed in pH 8.3 EDTA-bicine-borate buffer in a medium containing 32%V/V dimethylformamide, and the absorbance is measured at 505 nm. The molar absorptivity is 16 500 l mol–1 cm–1, and in the determination of 0.75 µg ml–1 of palladium the relative standard deviation is about 2%. The effect of interferences was studied and the selectivity of the reaction was enhanced by using appropriate masking agents. The method was applied to the determination of palladium in synthetic mixtures, hydrogenation catalysts and carbenicillin (semi-synthetic penicillin).

Spectrophotometric determination of indium in nickel alloys and zinc ores with 1-(2-pyridylmethylideneamine)-3-(salicylideneamine)thiourea.

A sensitive method for the spectrophotometric determination of indium with 1-(2-pyridylmethylideneamine)-3-(salicylideneamine)thiourea is proposed. A yellow complex is formed at pH 4.5 (succinate buffer) in a medium containing 40% dimethylformamide, and the absorbance is measured at 415 nm. The molar absorptivity is 6.2 x 10(4)l.mole(-1).cm(-1). The relative standard deviation of the procedure is 1.5%. The method has been applied to determination of indium in a nickel alloy and three zinc ores, with prior isolation of indium by co-precipitation with ammonia and extraction into n-butyl acetate from 5M hydrobromic acid.

Spectrophotometric determination of zinc with 1-(2-pyridylmethylidene)-5-(salicylidene)thiocarbohydrazone

Abstract The absorbance of the yellow complex formed in pH 4.8 acetate buffer is measured at 410 nm in 40% (v/v) dimethylformamide. The molar absorptivity is 68 000 l mol −1 cm −1 . The effect of interferences is discussed, and the method is applied to zinc in tap water and standard alloys.

Spectrophotometric determination of palladium by solvent extraction as the Pd(II)-biacetylmonoxime 2-pyridylhydrazone complex

Abstract Determination of trace levels of palladium(II) is described. The method relies upon the extraction of palladium(II)-biacetylmonoxime 2-pyridylhydrazone (BMPH) from aqueous acidic solution into chloroform to form a purple-reddish complex. The molar absorptivity of the Pd-BMPH complex is about 7500 liters mol−1 cm−1 at 560 nm in the chloroform extract. The highly colored chloroform extract is suitable for spectrophotometric determination. The method devised has been applied to the determination of palladium in Pd CaCO 3 catalyst with good results.

Spectrophotometric determination of cobalt as the orange cobalt-biacetylmonoxime 2-pyridylhydrazone complex

Abstract A spectrophotometric method for the determination of cobalt is described. The method is based on the formation of an orange color by reaction of cobalt(II) with biacetylmonoxime 2-pyridylhydrazone in basic solutions. The molar absorptivity at 480 nm is about 9.2 × 10 3 liters mol −1 cm −1 (pH 10) and spectrophotometric sensitivity is 0.0062 μg Co cm −2 for absorbance = 0.001.

Spectrophotometric determination of cobalt in hydrofining catalysts, alloys and salts with biacetylmonoxime 2-pyridylhydrazone

Biacetylmonoxime 2-pyridylhydrazone (BMPH) has been examined to evaluate its usefulness as a selective spectrophotometric reagent for cobalt. The yellow coloration is formed at an initial pH of 5–6 in a medium containing 20% of dimethylformamide and measured at 430 nm at a final concentration of 0.5 N perchloric acid. The molar absorptivity is 3700 l mol–1 cm–1. The method has been applied to the determination of cobalt in synthetic mixtures, hydrofining catalysts, alloys and chemicals with good results. The BMPH chromogen shows a wide range of application.

Spectrophotometric determination of zinc with biacetyl mono(2-pyridyl)hydrazone with application to its determination in tap waters and in alkali and alkaline earth metal chemicals

A spectrophotometric method is proposed for the determination of zinc involving the measurement (at 440 nm in a pH 10 borate buffer containing 20% ethanol) of the yellow colour produced by zinc with biacetyl mono(2-pyridyl)hydrazone (BPH). The molar absorptivity is highly sensitive, about 52 000 l mol–1 cm–1. Conditions for optimum colour development and the nature of the reaction as well as interferences were studied. The method was applied to the determination of zinc in drinking waters and in pure alkali and alkaline earth metal chemicals. Good precision and accuracy were obtained.

Spectrophotometric determination of zinc in pharmaceutical preparations with biacetyl mono(2-pyridyl)-hydrazone☆

Abstract The biacetyl mono(2-pyridyl)hydrazone (BPH) spectrophotometric procedure for zinc (λ max = 440 nm, ϵ = 52,100 liters mol −1 cm −1 , 1 ml BPH at 0.25% in ethanol/25 ml, 20% of ethanol as medium, boric acid/sodium hydroxide, pH 10, buffer) has been applied to the determination of zinc in pharmaceutical preparations (ophthalmic solutions, mouthwash liquids, and cream ointments) with good results.