H. M. Fahmy

Spectrophotometric determination of ciprofloxacin in pure form and in tablets through charge-transfer complexation reactions

Three simple, quick and sensitive spectrophotometric methods are described for the determination of ciprofloxacin. The methods are based on the reaction of this drug as ann-electron donor with 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ), 7,7,8,8,-tetracyanoquinodimethane (TCNQ) andp-chloranil (CL) as π-acceptors to give highly coloured complex species. The coloured products are quantitated spectrophotometrically at 460, 843 and 550 nm for DDQ, TCNQ and CL, respectively. Optimization of the different experimental conditions is described. Beers law is obeyed in the concentration ranges 5–50, 1.5–15 and 20–200 μg ml−1 ciprofloxacin, but the concentration ranges for best accuracy are 10–48, 2.5–15 and 35– 195 μg ml−1 of drug for DDQ, TCNQ and CL, respectively. The relative standard deviations are less than 1.5%. Applications of the suggested methods to ciprofloxacin tablets are presented and compared with the USP method. The stability constants of the 1∶1 DDQ and CL complexes were 1.086 × 104 and 2.581 × 104 lmol−1, respectively, whereas for the 1∶2 TCNQ complex it was 3.62 × 1081. mol−1.

Polarographic activity of the arylhydrazones of α-cyanoketones as a criterion of their acidity

Abstract The polarographic behaviour of phenylhydrazonomesoxalonitrile (2) and ethyl phenylhydrazonomesoxalonitrile (3) as well as p K ′ and p K a values are reported for a series of arylhydrazones of α-cyanoketones.

Electrochemical oxidation of substituted thiazoles: 2-amino-4-ethoxycarbonyl-5- methylthiazole and N-ethoxycarbonyl-N′- (4-ethoxycarbonyl-5-methylthiazol-2-yl) thiourea

Abstract The behaviour of two substituted thiazoles at the rotating platinum disc electrode is reported and discussed. The main products of oxidation in acetonitrile are the azo and hydrazo dimeric compounds. The uncommon stability of this latter product with its azine tautomeric form is explained through hydrogen bonding. The thiazole ring is unattacked. An oxidation mechanism is proposed and discussed.

Effect of substituents on the polarographic behaviour of α-arylhydrazononitriles: Further evidence for the mechanism of polarographic reduction of α-arylhydrazononitriles

Abstract The polarographic behaviour of the α-arylhydrazonomesoxalonitrile derivatives (IIb-i) and of 2-arylhydrazono-3-keto-3-phenylpropionitriles (IIIb-f) was investigated. With the exception of the nitro-substituted derivatives IIh, i and IIIf all the investigated compounds showed polarographic waves similar to that of their respective parent compounds IIa and IIIa. The m-nitro derivatives IIh and IIIf were firstly reduced in a 4 e wave to the corresponding hydroxylamino derivatives which were subsequently reduced in the manner common to other α-arylhydrazononitriles. On the other hand, the p-nitro derivative IIi was first reduced to the hydroxylamino derivative which then lost water to yield the corresponding quinoneimine. Reduction of the latter product in a 2 e wave gave the p-amino derivative IIe, which then underwent 4 e reduction to p-phenylenediamine and aminomalonitrile. The E1/2 values corresponding to reduction of the arylhydrazonic moiety of compounds IIa-i and IIIa-f at different pH values were correlated to Hammetts different sigma sets. Analysis of the results provided evidence for the suggested mechanism for reduction of these compounds.

Polarographic behaviour of dimedone-2-arylazo derivatives in alcoholic aqueous media

Abstract The polarographic behaviour of a series of the title compounds was studied in alcoholic buffered media. These molecules predominate in the azo form and are reduced in a 4 e − irreversible process. The results were confirmed through spectrophotometric p K a determination, CPE, the use of models, and Hammetts linear relationships. The kinetic parameter k ° f,h was also determined.

Polarographic behaviour of some p-nitrophenyl-diazo-aryl sulphides in aqueous buffered media

Abstract The polarographic behaviour of some p -nitrophenyl-diazo-aryl sulphides in 40% ethanolic aqueous buffers is reported and discussed. The mechanism of electrode processes corresponding to the observed cathodic waves is proposed and clarified by means of model compounds and identification of controlled potential electrolysis products.

Chelate formation by hydrazones

SummarySix new hydrazones chelating agents (1–6) have been prepared and characterized by physical and spectral methods. Only two of these ligands (1 = HL1) and (2 = HL2) yield stable complexes with divalent metals NiII and CuII. Hydrazones (1) and (2) behave as monobasic bidentate ligands towards the metal cations. The spectroscopic evaluation and elemental analyses are all in agreement with structural formulae M(L1)2 and M(L2)2.

Polarographic and spectrophotometric behaviour of substituted 1,3-indandione: Part I. 2-phenylazo-1,3-indandione

Abstract The polarographic and spectrophotometric behaviour of 2-phenylazo-1,3-indandione were studied in buffer solutions covering the pH range ∼3–12. A mechanism for reduction of the electroactive groups was proposed; the existence of a linear free energy relationship was also tested.

Electroreduction of a series of arylazo thiohydantoin derivatives at the DME

Abstract The polarographic reduction data of a series of 5-arylazo-1-phenyl-2-thiohydantoin derivatives in 40% by volume ethanolic aqueous buffers covering a wide range of pH are reported and discussed. A mechanism interpreting the electrode process, in both acid and alkaline media, is proposed and confirmed via the identification of CPE products, Hammetts -E1/2 relations and pKa determinations

Effect of ring type on ionization of the hydrazono linkage in aqueous media

Abstract The acid-base equilibria for a series of hydrazones in ethanolic aqueous media is reported and discussed through correlation of polarographic and potentiometric data.