62972-60-5Relevant academic research and scientific papers
Spectrophotometric determination of H2-receptor antagonists via their oxidation with cerium(IV)
Darwish, Ibrahim A.,Hussein, Samiha A.,Mahmoud, Ashraf M.,Hassan, Ahmed I.
, p. 33 - 40 (2008/09/17)
A simple, accurate and sensitive spectrophotometric method has been developed and validated for determination of H2-receptor antagonists: cimetidine, famotidine, nizatidine and ranitidine hydrochloride. The method was based on the oxidation of these drugs with cerium(IV) in presence of perchloric acid and subsequent measurement of the excess Ce(IV) by its reaction with p-dimethylaminobenzaldehyde to give a red colored product (λmax at 464 nm). The decrease in the absorption intensity of the colored product (ΔA), due to the presence of the drug was correlated with its concentration in the sample solution. Different variables affecting the reaction were carefully studied and optimized. Under the optimum conditions, linear relationships with good correlation coefficients (0.9990-0.9994) were found between ΔA values and the concentrations of the drugs in a concentration range of 1-20 μg ml-1. The assay limits of detection and quantitation were 0.18-0.60 and 0.54-1.53 μg ml-1, respectively. The method was validated, in terms of accuracy, precision, ruggedness and robustness; the results were satisfactory. The proposed method was successfully applied to the determination of the investigated drugs in pure and pharmaceutical dosage forms (recovery was 98.3-102.6 ± 0.57-1.90%) without interference from the common excipients. The results obtained by the proposed method were comparable with those obtained by the official methods.
Kinetics and mechanism of the heterogeneous oxidation of N-substituted-p-phenylenediamines over supported zinc oxide
Salem, Ibrahim A.
, p. 249 - 261 (2007/10/03)
The kinetics and mechanism of the oxidation of some N-substituted-p-phenylenediamines over ZnO supported with some transition metal sulfates were investigated at 25°C. The rate of reaction decreased in the following order; N,N,N′,N′-tetramethyl-p-phenylenediamine, TMPPD > N,N-diethyl-p-phenylenediamine, DEPPD > N,N-dimethyl-p-phenylenediamine, DMPPD, due to the positive inductive effect of alkyl groups. For the oxidation of DEPPD, the rate of reaction was observed to have the order: Cu(II) > Fe(III) > Ni(II) > Cr(III) > Mn(II) > Co(II). The initial rate of reaction was decreased with decreasing pH as a result of the protonation of the diamine nitrogen atoms. Also, it follows a first order dependence of the initial concentration of the diamine and attained a maximum at higher concentrations. Moreover, it increased with increasing amount of the oxidant. Greater amounts, however, reduced the rate of reaction as a result of the adsorption of the formed p-semiquinonediimine, S+, by the support. A mechanism is proposed which implies two consecutive electron transfer steps as well as a synproportionation reaction between the diamine and the totally oxidized p-quinonediimine, T.
A Frontier Orbital Study of Substituent Effects in the Deamination of N-Substitued Quinone Di-imines
Grampp, Guenter
, p. 2001 - 2004 (2007/10/02)
The substituent effects on the rate constant of the acid and alkaline deamination of quinone di-imines are explained, using the frontier orbital (FO) perturbation theory.The main contributions to the pertubation energy are electrostatic and orbital interactions.The alkaline deamination is both orbital and charge controlled, whereas the acid deamination is only an orbital-controlled reaction.
