Spectrophotometric determination and kinetic studies of condensation of aromatic aldehydes with 1,3-dimethylbarbituric acid

The condensation reaction of 1,3-dimethylbarbituric acid with aromatic aldehydes in ethanol has been investigated spectrophotometrically at 25–35°C. The reaction follows overall second-order kinetics, first-order each in reactant. From the dependence of the rate constants on temperature, activation parameters have been calculated. The rate of condensation increases with the presence of electron donating groups on the aromatic ring of the aldehyde. The rate-determining step involves dehydration of the aldol intermediate. The reaction was found to be catalyzed by HCl solutions. Based on this reaction, determination of 10 aromatic aldehydes in a concentration range of 0.13–70.25 μg/ml is proposed. The method was applied for determination of barbituric and 1,3-dimethylbarbituric acids also.     

New method for detection and spectrophotometric determination of quinones

The reaction between 3-phenylthiazolidine-2,4-dione (I) and p-benzoquinone (II), tetrachloro-p-benzoquinone (III), and 1,4-naphthoquinone (IV) in ammoniacal medium is applied for detection and spectrophotometric determination of quinones. The absorbance-concentration relationship is linear up to 18 μg/ml of quinone concentration. The lower limits of identification in the detection reaction are 2.5, 3.0, and 1 μg for (II), (III), and (IV), respectively, which reflect high sensitivity. The reaction between (I) and quinones is proved to be a condensation reaction and highly selective.     

Quinone—cyanide reactions: their use for the determination of quinones and cyanide

Both quinones and cyanide can be determined in the μg—ng ml^-1 range by measuring the fluorescence of the addition products produced. The yield is low (except for the 2-sulfonic acid of 1,4-naphthoquinone) in aqueous solution and 1:1 DMSO:water is the recommended medium for determinations of quinones. The 2-sulfonic acid of 1,4-naphthoquinone permits the determination of trace amounts of cyanide in aqueous solution; there are few interferences.     

Determination of chlorobenzenes in water by drop-based liquid-phase microextraction and gas chromatography-electron capture detection

A drop-based liquid phase microextraction and gas chromatographic-electron capture detection (GC-ECD) method was described for the determination of chlorobenzenes including chlorobenzene, 1,2-dichlorobenzene, 1,3-dichlorobenzene, 1,4-dichlorobenzene and 1,2,3-trichlorobenzene in 5 ml of water. The method used 2 microl of n-hexane as extraction solvent, 5 min extraction time, a stirring rate of 600 rpm and sample ionic strength of 3 M maintained with sodium chloride at 25 degrees C (ambient temperature). The limits of detection (LODs) ranged from 0.004 microg l(-1) (for 1,3-dichlorobenzene) to 0.008 microg l(-1) (for monochlorobenzene). The dynamic linear range for all investigated chlorobenzenes was 1-50 microg l(-1). Recoveries of chlorobenzenes from fortified distilled water are over 90% for three different fortification levels (5, 15 and 45 microg l(-1)) and relative standard deviations of the recoveries are below 6%. Analysis of fortified (5 microg l(-1)) real water samples revealed that matrices had no adverse effect on extraction efficiency of proposed method. The recovery of fortified real water samples was from 90 to 94% with relative standard deviations below 6%.     

Spectrophotometric determination of rifampicin through chelate formation and charge transfer complexation in pharmaceutical preparation and biological fluids

Two simple and accurate spectrophotometric methods for determination of Rifampicin (RIF) are described. The first method is based on charge transfer (CT) complex formation of the drug with three pi-electron acceptors either 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ), 7,7,7,8-Tetracyanoquinodimethane (TCNQ) or 2,3,5,6-Tetrachloro-1,4-benzoquinone (p-chloranil) in acetonitrile. The method is followed spectrophotometrically by measuring the maximum absorbance at 584 nm, 761 nm (680 nm) or 560 nm for DDQ, TCNQ and p-chloranil, respectively. Under the optimized experimental conditions, the calibration curves showed a linear relationship over the concentration ranges of 5-140 microg/ml, 2-45 microg/ml (5-120 microg/ml) and 15-200 microg/ml, respectively. The second method is based on the reaction of RIF with iron(III) forming a water insoluble violet complex which is extracted into chloroform. The method determines RIF in concentration range of 10-240 microg/ml at 540 nm. The proposed methods applied to determination of RIF in capsule, human serum and urine samples with good accuracy and precision. The results were compared statistically with the official method and showed no significant different between the methods compared in terms of accuracy and precision.     

Chemiluminescence assay for quinones based on generation of reactive oxygen species through the redox cycle of quinone

A sensitive and selective chemiluminescence assay for the determination of quinones was developed. The method was based on generation of reactive oxygen species through the redox reaction between quinone and dithiothreitol as reductant, and then the generated reactive oxygen was detected by luminol chemiluminescence. The chemiluminescence was intense, long-lived, and proportional to quinone concentration. It is concluded that superoxide anion was involved in the proposed chemiluminescence reaction because the chemiluminescence intensity was decreased only in the presence of superoxide dismutase. Among the tested quinones, the chemiluminescence was observed from 9,10-phenanthrenequinone, 1,2-naphthoquinone, and 1,4-naphthoquinone, whereas it was not observed from 9,10-anthraquinone and 1,4-benzoquinone. The chemiluminescence property was greatly different according to the structure of quinones. The chemiluminescence was also observed for biologically important quinones such as ubiquinone. Therefore, a simple and rapid assay for ubiquinone in pharmaceutical preparation was developed based on the proposed chemiluminescence reaction. The detection limit (blank + 3SD) of ubiquinone was 0.05 μM (9 ng/assay) with an analysis time of 30 s per sample. The developed assay allowed the direct determination of ubiquinone in pharmaceutical preparation without any purification procedure. Figure Chemiluminescence generated through the redox cycle of quinone     

Highly sensitive and selective spectrophotometric and spectrofluorimetric methods for the determination of ropinirole hydrochloride in tablets

Three sensitive, selective, accurate spectrophotometric and spectrofluorimetric methods have been developed for the determination of ropinirole hydrochloride in tablets. The first method was based on measuring the absorbance of drug solution in methanol at 250 nm. The Beer's law was obeyed in the concentration range 2.5-24 microg ml(-1). The second method was based on the charge transfer reaction of drug, as n-electron donor with 7,7,8,8-tetracyanoquinodimethane (TCNQ), as pi-acceptor in acetonitrile to give radical anions that are measured at 842 nm. The Beer's law was obeyed in the concentration range 0.6-8 microg ml(-1). The third method was based on derivatization reaction with 4-chloro-7-nitrobenzofurazan (NBD-Cl) in borate buffer of pH 8.5 followed by measuring the fluorescence intensity at 525 nm with excitation at 464 nm in chloroform. Beer's law was obeyed in the concentration range 0.01-1.3 microg ml(-1). The derivatization reaction product of drug with NBD-Cl was characterized by IR, 1H NMR and mass spectroscopy. The developed methods were validated. The following analytical parameters were investigated: the molar absorptivity (epsilon), limit of detection (LOD, microg ml(-1)) and limit of quantitation (LOQ, microg ml(-1)), precision, accuracy, recovery, and Sandell's sensitivity. Selectivity was validated by subjecting stock solution of ropinirole to acidic, basic, oxidative, and thermal degradation. No interference was observed from common excipients present in formulations. The proposed methods were successfully applied for determination of drug in tablets. The results of these proposed methods were compared with each other statistically.     

Study of methanol catalyzed reaction between sodium 1,2-naphthoquine-4-sulfonate and hydroxyl ion and its application in the determination of methanol

A novel and simple spectrophotometric method for the direct determination of methanol with 1,2-naphthoquinone-4-sulfonate (NQS) is developed in this paper. It is based on the fact that methanol can catalyze the reaction between 1,2-naphthoquinone-4-sulfonate and hydroxyl ion to form 2-hydroxy-1,4-naphthoquinone in buffer solution of pH 13.00. Beer's law is obeyed in a range of 0.26-15.8 mg/ml at the maximal absorption wavelength of 454 nm. The equation of linear regression is A = 0.01998 + 0.05944C (mg/ml), with a linear regression correlation coefficient of 0.9977. The detection limit is 0.25mg/ml (3sigma/k), while R.S.D. is 2.0% and the recovery rate is in a range of 96.5-103%. The detailed mechanism for the formation of the products is proposed and discussed.     

Simultaneous determination of manganese and zinc in mixtures using first- and second-derivative spectrophotometry

A new direct spectrophotometric determination of manganese with 5,8-dihydroxy-1,4-naphthoquinone (naphthazarin,NAZA) is reported. Absorption maximum, molar absorptivity and Sandell's sensitivity of 1:2 (M:L) complex are 695 nm, 1.88x10(4) l mol(-1) cm(-1) and 2.92 ng cm(-2), respectively. A linear calibration graph is obtained up to a concentration of 7.2 mug ml(-1) of manganese. The optimum range for determination (Ringbom) is between 0.20 and 6.8 mug ml(-1). A rapid method for simultaneous determination of manganese and zinc in their mixture using derivative spectra is described. The range 0.28-5.6 mug ml(-1) manganese could be determined in the presence of 0.33-6.8 mug ml(-1) zinc and vice versa. The developed method was applied to the simultaneous spectrophotometric determination of manganese and zinc in some synthetic mixtures and was found to give satisfactory results.     

Polyazomethines derived from polynuclear dihydroxyquinones and siloxane diamines

New polyazomethines have been synthesized based on polynuclear dihydroxy quinones (5,8-dihydroxy-1,4-naphthoquinone and 1,4-dihydroxyanthraquinone) and siloxane diamines differing by the siloxane sequence length (1,3-bis(3-aminopropyl)tetramethyldisiloxane and α,ω-bis(3-aminopropyl)oligodimethylsiloxane having about 12 siloxane units/sequence). The structures were verified by spectral analyses. Solubility tests, GPC and viscosity measurements were performed. Some properties of the resulted polymers were investigated by thermal (TGA and DSC), electrical, spectral (UV-Vis) and electrochemical (differential pulse voltammetry) methods.     

Spectrophotometric study of the reaction mechanism between DDQ as pi-acceptor and potassium iodate and flucloxacillin and dicloxacillin drugs and their determination in pure and in dosage forms

Two simple and accurate spectrophotometric methods are presented for the determination of beta-lactam drugs, flucloxacillin (Fluclox) and dicloxacillin (Diclox), in pure and in different pharmaceutical preparations. The charge transfer (CT) reactions between Fluclox and Diclox as electron donors and 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ) pi-acceptor and potassium iodate via oxidation reduction reaction where the highly coloured complex species or the liberated iodine have been spectrophotometrically studied. The optimum experimental conditions have been studied carefully. Beer's law is obeyed over the concentration range of 2-450 microg ml(-1) for Fluclox and 10-450 microg ml(-1) for Diclox using DDQ reagent and at 50-550 microg ml(-1) for Fluclox and 50-560 microg ml(-1) for Diclox using iodate method, respectively. For more accurate results, Ringbom optimum concentration range is calculated and found to be 6-450 and 15-450 microg ml(-1) for Fluclox and Diclox using DDQ, respectively, and 65-550 and 63-560 microg ml(-1) for Fluclox and Diclox using iodine, respectively. The Sandell sensitivity is found to be 0.018 and 0.011 microg cm(-2) for DDQ method and 0.013 and 0.011 microg cm(-2) for iodate method for Fluclox and Diclox, respectively, which indicates the high sensitivity of both methods. Standard deviation (S.D.=0.01-0.80 and 0.07-0.98) and relative standard deviation (R.S.D.=0.13-0.44 and 0.11-0.82%) (n=5) for DDQ and iodate methods, respectively, refer to the high accuracy and precision of the proposed methods. These results are also confirmed by between-day precision of percent recovery of 99.87-100.2 and 99.90-100% for Fluclox and Diclox by DDQ method and 99.88-100.1 and 99.30-100.2% for Fluclox and Diclox by iodate method, respectively. These data are comparable to those obtained by British and American pharmacopoeias assay for the determination of Fluclox and Diclox in raw materials and in pharmaceutical preparations.     

Spectrophotometric Determination and Kinetic Studies of Condensation of Aromatic Aldehydes with 2-Thiobarbituric Acid

The condensation reaction of 2-thiobarbituric acid with aromatic aldehydes in ethanol has been investigated spectrophotometrically at 30-50°;C. The reaction was catalyzed by HCl solutions. The reaction follows overall second order kinetics, first order each in reactant. Activation parameters have been calculated from the dependence of the rate constants on temperature. The rate of condensation increases with the presence of electron donating groups on the aromatic ring of the aldehyde. The rate-determining step involves dehydration of the aldol intermediate. Based on this reaction, determination of 13 aromatic aldehydes in a concentration range of 0.149-76 mu;g/ml is proposed.     

Chemistry of fluorinated quinones I. The Diels-Alder reactions of fluoranil

The Diels-Alder reaction of fluoranil with cyclopentadiene, 1,3-butadiene, and 1-acetoxy-1,3-butadiene gave 1,4, 5, 8-bis(methylene)-4a, 8a, 9a, 10a-tetrafluoro-1, 4, 4a, 5, 8, 8a, 9a, 10a-octahydroanthraquinone (I), 2, 3, 4a, 8a-tetrafluoro-4a, 5, 8, 8a-tetrahydro-1,4-naphthoquinone (III), and 5-acetoxy-2, 3, 4a, 8a-tetrafluoro-4a, 5, 8, 8a-tetrahydro-1,4- naphthoquinone (VI), respectively. Hydrogenation of I gave the expected saturated diketone(II). Hydrogenation of III afforded, with elimination of the two tertiary fluorines, 2,3-difluoro-5, 6, 7, 8-tetrahydro-1, 4- dihydroxynaphthalene (IV). In hydrogenation of VI, acetic acid and two moles of hydrogen fluoride were eliminated to give 2,3-difluoro-1, 4-dihydroxynaphthalene(VII). Both dihydroxy compounds IV and VII yielded on oxidation with ferric chloride the corresponding quinones, 2, 3- difluoro-5, 6, 7, 8-tetrahydro-1, 4-naphthoquinone (V) and 2, 3-difluoro-1, 4-naphthoquinone (VIII), respectively. Equivalent amounts of compounds IV and V gave a red-brown semiquinone IX, and a mixture of VI and VIII gave a dark-violet semiquinone X.     

A rapid and facile synthesis of new spiropyrimidines from 5-(2-arylethylidene-2-oxo)-1,3-dimethylpyrimidine-2,4,6-triones

A series of new tetraazaspiro[5,5]-undec-4-ene-2,7,9,11-tetraones have been obtained by reaction of 5-(2-arylethylidene-2-oxo)-1,3-dimethylpyrimidine-2,4,6-triones with ureas. A three-component one-pot procedure to the spiranes synthesis was also developed. One-pot reaction of arylglyoxals, 1,3-dimethylbarbituric acid, and dimethylurea led to imidazolyl-1,3-dimethylbarbituric acids. Mechanisms of studied reactions were discussed.     

Colour reaction of free chlorine with p-amino-N,N-diethylaniline in the presence of alcohol and its analytical application

A simple, precise, rapid-colour-forming and stable spectrometric method has been developed for determining free chlorine in water. p-Amino-N,N-diethylaniline reacts with free chlorine almost instantaneously in the presence of alcohol to form a red oxidized product with absorption maximum at 513 nm. Beer's law is obeyed in the free chlorine concentration range of 0-2 microg ml(-1). The molar absorptivity is 1.79 x 10(4) l mol(-1) cm(-1), limit of detection 0.0036 microg ml(-1), relative standard deviation 1.51%, and amount of free chlorine 7 microg. The colour reaction rate and absorbance are independent of temperature in the range 3-45 degrees C and the stable absorptivity lasts for at least 1 h. The method is satisfactory for the determination of free chlorine in aqueous solution.     

New NH-substituted 1,4-naphtho- and 1,4-benzo- quinones: Synthesis,characterization and potential antiproliferative effect against MDA-MB-231 cells

Abstract

Eleven new alkyl and aryl amino quinones were synthesized from quinones (2,3-dibromo-1,4-naphthoquinone 1, 2-bromo-1,4-naphthoquinone 2, p-benzoquinone 3 or 2,6-dichloro-1,4-benzoquinone 8) with primary amines. The structures of all compounds were characterized by spectroscopic technics and elemental analysis. The structure of 2-((6,6-Dimethylbicyclo[3.1.1]heptan-2-yl)methylamino)-3-bromonaphthalene-1,4-dione (5a) was established by single crystal diffraction. 2-(2-(Ethylthio)ethylamino)naphthalene-1,4-dione (6b) was found to have noteworthy antiproliferative effect against MDA-MB-231 cells.     

Preparation and electrochemical properties of palladium(0) complexes coordinated by quinones and 1,5-cyclooctadiene

The complexes Pd(quinone)(COD) (COD = 1,5-cyclooctadiene) are prepared by a ligand substitution reaction of Pd₂(DBA)₃ (DBA = dibenzylideneacetone) in the presence of both quinone and COD. Palladium(0) complexes coordinated by quinones only are formed in the reaction in the absence of COD. The cyclic voltammetric behavior of Pd(quinone)(COD) has been studied. The reduction potentials for quinones shifted toward negative values on coordination to palladium(0). The oxidation potentials for the central palladium(0) in Pd(quinone)(COD) depend on the electron-withdrawing ability of the free quinones, and are in the following series: quinone = p-benzoquinone < 5,8-dihydro-1,4-naphthoquinone ～ 1,4-naphthoquinone < duroquinone. The shift of oxidation potentials for Pd(quinone)(COD) on changing the quinones as ligands is in contrast to that of Pd(quinone)(triphenylphosphine)₂.     

Synthesis of naphtho[2',3':4,5]imidazo[2,1-<Emphasis Type="Italic">b</Emphasis>][1,3]-thiazole-5,10-dione and naphtho[2',3':4,5]imidazo-[2,1-<Emphasis Type="Italic">b</Emphasis>][1,3]benzothiazole-7,12-dione

The reaction of 2,3-dibromo-1,4-naphthoquinone with 2-aminothiazole in MeONa/MeOH at 60oC for 3 h gave naphtho[2',3':4,5]imidazo[2,1-b][1,3]thiazole-5,10-dione in 64% yield. The reaction of 2,3-dibromo-1,4-naphthoquinone with 2-aminobenzothiazole under the above-mentioned conditions gave 2-(benzo[d]thiazol-2-ylamino)-3-bromonaphthalene-1,4-dione in 64% yield, which on treatment with Na/THF or NaN₃/acetone under reflux conditions gave naphtho[2',3':4,5]imidazo[2,1-b][1,3]- benzothiazole-7,12-dione in 69 and 56% yields, respectively.     

Spectrophotometric and spectrofluorimetric methods for the determination of ramipril in its pure and dosage form

This paper describes three sensitive spectrophotometric and spectrofluorimetric methods for determination of ramipril in its pure form and pharmaceutical tablets. The first method is based on the oxidation of the drug with 1-chlorobenzotriazole reagent (CBT) in strong alkaline medium followed by measuring the absorbance at 350 nm. The method obeys Beer's law over concentration range 15-50 microg ml(-1). For the second and third, both are non-extractive methods based on the formation of ternary complex between copper (II), eosin and ramipril in the presence of methylcellulose as surfactant. Spectrophotometrically, under the optimum condition, the ternary complex showed an absorption maximum at 543 nm. The method obeys Beer's law over concentration range of 20-80 microg ml(-1). A fluorescence quenching method for the determination of ramipril by forming this ternary complex was also investigated for the propose of enhance the sensitivity of the determination. The methods are simple, sensitive, and accurate. The results obtained are reproducible with a coefficient of variation less than 2%. The proposed have been successfully applied to the assay of ramipril in tablets. The results compare favorably with official method.     

Rapid test methods for minor components analysis of hydraulic cement. Spectrophotometric determination of manganese oxide content of Portland cement and cement raw meal

A rapid, sensitive and highly selective spectrophotometric method for the determination of manganese oxide content of Portland cement and cement raw meal is developed. The method is based on the reaction of manganese(II) with 1,2,4 trihydroxyanthraquinone (purpurin, PURP) in 50% v/v ethanol-water solution at pH 8.5. The solution equilibria of manganese chelates are demonstrated and characterized for delineating optimal conditions of the complexation reaction and analytical aspect of the Mn-PURP system. The analysis of cement materials of variable manganese content is feasible over the concentration range 1.67-8.13 microg ml(-1) Mn, the limit of detection (at the 95% confidence level) of the method is 68 ng ml(-1) for manganese. Under optimum conditions, the use of first derivative spectrophotometry has the advantage of high sensitivity than normal spectrophotometric method and allows the determination of 0.5 microg ml(-1) of manganese.