Analytical applications of the photochemical action of light: Determination of ferric iron by photochemical reduction in the presence of citric and mandelic acids

A new method has been developed for the determination of ferric sulphate through its photochemical reduction with citric and mandelic acids in sunlight. The method consists in irradiating with sunlight a measured volume of the ferric sulphate solution together with an excess of citric or mandelic acid in a quartz or pyrex glass beaker until reduction is complete. The ferrous salt formed is determined by titration with a standard solution of sodium vanadate in the presence of the proper concentration of sulphuric and phosphoric acids, employing diphenylbenzidine or diphenylamine sulphonate as internal indicators. The photoreduction is greatly retarded by sulphuric acid.     

Chlorpromazine hydrochloride as a new redox indicator in vanadametry

Chlorpromazine hydrochloride is proposed as an indicator in the vanadametric titration of iron(II) and molybdenum(V). It gives a sharp, reversible colour change from green to violet at the equivalence point. It has advantages over the diphenylamine class of indicators. Its redox and transition potentials are reported.     

Volumetric estimation of uranium-part III, with ceric sulphate

Summary The use of diphenylamine, diphenylbenzidine, diphenylamine sulphonate and N-phenylanthranilic acid as inside indicators in the titration of uranium IV salt with ceric sulphate has been investigated in detail. Experimental conditions have been defined under which these indicators function efficiently.     

Efficient method for the oxidation of aldehydes and diols with tert-butylhydroperoxide under transition metal-free conditions

An efficient, mild, and simple protocol is presented for the oxidation of aldehydes and diols to carboxylic acids utilizing 70% aq TBHP as oxidant and t-BuOK as additive. The oxidation of aldehydes could be achieved by two methods under aqueous medium. Excellent yields of products were obtained in short reaction times. Notably, the products were isolated by simple filtration technique and do not involve chromatographic separation. These reactions may prove to be valuable alternatives to traditional metal-mediated oxidations. Oxidation does not require any transition metals or organic solvents in reaction, making this protocol green.     

Non-aqueous cerimetric determination of phenylhydrazides

A non-aqueous oxidimetric method is described for the determination of some carboxylic acid phenylhydrazides with ammonium hexanitratocerate(IV) in acetonitrile. The end-points have been detected visually with chemical indicators (diphenylamine, diphenylbenzidine, Methyl Red, Malachite Green, Janus Green, Gentian Violet) and potentiometrically. The compounds are smoothly, rapidly and quantitatively oxidized with a two-electron change per hydrazino group. The method is simple, accurate, reliable and widely applicable.     

Studies in bivalent chromium salts

Summary The above estimations show that stannous chloride and uranyl acetate can be estimated with the help of chromous sulphate. In the case of tin, excess of ferric iron is added and its excess found by titration with chromous sulphate, using neutral red or phenosafranine as indicator. In the case of uranyl acetate chromous salt titration, the above two indicators work satisfactorily in the absence of excess of sulphuric acid, whereas methyl red and p-ethoxycrysodine give good end points even in the presence of excess acid. In the alternative procedure for estimation of uranium, chromous sulphate serves the purpose of a Jone's reductor.Ammonium metavanadate solution can be titrated directly against chromous sulphate. N-phenylanthranilic acid, diphenylamine, diphenylbenzidine and diphenylamine sulphonic acid serve satisfactorily as internal indicators for the VO_3– to VO²⁺ change. It has been shown that ferric and cupric salts do not interfere in the above titrations. Mixtures of vanadate and dichromate or vanadate and ceric sulphate can also be titrated in the same manner using the same indicators.Part VI: cf. Z. analyt. Chem. 162, 33 (1958).     

Cyclic voltammetry of solid diphenylamine crystals immobilized on an electrode surface and in the presence of an aqueous solution

Diphenylamine solid crystals have been mechanically attached to platinum or gold electrodes by four different methods and investigated by cyclic voltammetry in the presence of aqueous acidic media. It is demonstrated that the oxidative dimerization and polymerization (observed in non-aqueous solutions or mixed solvent systems) can also be accomplished by using diphenylamine microcrystals in contact with the electrode metal in the presence of aqueous solutions. Formation of a thin polymer layer has been observed even in the areas of the electrode that were not in direct contact with the diphenylamine microparticles. This finding can be explained by surface diffusion of the organic molecules or by oversaturation of the solution close to the diphenylamine microcrystals. A gradual growth of the voltammetric peaks characteristic of the polymer has been observed, while the irreversible wave due to the formation of cation radicals and their dimerization has shown a stationary behaviour. The redox transformation of the oligomeric compound formed at the surface is accompanied by a clear colour change: at pH 0 the colourless reduced form is converted to the bright-blue (violet) oxidized form. Electronic Publication     

Vanadametry Estimation of Thiosulphate

1.(a) We have found that sodium thiosulphate is quantitatively oxidized to tetrathionate in five minutes at room temperature (28°) by excess sodium vanadate in a medium containing sulphuric acid at 0.06N to 0.1N concentration and a little copper sulphate as catalyst. (b) Quantitative emulation of sodium thiosulphate to tetrathionate has also been achieved by the action of excess sodium vanadate during five minutes at room temperature in a medium containing 2.0N—8.0N acetic acid and a little copper salt as catalyst. Further oxidation to sulphate does not occur, even if the mixture is heated to boiling. (c) The excess of unreacted vanadate in 1(a) and 1(b) can be titrated with a standard solution of ferrous ammonium sulphate using diphenylbenzidine as indicator, after adding the requisite quantity of syrupy phosphoric acid. 2. On the other hand, sodium thiosulphate is easily and quantitatively oxidized to sulphate at room temperature, when. acted upon by excess sodium vanadate in a medium containing hydrochloric acid at an overall concentration of 5-6N and 1.0 ml of iodine monochloride as catalyst. The time required for reaction is ten minutes. The unreacted vanadate can be estimated by titration with a standard solution of ferrous ammonium sulphate, using N-phenylanthranilic acid as indicator or with diphenylbenzidine as indicator after suitably diluting and adding phosphoric acid.     

Paired Electrochemical Reactions and the On‐Site Generation of a Chemical Reagent

While the majority of reported paired electrochemical reactions involve carefully matched cathodic and anodic reactions, the precise matching of half reactions in an electrolysis cell is not generally necessary. During a constant current electrolysis almost any oxidation and reduction reaction can be paired, and in the presented work we capitalize on this observation by examining the coupling of anodic oxidation reactions with the production of hydrogen gas for use as a reagent in remote, Pd‐catalyzed hydrogenation and hydrogenolysis reactions. To this end, an alcohol oxidation, an oxidative condensation, intramolecular anodic olefin coupling reactions, an amide oxidation, and a mediated oxidation were all shown to be compatible with the generation and use of hydrogen gas at the cathode. This pairing of an electrolysis reaction with the production of a chemical reagent or substrate has the potential to greatly expand the use of more energy efficient paired electrochemical reactions.     

Thiourea and its organic derivatives

Summary 0.05 N potassium dichromate is used as a redox reagent for the determination of thiourea and some of its alkyl and aryl derivatives by visual and potentiometric methods. In visual titrations amylose (in presence of potassium iodide), diphenylamine or diphenylbenzidine are used as indicators. These methods are simple, accurate, instantaneous and of wide applicability.

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Zusammenfassung Zur volumetrischen Bestimmung von Thioharnstoff sowie von einigen seiner Alkyl- und Arylderivate wird 0,05 n Kaliumdichromatlösung verwendet. Der Endpunkt wird visuell (mit KJ-Stärke, Diphenylamin oder Diphenylbenzidin) oder potentiometrisch ermittelt. Das Verfahren ist einfach und genau, läßt sich schnell durchführen und bietet viele Anwendungsmöglichkeiten.

     

Magnetic solid‐phase extraction for determination of the total malachite green,gentian violet and leucomalachite green,leucogentian violet in aquaculture water by high‐performance liquid chromatography with fluorescence detection

In this study, magnetic multi‐walled carbon nanotube nanoparticles were synthesized and used as the adsorbent for the sums of malachite green, gentian violet and leucomalachite green, leucogentian violet in aquaculture water samples followed by high performance liquid chromatography with fluorescence detection. This method was based on in situ reduction of chromic malachite green, gentian violet to colorless leucomalachite green, leucogentian violet with potassium borohydride, respectively. The obtained adsorbent combines the advantages of carbon nanotubes and Fe₃O₄ nanoparticles in one material for separation and preconcentration of the reductive dyes in aqueous media. The structure and properties of the prepared nanoparticles were characterized by transmission and scanning electron microscopy, X‐ray diffraction, and Fourier‐transform infrared spectroscopy. The main parameters affecting the adsorption recoveries were investigated and optimized, including reducing agent concentration, type and amount of sorbent, sample pH, and eluting conditions. Under the optimum conditions, the limits of detection in this method were 0.22 and 0.09 ng/mL for malachite green and gentian violet, respectively. Product recoveries ranged from 87.0 to 92.8% with relative standard deviations from 4.6 to 5.9%. The results indicate that the sorbent is a suitable material for the removal and concentration of triphenylmethane dyes from polluted environmental samples.     

Oxidative polymerization of diphenylamine: A mechanistic study

The mechanism of oxidative polymerization of diphenylamine is considered. The kinetic study of diphenylamine polymerization and of the structure and molecular-mass characteristics of the reaction products has shown that the degree of oxidation of intermediates plays the key role in polyrecombination. The relationship between the polymerization procedure and the molecular mass of polydiphenylamine was revealed.     

Electrochemical behaviour of triclosan at a screen-printed carbon electrode and its voltammetric determination in toothpaste and mouthrinse products

Cyclic voltammetry was used to investigate the electrochemical behaviour of triclosan (2,2,4′-trichloro-2′-hydroxydiphenyl ether) at a screen-printed carbon electrode (SPCE). It was found that a single anodic peak occurred over the pH range 6.0–12.0; this peak was considered to result from an irreversible oxidation reaction at the phenolic moiety. A plot of E_p versus pH was constructed and from the break point a pK_a value of 7.9 was obtained, thus agreeing with the literature value. Detailed voltammetric studies were performed at pH 10, where the analyte exists as an anion. It was demonstrated that, at an initial potential of 0 V, the anion underwent electrosorption prior to electrochemical oxidation. The oxidation reaction appeared to involve a one-electron transfer, as deduced from a calculated n_a value of 0.5; the same value was obtained at pH 7.0. In contrast to triclosan, triclosan monophosphate was found to be electrochemically inactive when subjected to voltammetry under the stated conditions.

The electrochemical oxidation of triclosan at a SPCE was exploited for its determination (0.3%) in commercial toothpaste and mouthrinse products using differential pulse voltammetry. The recovery and precision data indicated that this approach may have application in routine quality control analysis.     

Synergistic enhancement of the horseradish peroxidase-catalyzed oxidation of luminol by 4-substituted phenylboronic acids

Combinations of 4-substituted phenylboronic acids [phenyl, iodo, bromo, and trans-4-(3-propenoic acid) substituents] have been discovered to have synergistic effects in the horseradish peroxidase (HRP) catalyzed chemiluminescent oxidation of luminol. Three types of effect have been observed: 1. synergistic reduction in the background light emission of a luminol-peroxide assay reagent to a value lower than the background obtained with either enhancer individually; 2. increase in signal to background ratio (S B ) in the presence of HRP to a value higher than the S B obtained with either enhancer individually (synergy) or to a value higher than the combined S B obtained with each enhancer (synergistic enhancement); and 3. for some combinations of enhancers, an increase in signal in the presence of HRP to a value higher than the signal obtained with either enhancer individually (synergy), or to a value higher than the combined signal obtained with each enhancer (synergistic enhancement). The magnitude of the effect was moderate but the synergistic decreases in background and increases in signal produced increases in S B up to four-fold. Examples of synergistic pairs of enhancers included 4-biphenyl and 4-bromophenylboronic acid; 4-biphenyl and 4-iodophenylboronic acid; and trans-4-(3-propenoic acid) and 4-iodophenylboronic acid. Generally, synergy was obtained at several concentrations of all of the combinations of enhancers tested, and at different time points in the reaction due to the different light emission kinetics of the enhanced reactions. The mechanism of this synergistic effect has not been elucidated but may involve the enhancers acting at different points in the complex chemiluminescent peroxidase catalyzed oxidation reaction.     

十种以碱性染料制备的PVC膜ReO4-离子选择电极——碱性染料结构对ReO4-电极性能的影响

本文以不同碱性染料制备了十种PVC膜ReO₄^-离子选择电极,测试和比较了它们的性能,筛选出六种较优者,并根据其差别初步探讨了碱性染料结构对ReO₄^-电极性能的影响.     

Electrochemical synthesis and characterization of polydiphenylamine

Electrochemical oxidation of diphenylamine(DPA)in acetonitrile solution producedan adhesive conducting polydiphenylamine(PDPA)film on the electrode,which exhibited multiplecolour variation in a wide range of potential.The polymer was characterized by cyclic voltam-merry,FTIR and ESR.The results indicate that the electropolymerization of diphenylamine per-forms via the 4,4＇C—C phenyl-phenyl coupling mechanism.FTIR,ESR and conductivity mea-surements for the different states of PDPA show that polydiphenylamine can be reversibly dopedand dedoped either chemically or electrochemically.It is evidenced also that there are paramagneticspecies—polarons in PDPA supposed to be the current carrier.     

Fluorescence response of a 4-trifluoroacetylaminophthalimide to iodide ions upon 254 nm irradiation in MeCN

The title trifluoroacetylaminophthalimide derivative produced a violet fluorescence (lambdaFLmax 392 nm) in MeCN, and it displayed a green emission (lambdaFLmax 506 nm) after irradiation at 254 nm in the presence of iodide ions. The corresponding amidate ion of the trifluoroacetamide was identified as the green fluorescence emitter. The deprotonation reaction may be caused by proton-abstracting solvated electrons generated by a photochemical charge--transfer-to-solvent process from I(-) to MeCN.     

Synthesis of 4,5-diaryl-2-(n-methyl-3-carbazolyl)- and 4,5-diaryl-2-(n-methyl-1,2,3,4-tetrahydro-7-carbazolyl) imidazoyl radicals

A number of imidazoles were obtained by the reaction of substituted benzils with aldehydes of the carbazole series. Chlorobenzene solutions of the imidazoles take on a green coloration on oxidation with lead dioxide. The presence of free radicals in these solutions is confirmed by the ESR spectra and by the reaction with hydroquinone, diphenylamine, carbazole, and ,-diphenyl--picrylhydrazine.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1550–1551, November, 1971     

Stabilized gold nanoparticles by reduction using 3,4-ethylenedioxythiophene-polystyrenesulfonate in aqueous solutions: nanocomposite formation, stability, and application in catalysis

Herein, we report a one-pot synthesis of highly stable Au nanoparticles (AuNPs) using 3,4-ethylenedioxythiophene (EDOT) as a reductant and polystyrene sulfonate (PSS-) as a dopant for PEDOT and particle stabilizer. The synthesis demonstrated in this work entails the reduction of HAuCl4 using EDOT in the presence of PSS-. The formation of AuNPs with concomitant EDOT oxidation is followed by UV-vis spectroscopy at various time intervals. Absorption at 525 nm is due to the surface plasmon band of AuNPs (violet), and broad absorption above 700 nm is due to oxidized PEDOT that was further characterized to be in its highly oxidized (doped) state, using FT-Raman spectroscopy. Transmission electron microscopy shows a polydisperse nature of the particles, and the selected area electron diffraction pattern reveals the polycrystalline nature of AuNPs. With stabilizers such as sodium dodecylsulfate (SDS) (green) and polyvinylpyrrolidone (PVP) (blue), the absorbance around 525 nm was found to be negligibly small, while PSS- showed high absorbance at 525 nm (violet) and above 700 nm (oxidized PEDOT). PSS- also allows complete oxidation of EDOT and serves as an effective dopant for PEDOT. While AuNPs covered by PEDOT alone cannot be dispersed in aqueous solutions, PSS- renders Au-PEDOT water soluble. The hydrodynamic diameter of the nanocomposite estimated from the dynamic light scattering (DLS) measurements increases in the order Na-PSS < SDS < PVP. Interestingly, the color of the Au(nano)-PEDOT/PSS- aqueous dispersion changed reversibly between violet and blue and vice versa on addition of NaOH and HCl, respectively. This reversible color change appears to be a combination effect of acid/base on the properties of PEDOT, in turn changing the environment around the embedded AuNPs. The nanoparticle dispersion also exhibited very high stability in presence of 3.0 M NaCl. Remarkably, the nanocomposite Au(nano)-PEDOT/PSS- was found to function as an effective catalyst to activate the reduction of 4-nitrophenol to 4-aminophenol in the presence of excess NaBH4, and the calculated apparent rate constant value of 4.39 x 10-2 s-1 is found to be higher than those obtained using other nanocomposites with SDS and PVP and comparable to the values reported in the case of other encapsulants.     

Catalytic oxidation of 2-ethyl-5,6,7,8-tetrahydro-9,10-anthrahydroquinone

Catalytic oxidation rate of 2-ethyl-5,6,7,8-tetrahydro-9,10-anthrahydroquinone (ETHAHQ) using oxygen in a stirred reactor was studied. It was found that NaOH and some amines exhibit catalytic properties suitable for this oxidation. In the presence of NaOH with its amountof-substance concentration of 2 mmol/l_(l)-phase, five times increased reaction rate is achieved. Additionally, mineral acids (sulphuric and phosphoric) and antioxidants (diphenylamine, N-isopropyl4-diphenylamine) were used for a thorough study of partial mechanism steps and their rates during oxidation. Experimental results were used for determination of the rate limiting step of the ETHAHQ oxidation. It was the hydrogen elimination from hydroxyl of hydroquinone.