1,2-Naphthoquinone-2-thiosemicarbazone as a new acid-base indicator in isopropyl and tert-butyl alcohol media

1,2-Naphthoquinone-2-thiosemicarbazone is proposed as an acid-base indicator for use in isopropyl and tert-butyl alcohol media. The dissociation constants have been determined in both media and the colour transition, sensitivity and sharpness of the indicator are described by means of chromatic parameters. The indicator has been used for determination of some organic acids, with errors of less than 1%.     

Study of semicarbazones and thiosemicarbazones derived from 1,2-naphthoquinone, as acid-base indicators: Evaluation of their transition limits through the chromaticity co-ordinates

The use of 1,2-naphthoquinone-2-semicarbazone, 1,2-naphthoquinone-2-semicarbzone-4-sulphonic acid and 1,2-naphthoquinone-2-thiosemicarbazone-4-sulphonic acid as acid—base indicators has been studied. The sharpness of the indicator transitions has been investigated by means of photometric titrations and the colour quality specified with the aid of the CIE chromaticity system. The results show that the three substances are satisfactory as neutralization indicators.     

Application of a Schiff base derived from sulfanilamide as an acid-base indicator

The present paper firstly announces the possibility of using a Schiff base as an acid-base indicator. This surprising phenomenon can be considered as an interest due to the fact that Schiff bases are usually unstable in solutions and definitely undergo hydrolysis. It was found that such a specific observation depends merely upon the chemical structure and type of the substitute of amine that reacts with aldehyde to give the Schiff base. The latter reagent 4[(4-dimethylamino-benzylidene)-amino]-benzene sulfonamide was synthesized from the condensation of sulfanilamide with p-dimethylaminobenzaldehyde. The reagent solution shows a reproducible change in its color due to the addition of acid and base. A UV-Vis spectroscopic characterization and acid-base equilibrium study of the reagent for its possible use as an indicator were investigated. The results show that the reagent is an amphoteric which possesses four ionization constants K_a1, K_a2, K_b1 and K_b2 of weak dibasic and diacidic properties. The value of pK_a2 (9.80) is parallel to the observed transition interval pH 9.5 (yellow) and pH 10.5 (colorless), which is considered to be the indicator exponents pK_i. It was concluded that the benzyl sulfonamide group plays a key role in the stability of the reagent towards hydrolysis and also for indicator characteristics through breaking the conjugation.     

The use of 2,6-dichlorophenolindophenol as indicator in acid-base titrations

2,6-Dichlorophenolindophenol shows acid-base indicator properties. Its colour is red in acidicmedia and blue in alkaline media. 'Ihe transitional pH value is 5.7 and the colour change is sharp and easy to observe. The use of the indicator in various acid-base titrations, as well as the effects of neutral salts, alcohol and temperatures, were checked. The absorption spectra of the acidic and basic forms of the indicator are presented.     

Titration of vanadium(IV) with cerium(IV) sulphate, with ferroin as indicator, in aqueous alcohol as a facile reaction medium

A new procedure for the titration of vanadium(IV) with cerium(IV) sulphate, with ferroin as indicator, in aqueous alcohol medium, is reported. The visual titration gives accurate results but potentiometric titration fails in this medium; this failure is attributed to the sluggish indicator electrode behaviour. Experimental conditions for preliminary quantitative photochemical reduction of vanadium(V) with alcohol have been established.     

Evaluation of the physiologically based extraction test as an indicator of metal toxicity in mussel tissue

In order to estimate the bioaccessibility of metals from mussel tissues, an in vitro physiologically based extraction test was applied to simulate the human gastrointestinal conditions. The samples were subjected to human body temperature, and Ag, Co, Cr, Cu, Mn, Ni, Pb and Sn were sequentially extracted with simulated gastric solution, followed by extraction with a simulated intestinal solution. Both gastric and intestinal extracted solutions and microwave-digested residue were analysed by ICP-MS. The procedure was applied to a certified reference material NIST 2977 (mussel tissue) to prove the accuracy of the method. Some mussel tissue samples from Northern Spain were subjected to this procedure to determine their metal content and their metal oral bioaccessibility.     

Nitroalkanes in aqueous medium as an efficient and eco-friendly source for the one-pot synthesis of 1,4-diketones, 1,4-diols, delta-nitroalkanols, and hydroxytetrahydrofurans

The Michael addition of primary aliphatic nitro compounds to alpha,beta-unsaturated enones, performed in aqueous media, provides the one-pot synthesis of 1,4-diketones, 1,4-diols, delta-nitroalkanols, and hydroxytetrahydrofurans, respectively, by the appropriate choice of the reaction conditions.     

Use of brucine as an oxidation-reduction indicator in cerimetry

Summary Brucine has been found to work satisfactorily as an inside indicator in the titration of molybdenum(V) and hydroquinone with ceric sulphate. It does not give a good indication of the end point in the titration of arsenic(III) in sulphuric acid medium, using osmium tetroxide as a catalyst or in hydrochloric acid medium using iodine monochloride as a catalyst. Brucine cannot also be used in the titration or uranium(IV) with ceric sulphate. A 0.1 per cent solution of brucine in 2 N–3 N acetic acid has been found to be stable for nine months without showing any discoloration.     

Study of radical methyl methacrylate-methacrylic acid copolymerization in isopropyl alcohol by dynamic laser scattering and C-NMR spectroscopy

The copolymerization of methyl methacrylate and methacrylic acid in isopropyl alcohol is studied by kinetic, dynamic laser scattering and ¹³C-NMR methods. Correlations are established between the dependence of the copolymerization rate, the apparent average molecular weight, the diffusion coefficients and the configurational triad composition on the monomer feed. These correlations and the fact that both copolymerization constants are smaller than unity (r_MMA = 0.63 ± 0.03; r_MA = 0.25 ± 0.05) are in good agreement with the assumption that a comonomer complex takes part in the propagation reaction. A new Markov chain method for the estimation of the configurational triad mole fraction which accounts for the complex participation in a macromolecule formation is developed. Qualitative criteria for evidence the participation of the comonomer complex in copolymerization are proposed using experimental and terminal model calculated mole fractions of the compositional triads and diads.     

Arsenazo III as metallochromic indicator for complexometric determination of calcium in slightly alkaline medium

Arsenazo III is proposed as metallochromic indicator for calcium in slightly alkaline medium. The visual titration with EDTA was performed at pH 8 and 40 microg-12 mg of calcium were determined. The interference of some ions was considered and it was found that phosphate does not interfere appreciably. Spectrophotometric detection of the end-point was used for titration of calcium in the presence of magnesium at pH 9. For the estimation of the titration error, the conditional stability constants of the calcium-arsenazo III complex were found.     

Chemical instabilities in oxidation of 1,4-naphthalenediol in homogeneous medium: I. The deterministic character of 1,4-naphthodiol oxidation and its quantitative parameters

The chemical oscillatory processes that occur upon oxidation of 1,4-naphthalenediol in the presence of oxygenated cobalt(II) complexes in a homogeneous medium have been studied. The limits of the reagent and catalyst concentrations, pH, and temperature at which chemical oscillations are generated have been determined. The types of dynamics of the occurring processes and the dynamic parameters have been determined based on discrete Fourier transform, reconstruction of dynamics from time series of data, and calculations of the Lyapunov characteristic exponents and the Komogorov-Sinai entropy.     

Hair as an indicator of environmental exposure in Hong Kong

Eleven human hair samples were taken from the Chinese residents of Hong Kong for the study of hair trace elemental level and environmental exposures. Absolute neutron activation analysis and Ge(Li) gamma-ray spectrometry were applied in the determination of the trace elemental level. All results are reported in parts per million except for sulfur and oxygen which are reported in percent. The trace element content of hair from a drug addict was found to be considerably different from other sampled people. Comparison of the normal concentrations of the trace elements of the Chinese residents of Hong Kong was made with those from people of various other national, socio-cultural and environmental backgrounds. It was found that together with a few other trace elements, Ni, Sr, Zr and Hg content of the Chinese Residents of Hong Kong show a higher level than those of the other sampled people.     

Kinetic features of the reaction of polyvinyl alcohol with epichlorohydrin in an alkaline medium

Russian Journal of General Chemistry - The kinetics of the reaction of polyvinyl alcohol with epichlorohydrin in an aqueous sodium hydroxide solution has been studied. The process rate has been...     

Study of the morphology of poly(methyl methacrylate) as polymerized by the redox system Ce(IV)–isopropyl alcohol

Methyl methacrylate has been polymerized in aqueous nitric acid at 30°C, with the redox system ceric ammonium nitrate–isopropyl alcohol as initiator. The gravimetric method has been used to follow the reaction. After a short induction period polymerization started, and conversion attained a maximum value with extent of reaction, whereas the ceric ion is exhausted. The size, distribution, and number of PMMA particles formed were measured by scanning electron microscope. From the electron micrographs it was found that the particles are formed over a short period, and that the particle size distribution seems to be determined by flocculation and coagulation of the particles, because these are not stabilized. Average-molecular weight was found to increase at high conversions and the molecular weight distribution became broader as particle size increased. Particle size increased with conversion, whereas the number of particles remained constant.     

1,4-Anhydro-2,3,6-Tri-O-Methyl-D-Glucitol Formed as an Artifact in the Reductive Cleavage of Permethylated 1,4-Linked Glucopyranosides

Abstract

1,5-Anhydro-2,3,6-tri-O-methyl-d-glucitol (1) is formed as the major product in the reductive cleavage of permethylated 4-linked glucopyranosyl residues, but a small amount of 1,4-anhydro-2,3,6-tri-O-methyl-d-glucitol (2) is formed as an artifact when water is present. The formation of 2 can be minimized by carrying out the reductive cleavage under anhydrous conditions. The independent synthesis of 2 and its 5-O-acetyl derivative (4) is described.     

Aqueous acetic acid as a medium for the facile use of ferroin as redox indicator in the presence of perchloric acid

Ferroin cannot be used as an indicator in perchloric acid medium because of precipitation of ferroin perchlorate. There is no precipitation, however, if the solution contains 30%(v/v) of acetic acid.