Showing papers on "Nitrobenzene published in 1988"

Biodegradation studies of aniline and nitrobenzene in aniline plant wastewater by gas chromatography

Abstract: A gas chromatographic (GC) method has been developed for studying the biodegradation of aniline and/or nitrobenzene in aniline plant waste water. The effects of various parameters have been reported and critically discussed. The results are precise and afford simultaneous determination of aniline and nitrobenzene.

Surface-enhanced raman spectroscopy as a probe of electroorganic reaction pathways. 1. Processes involving adsorbed nitrobenzene, azobenzene, and related species

Abstract: Etude par spectrometrie SERS et par voltammetrie cyclique de l'adsorption et de la reduction electrochimique de l'azobenzene et du nitrobenzene sur une electrode d'or

Electrochemical detection in the high-performance liquid chromatographic analysis of plant phenolics.

Abstract: The electrochemical behaviour of several phenolic compounds of biological interest in vegetable materials was studied. Oxidation potentials of the examined compounds and voltammetric curves of some representative phenols are reported. As a practical application of electrochemical detection in HPLC, the analysis of monomeric units emanating from nitrobenzene oxidative hydrolysis of wheat straw lignin is described. Electrochemical detection simplifies the analysis, permitting the direct injection of the reaction mixture without interference from nitrobenzene. Aniline formed by the reduction of nitrobenzene is also detectable and may be used as an oxidisability index of the vegetable matter.

Piezoelectric quartz crystal detection of benzene vapour using chemically modified cyclodextrins

Abstract: Three chemically modified cyclodextrins have been prepared, characterised by n.m.r. spectroscopy, and studied for their possible role as piezoelectric crystal coating detectors towards benzene vapour. 2,6-Per-O-methyl-β-cyclodextrin 3-perbenzoate (DMsCD-B7) is not recommended. 2,6-Per-O-(t-butyldimethylsilyl)-α-cyclodextrin (DSαCD) was found to be the best for the ca. 0.08–ca. 400 mg dm–3 range of benzene vapour in air. 2,6-Per-O-allyl-α-cyclodextrin (DAαCD) is a possible alternative. Both detector systems function for > 20 days. The detectors are selective towards benzene vapour over methane, propane, butane, pentane, ethyne, ammonia, nitrobenzene, and toluene. Toluene gives rise to the most serious interference. For the preferred DSαCD sensor, toluene only gives < 20% of the decrease in frequency observed with the corresponding amount of benzene. However, the interference is slightly greater for the DAαCD sensor.

Functionalizatiow of Benzene by its Reaction with Nitrogen Oxides Over Solid-Acid Catalysts

Abstract: Silica-supported benzenesu1fonic acids were found to be highly active catalysts for the vapor-phase nitration of benzene with nitrogen dioxide to yield nitrobenzene at 443 K. The decay of the activities was not observed during the course of the reaction. The quantitative conversion of both benzene and nitrogen dioxide was accomplished. A direct synthesis of phenol was found to be possible through a vapor-phase reaction of benzene with dinitrogen monoxide over H-ZSM-5 zeolite at 603 K. The phenol yield on benzene basis was 6%.

Gas‐phase electrophilic addition reactions of chlorinated alkyl ions

Abstract: Chemical ionization was used to study gas-phase electrophilic addition reactions of chloromethyl ions ([CHxCl3-x]+, x = 0, 1, 2) with a number of substituted benzenes (C6H5Y, Y = NH2, OH, CHO, CN, NO2). Mass-analyzed ion kinetic energy spectrometry was used to characterize the reaction products with respect to the site of electrophilic addition (ring v. substituent). In some cases, examination of secondary reaction products (ion–molecule adduct which has undergone an elimination reaction in the ion source) aided in establishing the original site of electrophilic addition. Aniline, benzonitrile and nitrobenzene exhibited preferential substituent interaction, while phenol and benzaldehyde gave a mixture of ring and substituent reaction products. These gas-phase results differ considerably from solution-phase Friedel–Crafts alkylation; however, they are consistent with the notion of preferential σ-bond formation at polarizable centers of negative charge.

The effect of the diluent on the extraction of lanthanide complexes of macrocyclic ionophores

Abstract: Solvent extraction studies have been carried out on aqueous complexes of La(Ill), Eu(III) and Lu(III) with macrocyclic ligands DAPDA (1,7-diaza-4,10,13-tri-oxacyclopentadecane-N,N’-diacetic acid) and DACDA (1, 10-diaza-4,7,13,16-tetraoxacyclooctadecane-N,N’-diacetic acid) using TTA (thenoyltrifluoroacetone) as the extractant in chloroform and nitrobenzene. EDDA (ethylenediamine-N,N’-diacetic acid), a non-cyclic polyaminopolycarboxylic acid, was also included for comparison purposes These results, along with our earlier work in benzene medium, have been used to elucidate the nature of extracted species. It appears that nitrobenzene, a diluent of high dielectric constant, favors the extraction of ion pairs instead of the mixed complexes observed earlier using the relatively inert diluent, benzene.

Cationic Polymerization of N-Vinylcarbazole and N-Vinyl-2-Pyrrolidone Initiated by Carboxyl Groups on Carbon Fibers

Abstract: The effects of solvent and temperature on the grafting of poly(N-vinylcarbazole) (NVC) onto carbon fiber by cationic polymerization initiated by carboxyl groups on the surface were investigated in order to obtain poly-NVC-grafted carbon fiber with a higher percentage of grafting It was found that the rate of the polymerization of NVC increased, depending on the dielectric constant of the solvent, in the following order: toluene < 1,2-dichloroethane < nitrobenzene. However, the percentage of grafting of poly-NVC onto the carbon fiber obtained from polymerization in nitrobenzene was smaller than that in toluene. This may be due to differences in the chain transfer of the growing polymer cation to NVC and these solvents. Furthermore, poly-NVC-grafted carbon fiber with a higher percentage of grafting was formed at a lower polymerization temperature, i.e., 60°C. In addition, it became apparent that carbon fiber is capable of initiating the cationic polymerization of N-vinyl-2-pyrrolidone (NVPD), and p...

Selective reduction of nitrobenzene to nitrosobenzene on oxidic catalysts

Abstract: Pure unpromoted Mn3O4 appears to be a very suitable catalyst for the selective reduction of nitrobenzene to nitrosobenzene; the oxygen vacancies required to split off oxygen atoms can be created both by the phenyl group of nitrobenzene itself and by an additional reducing agent like e.g. methane.

Effect of solvent structure on electron reactivity: 2-propanol/water mixtures

Abstract: The reactivity of solvated electrons with efficient (nitrobenzene, acetone) and inefficient (phenol, toluene) scavengers is affected greatly by the solvent composition in 2-propanol/water mixed solvents. 2-Propanol is the only secondary alcohol that is completely miscible with water. The variation of the nitrobenzene rate constant k2 with solvent composition displays four viscosity zones, as in primary and tertiary alcohol/water mixtures. In zone (c), where the Stokes–Smoluchowski equation applies, the nitrobenzene k2 values in the secondary alcohol/water mixtures are situated between those in the primary and tertiary alcohols, due to the relative values of the dielectric permittivity e. The charge–dipole attraction energy varies as e−1.The two water-rich zones (c) and (d) are characterized by a large change of viscosity η and a small change in solvation energy (trap depth) Er; here k2 for all the scavengers correlates with the inverse of the viscosity. In the two alcohol-rich zones (a) and (b) the change...

Substituent Effects in the Nitrobenzene and Copper (II) Oxidations of Some Hydroxystilbene Lignin Model Compounds

Abstract: The nitrobenzene and copper (II) Oxidations of 4-hydroxystilbenes 2 gave moderate yields of p-hydroxybenzaldehyde. No aldehyde was obtained in the absence of water. A Hammett Substituent effect study found a ρ value of — 0.48 versus σ for both the copper (II) and nitrobenzene oxidations. These results are consistent with a homolytic mechanism involving the benzylic hydroxyl groups of intermediate alcohols 1. A polar transition state in the rate-controlling cleavage of benzyl radicals is postulated to explain the σ dependence.

Process for the preparation of amino-1,3 benzenediol

Abstract: High purity amino-1,3-benzenediols are prepared by (a) contacting a 1,3-bis(alkylcarbonato)benzene with a nitrating agent under reaction conditions such that a 1,3-bis(alkylcarbonato)nitrobenzene is formed, (b) contacting the 1,3-bis(alkylcarbonato)nitrobenzene with a hydrolyzing agent under conditions such that a nitro-1,3-benzenediol is produced, and (c) contacting the nitro-1,3-benzenediol with a reducing agent under conditions such that an amino-1,3-benzenediol is produced. Of the amino-1,3-benzenediols, 4,6-diamino-1,3-benzenediol is particularly useful in the preparation of high molecular weight polybenzoxazoles.

Selectivity in the Phase Transfer Catalytic Hydrogenation of Nitrobenzene by Transition VIII Metals

Abstract: The phase transfer hydrogenation of nitrobenzene to p-aminophenol has been investigated for the catalysts Pt, Pd, Rh and Ru. The influence of factors such as surfactant concentration, sulfuric acid concentration, hydrogen pressure and temperature on the reaction was determined. It was found that the rate-determining step for the catalytic hydrogenation of nitrobenzene is the catalytic process by which the hydrogen atom is absorbed on the metal surface. A reaction model is suggested which accounts for the observed hydrogenation selectivity and explains how these factors affect product composition and yield. It is shown that Pt favors p-aminophenol production, while Pd favors aniline production.

Voltammetric determination of nitrobenzene with a chemically modified carbon paste electrode. Application to wines, beers and cider

Abstract: A method for the determination of nitrobenzene with a sepiolite modified carbon paste electrode is presented. Nitrobenzene is adsorbed on the electrode at open circuit (pH 3.5), and determined by differential pulse voltammetry and cyclic voltammetry at pH 5.5 in 0.5 mol/l KNO3. The calibration is linear up to 0.4 μg × ml−1. The method was applied to the determination of nitrobenzene in wines, beers and cider. The error was ±2% and the standard deviation 5%.

Acute Lethal Toxicity Quantitative Structure-Activity Relationships for Electrophiles and Pro-Electrophiles: Mechanistic and Toxicokinetic Principles

Abstract: Published data on acute lethal toxicity of aniline and nitrobenzene derivatives to fish can be correlated with an electrophilic reactivity descriptor based on substituent constants (proposed to relate to electrophilicity of the corresponding C-nitroso compounds, the aniline and nitrobenzene derivatives being regarded as pro-electrophiles). Likewise, published data on acute lethal toxicity of reactive halogen compounds can be correlated with an electrophilic reactivity parameter based on measured rate constants for reaction with a reference nucleophile, 4-nitrobenzylpyridine. In both cases, incorporation of a lipophilicity descriptor does not improve the quantitative structure-activity relationship (QSAR). A toxicokinetic model is proposed, whereby the electrophilic reaction leading to the toxic effect is assumed to take place in an aqueous biological medium separated from the external aqueous environment by a lipid barrier. Based on consideration of whether environment-lipid partition, lipid-aqueous biological medium partition, or reaction with biological nucleophiles is likely to be the rate-determining step, outlying behavior of some of the compounds can be rationalized, and the QSARs can, with justification, be improved by elimination of these compounds.

Phase transfer of the 12-tungstosilicate anion across the water/nitrobenzene interface

Abstract: The transfer behaviour of the heteropoly anion [SiW12O40]4– across the water/nitrobenzene interface has been investigated using cyclic voltammetry and chronopotentiometry with cyclic linear current scanning. It was found that the heteropoly anion with a negative charge of 4 can transfer from the aqueous phase to the organic phase electrochemically. The transfer process is diffusion-controlled at a lower scan rate, but it is partially kinetically controlled at a higher scan rate. The effects of some higher-valent cations such as Sr2+, Co2+, Ni2+, Zn2+, Fe2+ and Fe3+, as well as some anions such as NO–3, Cl–, SO2–4 and PO3–4etc. on the phase transfer have been systematically observed from cyclic voltammograms. The formal transfer potential and the transfer free energy for the heteropoly anion across the water/nitrobenzene interface have been calculated according to the voltammetric data.

Extraction of technetium from ascorbic acid medium with crown ethers

Abstract: The extraction of technetium from ascorbic acid medium with dibenzene-18-crown-6 /DB-18C6/ and 18-crown-6 /18C6/ dissolved in benzene and nitrobenzene was studied. The effect of crown ether substition, concentration of the extracting agent as well as the pH of the aqueous solution on the distribution coefficient was investigated. Nitrobenzene was found to be a rather promising diluent.

Axial co-ordination and ion-pair formation for R,S,R,S-1,4,8,11-tetramethyl-1,4,8,11-tetra-azacyclotetradecanenickel(II) perchlorate in various mixed solvents with nitrobenzene

Abstract: Conductance measurements of the complex R,S,R,S-[NiL][ClO4]2(L = 1,4,8,11-tetramethyl-1,4,8,11-tetra-azacyclotetradecane), in mixed solvents of N,N-dimethylacetamide (dma) and acetonitrile with nitrobenzene, which are of iso-relative permittivity, have shown that the first ion-pair formation constant (1 190 dm3 mol–1) in nitrobenzene of much lower basicity decreases with increasing fraction of dma and MeCN, although MeCN is axially bonded to the nickel but dma is hardly co-ordinated. The axial co-ordination constant, KNiS=[NiL(S)2+]/[NiL2+][S], of twenty donor solvents (S) in nitrobenzene as a non-co-ordinating diluent was also determined spectrometrically. It was found that the oxygen-donor co-ordinating solvents such as acetone and water for which Gutmann's donor number (DN) is less than 20 are not co-ordinated to the nickel, and the nitrogen-donor co-ordinating solvents with a nitrile group such as acetonitrile tend to be strongly co-ordinated in spite of their lower DN. These results show no correlation of KNiS with DN and are discussed in terms of the π-acceptor properties of the C–N bond, steric hindrance due to the four methyl groups, and self-interactions of the donor solvents.