Search Results

You are looking at 31 - 40 of 245 items for :

  • "formaldehyde" x
  • Refine by Access: All Content x
Clear All

The investigations concerning the thermal behaviour of a series of Ni(II) and Cu(II) complexes of type [MLCln]· mH2O ((1) M:Ni, L:L(1), n=1, m=2; (2) M:Cu, L:L(2), n=1, m=2; (3) M:Ni, L:L(3), n=2, m=0; (4) M:Cu, L:L(3), n=1, m=2) are presented in this paper. The ligands L(1)-L(3) have been synthesised by template condensation of 1,2-diaminoethane with formaldehyde and 2-amino-1,3,4-thiadiazole-5-thiole or 2-acetamino-1,3,4-thiadiazole-5-sulfonamide. The bonding and stereochemistry of the complexes have been characterised by IR, electronic and magnetic studies at room temperature. The thermal behaviour provided confirmation of the complex composition as well as the number and the nature of water molecules and the intervals of thermal stability. The different nature of the ligands and/or the metallic ions generates a different thermal behaviour for complexes. The complexes do not show biological activity against HIV virus.

Restricted access

Abstract  

Thermal behaviour of cure-accelerated phenol-formaldehyde (PF) resins was studied using the addition of commercial mixture of water soluble oil shale alkylresorcinols (AR) to PF resin, 5-MR being as model compound. The acceleration effect of AR is based on the promotion of condensation of resin methylol groups and subsequent reaction of released formaldehyde with AR. Commercial PF resins SFŽ-3013VL and SFŽ-3014 from the Estonian factory VKG Resins have been used. The chemical structure of resins was characterised by 13C NMR spectroscopy. TG-DTA analysis was carried out using labsysTM instrument Setaram. By TG-DTA measurements, the shift of exothermic and endothermic peaks and the changes of mass loss rate in the ranges of 1.5–10 g AR/100 g PF resin were studied. The effect of AR on the curing behaviour of PF resins was also followed by gel time. Testing of the plywood when using PF resin with 5 mass% of AR shows that the press time could be reduced by about 15%.

Restricted access
Journal of Radioanalytical and Nuclear Chemistry
Authors: Satyabrata Mishra, Falix Lawrence, R. Sreenivasan, N. Pandey, C. Mallika, S. Koganti, and U. Kamachi Mudali

Abstract  

Removal of nitric acid from high level liquid wastes (HLLW) of nuclear fuel reprocessing plants is warranted for simplifying the procedure for waste fixing. Chemical denitration aims to reduce the waste volume by destroying the acidity and subsequent concentration by adding suitable reductants. Reduction of nitric acid to gaseous products is an attractive way to accomplish denitration. Nitric acid reduction with formaldehyde proceeds with the formation of CO2, NO2, NO or N2O depending on the reaction conditions and all the reaction products except water can be eliminated from the system in gaseous form. The HNO3–HCHO reaction is governed by a complex mechanism of exhibiting relatively long induction period, depending upon the temperature, concentration of reactants and nitrous acid reaction intermediate. In the present work, a homogeneous denitration process with formaldehyde which offers safety and is governed by controlled kinetics was demonstrated on a laboratory scale. The induction period before commencement of the reaction was eliminated by maintaining the reaction mixture at a pre determined temperature of 98 °C. Based on the results accrued from lab scale experiments, the equipment for pilot plant scale operation was designed, the reaction efficiency for continuous denitration was determined and the investigation of nitric acid destruction was extended to full-scale plant capacity. The role of organics in the waste in foaming up of the reaction mixture was also studied using a synthetic waste solution.

Restricted access

A high-performance liquid chromatographic (HPLC) method with fluorescence detection after precolumn formaldehyde derivation was developed to detect concentrations of amoxicillin (AMX) in poultry plasma. Proteins in plasma samples spiked with AMX were precipitated with a phosphate buffer and trichloroacetic acid. After precolumn treatment of the extraction product of AMX with formaldehyde under acidic and heating conditions, HPLC analysis with fluorescence (FL) detection at an excitation wavelength of 355 nm and an emission wavelength of 450 nm was performed. A mobile phase comprising acetonitrile and a buffer solution (0.05 M KH2PO4 pH = 5.6), which yielded AMX retention time 8.58 min, was suitable for detection of AMX. The calculated standard curve of the reaction product was linear, and the correlation coefficient was greater than 0.999. The limit of detection and quantification, the accuracy, and the precision were evaluated. Recoveries of spiked amoxicillin were >92%, with a coefficient of variation in the range of 0.35–0.89%. This method has been successfully applied to a pharmacokinetic study after oral administration of amoxicillin to poultry.

Open access

A group of thirteen newly synthesized potential herbicides, N -aryltrichloroacetamides or 2-(chlorophenoxy)acyl derivatives, have been initially investigated by reversed phase (RP) TLC. The lipophilicity of the substances was described by retention factors in water, log k w , calculated from experimental RP TLC data, and by log P values calculated by use of software. Biological activity was examined by use of the BioArena system of TLC separation then (micro)biological detection. The potential role of formaldehyde (HCHO) in the toxic antibacterial action of substances against Pseudomonas savastanoi pv. phaseolicola bacterial cells was investigated. The effect of HCHO capturers (L -arginine and reduced glutathione) and Cu 2+ ions on the bioactivity and mechanism of toxicity of the substances was examined. It was established that HCHO and its potential reaction products (e.g. 1 O 2 , O 3 ) are crucial in the mechanism of action of these molecules. Correlations between the lipophilicity and bioactivity of the test compounds were also analyzed. It seems that hydrophobicity is not the decisive factor affecting the bioactivity of these substances.

Restricted access

Abstract  

The curing kinetics of a bi-component system about o-cresol-formaldehyde epoxy resin (o-CFER) modified by liquid crystalline p-phenylene di[4-(2,3-epoxypropyl) benzoate] (p-PEPB), with 3-methyl-tetrahydrophthalic anhydride (MeTHPA) as a curing agent, were studied by non-isothermal differential scanning calorimetry (DSC) method. The relationship between apparent activation energy E a and the conversion α was obtained by the isoconversional method of Ozawa. The reaction molecular mechanism was proposed. The results show that the values of E a in the initial stage are higher than other time, and E a tend to decrease slightly with the reaction processing. There is a phase separation in the cure process with LC phase formation. These curing reactions can be described by the Šesták–Berggren (S–B) equation, the kinetic equation of cure reaction as follows:
\documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{upgreek} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} $${\frac{{{\text{d}}\alpha }}{{{\text{d}}t}}} = A\exp \left( { - {\frac{{E_{\text{a}} }}{RT}}} \right)\alpha^{m} \left( {1 - a} \right)^{n}$$ \end{document}
.
Restricted access

The most current in vitro and in vivo results in the BioArena system and under greenhouse conditions provide a good opportunity for a fundamental renewal of biological detections and interactions in layer liquid chromatography. The adsorbent bed in a column liquid arrangement is not suitable for biological detection because the living cells do not grow there. Contrarily, the planar adsorbent layer enables the in situ biodetection of antimicrobials and the interactions among separated compounds, cells, and further various cofactors (molecules), making the study of mechanisms of action possible. The basic elements of the time- and dose-dependent quadruple immune response of plants to pathogens in relation to the function and reactions of formaldehyde and its reaction products (mainly endogenous ozone) were demonstrated. This finding opens a new horizon in the field of disease resistance in plants and perhaps in general in the biological world. These results give a good basis and possibility for studying and understanding the unique high-dilution phenomena as well, and at that time, they promise the elimination of century contradictions in this field.

Restricted access

Abstract  

The title terpolymer (8-HQ5-SAMF-II) is synthesized by the condensation of 8-hydroxyquinoline 5-sulfonic acid (8-HQ5-SA) and melamine (M) with formaldehyde (F) in the presence of acid catalyst and using 2:1:3 M proportions of the reacting monomers. The synthesized terpolymer resin is then characterized by different physicochemical techniques viz. number average molecular mass determination, intrinsic viscosity determination, and spectral studies like UV–Visible, IR, 1H NMR, and 13C NMR spectra. The morphology of synthesized terpolymer was studied by scanning electron microscopy (SEM). The thermogravimetry of the terpolymer resin prepared in this study has been carried out by non-isothermal thermogravimetry technique in which sample is subjected to condition of continuous increase in temperature at linear rate. Thermal study of the resin was carried out to determine their mode of decomposition and relative thermal stabilities. Thermal decomposition curves were studied carefully with minute details. The Freeman-Carroll and Sharp-Wentworth methods have been used in the present investigation to calculate thermal activation energy and different kinetic parameter of the terpolymer resins. Thermal activation energy E a calculated with the two above-mentioned methods are in close agreement. The advantage of Freeman-Carroll method is to calculate both the order of reaction n and energy of activation in one single stage by keeping heating rate constant. By using data of thermogravimetry, various thermodynamic parameters like frequency factor Z, entropy change ΔS, free energy change ΔF, and apparent entropy S* have been determined using Freeman-Carroll method.

Restricted access

The aldol condensation of methyl acetate with formaldehyde to form methyl acrylate was studied in a continuous-flow reactor using a series of supported cesium basic catalysts with commercially available materials (ZSM-5, SiO2, and γ-Al2O3) as carriers prepared by vacuum impregnation. The catalysts were characterized by N2 adsorption-desorption, Fourier transform-infrared (FT-IR), X-ray diffraction (XRD), and temperature-programmed desorption of ammonia and carbon dioxide (NH3/CO2-TPD). The obtained results indicated that the selectivity of methyl acrylate was mainly influenced by the properties of supports. The formation of acetone is approximately proportional to the acidity of supports. The basicity of the catalysts was favorable to the formation of methyl acrylate according to the results of CO2-TPD. The hydrolysis of methyl acetate was inhibited over Cs-HT-SiO2 prepared by SiO2 after hydrothermal treatment. Furthermore, SiO2 with the large mesoporous volume is superior to other supports, which shows the best catalytic activity for the aldol condensation reaction. On the other hand, the catalytic performance of zeolite basic catalysts was strongly influenced by the effect of reactant diffusion. Internal diffusion resulted in the increase of conversion of methyl acetate with increasing specific surface area, while the conversion of methyl acetate decreased with increasing the weight hourly space velocity (WHSV) due to the external diffusion.

Restricted access

Abstract  

The self-condensation reactions of 2- and 4-mono-methylol phenols (2-MMP and 4-MMP), in the presence of varying concentrations of NaOH, have been studied by differential scanning calorimetry (DSC). The reaction exotherms were analysed to derive the activation energy, Ea, and the heat of reaction, HT, for the condensation reactions. In the case of 2-MMP an increase in NaOH:2-MMP molar ratio caused an increased in Ea and a decrease in HT up to a molar ratio of 0.6:1. However, for 4-MMP, an increase in NaOH concentration caused an increase in Ea up to a molar ratio of 0.3:1 beyond which there appeared to be no further effect. The presence of NaOH had no effect on HT for this compound. The results suggest that in the range of NaOH concentration used the effect of NaOH was substantially greater on 2-MMP compared to 4-MMP.

Restricted access