Presence Of Hexamethylenetetramine Research Articles

Sensitive spectrofluorimetric determination of aluminium(III) with Eriochrome Red B

A spectrofluorimetric method is reported for the determination of Al(III), based on the formation of a fluorescent Al(III)-Eriochrome Red B complex in the presence of hexamethylenetetramine at 60°C. Fluorescence measurements were made at 2°C and all variables that affect the development of the complex are reported. The method is very selective and the detection limit is 0.1 ng ml −1. It was applied to the determination of Al(III) in tap water.

Formation of AlPO 4-15 and CoAPO-15 in the presence of hexamethylenetetramine

Two materials, AlPO 4-15 and CoAPO-15, with the same aluminophosphate lattice have been obtained by hydrothermal synthesis in the presence of hexamethylenetetramine (HMTA). Their formation is attributed to the influence of species that arise through the decomposition of HMTA, the latter process taking place under synthetic conditions. The Co 2+ ion in CoAPO-15 occupies tetragonally deformed octahedral sites, and this causes a slight expansion of the unit cell of CoAPO-15 in comparison to that of AlPO 4-15. The Co 2+ ion is coordinated not only by the O atoms of the system but also by NH 3 molecules.

Formation of rod-like zinc oxide microcrystals in homogeneous solutions

The formation of zinc oxide microcrystals obtained from hydrolysis of zinc nitrate and zinc chloride in the presence of hexamethylenetetramine has been studied by X-ray diffraction, electron microscopy and IR spectroscopy. Prisms, needles and spherulitic aggregates are formed depending on several factors such as reactant concentrations, pH and temperature. It is shown that the formation of prisms and needles is mainly determined by kinetic conditions with prisms favoured at lower temperatures (< 80 °C), where faces can be developed from the solution complexes. The formation mechanism of the monodispersed prisms and needles occurs by coupling of microcrystalline spheres through their c axes forming embryonic rod particles which later grow. On the other hand, the formation of spherulitic aggregates is more the consequence of solution heterogeneity, i.e. high reactant concentrations.

Kinetics of curing of epoxide oligomers by dicyandiamide

Kinetics of the reaction between oligomeric diane epoxides of different functionality with respect to epoxide groups, and dicyandiamide in the presence of hexamethylenetetramine has been investigated. The reaction rate is proportional to the concentration of epoxide groups. Curing of oligomers proceeds - up to the complete conversion of epoxide groups - as two concurrent reactions: epoxide-amine and epoxide-hydroxyl. The ratio of the initial rates of the two reactions is 3 : 1 and their respective activation energies are 49·9 and 54·0 kJ/mole. The total reaction heat is 101 kJ/mole.

Titrimetric Determination of Ascorbic Acid Using Chloranil

Ascorbic acid is oxidized and quantitatively titrated with chloranil (2,3,5,6-tetrachloro-1,4-benzoquinone) in the presence of hexamethylenetetramine in acetone-water; the end point is determined visually by the appearance of a golden yellow color. Colored solutions are assayed by setting the initial absorbance at 451 nm to zero or the minimum, titrating with chloranil solution, and measuring absorbance after each increment of titrant. A plot of the volume of chloranil added against the absorbance gives a straight line with the volume intercept as the end point. Interference by the thiol group of cysteine, glutathione, etc., is avoided by masking with acrylamide; interference by iron(II) is masked with ammonium thiocyanate and sodium potassium tartrate. Hydrogen sulfite and thiourea (which do not interfere) are added as antioxidants during extraction of ascorbic acid from drugs and fruits.

Infrared investigation of the structure of ureaformaldehyde oligomers synthesized in the presence of amines

The IR spectra of urea-formaldehyde oligomers synthesized in the presence of hexamethylene tetramine (HMTA) and ammonia have been investigated. Absorption bands relating to the triazinone ring have been identified, and the number of rings in the oligomer has been quantitatively evaluated on the basis on the absorption bands. The mechanism of formation of cyclic structures during the reaction of condensation of urea with formaldehyde is described and the role of HMTA and the influence of the HMTA concentration on the degree of substitution of the rings formed is revealed. A scheme of formation of cyclic structures is proposed.

NMR 1H structural study of urea-formaldehyde resins

A method was developed to determine the structure of urea-formaldehyde resins using NMR 1H spectra of solutions in D 2O. Spectra were obtained of model compounds of linear cyclic structure, model systems and resins of industrial type and the signals were assigned. The formation of monomethylol urea, symmetrical and asymmetrical dimethylol urea, trimethylol urea and hemiformal was observed using spectra at the first stages of condensation in neutral solution and methylene bridges in acid solution. The formation of triazinone rings stabilized by methylol groups at “amine” nitrogen, in urea-formaldehyde resins obtained in the presence of hexamethylene tetramine, was confirmed.

Effect of Fe 2+ and V 5+ ions upon kinetics of oxidation of U 4+ by chlorate in perchloric acid and sulfuric acid solutions

A method was developed to determine the structure of urea-formaldehyde resins using NMR 1H spectra of solutions in D2O. Spectra were obtained of model compounds of linear cyclic structure, model systems and resins of industrial type and the signals were assigned. The formation of monomethylol urea, symmetrical and asymmetrical dimethylol urea, trimethylol urea and hemiformal was observed using spectra at the first stages of condensation in neutral solution and methylene bridges in acid solution. The formation of triazinone rings stabilized by methylol groups at “amine” nitrogen, in urea-formaldehyde resins obtained in the presence of hexamethylene tetramine, was confirmed.

The Determination of Phenol in the Presence of Hexamethylenetetramine and Formaldehyde

The Determination of Phenol in the Presence of Hexamethylenetetramine and Formaldehyde