Electrochemical Preconcentration of Iodide and Its Determination by Cathodic Stripping Voltammetry

The effects of some factors (the nature and structure of organic compound R, the nature of the electrode material, the composition and concentration of the supporting electrolyte, the potential and time of electrolysis) on the formation and dissolution of electrochemical concentrates of the composition I₂BrR were studied. The results obtained were used for determining iodide by cathodic stripping voltammetry in the concentration range of 6 to 500 g/L. The detection limit for iodide was found to be 0.2 g/L at an electrolysis time of 3 min.     

Effect of the pH of the medium on the electronic absorption spectra and structure of 3-methyl-1-phenyl-4-phenylazo-5-pyrazolone

On the basis of the electronic absorption spectra it was found that 3-methyl-1-phenyl-4-phenylazo-5-pyrazolone exists in acidic solutions in mono- and diprotonated forms. It was established by means of calculations by the Pariser—Parr—Pople (PPP) method that in the neutral and protonated forms the quinone hydrazone tautomer of the phenylazopyrazolone is more stable than the azo tautomer, and it was determined that the protonation center is the N₍₂₎ atom of the pyrazolone ring. The diprotonated form is most likely the quinone hydrazone tautomer protonated at the heteroring N₍₂₎ atom and the -nitrogen atom of the azo group. In an alkaline medium the phenylazopyrazolone exists in the form of an anion with predominance of the azo form. The effect of substituents ion the diazo component of the phenylazopyrazolone on the long-wave bands of the electronic absorption spectra in various media was explained on the basis of calculation of the distribution of the -electron density during electron transitions.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1331–1336, October, 1991.     

Tautomerism in Athraquinones: II. α-Hydroxy-substituted Anthraquinones

The fine structure of experimental π_l,π*-absorption bands of the α hydroxyanthraquinones originates from the prototropic anthraquinoid tautomerism. The tautomeric transformations occur both in the ground and excited states of the molecules; therewith the excited states are more sensitive to the tautomerization than the ground ones. The wavelength and intensity of the π_l,π*-bands, the values of all quantum-chemical characteristics studied for the tautomers of α hydroxyanthraquinones are linearly related to the number of hydroxy groups. The effect of the isomerism of di- and trihydroxyanthraquinones on this relationship was considered.__________Translated from Zhurnal Organicheskoi Khimii, Vol. 41, No. 5, 2005, pp. 722–729.Original Russian Text Copyright © 2005 by Fain, Zaitsev, Ryabov.     

Ring-chain tautomerism of substituted hydrazones

1-Hydrazino-2-propanol reacts with aliphatic carbonyl compounds to form the corresponding (2-hydroxypropyl)hydrazones. 1-(N-Alkylhydrazino)-2-propanols, on the other hand, give tautomeric mixtures of alkyl-substituted perhydro-1,3,4-oxadiazines and N-alkyl-N-(2-hydroxypropyl)hydrazones. As compared with derivatives of 2-(N-alkylhydrazino)ethanols, the position of the equilibrium in the investigated cases is shifted to favor the cyclic forms.See [1] for communication I.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 301–308, March, 1971.     

Investigation of the structure of 1,2-dihydro-3-(2-hydroxyphenyl)-4-nitropyrazol-5(3H)-one by spectroscopic and quantum-chemical methods

The structure of the previously synthesized 1,2-dihydro-3-(2-hydroxyphenyl)-4-nitropyrazol-5(3H)-one (I) was studied by ¹H and ¹³C NMR, IR, and electronic spectra. It was established that the NMR spectra of compound (I) do not contain signals for the H atom at position 4 and the C atoms of the carbonyl groups; in the crystalline state and in solutions the IR spectra do not contain v_c=o bands, while the electronic spectra do not contain absorption in the region of 250 nm. On the basis of the foregoing it is concluded that compound (I) exists in the OH form. The distribution of -electron density in the molecule of (I) and the nature of the bands in its electronic absorption spectrum were studied by quantum-chemical methods in the PPP approximation.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1510–1516, November, 1990.     

Product structure in the reaction of dimethyl acetylenedicarboxylate with 2-furyl-1,2,3,4-tetrahydroquinolines

Dimethyl acetylenedicarboxylate reacts with 4-substituted and 3,4-fused 2-furyl-1,2,3,4-tetrahydroquinoline derivatives at the furan fragment according to the [4 + 2]-cycloaddition pattern. The reaction is not stereoselective, and it yields two diastereoisomeric 7-oxabicyclo[2.2.1]hepta-2,5-dienes whose structure was determined by X-ray analysis and NMR spectroscopy.     

The Reaction of Maleic and Phthalic Anhydrides with 2-Methylimidazole

The reaction of maleic anhydride with 2-methylimidazole in acetonitrile and DMF is accompanied by the appearance of strong absorption bands in the visible part of the spectrum due to the formation of molecular complexes. In acetonitrile the reaction proceeds by two routes via the formation of an amide and the molecular complex. Phthalic anhydride reacts with 2-methylimidazole to give amide but not to form molecular complexes.     

Synthesis of new titanatranes containing organic substituents in the atrane fragment

Titanatrane CpTi(OCH(CH₃)CH₂)₃N (3) was prepared by the reaction of CpTiCl₃ with N(CH₂CH(CH₃)OH)₃ in the presence of triethylamine. The reaction of CpTi(OMe)₃ (8) with N(CH₂CH₂OH)₂(CH₂CHPhOH), erythro-N(CH₂CH₂OH)₂(CHPhCHPhOH), and N(CH₂CH₂OH)₂(CH₂CPh₂OH) gave cyclopentadienyltitanatranes 12–14. Compound 8 reacts with threo-N(CH₂CH₂OH)₂(CHPhCHPhOH) to give a mixture of threo-CpTi(OCH₂CH₂)₂(OCHPhCHPh)N and threo-MeOTi(OCH₂CH₂)₂(OCHPhCHPh)N. Slow hydrolysis of the latter product gave threo-[Ti₃O(OMe){(OCH₂CH₂)₂₋ (OCHPhCHPh)N} ₃]₂, which was studied by X-ray diffraction analysis. The crystal structures of 3 and 12 were also determined by X-ray diffraction analysis. The titanium coordination polyhedron in these complexes is a distorted trigonal bipyramid in which the equatorial positions are occupied by three oxygen atoms and the axial positions contain the N atom and the Cp group. The titanium—nitrogen distances (2.313(2), 2.291(2) Å in two independent molecules of 3 and 2.271(2) Å in compound 12) confirm the presence of Ti←N transannular interaction. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2736–2744, December, 2005.