Heteroanalogs of alloxazines

The properties of derivatives of 6,8-dimethyl-7,9-dioxo-5H-6,7,8,9-tetrahydropyrimido[4,5-b][4,5-e][1,4]thiazines have been investigated. These substances are stable in the crystalline form and are readily oxidized in moist solutions in chloroform or methylene chloride, being converted to 9a-hydroxy derivatives. In the example of the 4-dimethylamino derivative, a stagewise mechanism has been shown for the process of one-electron oxidation of the thiazines, proceeding through the formation of a free-radical structure. The thiazinyl radicals have been found to be capable of one-electron redox reactions. A tendency of the thiazines to form 9a-derivatives has been noted.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1129–1134, August, 1992.     

The clemmensen reaction of tigogenin. A reinvestigation

The reaction of tigogenin ($\text{1b}$) with amalgamated zinc yields tetrahydrotigogenin ($\text{2b}$) and the furostan $\text{3}$. While $\text{2b}$ undergoes acid catalyzed elimination to give the rearranged product $\text{7}$, $\text{3}$ spontaneously decomposes to a mixture of $\text{4}$ and $\text{5}$.     

A reinvestigation of the hyperfine structure in fluoroform

The hyperfine structure of the J = 1 - 0 rotational transition of the CF₃H and CF₃D molecules has been reinvestigated with a high resolution beam maser spectrometer equipped with a nozzle source. Considerable gain in S/N ratio compared with previous measurements performed with a normal effuser source is obtained. The experimental result eliminate discrepancies between the results of previous investigations.     

Polychlorination of thiophene. A reinvestigation

Some old controversies in the literature with regard to the structures of trichlorothiophenes have been elucidated. In the course of these studies, we found that the best method for the preparation of 2,3,5-trichlorothiophene is the direct chlorination of thiophene in the presence of catalytic amounts of ferric chloride. If 2,5-dichlorothiophene is available 2,3,5-trichlorothiophene can also be obtained in good yields through chlorination with thionyl chloride and sulfuryl chloride, using aluminum trichloride as catalyst.     

Reduction with N-benzyl-1,4 dihydronicotinamide. A reinvestigation.

3- or 4-Formylpyridines, cyclohexen -2 one andg-nitrostyrene can be reduced with BNAH: these substrates were previously reported to be inert or very unreactive toward this reagent.     

Phase transitions in thallous nitrate. A reinvestigation

A detailed reinvestigation of the phase transitions in thallous nitrate using DSC, X-ray, IR and optical microscopy has been undertaken. The DSC measurements on anhydrous samples show that the orthorhombic [OR] → hexagonal [HEX] transition sets in at 349 ± 1 K and peaks around 353 K. However, its intensity depends upon several factors such as particle size, moisture content and thermal history of the sample. The HEX→cubic [C] transition sets in around 405 K and shows two peaks at ～409 K and 413 K. Their relative intensities depend on the moisture content and thermal history of the sample. On cooling, the peaks show hysteresis and, by selective thermal cycling, the pairs of transitions, which correspond to the same process during heating and cooling, have been identified. IR spectra recorded in the OR and HEX phases at room temperature show that the symmetric stretching frequency (～1040 cm^?1) of the nitrate ion gets damped in the HEX phase. X-ray and optical microscopy data are in good agreement with the DSC observations.     

Structures of the covalent hydrates and products of acidic hydrolysis of rheumycin and fervenulin

It is shown that pyrimido[5,4-e]-1,2,4-triazinediones are hydrated at the N(₄)-C(_4a) bond in aqueous acidic media. The equilibrium constants of these processes were measured by PMR spectroscopy. The structure of the covalent adduct of fervenulin was established by x-ray diffraction analysis. Formic, 5-diazo-3-methylbarbituric, and methylparabanic acids were identified among the products of destruction of the hydrates in acidic media.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 12, pp. 1654–1660, December, 1988.     

A reinvestigation of the bamberger-ham phenazine. Synthesis: A limitation

The Bamberger-Ham condensation of 4-substituted nitrosobenzenes in concentrated sulfuric acid reported as a method of synthesis for phenazine N-oxides has been found to be limited to electron donating substituents. Methyl 4-nitrosobenzoale has been found to react under these conditions to give dimethyl 2-nitrodiphenylamine-4, 5-diearboxylate ( 2 ). Compounds of unknown structure previously reported to arise from acid treatment of 4-bromo- and 4-chloronilrosobenzene have been shown to be 4, 5-dibromo-2-nitrosophenylamine ( 10 ) and the analogous dichloro compound. Treatment under stronger acidic conditions (oleum) converted 10 but not 2 into the corresponding phenazine N-oxide. Mechanistic implications are discussed.     

The dipole moments and molecular structure of chloral and bromal hydrates

The dipole moment of chloral hydrate is 2·07 D and 2·65 D at 35° in benzene and dioxane solutions respectively. Bromal hydrate has a moment of 2·56 D in benzene solution. The moments observed can reasonably be accounted for on the scheme of Smith et al. and the results have been discussed in terms of the possible structures of these molecules.     

Ferrocene-containing polymers. A reinvestigation of the polyrecombination of ferrocene

Earlier work by Korshak and other Russian authors on the preparation of polyferrocenylenes by the recombination reaction of ferrocene in the presence of tert-butyl peroxide has been reinvestigated. It has been demonstrated that, under carefully controlled conditions at temperatures near 200°, ferrocene can indeed be polymerized to give soluble polymeric compounds, comparable in molecular weight range and physical properties with Korshak's products. These polymers, however, possess overall elemental compositions distinctly differing from that of polyferrocenylene. Spectroscopic and elemental analyses, corroborated by the isolation not only of biferrocenyl and terferrocenyls, but also of diferrocenylmethane and ferrocenylmethyl tert-butyl ether as by-products, indicate the polymer chains to be composed of small polyferrocenylene segments interlinked by methylene and aliphatic ether groups. These bridging groupings are believed to have arisen through the involvement of methyl and tert-butyl radicals generated by thermal decomposition of the tert-butyl peroxide, with methylferrocene postulated as an additional intermediate. Consistent with the presence of such non-ferrocene constituents, the polymers exhibit poor hydrolytic stability and, in thermogravimetric analysis, show a thermal stability behavior inferior to that expected for a polymeric compound strictly composed of ferrocenylene units.     

On the regiochemistry of the methylphenylcyclopropenone dimer. A reinvestigation

The regiochemistry of the previously reported dimer of methyhlphenylcyclopropenone is corrected through analysis of the long-range ¹H, ¹³C correlated (COLOC) 2D nmr spectrum.     

A reinvestigation of phenylene- and polyphenylene-mercurials

Evidence is presented to show that ortho-phenylenemercury is a trimer; no evidence was obtained for the previously reported hexameric form. Similarly, ortho-biphenylenemercury and its perfluoro-analogue exist as trimers and not tetramers, while ortho-terphenylenemercury is a dimer.     

Stability of rare gas structure H clathrate hydrates

Molecular dynamics simulations are used to study the stability of structure H (sH) clathrate hydrates with the rare gases Ne, Ar, Kr, and Xe. Simulations on a 3 x 3 x 3 sH unit cell replica are performed at ambient pressure at 40 and 100 K temperatures. The small and medium (s+m) cages of the sH unit cell are assigned rare gas guest occupancies of 1 and for large (l) cages guest occupancies of 1-6 are considered. Radial distribution functions for guest pairs with occupancies in the l-l, l-(s+m), and (s+m)-(s+m) cages are presented. The unit cell volumes and configurational energies are studied as a function of large cage occupancy for the rare gases. Free energy calculations are carried out to determine the stability of clathrates for large cage occupancies at 100 K and 1 bar and 20 kbar pressures. These studies show that the most stable argon clathrate has five guests in the large cages. For krypton and xenon the most stable configurations have three and two guests in the large cages, respectively.     

A reinvestigation of the cyclodesulfurization of thiosemicarbazides

A recent report describing the preparation of 2-(substituted-amino)-3,4-dihydro-5H-1,3,4-benzotriazepin-5-ones (3), by the cyclodesulfurization of hydrazides prepared from o-aminobenzoylhydrazine ( 1 ) and isothiocyanates, is erroneus. The products resulting from this reaction sequence are, instead, 2-(substituted-amino)-5-(o-aminophenyl)-1,3,4-oxadiazoles ( 4 ). Alternate syntheses of the oxadiazoles led to the correct structural assignments.     

Theoretical study on the structure of the BrO hydrates

The hydrates of bromine monoxide, BrO(H2O)n, n = 1-4, have been studied by means of ab initio calculations at the B3LYP/aug-cc-pVTZ level of theory. These systems could be formed in the troposphere and participate in chemical reactions involved in the depletion of ozone. Several conformations are obtained and discussed for each of the hydrates mentioned. Two rather different intermolecular interactions are found, namely, conventional hydrogen bonding and Br...O associations. In contrast with a more traditional point of view in which hydrogen bonds could be assumed as the preferential interaction for the formation of these complexes, it is the Br...O association which yields the most stable conformations. Equilibrium geometries, harmonic frequencies, and relative energies have been calculated for the bromine monoxide hydrates for the first time. The theoretical binding energies indicate that the stabilization of the hydrates increases with the number of water molecules added. Cooperative effects are suggested to play a significant role in this stabilization. An analysis of relevant properties depending on the electron density in the bond critical points of the Br...O associations has been done for the first time, showing characteristic features of this interaction in comparison with the hydrogen bonds formed.