Rearrangement of 3-methoxy substituted [2, 1]benzisoxazole- and naphth[2,3-c]isoxazolequinones in dimethyl sulfoxide solution

The reactions of the 3-methoxy-isoxazole quinones 1 and 9 in a highly polar solution of dimethyl sulfoxide have been studied. Quinones of type 2, 4/11, 5/12, 6 and 7/13 have been isolated; nmr measurements give a detailed insight into the reaction mechanism.     

Formation of a Tc(III)-adenosine diphosphate complex

A⁹⁹Tc-ADP complex was prepared when KTcO₄ was reduced in aquous medium by SnCl₂, Na₂S₂O₄, NaBH₄ or Zn in the presence of ADP in excess. The resulting solution was studied by chromatography and spectrophotometry. Electrochemical reduction and substitution on [Tc^III(tu)₆]³⁺ were investigated as alternative synthetic routes. The anionic Tc-ADP complex was isolated as a solid. Cerimetric titrations confirmed the oxidation state +3 for the central atom. IR and¹H-NMR data showed that the purine base is bonded to the Tc central atom but not the ribose moiety. No oxo groups seemed to be directly bonded to the Tc atom. The complex is rather stable in neutral solutions. However, it decomposes to pertechnetate and TcO₂ at extreme pH values.     

Selective hydrogenation and dehydrocyclization of 3-methyl-4-benzyl-2,6-diphenylpyridine

3-Methyl-4-benzyl-2,6-diphenylpiperidine was obtained by hydrogenation of 3-methyl-4-benzyl-2,6-diphenylpyridine in the presence of rhenium heptasulfide; this confirms the common character of the method of selective hydrogenation of aryl(aralkyl)-substituted pyridine bases to give similarly substituted piperidines. Dehydrocyclization of this pyridine base by heating with sulfur leads to 10-mercapto-1,3-diphenyl-2-azaanthracene, which was obtained under the same conditions from 1,2-diphenyl-1,2-bis(3-methyl-2,6-diphenyl-4-pyridyl)ethane.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 375–376, March, 1982.     

Defect concentration in Ti-substituted YIG from TG curves

The article discusses theory and experiment about the measurement of defect concentration in Ti-substituted yttrium iron garnet by means of thermogravimetry techniques. The two possible cases arising from oxygen interchange with atmosphere, oxygen vacancies and interstitial cations, may be analyzed quantitatively from the derived expressions. The possibility of another type of defects being present in the samples, not associated to oxygen evolution, is not excluded. Measurements were carried out in air and CO₂ for different Ti contents. The substitution tends to increase slightly the defect parameter θ in YIG, while a CO₂ reducing atmosphere is much more effective than the Ti substitution for increasing θ. Calculations for a given single-phased sample sintered in air show two possibilities: a deficit of one oxygen atom for every 2.5 unit cells of 96 atoms, or one excess cation for every 3.5 cells. Other samples show very similar results. The accuracy involved in the measurements is about 2–3%.     

Stabilization of a standard gas mixture generator with diffusion tubes

Summary The generator contains diffusion tubes of known length and internal diameter. Once produced, the mixture of the carrier gas and acetone, the reference material, is sent through a chromatographic flame ionisation detector. Its signal reaches a constant level after a time corresponding to the stabilization time of the generator. The technique described is simple and gives repeatable results.     

New polythiophenes bearing electron-acceptor phthalocyanine chromophores

Two new donor-acceptor copolymers comprising a polythiophene backbone, and bearing phthalocyanine chromophores on the side chains have been prepared. Preliminary photophysical characterization of these materials by FTIR photoinduced absorption indicates that electron transfer from the polythiophene to the phthalocyanine units takes place.     

Benzylic cleavage and McLafferty rearrangement under electron ionization conditions in the fragmentation of 5,6-dialkyl-2, 4-diarylpyrimidines

Several 5,6-dialkyl-2,4-diarylpyrimidines were prepared and their electron ionization (EI) mass spectra reported. The benzylic cleavage takes place easily together with an important McLafferty rearrangement. The involvement of the nitrogen atom appears to be important in the fragmentation of 5-methyl-substituted pyrimidines. In contrast, the 6-methyl-substituted pyrimidines undergo benzylic cleavage without hydrogen transfer. Thus, the difference in the mass spectrometric behaviour allows the identification of these isomeric compounds which, in contrast, exhibit only small differences in their NMR spectra. Copyright 1999 John Wiley & Sons, Ltd.     

Dehydration and crystallization process in sol-gel zirconia

Sol-gel zirconia was characterized using high-resolution thermogravimetry (Hi-Res TG) and differential scanning calorimetry (DSC) and compared with X-ray diffraction, Raman scattering, and UV-Vis spectroscopy. ZrO_2-x(OH)_2x·yH₂O annealed below 400°C show typical behavior of amorphous material. As the annealing temperature is increased, the tetragonal and monoclinic phases crystallize. Typical Hi-Res TG curve shows that the samples are continuously dehydrated in a long temperature range, between room temperature and 600°C. The total mass loss relative to the initial mass is of about 29%. The DSC analysis coupled with TG and structural information, indicate that the exothermic processes about 355 and 447°C can be related to the nucleation process of the formation of tetragonal zirconia, with bulk crystallization at 447°C. This revised version was published online in July 2006 with corrections to the Cover Date.     

Low-tempereture photolysis of diazoketones: the conformational isomerism of benzoylphenylmethylene and the IR spectrum of anthronylidene

Low-temperature photolysis of benzoylphenyldiazomethane, 1, and diazoanthrone, 2, in the polycrystal phase resulted in the high-intensity ESR spectra of benxoylphenymethylene 1a and anthronylidene 2a, respectively. Photolyses of argon matrix-isolated 1 and 2, coupled with IR spectroscopy, have now been carried out. Photolysis of 1 yielded the IR spectrum of diphenylketene as the only IR-observable product and indicated the presence in the matrix of the two s-E, s-Z, isomers of 1. On the other hand, photolysis of 2 yielded the IR spectrum of carbene 2a as the only observable product.