Unexpected ring transformation to pyrrolo[3.2-b]pyridine derivatives. Fused azolium salts. 22

2-Arylsulfanyl and 2-benzylsulfanylpyridinium N-arylimides (2) easily prepared from 3-aryltetrazolopyridinium salts (1) with aryl and benzylthiolates, respectively, reacted with various dipolarophiles yielding cycloadducts that underwent transformation to give tetrahydropyrrolo[3,2-b]pyridines (5, 6, and 8) in good yields. A similar rearrangement (formation of 15) was also observed in the case of parent derivatives being unsubstituted in position 2 (12). The abscence of any significant solvent effect, comparison of the sulfur and non-sulfur analogues, as well as the stereoselective nature of the observed ring transformation seem to support a sigmatropic mechanism. Structure elucidation of the products has been carried out by single-crystal X-ray diffraction and (1)H NMR experiments.     

Synthesis of condensed systems containing the tetrazole ring by base-catalyzed intramolecular cyclization of quaternary ammonium salts

Quaternary ammonium salts containing propargyl and 3-(2-methyltetrazol-5-yl)propargyl groups undergo base-catalyzed cyclization at room temperature with self heating to form condensed heterocyclic systems containing the tetrazole ring. Heating at 90–92°C for 2 h is necessary to cyclize the allyl analogs of the starting salts.Communication 234 of the series Research on Amines and Ammonium Compounds. For 233, see [1].Institute of Organic Chemistry, National Academy of Sciences of the Republic of Armenia, Erevan 375094. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 390–394, March, 1999.     

A facile synthesis of new 3-(2-benzimidazolyl)-2-alkyl-4-(3H)-quinazolinones under microwave irradiation

Preparation of 2-amino-N-(1-H-benzimidazol-2-yl)benzamide and a variety of new 3-(2-benzimidazolyl)-2-alkyl-4-(3H)-quinazolinones using isatoic anhydride, 2-aminobenzimidazole and orthoesters under microwave irradiation are described.     

Anodic Stripping Voltammetry of Heavy Metals at Nanocrystalline Boron‐Doped Diamond Electrode

Boron‐doped Diamond (BDD) electrode has become one of the important tools for heavy metal detection. By studying some analytical parameters of DPASV method, like deposition time and potential in different electrolyte concentrations (acetate buffer), the conditions for detecting very low metal ion levels (Zn, Cd, Pb, and Cu) could be chosen. Diluted electrolyte (0.01 M buffer) was one of the factors favoring low detection and quantification limits, but its quantification range is short in comparison to more concentrated media. For ?1.7 V deposition potential, the detection of single metal at ppb levels was reached in 60 s deposition time. Understanding different metal‐metal interactions shows the limits to the simultaneous determination of heavy metals at BDD. Quantification was possible for the simultaneous determination of Zn, Cd and Pb despite the overlapping of Zn and Cd peaks. The performance of the BDD was compared with that of another C‐based solid electrode: the glassy carbon electrode (without mercury plating). A lower base line current, wider potential range, higher sensitivity (3 to 5 times higher than GC) and longevity of the material were noticed for the BDD.     

Development of the FTIR properties of nano-structure silica gel doped with different rare earth elements,prepared by sol-gel route

Structural characteristics of pure silica gel (silica-xerogel, SiO₂) and silica gel doped with some rare earth elements (REEs) such as, praseodymium Pr³⁺, and Europium Eu³⁺, Erbium Er³⁺ and Holmium Ho³⁺ ions, with different concentrations ranging from 1 up to 6%, in the form of monolith materials were prepared by sol-gel technique, Using tetra-ethoxysilane as precursor materials, which are of particular interest for sol-gel integrated optics applications. Some structural features of sol-gel derived monolith are analyzed, namely the structure of nano-particle momolith samples, based on X-ray diffraction (XRD) and Fourier Transform Infrared (FTIR). We show that the XRD spectra of α-crystobalite are obtained for the pure samples at 1100°C and even by doping with the four REEs ions.     

Ylures sans sel,evolution en phosphoranes et equilibre ylure ⇌ phosphorane : I Synthese et structure

Synthesis of new salt-free ylids $\text{9}$,$\text{12}$ to $\text{16}$, $\text{19}$, $\text{20}$, $\text{22}$, $\text{27}$ and $\text{29}$ and phoiphoranes $\text{10}$, $\text{17}$, $\text{18}$, $\text{21}$, $\text{23}$, $\text{30}$ to $\text{33}$ by addition of a trivalent phosphorus compound (phosphites and amino-phosphines ) $\text{1}$ to $\text{7}$ with dimethyl acetylencedicartboxylate in presence of a protic trapping reagent are described. The results are consistent with trapping of carbanionic species. In relation with the. cyclic of acyclic structure of the triivalent phosphorus compound and the protic trapping reagent ie : methanol, phenol, carboxylic acid, etc.., several pathways are involved. Clearly), three phenomena are shown : one can obtain an ylid via a phosphorane or conversely a phosphorane via an ylid or an equilibrium Phoiphorane ? ylid. Results are dealing with thermodynamic or kinetically controlled reactions.     

Heterocycles from carbohydrate precursors. Part XIX. The X-ray crystal structure determination of the reaction product of 4-(2-acetoxyethylidene)-4-hydroxy-2,3-dioxobutyro-1,4-lactone-2-(p-bromophenylhydrazone) with methylhydrazine

X-ray crystallographic data show that the product obtained in the reaction of 4-(2-acetoxy-ethylidene)-4-hydroxy-2,3-dioxobutyro-1,4-lactone-2-(p-bromophenylhydrazone) with methyl-hydrazine is the bicyclic compound 2,6-dimethyl-3,4-dioxo-2,3,4,6,7,8-hexahydropyridazino-[4,3-c]pyridazine 4-(p-bromophenylhydrazone) ( 10 ) and not as originally suggested 1-methyl-3-(1-methylpyrazolin-3-yl)-4,5-pyrazoledione 4-(p-bromophenylhydrazone) ( 8 ).     

Solvation numbers and hydration constant for thorium(IV) in ethanol-water medium

The solvation number and hydration constant of Th⁴⁺ in ethanol-water medium were determined at 25°C using UV-spectral and electrochemical measurements. A solvate formation equilibrium is demonstrated and characterized. Three molecules of ethanol (S) can bond to the metal cation with strengths comparable to that for H₂O to form ThS₃(H₂O) ₃ ⁴⁺ Formation of thorium monochelate with lawsone (2-hydroxy-1,4-naphthoquinone) eliminates bonding with alcohol molecules. The dissociation constant of the chelating agent_sK_a and the formation contant of the monochelated metal ion_sK _f ^* that are essentially independent of the solution composition are evaluated. Hydration titrations involving thorium-lawsone monochelate are performed and the data obtained from the changes of pH with solvent composition are analyzed. The solution independent constant,_sK _f ^* for thorium-lawsone complex formation in mixed aqueous ethanol is given by $$log_s K_f * = vpK_a + log_s K_h - log[LH] - vpH + 3logv$$ where vpK_a is the dissociation constant of the chelating agent LH in the solvent system of ν volume fraction of water and_sK_h is the solution-independent hydration constant of thorium (IV) in the solvent system. Log-values for the constants_sK_h,_sK _f ^* and_sK _a ^* are found to be 7.8±0.02, 11.38±0.04 and ?0.753, respectively.