Microwave‐Assisted Convenient Synthesis of α,β‐Unsaturated Esters and Ketones via Aldol‐Adduct Elimination

Various fluorinated 3‐oxo ester/1,3‐diketones were reacted with carbonyl compounds, in presence of piperidine and under microwave irradiation, to afford (E)‐α,β‐unsaturated esters and ketones in good yields. The systematic study reveals that the reaction proceeded through the formation of aldol adduct. The method provides a new and simple way for C,C bond formations.     

Pyridylazole chelation of oxorhenium(V) and imidorhenium(V). Rates and trends of oxygen atom transfer from Re(V)O to tertiary phosphines

The concerned azoles are 2-(2-pyridyl)benzoxazole (pbo) and 2-(2-pyridyl)benzthiazole (pbt). These react with ReOCl(3)(PPh(3))(2) in benzene, affording Re(V)OCl(3)(pbo) and Re(V)OCl(3)(pbt), which undergo facile oxygen atom transfer to PPh(2)R (R = Ph, Me) in dichloromethane solution, furnishing Re(III)(OPPh(2)R)Cl(3)(pbo) and Re(III)(OPPh(2)R)Cl(3)(pbt). The oxo species react with aniline in toluene solution, yielding the imido complexes Re(V)(NPh)Cl(3)(pbo) and Re(V)(NPh)Cl(3)(pbt). The X-ray structures of pbt, ReOCl(3)(pbt), Re(OPPh(3))Cl(3)(pbt), and Re(NPh)Cl(3)(pbo) are reported. The lattice of pbt consists of stacked dimers. In all the complexes the azole ligand is N,N-chelated and the ReCl(3) moiety is meridionally disposed. In ReOCl(3)(pbt) the metal-oxo bond length is 1.607(9) A. The second-order rates and the associated activation parameters of the oxygen atom transfer reactions of the Re(V)O chelates with PPh(2)R are reported. The large and negative entropy of activation (approximately -24 eu) is consistent with an associative pathway involving nucleophilic phosphine attack. The rate increases with phosphine basicity (PPh(2)Me > PPh(3)) and azole heteroatom electronegativity (O(pbo) > S(pbt)). Logarithmic rate constants for ReOCl(3)(pbo), ReOCl(3)(pbt), and ReOCl(3)(pal) are found to correlate linearly with Re(VI)O/Re(V)O reduction potentials (pal is pyridine-2-(N-p-tolyl)aldimine). The relatively low rate constant of ReOCl(3)(pbt) compared to that of ReOCl(3)(pal) is consistent with the observed shortness of the metal-oxo bond in the former. Crystal data are as follows: (pbt) empirical formula C(12)H(8)N(2)S, crystal system orthorhombic, space group Pca2(1), a = 13.762(9) A, b = 12.952(8) A, c = 11.077(4) A, V = 1974(2) A(3), Z = 8; (ReOCl(3)(pbt)) empirical formula C(12)H(8)Cl(3)N(2)OSRe, crystal system monoclinic, space group P2(1)/c, a = 11.174(7) A, b = 16.403(10) A, c = 7.751(2) A, beta = 99.35(4) degrees, V = 1401.8(13) A(3), Z = 4; (Re(NPh)Cl(3)(pbo)) empirical formula C(18)H(13)Cl(3)N(3)ORe, crystal system monoclinic, space group P2(1)/c, a = 9.566(6) A, b = 16.082(8) A, c = 11.841(5) A, beta = 94.03(4) degrees, V = 1817(2) A(3), Z = 4.     

Synthesis, characterization, and reactivity of mononuclear O,N-chelated vanadium(IV) and -(III) complexes of methyl 2-Aminocyclopent-1-ene-1-dithiocarboxylate based ligand: reporting an example of conformational isomerism in the solid state

Vanadium(IV) and -(III) complexes of a tetradentate N(2)OS Schiff base ligand H(2)L [derived from methyl 2-((beta-aminoethyl)amino)cyclopent-1-ene-1-dithiocarboxylate and salicylaldehyde] are reported. In all the complexes, the ligand acts in a bidentate (N,O) fashion leaving a part containing the N,S donor set uncoordinated. The oxovanadium(IV) complex [VO(HL)(2)] (1) is obtained by the reaction between [VO(acac)(2)] and H(2)L. In the solid state, compound 1 has two conformational isomers 1a and 1b; both have been characterized by X-ray crystallography. Compound 1a has the syn conformation that enforces the donor atoms around the metal center to adopt a distorted tbp structure (tau = 0.55). Isomer 1b on the other hand has an anti conformation with almost a regular square pyramidal geometry (tau = 0.06) around vanadium. In solution, however, 1 prefers to be in the square pyramidal form. A second variety of vanadyl complex [VO(L(cyclic))(2)](I(3))(2) (2) with a new bidentate O,N donor ligand involving isothiazolium moiety has been obtained by a ligand-based oxidation of the precursor complex 1 with iodine. Preliminary X-ray and FAB mass spectroscopic data of 2 have supported the formation of a heterocyclic moiety by a ring closure reaction involving a N-S bond. Vanadium(III) complex [V(acac)(HL)(2)] (3) has been obtained through partial ligand displacement of [V(acac)(3)] with H(2)L. Compound 3 has almost a regular octahedral structure completed by two bidentate HL ligands along with an acetylacetonate molecule. Electronic spectra, magnetism, EPR, and redox properties of these compounds are reported.     

Thermostable and Alkalistable Endoxylanase of the Extremely Thermophilic Bacterium Geobacillus thermodenitrificans TSAA1: Cloning, Expression, Characteristics and Its Applicability in Generating Xylooligosaccharides and Fermentable Sugars

Xylanase encoding gene (1,224 bp) from Geobacillus thermodenitrificans was cloned in pET28a (+) vector and successfully expressed in Escherichia coli BL21 (DE3). The deduced amino acid sequence analysis revealed homology with that of glycosyl hydrolase (GH) 10 family with a high molecular mass (50 kDa). The purified recombinant xylanase is optimally active at pH 9.0 and 70 °C with T _1/2 of 10 min at 80 °C, and retains greater than 85 % activity after exposure to 70 °C for 180 min. The enzyme liberates xylose as well as xylooligosaccharides from birchwood xylan and agro-residues, and therefore, this is an endoxylanase. The xylan hydrolytic products (xylooligosaccharides, xylose, and xylobiose) find application as prebiotics and in the production of bioethanol. The xylanase being thermostable and alkalistable, it has released chromophores and phenolics from the residual lignin of pulps, suggesting its utility in mitigating chlorine requirement in pulp bleaching.     

Novel Synthetic Approach to Thiophosphinates Incorporating Different N-Heterocycles

Eight new cycloiminylidenamidothiophosphinates incorporating pyridine, pyrimidine, thiazole, and benzothiazole heterocycles were synthesized by phosphorylation of the quaternary iminium salts of the heterocycles by diphenylchlorophosphine followed by in situ sulfurization by elemental sulfur. Crystalline solid products were well characterized by elemental analysis and NMR spectroscopy.     

Electrodeposition of lead on glassy carbon and mercury film electrodes from a distillable room temperature ionic liquid,DIMCARB

The electrochemical reduction of Pb²⁺ has been studied in the ‘distillable’ ionic liquid DIMCARB (a mixture of adducts of dimethylamine and carbon dioxide, comprising both neutral and ionic moieties). Voltammetric results show that Pb²⁺ is reduced in a single step to form Pb metal via a nucleation and growth mechanism on a glassy carbon electrode. Ex situ powder X-ray diffraction studies on deposited lead show the presence of both α- and β-PbO₂, as well as elemental lead, suggesting the finely deposited lead particles are in an active rather than passive state. Chronamperometric and scanning electron microscope measurements show that the nucleation and growth follows a progressive nucleation mechanism on glassy carbon. Large peak–peak separations for the Pb reduction and oxidation are consistent with this mechanism and do not suggest electrochemical reversibility. However, experiments with co-deposition of Hg show that this irreversibility is a result of deposition onto a solid glassy carbon surface rather than a solvent effect. The diffusion coefficient of Pb²⁺ in DIMCARB has been calculated to be 1.8±0.4×10⁻⁷ cm² s⁻¹. Electronic supplementary material Supplementary material is available in the online version of this article at and is accessible for authorized users. This work is dedicated to Piero Zanello on the occasion of his 65th birthday in recognition of his numerous contributions to inorganic electrochemistry.     

Vibrational spectroscopy investigation using ab initio and density functional theory analysis on the structure of 2-amino-5-methylphenol

The laser Raman and Fourier transform infrared spectra of 2-amino-5-methylphenol were recorded in the solid phase. The equilibrium geometry, harmonic vibrational frequencies, infrared intensities, Raman scattering activities, depolarization ratios and reduced masses were calculated by HF and density functional B3LYP methods by using 6-311+G(d,p) basis set. The scaled theoretical wavenumbers showed very good agreement with the experimental values. The thermodynamic functions of the title compound were also performed at HF/6-31G(d,p)/6-311+G(d,p) and B3LYP/6-31G(d,p)/6-311+G(d,p) levels of theory. A detailed interpretations of the infrared and Raman spectra of 2-amino-5-methylphenol is reported. The theoretical spectrograms for FT-IR spectra of the title molecule have been constructed.     

Vibrational spectra and assignments of 2-amino-5-iodopyridine by ab initio Hartree-Fock and density functional methods

The Fourier transform Raman and Fourier transform infrared spectra of 2-amino-5-iodopyridine were recorded in the solid phase. The equilibrium geometry, harmonic vibrational frequencies, infrared intensities and Raman scattering activities were calculated by HF and DFT (B3LYP) methods with the 6-31G(d,p) basis set for C, N, H and LANL2DZ pseudopotential for I. The scaled theoretical wavenumbers showed very good agreement with the experimental ones. A detailed interpretation of the infrared and Raman spectra of 2-amino-5-iodopyridine is reported on the basis of the calculated potential energy distribution. The theoretical spectrograms for the IR spectrum of the title molecule have been constructed.     

Titanium aminophosphates as efficient,economical, and recyclable catalysts for the synthesis of xanthenediones

Titanium aminophospates have been used as catalysts in the synthesis of xanthenediones at room temperature. Among the three catalysts tested, titanium n-propyl aminophosphate (TNPAP) was found to be more efficient catalyst for the synthesis of xanthenediones. The solvent-screening studies for this catalytic reaction reveals that MeOH: H₂O was the most suitable solvent system, yielding higher amounts (89%) of products. The TNPAP catalyst was found to be reusable for five successive cycles. The optimized reaction conditions are 1.0?mmol of benzaldehyde, 2.0?mmol of dimedone, methanol/water (5.0?mL) as solvent, rt, and 100?mg of TNPAP. A plausible mechanism for the catalytic reactions has been proposed.