Nucleophilic additions of primary and secondary amines to pentacyclo[5.4.0.02,6.03,10.05,9]undecane-8,11-dione

The crystal structures of three compounds formedvia nucleophilic attack of a heterocyclic secondary amine on PCU-8,11-dione, with the concomitant intramolecular attack of one keto oxygen on the carbon of the other ketone, are presented. In all three compounds, the bridging oxygen contains substantial p-character, and the bonds to the attacking nitrogen are significantly shorter than would be expected.     

The crystal structure of eudesma-4(15),7(11)-dien-8α, 12-olide: a sesquiterpene lactone fromTrattinickia rhoifolia Willd

The title compound, formula C₁₅H₂₀O₂, is orthorhombic, P2₁2₁2₁ witha=8.747(2),b=12.025(3),c=12.554(3)Å,Z=4, andD _m =1.32(2)g/ml. The structural analysis shows that the compound corresponds to eudesma-4(15),7(11)-dien-8,12-olide, a sesquiterpene lactone previously isolated fromAster umbellatus but whose crystal structure was unknown.     

Kinetics and thermodynamics of ferrous-ferric equilibrium in sodium aluminoborate glasses

The oxidation-reduction equilibrium between ferrous and ferric iron in sodium aluminoborate glass melts having molar composition 15Na₂O·10Al₂O₃·75B₂O₃ has been studied as a function of temperature. The reaction was observed to follow first order kinetics. The energy of activation for the above reaction was calculated. Equations previously suggested to represent the Fe²⁺–Fe³⁺ equilibrium were discussed and a new equation is proposed. The enthalpy of the reaction was ?8.80 kcal mol^?1.     

Degradation Kinetics of an Epoxy/Cycloaliphatic Amine Resin Under Isothermal and Non-isothermal Conditions

A study of an epoxy-cycloaliphatic amine system has been realized using a thermogravimetric technique (TG). Isothermal and non-isothermal (dynamic) methods were employed to determine the kinetic data of this system. Five methods were used for determining the activation energies of this system in the dynamic heating experiments. In two of them (Flynn-Wall-Ozawa, and Kissinger) it is not necessary to have a prior knowledge of the reaction mechanism of the degradation behaviour for this system. In the other ones (Coats and Redfern, Horowitz and Metzger, and Van Krevelen et al.) it is necessary to know this reaction mechanism, besides Criado et al. method was used for determining it. The results have shown that good agreement between the activation energies obtained from all methods can be achieved if it is assumed that the degradation behaviour of this system is of sigmoidal-rate type. This revised version was published online in August 2006 with corrections to the Cover Date.     

Hexametaphosphate‐Capped Silica Mesoporous Nanoparticles Containing CuII Complexes for the Selective and Sensitive Optical Detection of Hydrogen Sulfide in Water

Cu^II‐macrocycle functionalized hexametaphosphate‐capped silica mesoporous nanoparticles have been prepared and used for the selective and sensitive detection of hydrogen sulfide in aqueous environments. The possibility of using different metal complexes combined with different capping anions and choice of different dyes or other sensing molecules as indicators makes this new protocol highly appealing for the preparation of new sensing systems for sulfide detection in different environments.     

Synthesis and electronic,magnetic and E.s.r. studies of some bimetallic alkoxides of copper(II) with niobium(V) and Tantalum(V)

Summary Novel bimetallic alkoxides of copper(II) of the type Cu[M(OPr-i)₆]₂ (M = Nb or Ta) have been synthesised by the interaction of CuCl₂ (1 mol) with K[M(OPr-i)₆] (2 mol). These bimetallic isopropoxides undergo facile alcohol interchange with primary alcohols such as MeOH, EtOH,n-PrOH andn-BuOH. However, witht-BuOH, the reaction cannot be driven to completion even under prolonged continuous azeotropic fractionation of the liberatedi-PrOH and the final product corresponded in analysis to Cu[Ta(OPr-i)₂(OBu-t)₄]₂.I.r., electronic and electron spin resonance spectral and magnetic susceptibility measurements indicate a distorted octahedralD _4h geometry for copper(II) in these bimetallic alkoxides.     

Surfactant-Assisted Acid Pretreatment of Sugarcane Tops for Bioethanol Production

Sugarcane tops is one of the largest biomass resources in India and in tropical countries such as Brazil in terms of surplus availability. Conversion of this feedstock to ethanol requires pretreatment to make it more accessible for the enzymes used in saccharification. Though several pretreatment regimens have been developed for addressing biomass recalcitrance, very few seem to be promising as an industrial process. A novel hybrid method involving use of mild acid and surfactant was developed which could effectively remove lignin and improve the sugar yield from sugar cane tops. Operational parameters that affect the pretreatment efficiency (measured as yield of sugars) were studied and optimized. Changes in structural properties of the biomass were studied in relation to the pretreatment process using scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier Transform Infrared (FTIR) analysis, and the changes in chemical composition was also monitored. The biomass pretreated with the optimized novel method could yield 0.798?g of reducing sugars per gram of pretreated biomass upon enzymatic hydrolysis.     

A novel alkylation procedure using MW irradiation for the synthesis of 1,2,3-trisubstituted 1,4,5,6,7,8-hexahydro-1,3-diazocinium salts from their corresponding 1,2-diaryldiazocines

In this work, we describe the synthesis of a series of 1,2,3-trisubstituted-1,4,5,6,7,8-hexahydro-1,3-diazocinium salts (1) by alkylation of the corresponding 1,2-diaryl-1,4,5,6,7,8-hexahydro-1,3-diazocines (2). Compounds 2 were obtained by ethyl polyphosphate-promoted cyclocondensation of N-aroyl-N′-arylpentamethylenediamines (3). Reaction of compounds 2 with alkyl iodides led to 1,2,3-trisubstituted 1,4,5,6,7,8-hexahydro-1,3-diazocinium iodides (1), a new family of cyclic amidinium salts. The best yields for the alkylation were achieved using a mixture of DCM–DMSO (10:1) as solvent. The reaction times of both, the cyclocondensation of compounds 3 and the reaction of 2 with alkyl halides, are dramatically decreased when using microwave irradiation.     

3D zinc(II) coordination polymers built up by triazole and benzene-polycarboxylate anions: Synthesis,crystal structure,thermal and photoluminescence characterization

Two coordination polymers of the formula [Zn₅(tmaH)₄(trz)₂(H₂O)₄] (1) and [Zn₃(bta)(trz)₂(H₂O)₄]·2H₂O (2) [tmaH₃ = benzene-1,3,5-tricarboxylic acid/trimesic acid, trzH = 1,2,4-triazole, btaH₄ = benzene-1,2,4,5-tetracarboxylic acid] have been synthesized and structurally characterized by X-ray single crystal diffraction analysis. Both complexes are 3D coordination polymers containing [Zn₄(trz)₂] units connected by benzene-carboxylate anions. In particular, an undulated layer containing 6- and 18-membered rings is outlined in the network of 1. Hydrogen bonds, involving the coordinated and lattice water molecules with carboxylate oxygen atoms, contribute to the stabilization of the networks. Their thermal stability was investigated by thermogravimetric analysis. The fluorescence spectrum of 1 features two peaks at 419 and 323 nm, originating from a π–π∗ intraligand transition and LMCT, respectively. For 2 a broad band at 410 nm is assigned solely as a π–π∗ intraligand transition.     

Highly selective and sensitive chromo-fluorogenic detection of the Tetryl explosive using functional silica nanoparticles

Silica nanoparticles containing polyamines and thiol groups have been used as probes for the selective detection of Tetryl.