An efficient route to aqueous phase synthesis of nanocrystalline γ-Al2O3 with high porosity: from stable boehmite colloids to large pore mesoporous alumina

In this paper we emphasise the important role of Pluronic F127 on the porosity of mesoporous alumina prepared from boehmite colloids. By focusing on the F127/boehmite interactions we show how the concepts of interface science may help to predict and improve the textural characteristics of mesoporous alumina. By varying the synthetic parameters, in particular the copolymer content, we show that the porosity of γ-Al(2)O(3) can be enhanced by 400% and the average pore diameter can be expanded from 5 to 14 nm. These results are discussed in terms of interactions between the Pluronic F127 and boehmite colloids, and are correlated to the critical micelle concentration (CMC) of the copolymer. The textural characteristics of the mesoporous alumina can be further improved either by introducing hydrocarbons in the preformed boehmite/copolymer sols or by concentrating the sols. In comparison with as-synthesised alumina, those prepared with F127 showed improved thermal stability. Furthermore, boehmite/copolymer sols were stable for all surfactant concentrations investigated and can give high quality coatings suitable for catalytic applications.     

KF promoted mesoporous γ-Al2O3 with strong basicity: Preparation,characterization and catalytic activitiy for transesterification to biodiesel

The present paper describes the preparation of KF/M-γ-Al₂O₃, efficient mesoporous solid bases. The procedure involves loading KF into a crystalline mesoporous γ-Al₂O₃ that was synthesized by the self-assembly of poly-4-vinylpyridine (P4VP) with Al³⁺ species. The synthesis is based on the strong acid-base interaction, hydrothermal treatment at 180°C and calcination at 550°C. Characterizations using XRD analysis and low temperature N₂ adsorption indicated that different amounts of KF could be introduced into crystalline mesoporous γ-Al₂O₃ to obtain catalysts with high BET surface areas, large pore volumes and uniform pore size distribution. Based on SEM images, KF/M-γ-Al₂O₃ catalysts have rough surface character and a large nanopore volume. CO₂-TPD curves registered for KF/M-γ-Al₂O₃ contain high temperature peaks, indicating strong basicity of the catalysts. Under the same reaction conditions KF/M-γ-Al₂O₃ catalysts exhibit much better activities for transesterification to biodiesel than KOH, NaOH, H₂SO₄, hydrotalcite and CaO. Enhanced activities appear to arise from strong basisity and large BET surface areas.     

The chemistry of localized singlet 1,3-diradicals (biradicals): from putative intermediates to persistent species and unusual molecules with a π-single bonded character

Localized singlet diradicals (biradicals) are key intermediates in chemical reactions involving homolytic bond-cleavage and formation processes. The molecular structure and electronic structure had been historically elusive due to the short-lived character of the reactive intermediates. In the last 15 years, a significant development of singlet diradical chemistry was achieved after the pioneering findings of long-lived singlet diradicals. In this tutorial review, the recent development of localized singlet diradical chemistry is summarized and discussed. The following subjects are included (a) the mechanism by which the ground state spin-multiplicity of localized 1,3-diradicals is controlled; (b) the substituent and heteroatom effect on the most stable electronic configuration of the singlet 1,3-diradicals, type-1 versus type-2; (c) the molecular design for the long-lived singlet ground state diradicals; (d) the generation and characterization of the singlet diradicals; and (e) the future prospects.     

The sila-Pummerer reaction of γ-silyl substituted cycloalkanoyl sulfoxides: the first examples and a new approach to 3-substituted cycloalk-2-enones

The thermal decomposition of 3-(α-trimethylsilyl)alkyl substituted 2-(phenylsulfinyl)cycloalkanones occurs via the γ-sila-Pummerer reaction, affording 3-substituted cycloalk-2-enones and unstable trimethylsilyl benzenesulfenate as an elimination by-product. The starting γ-silyl substituted cycloalkanoyl sulfoxides were obtained through the conjugate addition reaction of nucleophilic reagents to 2-(phenylsulfinyl)cycloalk-2-enones. The tandem conjugate addition/γ-sila-Pummerer reaction investigated here provides a new route to 3-substituted cycloalk-2-enones.     

Palladium-catalyzed 2-pyridylmethyl-directed β-C(sp~3)—H activation and cyclization of aliphatic amides with gem-dibromoolefins:A rapid access to γ-lactams

The direct Pd-catalyzed β-C(sp³) H activation and cyclization of aliphatic amides bearing a removable 2-pyridylmethyl directing group with gem-dibromoolefins is described for the first time to construct a variety of γ-lactams.     

A rationale of the Baeyer-Villiger oxidation of cyclohexanone to ε-caprolactone with hydrogen peroxide: unprecedented evidence for a radical mechanism controlling reactivity

We demonstrate, for the first time, in the Baeyer-Villiger oxidation of cyclohexanone with aqueous hydrogen peroxide under conditions aimed at obtaining ε-caprolactone, that a thermally activated radical reaction leads to the concurrent formation of adipic acid, even when a stoichiometric amount of the oxidant is used. In fact, ε-caprolactone is the primary reaction product, but it is more reactive than cyclohexanone, and quickly undergoes consecutive transformations. When titanium silicalite-1 (TS-1) is used as a catalyst, the high concentration of hydroxy radicals within its pores accelerates the reaction rates, and the consecutive formation of adipic acid (and of lighter diacids as well) becomes largely kinetically preferred. The proper choice of the solvent, which also may act as a radical scavenger, both without catalyst and with TS-1, is a powerful tool for controlling the rates of the various reactions involved.     

Enantioselective organocatalytic Friedel-Crafts alkylation reaction of indoles with 5-hydroxyfuran-2(5H)-one: access to chiral γ-lactones and γ-lactams via a Ugi 4-center 3-component reaction

5-Hydroxyfuran-2(5H)-one 1, a readily available renewable resource, was used as an electrophile in the Friedel-Crafts alkylation of indoles catalyzed by a diphenylprolinol silyl ether. Moderate catalyst loading was achieved because of the high reactivity of 5-hydroxyfuran-2(5H)-one 1 in this process. Reduction of the Friedel-Crafts adduct (FC adduct) afforded indoyl lactones in high yield and enantioselectivity. Moreover, the FC adduct was used as a chiral synthon in a diversity-oriented synthesis, as illustrated by its successful engagement in a 4-center 3-component Ugi reaction (U-4C-3CR) to afford chiral five-membered lactams in high yield and enantioselectivity.     

Trichoderma harzianum IOC-4038: A Promising Strain for the Production of a Cellulolytic Complex with Significant β-Glucosidase Activity from Sugarcane Bagasse Cellulignin

Sugarcane bagasse is an agroindustrial residue generated in large amounts in Brazil. This biomass can be used for the production of cellulases, aiming at their use in second-generation processes for bioethanol production. Therefore, this work reports the ability of a fungal strain, Trichoderma harzianum IOC-4038, to produce cellulases on a novel material, xylan free and cellulose rich, generated from sugarcane bagasse, named partially delignified cellulignin. The extract produced by T. harzianum under submerged conditions reached 745, 97, and 559 U L⁻¹ of β-glucosidase, FPase, and endoglucanase activities, respectively. The partial characterization of this enzyme complex indicated, using a dual analysis, that the optimal pH values for the biocatalysis ranged from 4.9 to 5.2 and optimal temperatures were between 47 and 54 °C, depending on the activity studied. Thermal stability analyses revealed no significant decrease in activity at 37 °C during 23 h of incubation. When compared to model strains, Aspergillus niger ATCC-16404 and Trichoderma reesei RutC30, T. harzianum fermentation was faster and its extract showed a better balanced enzyme complex, with adequate characteristics for its application in simultaneous saccharification and fermentation processes.     

Reactivity of [HFe3(CO)11]−1 toward alkynes: II. Reactions with monosubstituted alkynes: from alkylidyne to acetylide ligands on a triiron unit

The reactions of monosubstituted alkynes (RCCH (R = C₆H₅, C₃H₇, C(O)CH₃ or C(O)OCH₃) with [P(C₆H₅)₄][HFe₃(CO)₁₁] have been studied. Depending on the reaction conditions the complexes [P(C₆H₅)₄][Fe₃(CO)₁₀(μ₃-CCH₂R)] (A) and [P(C₆H₅)₄][HFe₃(CO)₉(μ₃-CCHR)] (B) can be isolated. The two types of complexes are interrelated by the addition of (B → A) or loss (A → B) of carbon monoxide. In two cases (R = C₆H₅, C₃H₇) the transformation B → [P(C₆H₅)₄][Fe₃(CO)₉(μ₃-CCR)] has been observed in refluxing 2-methoxyethanol, and for these two alkynes all the transformations

have been observed on a triiron unit.     

Chemistry of insect antifeedants from azadirachta indica (part 3): reactions on the C-22,23 enol ether double bond of azadirachtin and conversion to 22,23-dihydro-23-β-methoxyazadirachtin.

Azadirachtin (1) can be converted to the natural product 22,23-dihydro-23β-methoxyazadirachtin (2) via selective bromomethoxylation of the C-22,23 enol ether double bond and tri-n-butyltin hydride reduction; the corresponding acetic acid adduct on pyrolysis affords (1) in high yield. The antifeedant effects of the addition compounds were assessed.     

Novel Grignard reaction of chelated boric esters derived from diethyl (2R,3R)-tartrate: a one-step access to a bulky γ,γ,γ-trisubstituted γ-hydroxy-β-ketoester via selective arylation and sequent deboronation

Reaction of the tetracoordinated spiroborate esters derived from diethyl (2R,3R)-tartrate with Grignard reagents was further examined and found that sterically hindered MesMgBr has different reaction behavior from PhMgBr to the spiroborate esters. It has been proved that in the case of PhMgBr reaction, the formation of the chiral bicyclodiboronic ester (R,R)-2 was accomplished step by step via two 1,3-cyclizations of the hydrolytic products of the resulting boron compound. However, in the case of MesMgBr reaction, only one esteral group of the tartrate moiety was diarylated, and a bulky γ,γ,γ-trisubstituted γ-hydroxy-β-ketoester and mesitylboronic anhydride were provided after the resultant was worked up. The composition and structure of the products were authorized by the spectral and single crystal X-ray analysis. A formation mechanism of γ-hydroxy-β-ketoester and mesitylboronic anhydride was also suggested.     

Intramolecular Oxidative Coupling of the Bis Enolate Derived from Dimethyl β,β-Dimethylglutarate: A Facile Stereoselective Route to a Versatile Synthon for Preparation of Insecticidal Pyrethroids

Treatment of the bis enolate derived from dimethyl β,β-dimethylglutarate with silver chloride afforded dimethyl cis-3,3-dimethyl-1,2-cyclopropanedicarboxylate, a versatile synthon for the preparation of the acid component of cis-pyrethroids. A similar experiment utilizing iodine as the oxidant led to the isolation of the corresponding trans diester with good stereo-selectivity.     

The oxidative conversion of the N,S-bridged complexes [{RhLL'(μ-X)}2] to [(RhLL')3)(μ-X)2]+ (X = mt or taz): a comparison with the oxidation of N,N-bridged analogues

The structures of [{RhLL'(μ-X)}(2)] [LL' = cod, (CO)(2), (CO)(PPh(3)) or {P(OPh)(3)}(2); X = mt or taz], prepared from [{RhLL'(μ-Cl)}(2)] and HX in the presence of NEt(3), depend on the auxiliary ligands LL'. The head-to-tail arrangement of the two N,S-bridges is accompanied by a rhodium-eclipsed conformation for the majority but the most hindered complex, [{Rh[P(OPh)(3)](2)(μ-taz)}(2)], uniquely adopts a sulfur-eclipsed structure. The least hindered complex, [{Rh(CO)(2)(μ-mt)}(2)], shows intermolecular stacking of mt rings in the solid state. The complexes [{RhLL'(μ-X)}(2)] are chemically oxidised to trinuclear cations, [(RhLL')(3)(μ-X)(2)](+), most probably via reaction of one molecule of the dimer, in the sulfur-eclipsed form, with the fragment [RhLL'](+) formed by oxidative cleavage of a second.     

Crystal growth,structure determination and magnetism of a new m=3, n=1 member of the A3n+3mA′nB3m+nO9m+6n family of oxides: 12R-Ba12Rh9.25Ir1.75O33

Single crystals of a new Ba–Rh–Ir–O oxide were grown from a molten potassium carbonate flux. The new compound, Ba₁₂Rh_9.25Ir_1.75O₃₃, is structurally related to the 2H-hexagonal perovskite structure and contains pseudo one-dimensional chains of alternating units of ten face-sharing (Rh/Ir)O₆ octahedra and one (Rh/Ir)O₆ trigonal prism. The magnetic susceptibility of Ba₁₂Rh_9.25Ir_1.75O₃₃ is featureless, indicating the absence of magnetic order. The oxide is a semiconductor with a room temperature resistance of 280 Ω.     

Two-dimensional thallium(I) supramolecular polymer constructed from Tl?π interactions: A new precursor for the preparation of thallium(III) oxide with a nano-structural surface

A new two-dimensional thallium(I) supramolecular polymer, [Tl₂(μ₃-9-Ac)(μ₄-9-Ac)(H₂O)]_n (1) [9-HAc = 9-anthracene carboxylic acid]_, has been synthesized and characterized. The single-crystal X-ray data of compound 1 shows two types of Tl^I ions with coordination numbers of four and five. The thallium atoms have irregular coordination spheres, containing a stereo-chemically active lone pair with η⁵ Tl?C interactions in the vacant coordination sphere of the Tl^I ions, thus attaining total hapticities of 9 and 10 with O₅Tl1?C₅ and O₄Tl2?C₅ environments and Tl?π_(centroid) distances of 3.308 and 3.251 Å, respectively. The thermal stability of 1 was studied by thermo gravimetric (TG) and differential thermal analyses (DTA). Different morphologies of thallium(III) oxide with a nano-structural surface were prepared from compound 1 powders and compound 1 micro-rods. These nano-structures were characterized by X-ray powder diffraction (XRD) and scanning electron microscopy (SEM).