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Chiral Ph-dbfox (Ph-dbfox = (R,R)-4,6-dibenzofurandiyl-2,2′-bis(4-phenyloxazoline))/Zn(NTf2)2catalyzed enantioselective Friedel–Crafts reactions of β-CF3acrylates with pyrroles and indoles have been investigated, which afforded the corresponding chiral trifluoromethyl pyrrole and indole derivatives in high yields (90–99%) with a range of 66–99% ee values. With the aid of the chiral adduct of the asymmetric Friedel–Crafts reaction, the chiral trifluoromethylated heliotridane has been successfully constructed in good total yield. [ABSTRACT FROM AUTHOR]

The ruthenium catalysed cross-metathesis of terpenoids with methyl acrylate and methyl methacrylate was used to prepare new terpenoids and to improve, to a large extent, the synthesis of known terpenoids. In particular, the cross-metathesis of mono-unsaturated terpenoids was very efficient whereas the transformation of terpenoids incorporating two double bonds was more difficult due to side reactions. The cross-metathesis reactions were carried out under environmentally friendly conditions either in dimethyl carbonate or under solvent-free conditions. [ABSTRACT FROM AUTHOR]

Selective oxidation of tetralin by molecular oxygen over mesoporous CrMCM-41 molecular sieve catalyst using supercritical carbon dioxide (scCO2) solvent has been investigated. CrMCM-41 catalyst gave high selectivity (96.2%) and good yield (63.4%) of 1-tetralone. The presence of scCO2medium improves 1-tetralone selectivity and suppresses leaching of chromium from the CrMCM-41. The activity over recycled CrMCM-41 remains nearly the same under the present experimental conditions. The effect of the reaction parameters on CrMCM-41 was also studied in detail along with comparison of its catalytic activities with other mesoporous catalysts, viz.MnMCM-41, CoMCM-41, microporous CrAPO-5, CoMFI, and macroporous Cr/SiO2catalyst, respectively. In addition this catalytic system was also applied for the oxidation of other benzylic compounds such as indane, fluorene, acenaphthene and diphenylmethane. [ABSTRACT FROM AUTHOR]

A homodinuclear Ni2-Schiff base 1complex (0.1–1 mol%) promoted the direct catalytic asymmetric aldol reaction of β-keto esters with formaldehyde, giving hydroxymethylated adducts in 94–66% ee. [ABSTRACT FROM AUTHOR]

The structure of doped ceria plays an important role in its chemical reactivity and catalytic performance. However, for the majority of the dopants studied, whether a monophasic solid solution is formed or not is typically determined only by standard X-ray diffraction (XRD). In-depth structural characterization is lacking. In this paper we have prepared Zn-doped ceria nanocrystals exhibiting twice the oxygen storage capacity (OSC) of pure ceria. X-ray photoelectron spectroscopy (XPS) shows that the material is chemically inhomogeneous with zinc enrichment in the surface layer. X-ray fluorescence (XRF) reveals significant compositional inhomogeneity of the material after annealing in air at 1300 °C for 24 h. The standard structural characterization of this material using room temperature XRD and transmission electron microscopy (TEM) fails to reveal its correct phase composition. Based on clear evidence from in situ high temperature XRD we show that, after calcination at 500 °C, the material is not monophasic: X-ray amorphous ZnO is present within the material. The amorphous ZnO crystallizes at 800 °C and undergoes second-stage incorporation at even higher temperatures. This second-stage incorporation is not complete after annealing and trace amounts of ZnO remain according to synchrotron-based XRD. Our work provides valuable insight into the incorporation mechanism of zinc into the ceria lattice, and in particular, raises some doubts on the phase compositions reported in many previous studies on doped ceria. [ABSTRACT FROM AUTHOR]

Carbosilylation is a straightforward procedure to install both silyl and organic functional groups onto organic molecules. For example, allylsilylation of alkenes with allylsilanes affords 5-silyl-1-pentene derivatives. In this review paper, catalytic allylsilylations and arylsilylations of alkenes, alkynes, and cyclic acetals are summarized. Specific catalyses of Lewis and Brønsted acids, such as HfCl4 and proton-exchanged montmorillonite, will be discussed. Intramolecular reactions as well as intermolecular allyl- and arylsilylations have been achieved. In the case of the Brønsted acid catalyst, cationic Si species generated and acted as catalytically active species. The structure of the cationic Si species depends on the type of Brønsted acid used. A disilyl cation was proposed as the catalytically active site for carbosilylations of alkenes and alkynes, while a monomeric Si species was active for allylsilylation of cyclic acetals. [ABSTRACT FROM AUTHOR]

Non-toxic DAlCs, especially lighter dimethyl- and diethyl-carbonate, are regarded as very green alkylating reagents, particularly when coupled with metal-exchanged Y- and X-faujasites as catalysts. These reactions are selective, free from wastes or byproducts, and often require no additional solvent other than the carbonate. Nonetheless, this paper demonstrates that the operating temperature and the nature of the faujasite must be carefully chosen in order to avoid DAlC decomposition. In fact, at temperatures ranging from 150 to 240 °C, faujasites can promote decarboxylation of light DAlCs to the corresponding ethers CH3OCH3and CH3CH2OCH2CH3plus CO2. Heavier DAlCs (dipropyl- and dioctyl-carbonate) undergo a similar decomposition pathway, followed by further reactions to the corresponding alcohols (n-propanol and n-octanol) and alkenes [propylene and octene(s)]. These transformations not only consume DAlCs, but also give rise to dangerously flammable ethers, as well as undesirable alcohols, alkenes and CO2. The present work reports an original investigation of the decarboxylation of DAlCs on faujasites with the aim of providing operative boundaries to the experimental conditions to minimise unwanted decomposition. The reaction is strongly affected by the nature of the catalyst: the more basic zeolites, NaX and CsY, are by far more active systems than NaY and LiY. However, solid K2CO3proves to be rather inefficient. The temperature also plays a crucial role: for example, the onset of the decarboxylation of DMC requires a temperature of ∼30 °C lower than that for DEC and DPrC. Overall, awareness that certain zeolites cause decomposition of DAlCs under conditions similar to the ones used for DAlC-promoted alkylations allows determination of the correct experimental boundaries for a safer and more productive use of DAlCs as alkylating agents. [ABSTRACT FROM AUTHOR]

Furfural production through traditional processes is accompanied by acidic waste stream production and high energy consumption. Modern furfural production process concepts will have to consider environmental concerns and energy requirements besides economics, moreover will have to be integrated within widened biorefinery concepts. In this paper, some particular aspects of the chemistry of d-xylose reaction to furfural are addressed, with the aim to clarify the reaction mechanism leading to furfural and to define new green catalytic pathways for its production. Specifically, reducing the use of mineral acids is addressed by the introduction of alternative catalysts. In this sense, chloride salts were tested in dilute acidic solutions at temperatures between 170 and 200 °C. Results indicate that the Cl−ions promote the formation of the 1,2-enediol from the acyclic form of xylose, and thus the subsequent acid catalyzed dehydration to furfural. For this reason the presence of Cl−ions led to significant improvements with respect to the H2SO4case. The addition of NaCl to a 50 mM HCl aqueous solution gave 90% selectivity to furfural. Among the salts tested FeCl3showed very interesting preliminary results, producing exceptionally high xylose reaction rates. [ABSTRACT FROM AUTHOR]

This contribution reports about an in situFT-IR investigation and the catalytic reactivity of Mg/Me3+mixed oxides (Me = Cr, Fe, or Al; Mg/Me = 2, atomic ratio) in the gas-phase methylation of phenol with methanol. It is the second of two papers concerning the mentioned systems, and its purpose is twofold: to confute the classic and not accurate theory concerning the reaction mechanism, and to propose a novel interpretation based on the combined use of catalytic tests and in situmolecular spectroscopy. Results here reported highlight that: (i) the reaction mechanism in phenol methylation, when catalysed by basic systems, is not a classical electrophylic substitution, as generally reported in the literature, but proceeds through the formation of formaldehyde as an intermediate, and (ii) the catalytic behaviour in respect to both methanol and phenol reactants is strictly dependent on catalyst features. Although all investigated systems exhibit a basic-type behaviour with regard to phenol, which dissociates to yield an adsorbed phenolate species, the distribution of phenolic compounds obtained with the Mg/Al/O catalyst was that typically observed with acid catalysts, with prevailing formation of anisole when the reaction was carried out below 350 °C and of mono and poly-C-alkylated compounds when the reaction temperature was above 350 °C. On the contrary, the reactivity shown by both Mg/Fe/O and Mg/Cr/O systems was that reported in the literature as typical of mixed oxides possessing basic features. The extent of methanol decomposition into light compounds was maximum in the case of Mg/Fe/O catalysts, because of the pronounced redox behaviour typical of Fe3+species, whereas neither methanol dehydrogenation nor decomposition were ever observed with Mg/Al/O up to 400 °C. Reactivity tests and spectroscopic experiments hinted for methanol dehydrogenation to formaldehyde as the first step in the ring-methylation of phenol with Mg/Cr/O and Mg/Fe/O: in that case, o-cresol and 2,6-xylenol were the only reaction products. But, with Mg/Al/O systems, for which no methanol dehydrogenation occurred, the formation of anisole was due to the synergistic effect of stronger basic features and the presence of Lewis acidic sites, that facilitate the reaction between phenol and methanol after activation over the two different types of catalytic sites. [ABSTRACT FROM AUTHOR]

A series of α-acyloxyacrylate esters are candidate monomers for bio-based polymers, converted from biomass feedstock. Polymers from these monomers are useful materials for bio-based plastics showing high heat resistance and transparency. In this paper, a new efficient method for α-acyloxyacrylate ester synthesis with a strong inorganic acid, heteropolyacid, is presented. The reaction in the presence of the heteropolyacid catalyst was carried out in liquid phase under mild conditions and showed higher productivity than that of the conventional synthesis with a typical organic acid, p-toluenesulfonic acid. Among the various heteropolyacids examined, α-Keggin-type tungsten-based phosphotungstic acid, H3PW12O40, showed the best performance, suggesting that the acid strength of the heteropolyacid is the crucial property for this reaction. We also found that pyruvate ester was consecutively converted into α-acyloxyacrylate ester via2,2-diacyloxypropionate ester. [ABSTRACT FROM AUTHOR]