Search

The application of heterogeneous catalysis and green solvents to the set up of widely employed reactions is a challenge in contemporary organic chemistry. We applied such an approach to the synthesis and further conversion of tetrahydropyranyl ethers, an important class of compounds widely employed in multistep syntheses. Several alcohols and phenols were almost quantitatively converted into the corresponding tetrahydropyranyl ethers in cyclopentyl methyl ether or 2-methyltetrahydrofuran employing NH4HSO4 supported on SiO2 as a recyclable acidic catalyst. Easy work up of the reaction mixtures and the versatility of the solvents allowed further conversion of the reaction products under one-pot reaction conditions.

Selective ethanol synthesis from syngas through cascade multi-step reactions via methyl acetate (MA) intermediate route was investigated using a highly crystalline ferrierite (FER) zeolite and hybridized bifunctional Cu-ZnO-Al 2 O 3 /FER (CZA/FER). The extent of crystallinity of the FER zeolites played crucial roles for catalytic activities of syngas conversion to dimethyl ether (DME), DME carbonylation to MA and MA hydrogenation to ethanol. With an increase of crystallinity of FER, DME productivity by CO 2 (or CO) hydrogenation was largely enhanced due to a fast dehydration rate of methanol to DME on the CZA/FER having a large surface area of metallic copper nanoparticles. The bifunctional CZA/FER was utilized to convert MA to ethanol up to the similar equilibrium yield of ∼42 mol%. In addition, highly crystalline of FER@FER, which was synthesized by using a FER seed, showed a higher DME conversion to MA and stability due to the abundant presence of Bronsted acid sites with less defect sites. To verify the possible integration of two series cascade reactions such as direct syngas conversion to DME and its consecutive carbonylation to MA, the segregated double-layer formation in one bubbling fluidized-bed reactor was simulated. Two catalytic reaction regions with a light and dense-phase at similar reaction conditions were completely segregated at optimal linear velocity ranges (minimum fluidizing velocity, U mf ) by using two different catalyst particle sizes having an average size of 112.5 and 82.5 μm in a bottom and upper reaction zone, respectively. [ABSTRACT FROM AUTHOR]

The pyrolysis of sugarcane bagasse derived-humins (H-SCB) was evaluated in this work by considering independent, overlapping, or competing multistep reactions. An eight-stage parallel reaction model was used in the thermokinetic analysis. The most appropriate kinetic mechanism determined by the master-plot method showed that the second sub-stage proceeds via a 4th-order chemical reaction and the other steps are controlled by nucleation. Based on mathematical calculations, six consecutive-competitive reactions were studied and the modified Kilzer-Broido model was the most relevant to represent the pyrolysis of H-SCB. The kinetics is influenced by the reactivity of H-SCB in two parallel n-order reactions (n = 6.28 to volatile compounds and n = 1.35 to intermediate product). Diffusion-controlled reaction governed the secondary stage in the conversion to biochar. Competitively, nuclei growth occurs and the intermediate product decomposes into volatile products. By using multistep reactions to account for pyrolysis products, the predicted kinetic profiles agreed well with the experimental data. [Display omitted] • First study of the multistep kinetic behavior of pyrolysis of biomass-derived humins. • F 4 and A n mechanisms were found to be best fitted for the eight-stage parallel model. • Friedman and Vyazovkin methods yielded the average Ea of each sub-stage. • Reaction routes to products are established by the modified Kilzer-Broido model. • Multistep model showed good agreement with the experimental data. [ABSTRACT FROM AUTHOR]

Abstract: An electron ionisation study on the fragmentation of metastable molecular radical cations of ethyl 3-phenylpropanoate (ethyl dihydrocinnamate) and related arylalkanoic acid esters was performed by mass-analysed ion kinetic energy (MIKE) spectrometry. Six deuterium-labelled isotopomers of ethyl dihydrocinnamate were synthesised and studied by MIKE spectrometry. The fragmentation leading to ions C7H7O+ (m/z 107) involving migration of the alkoxycarbonyl group was also observed in the 70-eV mass spectra of related alkyl dihydrocinnamates, but it was found to be a high-energy process that does not compete at low energies in metastable molecular ions. Instead, the metastable ions of ethyl dihydrocinnamate undergo competing losses of carbon monoxide, ethanol and the combined loss of these neutral fragments, giving ionised styrene, C8H8 •+ (m/z 104). A highly specific H/D interchange involving the four hydrogen atoms at the benzylic α- and ortho-positions was found to precede the losses of ethanol and [ethanol+CO]. This represents another striking case of complete 4H – scrambling that enables the molecular ion to fully equilibrate the interchanging hydrogen atoms prior to fragmentation. A mechanism rationalising these observations and extending previously suggested mechanisms is proposed involving a series of distonic ions and the intermediacy of an ion/neutral complex. The metastable ions of the related esters exhibit in part similar fragmentation behaviour, but the McLafferty reaction turns out to be more favourable with higher alkyl dihydrocinnamates. For example, n-propyl 3-phenylpropanoate and isopropyl 3-phenylpropanoate react through highly distinct fragmentation channels. [Copyright &y& Elsevier]

Abstract: The combination of two reactions in one-pot multistep system requires the compatibility not only between the catalysts of both reactions, but also between all the reaction components and conditions. In the case of the coupling of alkene epoxidation and epoxide ring opening, it has been possible to synthesize cyanohydrin and azidohydrin derivatives through a simple process that involves a one-pot multistep process by using a mixture of two heterogeneous catalysts, a silica-grafted Ti catalyst and ytterbium chloride, whose efficiency depends on the reactivity of the starting alkene. In addition, in some cases the mixture of catalysts can be recovered and reused in several one-pot multistep cycles. However, this system is not possible with electron-deficient alkenes, as the basic catalyst required for epoxidation has shown to be incompatible with the ring-opening process. [Copyright &y& Elsevier]

In the presence of Pd(OAc)2 and norbornene as catalysts, two molecules of an ortho-substituted aryl iodide undergo aryl–aryl coupling to a palladium-bonded biphenylyl intermediate, which is hydrogenolyzed by benzyl alcohol to give 2,3′-disubstituted biaryl derivatives in satisfactory yields. A curious behaviour was observed with o-chloroiodobenzene, which gave activation of the C—Cl bond with four-membered ring formation...LAN-FR En présence de Pd(OAc)2 et de norbornène agissant comme catalyseurs, deux molécules d'iodure d'aryle substituées en ortho subissent une réaction de couplage aryle–aryle conduisant à un intermédiaire biphénylyle lié au palladium qui peut subir une réaction d'hydrogénolyse sous l'action de l'alcool benzylique pour conduire à la formation de dérivés biaryles 2,3′-disubstitués, avec des rendements satisfaisants. On a observé un comportement bizarre avec l'o-chloroiodobenzène donne lieu à une activation de la liaison C—Cl avec formation d'un cycle à quatre membres.[Traduit par la Rédaction] [ABSTRACT FROM AUTHOR]

Intensive and broad studies of chemical reactions concerning X(NSO)2 (X=Se, Te), X2Te(NSO)2 (X=F, Cl, Br) and X′2Te(NSC)2X′2 (X′=F, Cl) provides besides new interesting compounds also valuable intermediates for a better understanding of reaction pathways in chalcogen–nitrogen chemistry. Based on the mechanism elucidated for the formation of [SeSeNSN+]2[MF6−]2 or [ClSeSeNSN][SbCl6−] from Se(NSO)2 and MF5 (M=As, Sb, Nb) or Se(NSO)2 and SbCl5 respectively an interpretation of the reaction sequences of other procedure such as Te(NSO)2+SbCl5 or e.g. Cl2Te(NSO)2 with MCl3 (M=Ga, Al, Fe) could be provided. It was proved that a desulfurisation process is responsible for transforming Cl2Te(NSO)2 and derivated products in the presence of MCl3 into [(Cl2Te)2N+][MCl4−] and [ClTeSNSN+][MCl4−]. The results gained in these studies led directly to the synthesis of [SSNNN+][TeCl5−], the first ring with three cummulated nitrogen atoms. In order to learn more about the possible structures of Cl2Te(NSN)2TeCl2, careful and intensive investigations proved the formation of the cage N[Te(Cl)NSN]3. A thorough reinvestigation of the original synthesis of the cage yielded S4N4 as an additional product and by varying the stoichiometry between the educts TeCl4 and (CH3)3SiNSNSi(CH3)3 important intermediates could be detected and isolated. They provided the base for understanding the consecutive steps during the procedure between educts and to yield products. Fluorine substituted acyclic, cyclic, neutral and ionic chalcogen–nitrogen compounds are described as well as relationship among themselves and related compounds. Interesting and valuable correlations are presented and evaluated. [Copyright &y& Elsevier]

The application of heterogeneous catalysis and green solvents to the set up of widely employed reactions is a challenge in contemporary organic chemistry. We applied such an approach to the synthesis and further conversion of tetrahydropyranyl ethers, an important class of compounds widely employed in multistep syntheses. Several alcohols and phenols were almost quantitatively converted into the corresponding tetrahydropyranyl ethers in cyclopentyl methyl ether or 2-methyltetrahydrofuran employing NH 4 HSO 4 supported on SiO 2 as a recyclable acidic catalyst. Easy work up of the reaction mixtures and the versatility of the solvents allowed further conversion of the reaction products under one-pot reaction conditions.