Effect of phosphorus (P) on the structure and reactivity of biochars produced from the pyrolysis of acid-washed biomass loaded with P of various forms

This paper investigates the effect of phosphorus (P) on char structure and reactivity of char prepared from the fast pyrolysis of purposely-prepared P-loaded biomass samples at 1000 °C in absence of other inorganic species. Biomass was first acid-washed then loaded with P of three different occurrence forms (one organic P i.e. phytic acid, and two inorganic P i.e. orthophosphoric acid and polyphosphoric acid) at the same P content of 0.8 wt%. Experimental results show that both organic and inorganic P substantially increase char yields during pyrolysis from 6.2% for the biomass sample without P to 23.0–26.0% for P-loaded samples due to the enhanced crosslinking by P-containing structures in char, leading to increases in the char C and H contents and decrease in O content. The presence of P in biochars from fast pyrolysis of various P-loaded biomass samples plays important role in the evolution of char structure and intrinsic reactivity measured during low-temperature oxidation at 500 °C in air under chemical-reaction-controlled regime. After pyrolysis and subsequent char oxidation, all P in biomass either as organic or inorganic P are found to be present in forms of acid-insoluble organic structures. For char prepared from acid-washed wood, char reactivity increases with char conversion due to the increasing pore surface area at higher conversion. Comparatively, for char prepared from acid-washed wood loaded with various P at char conversion below 60%, the presence of P increases char intrinsic reactivity due to the enhanced crosslinking of reactive carbon structures and reduced condensation of char structures. However, at conversions above 60%, P-containing species in char lead to a significant decrease in char reactivity, due to the formation of abundant CO-P bonds, that is highly resistant to the oxidation in air, in the reacting chars.     

α-Diphenylphosphino-N-(pyrazin-2-yl)glycine as a ligand in Ni-catalyzed ethylene oligomerization

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Intermolecular interactions between natural humic substances and tricyclic antidepressants

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Light-intensity switch enabled nonsynchronous growth of fluorinated raspberry-like nanoparticles

Raspberry-like (RB) nanoparticles hold potential for diverse applications due to their hierarchical morphology. Here we developed a novel tandem synthetic approach of nonsynchronous growth based on photo-mediated reversible-deactivation radical polymerization, enabling simple, efficient and bottom-up synthesis of RB nanoparticles of uniform sizes at quantitative conversions of fluorinated monomers. Chain transfer agents of different chain lengths, concentrations and chemical compositions were varied to tune the diameter of RB particles. Importantly, fluorinated RB nanoparticles obtained with this method allow facile post modifications via both covalent bond formation and intermolecular physical interactions without disrupting the RB morphology. The facile nature of this method and versatility of the obtained fluorinated RB materials open new opportunities for the development of functional materials using nanoparticles.

Nonsynchronous growth of raspberry-like (RB) nanoparticles in a one-pot and bottom-up fashion, enabling simple post-modification of RB colloids through both covalent bond formation and supramolecular interaction.     

Visible-light-driven spirocyclization of epoxides via dual titanocene and photoredox catalysis

We describe the synergistic utilization of titanocene/photoredox dual catalysis driven by visible light for the radical opening/spirocyclization of easily accessible epoxyalkynes. This environmentally benign process uses the organic donor–acceptor fluorophore 2,4,5,6-tetra(9H-carbazol-9-yl)isophthalonitrile (4CzIPN) as a photocatalyst and Hantzsch ester (HE) as an electron donor instead of stoichiometric metallic reductants. The photocatalytic conditions showed exceptionally high reactivity for the synthesis of privileged and synthetically challenging spirocycles featuring a spiro all-carbon quaternary stereocenter. Cyclic voltammetry (CV) studies suggest that Cp₂Ti^IIICl is the catalytically active species.

We describe the synergistic utilization of titanocene/photoredox dual catalysis driven by visible light for radical opening/spirocyclization of easily accessible epoxyalkynes.

Over the last few decades, radical-based transformations have been increasingly used in organic synthesis due to their salient features, such as ease of generation, mild reaction conditions, and broad functional group compatibility.^1,2 As a mild single-electron-transfer (SET) reagent, titanocene monochloride (Cp₂Ti^IIICl) is considered a formidable tool in contemporary radical chemistry due to its ability to promote various fundamental radical-based transformations.^3–7 Cp₂Ti^IIICl was first introduced by Nugent and RajanBabu as a very mild stoichiometric reagent for the reductive opening of epoxides.^8–11 Later, the catalytic conditions developed by Gansäuer et al. (Scheme 1a)¹² employing stoichiometric amounts of active metals in combination with 2,4,6-collidine·HCl further expanded its applications and led to the discovery of a number of novel transformations.^13–16 The key to success was the formation of a stable complex A in reactions while decreasing the concentration of active Cp₂Ti^IIICl.^17,18 We were interested in the radical opening/cyclization reaction of epoxides which has attracted considerable attention from the synthetic community and has been used numerous times in the synthesis of natural products.^19,20 Nevertheless, this reaction required stoichiometric metallic reductants and proceeded slowly particularly with sterically hindered substrates even with high catalyst loading.²¹ Therefore, the development of an eco-friendly and efficient catalytic system with an expanded substrate scope is highly desirable.Open in a separate windowScheme 1Cp₂Ti^IIICl mediated radical opening/spirocyclization of epoxides; (a) generation of Ti^IIIvia a metal reduction approach; (b) dual titanocene/photoredox catalysis; (c) examples of drugs and natural products containing heterospirocycles.In recent years metallaphotoredox catalysis has been a new and rapidly growing research subject.^22–29 Photoredox processes can directly modulate the oxidation state of metals by electron transfer (ET).^30–33 Given that the generation of Ti^III is a SET process, we envisioned that the reduction could be facilitated by a photoredox-controlled process while overcoming the aforementioned limitations. On the other hand, spirocycles bearing a chiral spiro all-carbon quaternary carbon are particularly attractive synthetic targets in pharmaceutical development (Scheme 1c).^34–36 Such privileged rigid 3D structures offer the concomitant ability to project functionalities in all three-dimensional orientations and led to enhanced pharmacological activities of molecules. Thus significant attention has been paid to their synthesis.^37,38 Against this backdrop, here we describe our efforts on the synthesis of various heterospirocycles with the aid of photoredox catalysis.We chose epoxyalkyne 2a as a model substrate for optimization of reaction conditions. After a systematic variation of different reaction parameters, we were pleased to identify the optimal reaction conditions in which a mixture of Cp₂TiCl₂ (5.0 mol%), [Ir(dtbbpy)(ppy)₂]PF₆ (1a, 1.0 mol%, E^III/II_1/2 = −1.51 V vs. SCE in MeCN), HE (1.2 equiv.) and 2a (1.0 equiv.) in THF at room temperature under the irradiation of a 10 W 450 nm light emitting diode (LED) lamp for 12 hours afforded the desired product 3a in an excellent yield of 96% (13 : 1 d.r.) upon isolation (entry 1). Using a commercial 23 W compact fluorescent lamp (CFL) instead of the 10 W 450 nm LED did not compromise the overall yield of the reaction (entry 2). Notably, when the loading of Cp₂TiCl₂ was decreased to as low as only 2.0 mol%, the reaction still led to full conversion and produced 3a in 95% yield (entry 3). Further screening of other photosensitizers revealed that the cheap and readily obtained organic dye 4CzIPN 1b is a competent alternative, which led to full conversion with 94% isolated yield (entry 4). Importantly, the reaction did not proceed in the absence of Cp₂TiCl₂, HE, the photocatalyst, or visible light (entries 5–8). Various solvents, including DMF, MeOH, DMSO, and MeCN, were screened, and they all resulted in poor conversion. The use of other organic electron donors, such as triethylamine, triethanolamine, and ascorbic acid, afforded the product in poor yield.With satisfactory reaction conditions established, we then explored the scope of the cyclization reaction using 4CzIPN as the photosensitizer. Positively, the cyclization reaction worked well and afforded the desired variably heterospirocyclic products in good to excellent yield (Tables 2 and ​and3).3). The reaction allows the rapid construction of various 5/5, 5/6, 5/7 and 5/8 spiro-ring fused systems (3a–3k) bearing tetrahydrofuran or pyrrolidine motifs via the 5-exo cyclization pathway. Interesting, the diastereoselectivity of the cyclization reaction is highly correlated with the ring size in the substrates. Heterospirocycles containing a 5/5 spiro-ring fused system (3a–3f) were obtained with surprisingly high diastereoselectivity. In some cases (3b, 3c, and 3e) only a single isomer was obtained. The product 3d with a sterically hindered t-butyloxy carbonyl (Boc) protecting group on the N atom was obtained with reduced diastereoselectivity (5 : 1 d.r.). The diastereoselectivities dropped in 5/6, 5/7 and 5/8 spiro-ring fused systems. Given that enantioenriched epoxides could be easily obtained (e.g. via sharpless asymmetric epoxidation), this strategy provides access to optically active spirocycles featuring an all-carbon quaternary stereocenter with the transfer of stereochemical information from epoxides (3c, 3e and 3f). Bis-heterospirocyclic scaffolds were frequently employed in pharmaceutical chemistry. For example, bis-heterospirocyclic 3d is the core structure of DLK inhibitors³⁹ and XEN402 (ref. 40) (scheme 1c), which are used for treating neurodegeneration and congenital erythromelalgia respectively. Furthermore, 6-exo cyclization was also investigated under the standard conditions and smoothly produced a serious of drug-like 6-(trifluoromethyl)-3-pyridinesulfonyl piperidine derivatives including 6/5, 6/6 and 6/7 spiro-ring fused systems (5a–5k) in generally excellent yields. Moreover, cyclization reactions with epoxy-alkynes afforded products containing exocyclic-alkenes and free alcohols which were suitable for further functionalization. This approach provides access to a broad range of novel spirocyclic piperidine and pyrrolidine spirocycles which could be of interest to synthetic and medicinal chemists.Scope of 5-exo and 6-exo cyclization^a,b,c,d

ChemInform Abstract: Explaining Stability of Transition Metal Carbides — and Why TcC Does Not Exist.

The formation of transition metal (M) carbides M_xC_y and trends of their stability are systematically investigated using the USPEX code within the DFT.     

Colorimetric enantiodiscrimination of mandelic acid by indicator displacement assay

The colorimetric enantiodiscrimination between mandelic acid and L-proline-Cu(II) is exploited to develop enantioselective indicator displacement assays. The sensitivity of the assay could be tuned by using a colorimetric indicator. The chromophoric ligand, pyrocatechol violet, effectively competes with the mandelic acid guest for open coordination sites on L-proline-Cu(II). The DA could be increased to 0.12 by changing the ratio of(+)- and(à)-mandelic acid concentrations that were found to be optimal from the displacement experiments. The resultant enantiomer excess versus DA relationship is linear. From the calibration curves, the absorbance values of the unknowns may be calculated for the enantiomeric excess value and the colorimetric enantiodiscrimination of mandelic acid can thus be obtained.     

Deoxygenation of methyl laurate to hydrocarbons on silica-supported Ni-Mo phosphides: Effect of calcination temperatures of precursor

SiO2-supported Ni-Mo bimetallic phosphides were prepared by temperature-programmed reduction(TPR) method from the phosphate precursors calcined at different temperatures. Their properties were characterized by means of ultraviolet-visible diffuse reflectance spectroscopy(UV-Vis DRS), H2temperature-programmed reduction(H2-TPR), X-ray diffraction(XRD), transmission electron microscopy(TEM), CO chemisorption, H2 and NH3temperature-programmed desorptions(H2-TPD and NH3-TPD). Their catalytic performances for the deoxygenation of methyl laurate were tested in a fixed-bed reactor. When the precursors were calcined at 400 and 500?C, respectively, Ni Mo P2 phase could be formed apart from Ni2 P and Mo P phases in the prepared C400 and C500 catalysts. However, when the precursors were calcined at600, 700 and 800°C, respectively, only Ni2 P and Mo P phases could be detected in the prepared C600, C700 and C800 catalysts. Also, in C400, C500 and C600 catalysts, Mo atoms were found to be entered in the lattice of Ni2 P phase, but the entering extent became less with the increase of calcination temperature. As the calcination temperature of the precursor increased, the interaction between Ni and Mo in the prepared catalysts decreased, and the phosphide crystallite size tended to increase, subsequently leading to the decrease in the surface metal site density and the acid amount. C600 catalyst showed the highest activity among the tested ones for the deoxygenation of methyl laurate. As the calcination temperature of the precursor increased, the selectivity to C12 hydrocarbons decreased while the selectivity to C11 hydrocarbons tended to increase. This can be mainly attributed to the decreased Ni-Mo interaction and the increased phosphide particle size. In sum, the structure and performance of Ni-Mo bimetallic phosphide catalyst can be tuned by the calcination temperature of precursor.     

无机化学中的脱水缩合反应

将无机化学中的脱水缩合反应进行分类:发生在无机含氧酸之间的脱水缩合反应;发生在无机含氧酸酸式盐之间的脱水缩合反应和酸化含氧酸盐溶液而发生的脱水缩合反应。介绍了缩合反应及缩合反应产物的应用。