This article describes a divergent strategy to prepare grafted polymer chains with functional end groups for surface modification of nanoparticles with other functional groups. This preparation is ...achieved through a combination of surface-initiated atom transfer radical polymerization (ATRP) and click chemistry. First, the surface of the silica nanoparticles was modified with polystyrene (PSt) brushes via the “grafting from” approach. The terminal bromides of PSt-grafted silica nanoparticles were then substituted with azido groups. These azido-terminated PSt brushes on the nanoparticle surface were reacted with various alkyne-terminated functional end groups via click reactions. In all cases, FTIR and
1H NMR spectra indicated quantitative transformation of the chain ends of polystyrene brushes on silica nanoparticles into the desired functional group.
Copolymers containing water‐soluble poly(ethylene glycol) (PEG) side chains and precisely controlled functional microstructures were synthesized by sequence‐controlled copolymerization of donor and ...acceptor comonomers, that is, styrene derivatives and N‐substituted maleimides. Two routes were compared for the preparation of these structures: a) the direct use of a PEG–styrene macromonomer as a donor comonomer, and b) the use of an alkyne‐functionalized styrenic comonomer, which was PEGylated by copper‐catalyzed alkyne–azide cycloaddition after polymerization. The latter method was found to be the most versatile and enabled the synthesis of high‐precision copolymers. For example, PEGylated copolymers containing precisely positioned fluorescent (e.g. pyrene), switchable (e.g. azobenzene), and reactive functionalities (e.g. an activated ester) were prepared.
Präzise und zielgerichtet: PEGylierte wasserlösliche Polymere, die präzise positionierte fluoreszierende, schaltbare und reaktive Funktionalitäten wie Pyren, Azobenzol und aktivierte Estergruppen enthalten, wurden durch sequenzkontrollierte radikalische Polymerisation von Styrol und N‐substituierten Maleimiden und anschließende Modifizierung erhalten (siehe Bild).
Indium oxide catalyzes acetylene hydrogenation with high selectivity to ethylene (>85 %); even with a large excess of the alkene. In situ characterization reveals the formation of oxygen vacancies ...under reaction conditions, while an in depth theoretical analysis links the surface reduction with the creation of well‐defined vacancies and surrounding In3O5 ensembles, which are considered responsible for this outstanding catalytic function. This behavior, which differs from that of other common reducible oxides, originates from the presence of four crystallographically inequivalent oxygen sites in the indium oxide surface. These resulting ensembles are 1) stable against deactivation, 2) homogeneously and densely distributed, and 3) spatially isolated and confined against transport; thereby broadening the scope of oxides in hydrogenation catalysis.
Wählerischer Katalysator: Indiumoxid katalysiert selektiv die partielle Hydrierung von Acetylen in Gegenwart von überschüssigem Ethylen. Eine theoretische Analyse verknüpft die beobachtete Oberflächenreduktion mit der Bildung von robusten und wohldefinierten Sauerstoff‐Fehlstellen und umgebenden In3O5‐Ensembles, die als entscheidend für diese außergewöhnliche katalytische Funktion angesehen werden.
Poly(ε-caprolactone)–
graft–polystyrenes were successfully synthesized by grafting an azide end-functionalized polystyrene onto a PCL backbone with multiple pendant alkyne moieties using a “click” ...chemistry reaction. Both precursors, the PCL backbone and the PS side chains, were prepared separately by two different living/controlled mechanisms, ring-opening polymerisation and ATRP, respectively. Molecular weights, polydispersity indexes, and chemical compositions of the backbone and branches were controlled. The subsequent copper-catalysed Huisgen 1,3-dipolar cycloaddition of PS onto PCL was achieved at room temperature with high conversion. However, a bimodal molecular weight distribution was observed in size exclusion chromatography due to the presence of unreacted PS. Nevertheless, crude product was purified by selective fractionation in cyclohexane to achieve pure graft copolymers.
The use of modern microwave equipment affords an easy and safe handling in the laboratory routine. The described quartz reactor system was tested in different reaction types to show its versatile ...applications. Various liquid‐phase hydrogenations were carried out successfully. The construction of the reactor allows the direct introduction of gases into the reaction mixture so that the reduction can be performed with gaseous hydrogen.
A quartz reactor system was tested in different reaction types to show its versatile applications. Various liquid‐phase hydrogenations were carried out successfully. The construction of the reactor allows the direct introduction of gases into the reaction mixture so that the reduction can be performed with gaseous hydrogen.
This paper demonstrates that the observed rate of reaction of the liquid-phase selective hydrogenation of an alkyne is higher for an open and rough carbon nanofiber (CNF) layer positioned on a ...microchannel wall than for an unsupported flat plate catalyst or dense and smooth CNF layers. This enhancement can be contributed to two phenomena: (1) the kinetic reaction rate increases with a factor of 1.4, due to an increase of the open and freely accessible surface area of the CNF layer available for catalyst deposition; (2) the liquid–solid mass transfer increases with a factor of 2.8, due to an increase in the surface roughness of the CNF layer and the formation of large spherical islands of clustered CNFs. A thin layer of CNFs on a microchannel wall can therefore successfully be used to increase the overall rate of reaction per reactor volume compared to an unsupported flat plate catalyst.
Amine groups—functionalized gel-type resin (FCN) supported Pd catalysts exhibit attractive performance in hydrogenation of alkynes reagents, 2-butyne-1,4-diol and phenylacetylene. The selectivity to ...desired alkenes products attained ca. 94% at almost complete conversion of alkynes. This performance is unchanged under the recycling use of catalysts.
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Palladium catalysts (0.125–0.5
wt.% Pd) supported by amine groups—functionalized gel-type resin (FCN) were studied in the hydrogenation of alkynes reagents, 2-butyne-1,4-diol and phenylacetylene. The catalysts were prepared by two routes. The first, “OAc” is based on the immobilization of Pd-precursor in the pre-swollen resin from THF solution of Pd(OAc)
2, followed by chemical reduction of the Pd-centers. This method produces Pd particles of size in nano-scale. The second procedure, “aq” implies the deposition of Pd-species on dry resin beads using aqueous solution of PdCl
2. Reduction of these Pd-species gives relatively large Pd particles, dominating are 30–50
nm in size. The SEM studies performed over the cross-section of catalysts grains showed location of Pd in outer shell of polymer beads in both “OAc” and “aq” catalysts; however, thinner layer of Pd appears in “aq” series catalysts. In the presence of all catalysts, prepared by “OAc” and “aq” methods the selectivity towards alkenes is high, above 90%. The catalysts of “aq’ series are much more active and more selective than “OAc” analogues giving selectivity to alkene ca. 94% at almost complete conversion of alkynes. Moreover, catalytic performance of “aq’ series catalyst is unchanged under recycling use. The catalyst was recovered and reused 4 times, maintaining its catalytic efficiency.
The pressure-dependent rate coefficients for several reactions relevant to propyne pyrolysis were determined with ab initio quantum mechanical calculations and Rice−Ramsperger−Kassel−Marcus (RRKM) ...analyses. These reactions include the mutual isomerization of propyne and allene, the chemically activated reactions of propyne and allene with the H atom and of acetylene with methyl on the C3H5 potential energy surface. Propyne pyrolysis was experimentally studied in a flow reactor at 1210 K and 1 atm. A detailed reaction mechanism, employing the current RRKM rate coefficients, is shown to accurately predict the experimental acetylene and methane profiles determined in the flow reactor and literature shock-tube data of propyne and allene pyrolysis up to 1500 K.
A simple, highly reproducible protocol for the hydrogenation of alkenes and alkynes and for the hydrogenolysis of O‐benzyl ethers has been developed. The method features the in situ preparation of an ...active Pd0/C catalyst from Pd(OAc)2 and charcoal, in methanol. The mild reaction conditions (25 °C) and low catalyst loading required (0.025 mol %), as well as the absence of contamination of the product by palladium residues (<4 ppb), make this a sustainable, useful process for organic chemists. Alternatively, the protocol can be carried out under microwave activation, to shorten the reaction times, with cyclohexene as the hydrogen source.
Pd0/C: It's a kind of magic! A sustainable, simple and highly reproducible protocol for the hydrogenation of alkenes and alkynes (see scheme) and for the hydrogenolysis of O‐benzyl ethers has been developed with an in situ generated Pd0/C catalyst. The homemade Pd0/C catalyst allows mild reaction conditions (25 °C, 1 atm H2) and low catalyst loading (as low as 0.025 mol %), without any contamination of the product by palladium residues (<4 ppb).
Die charakteristischen Strukturmerkmale von (Alkin)Co2(CO)6‐Komplexen wurden genutzt, um neuartige intramolekulare 4+2‐Cycloadditionen zu ermöglichen. Die Reaktion solcher Komplexe mit einem ...Siloxydien und einer elektronenarmen dienophilen Gruppe an gegenüberliegenden Enden mit MeAlCl2 in Gegenwart von 2,6‐Di‐tert‐butylpyridin in CH2Cl2 liefert die überbrückten 4+2‐Cycloaddukte als einzelne Stereoisomere in guten Ausbeuten (siehe Schema).
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