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A simple and recyclable homogeneous catalytic system for the hydrogenation of carbon monoxide to methanol was established. The reaction is catalyzed by a molecular manganese complex using a high-boiling alcohol as the solvent for catalyst immobilization. The CO hydrogenation is assisted by the product itself and the solvent through the formation of a methyl or dodecyl formate ester intermediate mediated by catalytic amounts of NaOMe as the base. This allows the catalytic formation of methanol in alcohols combined with facile product separation and catalyst recycling via distillation. Initial turnover frequencies (TOF) of 2250 h−1 were reached under optimized conditions in 1-dodecanol/methanol as the reaction medium (T = 160 °C, p(H2/CO) = 80/10 bar). The performance was stabilized in batch-wise recycling over 6 runs achieving a total turnover number (TTON) of >12 000 corresponding to an enhancement of more than five times compared to single batch operation under identical conditions. Minimal leaching of the components of the organometallic catalyst was observed during distillative product separation and catalyst activity could be fully restored by re-addition of the base NaOMe. [ABSTRACT FROM AUTHOR]

This work focuses on the development and investigation of a Rh/TPP catalytic system for the synthesis of saturated aliphatic carboxylic acids from readily available oxygenated substrates, H2 and non-toxic, renewable CO2. Optimization of the reaction conditions and reagents was carried out using 2-butanol and 1-butanol as typical secondary and primary alcohols. Afterwards, the reaction system was investigated in-depth with a separate investigation of the reverse water–gas-shift-reaction and the carbonylation reaction as key steps of the overall tandem transformation. Based on these results, a reaction network was established with two distinct main pathways. While the secondary alcohols are converted preferentially via acid catalysed dehydration to the corresponding olefins followed by hydroxycarbonylation, the primary alcohols react primarily via nucleophilic substitution to the iodide compound followed by a Monsanto-type carbonylation. Based on these results, a broad range of alcohols including bio-based substrates was converted to the corresponding C1 elongated carboxylic acids. Additionally, other oxygenated substrates such as aldehydes, ketones and industrially relevant substrate mixtures were applied successfully. [ABSTRACT FROM AUTHOR]

Carbon capture and utilization is considered a promising approach for introducing CO2 into the chemical value chain, especially in combination with bioenergy applications (BECCU). We report here on the catalytic hydrogenation of CO2 to formic acid in a biphasic reaction system using aqueous solutions of amino acids as the product phase and possible capture solutions for biogenic CO2. The molecular structure of the ruthenium catalyst and the catalyst phase were matched through a combined design process identifying n-dodecanol (lauryl alcohol) as the preferred "green" solvent. A total turnover number (TON) of over 100 000 mole HCOOH per mole of catalyst (46 582 g HCOOH per g of Ru) with minimal contamination of the aqueous phase with metal or organic solvent was obtained. The resulting aqueous solutions attained almost quantitative conversions with up to 0.94 mol formic acid per mol amino acid (ca. 108 g HCOOH per kg). Such solutions may find use directly, or after upgrading, in agricultural applications without the need for energy intensive and costly isolation of pure formic acid. [ABSTRACT FROM AUTHOR]

A versatile synthetic pathway for the production of valuable alkyl phenols and anilines has been developed based on the selective hydrodeoxygenation of a wide range of hydroxy-, amino-, and nitro-acetophenone derivatives as readily available substrates. Bimetallic iron ruthenium nanoparticles immobilized on an imidazolium-based supported ionic liquid phase (Fe25Ru75@SILP) act as highly active and selective catalysts for the deoxygenation of the side-chain without hydrogenation of the aromatic ring. The catalytic system allows operation under continuous flow conditions with high robustness and flexibility as demonstrated for the alternating conversion of 3′,5′-dimethoxy-4′-hydroxyacetophenone and 4′-hydroxynonanophenone as model substrates. [ABSTRACT FROM AUTHOR]

Observing and understanding the phenomena associated with the reaction mechanisms and catalyst deactivation in molecular catalysis is a very challenging task in green chemistry. This knowledge is crucial for applying and scaling catalyzed reactions as well as preventing misproduction at a very early point. Over the years, experimental arrangements have evolved towards analysis of catalysts and reaction products in the so-called operando setups. This contribution reflects on the potential of operando studies to elucidate reaction and deactivation mechanisms in homogeneous catalysis as well as the outstanding opportunities that arise from the application of operando experimental setups. Such setups mostly rely on spectroscopic analysis, optionally coupled with chromatographic techniques that monitor the reaction system. This in turn means that not only the evolution of the reaction substrates and products can be monitored, but also changes of the molecular catalyst species that may affect the catalytic performance. Therefore, this review focusses on techniques to monitor the catalyst under real conditions. In this review, different spectroscopic techniques relevant for monitoring molecular transition metal catalysts in solution are covered, followed by numerical methods used in the chemometrics literature to undertake the challenge of untangling the complex raw signals and allocating them to individual chemical species. Finally, two exemplary case studies of industrially relevant chemical reactions are presented, namely the hydroformylation and the asymmetric hydrogenation. These examples illustrate the significance of the application of both the experimental setups as well as data processing and signal resolution to have an insight into the deactivation of catalytic systems. The operando approach shows high potential for the increased use in future research to develop stable and more selective catalysts which can be applied in greener processes. [ABSTRACT FROM AUTHOR]

We present an integrated process for in situ CO2 hydrogenation during bioethanol production by combining bio- and chemocatalysis. The biphasic catalytic system used comprises an aqueous whole-cell fermentation broth and a tailored organometallic catalyst in the organic phase. Glucose is converted to ethanol, and the by-product CO2 is simultaneously upgraded to formic acid in a single reactor unit. Under the optimized conditions, 26% of the generated CO2 was hydrogenated directly. [ABSTRACT FROM AUTHOR]

Upon CO2 pressurization, 2-methyltetrahydrofuran (2-MTHF) expands. The expanded phase exerts different solvation properties, triggering fractional lignin precipitation. Depending on the actual CO2 pressure, fractions of lignin with a gradient of different sizes and chemical properties are selectively precipitated. A range of raw materials and applications may be thus reached. [ABSTRACT FROM AUTHOR]

The oxidative carbonylation of toluene-2,4-diamine (TDA) with methyl formate (MF), which can be produced from CO2, provides a possible route for the non-phosgene production of isocyanate precursors and enables a valuable utilization of the greenhouse gas. Extensive analysis of the product spectrum has provided detailed insight into the reaction network leading to the target product toluene-2,4-dicarbamate (TDC) and the most important side products. The most prominent one has been identified as methylene-bridged tetracarbamate 5, which is also an interesting precursor for applications in polyurethane chemistry. The side products are caused by three different reaction paths: N-formylation by MF, condensation with in situ formed formaldehyde, and N-methylation by in situ formed dimethyl carbonate (DMC). The influence of the catalyst on product distribution was evaluated for PdCl2/CuCl2 and a large number of heterogeneous Pd-catalysts. The oxidic support materials ZrO2, CeO2 and SiO2 were found to partially suppress the undesired side reactions leading to higher yields of TDC and tetracarbamate 5. The ratio of TDC to 5 was demonstrated to be affected significantly by the choice of the support. The synthetic protocol was extended to the synthesis of dicarbamates from 4,4′-methylenedianiline (MDA) and 2,4-diaminomesitylene (17). These results encourage further investigations into the design of selective catalysts for the production of isocyanate precursors from CO2 as a C1 source. [ABSTRACT FROM AUTHOR]

An integrated two-step process for the production of methylformate (MF) from CO2, H2 and MeOH was developed. In the first step, the hydrogenation of CO2 to a formate-amine adduct is carried out in a biphasic system comprising n-decane as the catalyst phase and MeOH as the product phase. In the second step, the resulting methanol solution containing the formate-amine adduct is subjected to reactive distillation for esterification and isolation of methylformate. The selection of the amine played an important role for devising the overall process. Whereas in the hydrogenation step basic amines work best, medium to low basic amines are preferred in the esterification step. 1,2-Dimethyl-imidazole (1,2-DMI) was identified as an effective compromise for the integration of both steps. In the hydrogenation step, a bis(diphenylphosphino)methane ligand tailored with long alkyl chains ensured effective retention of the Ru-catalyst in the non-polar phase allowing straightforward reuse of the catalyst phase. In a semi-continuous set-up, repetitive hydrogenation (8 cycles) led to a total turnover number (TTON) of 38 000 at an average turnover frequency (TOF) of 1400 h−1 with a cumulative catalyst leaching of only 1.4 mol% for P and 2.0 mol% for Ru. Reactive distillation was demonstrated in a continuously operated rectification unit leading to the isolation of MF at the head of the column with a purity of 91.5%. [ABSTRACT FROM AUTHOR]

The author reflects on the 15 years of the journal related to green chemistry. The author states that the journal celebrated its 15th year by publishing web collection that covered topics important to green chemistry. The author notes that the journal has provided scientific basis for developing chemical technologies. The author mentions that the journal is attracting articles related to enzymatic and cellular processing.

The activation of CO2 is highlighted for two lead-structures of cobalt- and zinc-based homogeneous catalysts used in the copolymerization of epoxides and CO2. Following the activation of CO2 with in situ ATR-IR spectroscopy, a surprisingly facile insertion of CO2 into metal–phenoxide bonds was revealed. [ABSTRACT FROM AUTHOR]

Organic halides and polyoxometalates (POMs) were studied as catalyst systems for the insertion of carbon dioxide into epoxides originating from plant oils as biogenic feedstock. In the formation of methyl oleate carbonate, synergistic rate acceleration and increased cis-selectivity were observed using ammonium halide and transition metal substituted silicotungstate POMs catalysts in a combined system. Mechanistic insight into the cooperative action was gained by kinetic measurements and analysis of the stereochemical outcome of the reaction. For poly-epoxidised oleochemicals as substrates, the simple ammonium halide catalyst gave better performance as side reactions were encountered with the POM-containing system. [ABSTRACT FROM AUTHOR]

Hybrid sol–gel catalysts of zinc hexacyanocobaltate and SiO2 were prepared by co-precipitation of the double metal cyanide with silica. Hybrid catalysts prepared at moderately acidic conditions showed the best performance with respect to activity, selectivity and stability. The hybrid sol–gel materials displayed high catalytic activity for the copolymerisation of styrene oxide and carbon dioxide (up to 650 molSO (molZn h)−1) and high productivity (575 gPolymer gCatalyst−1). They also displayed good selectivity to the polymeric product (80–87%), while only little cyclic styrene carbonate was formed as side product. A detailed electron microscopy study of the hybrid sol–gel materials showed that the active phase consisted of thin platelets containing the metals in a molar ratio nZn/nCo = 2.1, whereby the double metal cyanide was closely associated with silica. [ABSTRACT FROM AUTHOR]

Hybrid sol–gel catalysts of zinc hexacyanocobaltate and SiO2 were prepared by co-precipitation of the double metal cyanide with silica. Hybrid catalysts prepared at moderately acidic conditions showed the best performance with respect to activity, selectivity and stability. The hybrid sol–gel materials displayed high catalytic activity for the copolymerisation of styrene oxide and carbon dioxide (up to 650 molSO (molZn h)−1) and high productivity (575 gPolymer gCatalyst−1). They also displayed good selectivity to the polymeric product (80–87%), while only little cyclic styrene carbonate was formed as side product. A detailed electron microscopy study of the hybrid sol–gel materials showed that the active phase consisted of thin platelets containing the metals in a molar ratio nZn/nCo = 2.1, whereby the double metal cyanide was closely associated with silica. [ABSTRACT FROM AUTHOR]

A new reaction concept that allows one to control the substrate selectivity of a catalytic reaction by supercritical fluid extraction is demonstrated for the hydroformylation of long-chain olefins as a prototypical example. [ABSTRACT FROM AUTHOR]