Tandem reactions are of great importance to efficiently execute multiple conversions in one synthesis step. Herein we present a multiphase system for the hydroformylation/aldol condensation, which is able to recycle...
Heteropolyacids have been identified as promising for catalyzing the reaction types, hydration and dehydration, which play an important role in the valorization of lignocellulose. Not only do they possess adaptable Brønsted acidity, but they also show a redox multi functionality. To increase the industrial applicability of this promising class of catalysts and to enable recycling, many different approaches for immobilization (such as multiphasic catalysis or grafting) and solidification (such as salt formation) have been pursued in recent years. This review summarizes these efforts and highlights the studied acidcatalyzed lignocellulose conversions, trends and current challenges.
One approach to recycle homogeneous catalysts is through multiphase catalysis. Multiphase catalysis is not only limited to liquid-liquid multiphase systems but also includes for example solid and liquid phases. In...
Olefins are essential
basic chemicals in all areas of the chemical
industry and can be produced from alcohols by dehydration. The amount
of alcohols produced from biomass sources is expected to rise in the
next decade. Various heterogeneously catalyzed processes have been
developed in previous works operating at a high reaction temperature
of 350 °C to obtain olefins from alcohols. In this work, we present
the conversion of C7 to C12
α-alcohols to the corresponding olefins using phosphoric acid as a
strong inorganic homogeneous acid catalyst. The reaction network was
investigated using a microwave reactor. A system with a reactive distillation
of the produced water and olefins was developed to shift the equilibrium
of the reaction toward the olefins. Mild reaction conditions were
utilized with temperatures ranging between 170 and 230 °C. The
catalyst was recycled successfully over 12 runs in batch reactions
and in semi-continuous flow experiments at 190 °C over 6 h. Up
to 93% yield of olefinic products were obtained with the corresponding
ether as the major side product.
Pyridinylidene-amides (PYAs) are a relatively new type of N-donor ligands that can exist in three isomeric forms and adopt various resonance structures. This makes them electronically flexible, and in order to evaluate their electronic profile using the Huynh electronic parameter (HEP), seven structurally diverse mixed N-heterocyclic carbenes (NHCs)/PYA palladium complexes of the type trans-[PdBr 2 ( i Pr 2 -bimy)(PYA)] were prepared and fully characterized by various spectroscopic and spectrometric methods. This study shows that PYAs are among the strongest, formally neutral N-donors, but they are still weaker than phosphines and organometallic ligands such as NHCs. Notably, the donating abilities of isomeric PYAs are distinct and can be further fine-tuned by the choice of two substituents making them structurally and electronically versatile. These characteristics and the ease of their preparation hold promise for a wide applicability in coordination chemistry.
Ethylene carbonate is a rather uncommon solvent in chemistry,
but
it can be used as a low-viscosity, polar, aprotic solvent. Its most
interesting feature is the melting point above room temperature, which
allows for crystallization of the ethylene carbonate-based catalyst
phase from the reaction solution. The dynamic phase behavior of such
reaction systems was investigated in depth in this work. Ethylene
carbonate and the hydroformylation product nonanal form a yield-dependent
thermomorphic multicomponent system during the Rh/sulfoXantphos-catalyzed
hydroformylation of 1-octene. This results in a limited conversion
due to the yield-dependent precipitation of the polar catalyst. Thus,
modifications to the system, such as the addition of decane to the
organic phase or water to the catalyst phase, have been investigated
to limit the precipitation of the catalyst.
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