Showing papers by "Christian V. Stevens published in 2022"

Recent advances in amine catalyzed aldol condensations

Abstract: During the past two decades, new insights have driven the development and optimization of aminated materials as aldol condensation catalysts. Amines, either primary or secondary, facilitate the reaction via an enamine mechanism. If the spatial placement with respect to the amine allows it, weak acid sites such as silanols or hydroxyls, can cooperate as hydrogen bond donors and aid in proton transfer steps. Furthermore, the reaction environment, i.e., support and solvent and their mutual interactions, is also a key determining factor. In particular, co-feeding small amounts of water suppresses the formation of inhibiting and site-blocking species. However, silica-based materials are susceptible to hydrolysis. This led to the development of water tolerant (bio)polymer supported amine catalysts which also exhibit selective component enrichment properties, opening up opportunities for further catalyst development.

Phospholipase cocktail: A new degumming technique for crude soybean oil

Abstract: Enzymatic degumming (EDG) is an emerging alternative process for decreasing the phosphorus content, increasing the oil yield, and preserving the oil quality. Purifine® 3G is a cocktail of phospholipases composed of phospholipase A2 (PLA2), phospholipase C (PLC), and phosphatidylinositol phospholipase C (PI-PLC). In this study, Purifine® 3G was applied to crude soybean oil, and the optimum degumming conditions (enzyme concentration, temperature, and water dosage) were determined using a central composite rotatable design (CCRD). The contents of diacylglycerols (DAGs) and free fatty acids (FFAs) in the studied system considerably increased at temperatures below 64 °C and enzyme concentrations above 100 mg/kg, while the phosphorus content decreased with increasing water amount and enzyme concentration. In particular, EDG with 200 mg/kg of Purifine® 3G conducted for 120 min at a temperature of 60 °C and water concentration of 3% (w/w) lowered the residual phosphorus content to 8.9 mg/kg and increased the FFA and DAG concentrations by 0.17% and 0.72%, respectively. Meanwhile, EDG retained the tocopherol content in crude soybean oil, maintaining its quality. Hence, Purifine® 3G increases the neutral oil yield (FFA and DAG), decreases the phosphorus content, and preserves the oil quality, which make it a commercially viable degumming agent.

Covalent Organic Framework supported Palladium Catalysts

Abstract: Covalent organic frameworks (COFs), as highly porous crystalline structures, are newly emerging materials designed with tuneable features. They have a high potential to be a host to immobilize metal catalysts....

Flow chemistry of main group and transition metal complexes

Abstract: The attractive heat and mass transfer properties of flow chemistry apparatus, combined with a small reactor volume allow for much safer operating conditions as well as a superior selectivity compared to standard batch reactions. The possibility to handle short-lived species led to the introduction of several new concepts such as ‘flash chemistry’, ‘space integration’, and ‘protecting group free flow synthesis’. Recently, the continuous flow synthesis of metal-NHC (NHC, N-heterocyclic carbene) complexes was reported, taking advantage of the fundamental mechanistic understanding along the reaction sequence leading to the metal-NHC bond formation using the weak base route. In addition to the synthesis of transition metal complexes, their use as efficient catalysts for various continuous flow organic transformations is well documented. Continuous flow reactors have earned their place as an important technology in organic synthesis, receiving increased interest in the past decade. The favorable heat and mass transfer capabilities, combined with the ease of scale-up, have not only made it a safer option in many cases, but often the only option when dealing with highly reactive, short-lived intermediates. In this review, an overview is given of the most recent advances made in the flow synthesis of organometallic compounds. This includes both main group and transition metal applications. Continuous flow reactors have earned their place as an important technology in organic synthesis, receiving increased interest in the past decade. The favorable heat and mass transfer capabilities, combined with the ease of scale-up, have not only made it a safer option in many cases, but often the only option when dealing with highly reactive, short-lived intermediates. In this review, an overview is given of the most recent advances made in the flow synthesis of organometallic compounds. This includes both main group and transition metal applications. the typical conditions used for organic reactions involving an alkyl halide and a carbonyl group in the presence of s- or p-block metals without isolating the organometallic intermediate. Therefore, the secondary/tertiary alcohols are produced in a one-pot reaction setup. a field of chemical synthesis where extremely fast reactions are conducted in a highly controlled manner to produce desired compounds with high selectivity. Fast heat and mass transfer derived from large surface-to-volume ratios of microreactors enable extremely fast and exothermic reactions to be conducted in a controlled way. reaction in which a halogen substituent moves to a new position on an aromatic ring system. when a sequence of reactions is conducted in a flow mode by adding components one at a time at different locations along the tubular reactor.

Continuous Flow Synthesis of NHC‐Coinage Metal Amido and Thiolato Complexes: A Mechanism‐based Process Development

Abstract: The first flow synthesis of a range of coinage metal amido and thiolato complexes are reported. Mild conditions and extremely short reaction times provide efficient and sustainable access to these valuable organometallic species.