Use of WO₄^2- on Layered Double Hydroxides for Mild Oxidative Bromination and Bromide-Assisted Epoxidation with H₂O₂

Tungstate, exchanged on a (Ni,Al) layered double hydroxide, is applied as a heterogeneous catalyst in the oxidation of bromide with H2O2 and the ensuing electrophilic bromination of olefins. The high halogenation activity of the catalyst in essentially neutral conditions mimicks the activity of V-bromoperoxidase enzymes. In water, aromatic and aliphatic olefins are selectively converted to bromohydrins; in methanol, methoxybromides are produced. In appropriate solvent conditions, the bromohydroxylation of geminally di-, tri-, and tetrasubstituted olefins proceeds via dehydrobromination to the epoxide. Evidence for this mechanism is provided by kinetic and labeling experiments. This one-pot alternative for the two-step halohydrin epoxidation process is enabled by the mild pH conditions; bromide is effective in substoichiometric, catalytic amounts. All new catalytic procedures are characterized by a high oxidative stability of the catalyst, high productivity of the catalyst on weight basis, high W turnover frequencies in ambient conditions (up to 50 mol of product per W per h), and high chemo-, regio-, and stereoselectivities

One-Pot Consecutive Reductive Amination Synthesis of Pharmaceuticals: From Biobased Glycolaldehyde to Hydroxychloroquine

Reductive amination plays a paramount role in the synthesis of amines. It is often proposed as a more ecofriendly synthesis process than the traditional SN2-type reactions of amines as it avoids toxic alkylation reagents such as alkyl halides. This work demonstrates the versatility of the reductive amination reaction via the synthesis of hydroxychloroquine (HCQ), one of the most renowned pharmaceuticals during this coronavirus pandemic. The novel green synthesis strategy is based on three consecutive reductive amination reactions conducted in a one-pot system, avoiding intermediary purification steps. Furthermore, a biobased C2 platform molecule, glycolaldehyde, was selected as a starting reagent. The newly developed reductive amination pathway was appraised using the CHEM21 Green Metric toolkit and compared with the commercially operating method

Kinetics of the Oxygenation of Unsaturated Organics with Singlet Oxygen Generated from H₂O₂ by a Heterogeneous Molybdenum Catalyst

A heterogeneous catalyst containing MoO42- exchanged on layered double hydroxides (Mo-LDHs) is used to produce 1O2 from H2O2, and with this dark 1O2, unsaturated hydrocarbons are oxidized in allylic peroxides. The oxidation kinetics are studied in detail and are compared with the kinetics of oxidation by 1O2, formed from H2O2 by a homogeneous catalyst. A model is proposed for the heterogeneously catalyzed 1O2 generation and peroxide formation. The model divides the reaction suspension in two compartments:  (1) the intralamellar and intragranular zones of the LDH catalyst; (2) the bulk solution. The 2-compartment model correctly predicts the oxidant efficiency and peroxide yield for a series of olefin peroxidation reactions. 1O2 is generated at a high rate by the heterogeneous catalyst, but somewhat more 1O2 is lost by quenching with the heterogeneous catalyst than using the homogeneous catalyst. Quenching occurs mainly as a result of collision with the LDH hydroxyl surface, as is evidenced by using LDH supports containing strong 1O2 deactivators such as Ni2+. A total of 15 organic substrates were peroxidized on a preparative scale using the best Mo-LDH catalyst under optimal conditions

Branching-First: Synthesizing C–C Skeletal Branched Biobased Chemicals from Sugars

A novel strategy to biobased chemicals with a branched carbon skeleton is introduced. Hereto, small sugars, such as 1,3-dihydroxyacetone, are coupled catalytically to obtain branched C₆ sugars, such as dendroketose, in high yield at mild conditions. By bringing this branching step up front, at the level of the sugar feedstock (<i>branching-first</i>), new opportunities for the synthesis of useful chemicals arise. Here, we show that the branched sugar can be efficiently valorized into (i) new branched polyols and (ii) short branched alkanes. The first route preserves most of the original sugar functionality by hydrogenation with Ru/C and renders access to branched polyols with three primary alcohol groups. These molecules are potentially interesting as plasticizers, cross-linkers, or detergent precursors. The second valorization route demonstrates a facile hydrodeoxygenation of the branched sugars toward their corresponding branched alkanes (e.g., 2-methylpentane). The highest alkanes yields (>65 mol % C) are obtained with a Rh/C redox metal catalyst in a biphasic catalytic system, following a HDO mechanism. In the short term, commercial integration of these monobranched alkanes, in contrast to branched polyols, is expected to be straightforward because of their drop-in character and well-known valuable octane booster role when present in gasoline. Accordingly, the <i>branching-first</i> concept is also demonstrated with other small sugars (e.g., tetroses) enabling the production of branched C₆–C₈ sugars and thus also branched C₅–C₈ alkanes after HDO

Potassium-Modified ZSM‑5 Catalysts for Methyl Acrylate Formation from Methyl Lactate: The Impact of the Intrinsic Properties on Their Stability and Selectivity

Methyl lactate (ML) conversion to methyl acrylate is studied in the gaseous phase over ZSM-5 zeolite catalysts. High acrylate selectivity and catalyst service time were achieved using the K-ZSM-5 catalyst with low content of Brønsted acid sites (below 1 μmol g–1) and an overall K-to-Al atom ratio of unity. Feeding of ML in methanol containing 5 to 25 vol % of water improves catalyst stability. As such, up to 80% acrylate yield at complete ML conversion, along with minor deactivation after days-on-stream and fully recoverable catalysis, is presented

Localization of <i>p</i>-Nitroaniline Chains Inside Zeolite ZSM-5 with Second-Harmonic Generation Microscopy

Localization of p-Nitroaniline Chains Inside Zeolite ZSM-5 with Second-Harmonic Generation Microscop

A Heterogeneous Tungsten Catalyst for Epoxidation of Terpenes and Tungsten-Catalyzed Synthesis of Acid-Sensitive Terpene Epoxides

A Heterogeneous Tungsten Catalyst for Epoxidation of Terpenes and Tungsten-Catalyzed Synthesis of Acid-Sensitive Terpene Epoxide

Metal Catalyst-Dependent Poisoning Effect of Organic Sulfur Species for the Hydroconversion of 5‑Hydroxymethylfurfural

The transformation of 5-hydroxymethylfurfural (HMF) into ring-saturated furanics is a vital step in carbohydrate valorization. In this work, we report on the remarkable catalyst poisoning effect of numerous sulfur species for HMF hydroconversion. The presence of minor amounts of dimethyl sulfoxide (DMSO) affects ring-saturated product selectivity for the metal-catalyzed reactions using molecular hydrogen, whereas it fully deactivates catalytic transfer hydrogenation (CTH) in 2-propanol. The degree of poisoning correlates with the thermodynamic favorability of the metal sulfide formation. Reduced sulfur species (sulfide or thiol) are the ultimate metal poisoning agent. Their easy formation from more oxidized sulfur compounds explains the observed poisoning effect for such species. Here, the metal’s oxophilicity determines the catalysts’ behavior in the presence of oxidized sulfur species by forming (or not) poisoning sulfur–metal interactions. To overcome the sulfur poisoning, we propose DMSO removal with organic solvent extraction and catalyst oxidation post-treatment. These findings pinpoint the crucial, though overlooked, role of the biobased HMF purity for reductive catalytic studies. We provide a deeper understanding of the noble metal poisoning by sulfur from different origins and oxidation states that may be present during HMF hydroconversion

Patterned Growth of Metal-Organic Framework Coatings by Electrochemical Synthesis

Patterned Growth of Metal-Organic Framework Coatings by Electrochemical Synthesi

Plasma-Enabled Selective Synthesis of Biobased Phenolics from Lignin-Derived Feedstock

Converting abundant biomass-derived feedstocks into value-added platform chemicals has attracted increasing interest in biorefinery; however, the rigorous operating conditions that are required limit the commercialization of these processes. Nonthermal plasma-based electrification using intermittent renewable energy is an emerging alternative for sustainable next-generation chemical synthesis under mild conditions. Here, we report a hydrogen-free tunable plasma process for the selective conversion of lignin-derived anisole into phenolics with a high selectivity of 86.9% and an anisole conversion of 45.6% at 150 °C. The selectivity to alkylated chemicals can be tuned through control of the plasma alkylation process by changing specific energy input. The combined experimental and computational results reveal that the plasma generated H and CH3 radicals exhibit a “catalytic effect” that reduces the activation energy of the transalkylation reactions, enabling the selective anisole conversion at low temperatures. This work opens the way for the sustainable and selective production of phenolic chemicals from biomass-derived feedstocks under mild conditions