Roman Matthessen

Tuning the catalytic performance of metal–organic frameworks in fine chemistry by active site engineering

The effect of a post-synthetic acid treatment on the catalytic performance of MOFs is evaluated for MIL-100(Fe), an iron-benzenetricarboxylate. The acid-treated frameworks are structurally robust as no differences have been found in XRD patterns after treatment. Porosity of the acid-treated MOFs gradually decreases, most probably as a consequence of anions remaining in the charged frameworks. Monitoring the modification of the MOFs by reactions of which the outcome depends on the acid properties of the catalyst suggests the presence of two types of active sites, with weak Bronsted acid sites in close vicinity to the Lewis acid open metal sites. This is supported by CO-chemisorption experiments which indicate a large increase of both Lewis and Bronsted acidity. In Diels–Alder reactions of oxygenated dienophiles with 1,3-cyclohexadiene, a strong increase of the activity is found for the acid-treated MOFs. This is explained by the enhanced activation of the dienophiles on the modified active sites.

Electrocarboxylation: towards sustainable and efficient synthesis of valuable carboxylic acids

Summary The near-unlimited availability of CO2 has stimulated a growing research effort in creating value-added products from this greenhouse gas. This paper presents the trends on the most important methods used in the electrochemical synthesis of carboxylic acids from carbon dioxide. An overview is given of different substrate groups which form carboxylic acids upon CO2 fixation, including mechanistic considerations. While most work focuses on the electrocarboxylation of substrates with sacrificial anodes, this review considers the possibilities and challenges of implementing other synthetic methodologies. In view of potential industrial application, the choice of reactor setup, electrode type and reaction pathway has a large influence on the sustainability and efficiency of the process.

Bio‐Based Nitriles from the Heterogeneously Catalyzed Oxidative Decarboxylation of Amino Acids

The oxidative decarboxylation of amino acids to nitriles was achieved in aqueous solution by in situ halide oxidation using catalytic amounts of tungstate exchanged on a [Ni,Al] layered double hydroxide (LDH), NH4 Br, and H2 O2 as the terminal oxidant. Both halide oxidation and oxidative decarboxylation were facilitated by proximity effects between the reactants and the LDH catalyst. A wide range of amino acids was converted with high yields, often >90 %. The nitrile selectivity was excellent, and the system is compatible with amide, alcohol, and in particular carboxylic acid, amine, and guanidine functional groups after appropriate neutralization. This heterogeneous catalytic system was applied successfully to convert a protein-rich byproduct from the starch industry into useful bio-based N-containing chemicals.

Electrochemical dicarboxylation of conjugated fatty acids as an efficient valorization of carbon dioxide

Carbon dioxide was electrochemically incorporated in internal conjugated dienes and the process was optimized to achieve satisfactory yields (>70%) even for less reactive substrates. Reactions were performed galvanostatically in an undivided cell at room temperature with a magnesium or aluminium sacrificial anode. Using an optimized electrosynthetic method for the dicarboxylation of 1,3-cyclohexadiene (optimal electrode material, CO2 pressure, amount of charge), the effect of molecular configuration and alkyl substitution on the reactivity of conjugated double bonds towards carboxylation was studied. Use of a bubble reactor at atmospheric pressure instead of a higher pressure reactor, and lowering of the current density made it possible to effectively perform the double carboxylation of internal conjugated double bonds in open chains. Conjugated linoleic acid methyl esters were used in this reaction for the first time and by searching for the optimal reaction conditions (solvent, supporting electrolyte, reactant concentration, amount of charge, current density) yields approaching 80% of the corresponding fatty triacid product could be obtained, at current efficiencies over 50%.