Laurens Claes

Pd-catalyzed decarboxylation of glutamic acid and pyroglutamic acid to bio-based 2-pyrrolidone

In order to recycle nitrogen from nitrogen-rich waste streams, particularly protein waste, we studied the decarboxylation of pyroglutamic acid and glutamic acid in a one-pot reaction to bio-based 2-pyrrolidone. After the screening of a wide range of supported Pd and Pt catalysts, 5 wt% Pd/Al2O3 displayed the highest yield (70%) and selectivity (81%) for the decarboxylation of pyroglutamic acid in water at 250 °C and under an inert atmosphere. Side products originate from consecutive reactions of 2-pyrrolidone; different reaction pathways are proposed to explain the presence of degradation products like propionic acid, γ-hydroxybutyric acid, γ-butyrolactone and methylamine. An extensive study of the reaction parameters was performed to check their influence on selectivity and conversion. This heterogeneous catalytic system was successfully extended to the conversion of glutamic acid.

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.

Adsorption and Separation of Aromatic Amino Acids from Aqueous Solutions Using Metal–Organic Frameworks

Metal-organic frameworks (MOFs) are investigated for the adsorption of aromatic amino acids l-phenylalanine (l-Phe), l-tryptophan (l-Trp), and l-tyrosine (l-Tyr) from aqueous solutions. After screening a range of water-stable MOFs, the hydrophobic Zr-MOF MIL-140C emerged as the best performing material, exhibiting uptakes of 15 wt % for l-Trp and 20 wt % for l-Phe. These uptakes are 5-10 wt % higher than those of large-pore zeolites Beta and Y. Both single-compound and competitive adsorption isotherms for l-Phe and l-Trp were experimentally obtained at the natural pH of these amino acid mixtures (pH 6.5-7) without additional pH modification. We find that the hydrophobic nature of MIL-140C and the capacity of l-Trp to form hydrogen bonds favor the uptake of l-Trp with its larger indole moiety compared to the smaller phenyl side group of l-Phe. On the basis of literature and vibrational analysis, observations of hydrogen-bonded l-Trp within the MIL-140C framework are evidenced by red- and blue-shifted -NH vibrations (3400 cm-1) in Fourier transform infrared spectroscopy, which were attributed to types N-Hl-Trp···πMIL-140C and N-Hl-Trp···OMIL-140C, respectively. MIL-140C is shown to be recycled at least three times for both aromatic amino acids without any loss of adsorption capacity, separation performance, or crystallinity. Desorption of aromatic amino acids proceeds easily in aqueous ethanol. Substantial coadsorption of negatively charged amino acids l-glutamate and l-aspartate (l-Glu and l-Asp) was observed from a model solution for wheat straw protein hydrolysate at pH 4.3. On the basis of these results, we conclude that MIL-140C is an interesting material for the recovery of essential aromatic amino acids l-Tyr, l-Phe, and l-Trp and of l-Glu and l-Asp from waste protein hydrolysates.

Metal-catalyzed reductive deamination of glutamic acid to bio-based dimethyl glutarate and methylamines

Glutamic acid is a promising renewable platform molecule which is abundantly available in biomass waste streams; it is also efficiently manufactured by fermentation. Here we report the reductive deamination of glutamic acid to bio-based dimethyl glutarate and methylamines. In order to recycle nitrogen in an industrially relevant co-product, glutamic acid was modified to N,N-dimethylglutamic acid by a mild reductive alkylation with Pd/C. Subsequently, selective C–N hydrogenolysis in methanol resulted in dimethyl glutarate and trimethylamine. A wide screening of transition metals (Pt, Pd, Rh and Ru) immobilized on various supports showed that the highest yields of dimethyl glutarate were obtained with Pt/TiO2. An FTIR study and kinetic experiments on metal-loaded and unloaded supports demonstrate that the interplay between the metal and the moderate acidity of the support results in the excellent C–N hydrogenolysis activity and selectivity. Finally, reaction parameter optimization resulted in 81% yield of dimethyl glutarate with 1 wt% Pt/TiO2 at 225 °C, 30 bar H2 after 8 h.

Bio-based N-alkyl-2-pyrrolidones by Pd-catalyzed reductive N-alkylation and decarboxylation of glutamic acid

Environmental regulations boost the search for new safer and less toxic bio-based solvents to replace controversial high-boiling solvents such as N-methyl-2-pyrrolidone and N,N-dimethylformamide in the chemical industry. Recently, N-alkyl-2-pyrrolidones and 5-methyl-N-alkyl-2-pyrrolidones were proposed as attractive alternative solvents for many applications. Here, we report a bio-based two-step chemocatalytic system for the synthesis of a broad range of N-alkyl-2-pyrrolidones starting from glutamic acid and C3–C5 carbonyl compounds. In the first step N-mono-alkylated derivatives of glutamic acid were synthesized in high yields (>85%) by a mild and efficient Pd-catalyzed reductive N-alkylation. Subsequently, thermally induced lactamization to the corresponding N-alkylpyroglutamic acid followed by Pd-catalyzed decarboxylation at 250 °C under inert atmosphere resulted in N-alkyl-2-pyrrolidones. Hydrolytic degradation was partially counteracted by the neutralization of the N-alkylpyroglutamic acid substrate with a base, resulting in yields up to 82%. Finally, both reaction steps were successfully combined in a one-pot process using the same Pd/Al2O3 catalyst in different conditions of gas atmosphere and temperature.

Synthesis and characterisation of alkyd resins with glutamic acid-based monomers

Alkyd resins are versatile polymers which have applications in inks and various coatings like decorative paints. They are mainly composed of fatty acids, polyols and aromatic diacids. In this work, glutamic acid as well as N-acylated and N-alkylated derivatives there of were evaluated as bio-based substitutes for these aromatic diacid monomers in the synthesis of alkyd resins. The resins were characterised in terms of structure, molecular weight, viscosity, oxidative thermal stability and colour. N-Palmitoylglutamic acid dimethyl ester can be successfully incorporated when the polycondensation is performed in two steps. In this approach, the bio-based diacid monomer is only supplied in the second step, because the removal of water in the first step is essential to avoid hydrolysis of the monomer amide bond and the subsequent formation of pyroglutamate groups. The molecular weight, viscosity and oxidative thermal stability are lower than for conventional alkyd resins. The mechanism of the discolouration of alkyd resins during polymerisation is mediated by free radical species, which were generated easily in the presence of free amino groups and/or unsaturated fatty acids. Light-coloured resins could be obtained by using saturated fatty acids or radical scavengers during polymerisation.