Palladium(ii)-catalyzed dehydrogenative coupling of aliphatic olefins would enable an efficient route to (conjugated) dienes, but remains scarcely investigated. Here, 2-hydroxypyridine (2-OH-pyridine) was found to be an effective ligand for Pd(ii) in the activation of vinylic C(sp2)-H bonds. While reoxidation of Pd(0) is challenging in many catalytic oxidations, one can avoid in this reaction that the reoxidation becomes rate-limiting, even under ambient O2 pressure, by working in coordinating solvents. Via kinetic studies the elementary steps governing this reaction were elucidated, resulting in enhanced performance (turnover frequency) of the Pd(ii)/2-OH-pyridine system. The diene product is formed via a consecutive activation of two olefins on the same Pd atom, followed by a beta-hydride elimination. The first olefin activation, viz. the C-H activation, determines the overall reaction rate under these conditions. The catalytic complex was studied by ESI-MS and X-ray absorption spectroscopy, revealing that the coordination sphere of the working palladium complex contains two 2-OH-pyridine ligands.

The atom-efficient esterification of phosphoric acid was investigated for the selective synthesis of phosphate mono-esters using an acid treated niobium oxide catalyst, avoiding the use of amines as is common in literature. Kinetic studies revealed that the heterogeneous catalyst exhibited higher selectivity for mono-esters compared to homogeneous acid catalysts, as supported by calculation of the relative reactivity of mono-ester and phosphoric acid with different catalysts. To characterize the catalyst, its Hammett acidity value (H0) was determined, while solid state 31P NMR enabled studying the adsorption of H3PO4. Due to the mild acidity of the niobium oxide, alcohols with acid-sensitive functions, including substituted double bonds, could be phosphorylated, enabling the synthesis of surfactants such as oleyl phosphate.

In order to deal with legacy additives in plastic waste streams, multiple extraction processes are being developed. For sustainability and economic reasons, these processes call for the parallel implementation of revalorisation routes for the extracted toxic compounds, especially when dealing with large volumes as in the case of phthalate plasticizers. On account of its intrinsic value, the recovery of the aromatic fragment from such end-of-life phthalate ester mixtures was prioritized in this work. To that end, a hydrolysis-decarboxylation process was designed using hydrophobic zeolites and heterogeneous Pt-catalysts, in water as a safe and environmentally benign solvent. By carefully tuning the reaction parameters, the selective formation of phthalic acid, benzoic acid or benzene can be achieved in near-quantitative yields, next to the recovery of alkene and alcohol side chain fragments (yields up to 99%).

The Pd-catalyzed C-H activation of natural tryptophan residues has emerged as a promising approach for their direct synthetic modification. While using water as the solvent and harnessing air as the oxidant is enticing, these conditions induce catalyst deactivation by promoting the formation of inactive Pd(0) clusters. In this work, we have studied optimized Pd-based catalytic systems via nonsteady state kinetic analysis and in situ X-ray absorption spectroscopy (XAS) to overcome catalyst deactivation, which enables the effective use of lower Pd loadings.

We report the use of novel biobased plasticizers prepared starting from citric acid (CA) in polylactic acid (PLA). Citric acid based plasticizers are well-known softeners for PLA, with citrate esters as the most commonly used class. However, citrate esters are known to leach out of the plastic material over time. This problem is currently addressed by acetylating the tertiary hydroxyl group of citric acid via complex and environmentally polluting processes. An alternative strategy consists in the reductive removal of the tertiary hydroxyl group, resulting in propane-1,2,3-tricarboxylic acid. Derivatizing this compound leads to novel plasticizers which have not been tested in PLA yet. Here, different esters of propane-1,2,3-tricarboxylic acid were synthesized and blended in PLA. Their influence on the thermal (Tg and Tm) and the mechanical properties (Young’s modulus, stress and strain) of PLA along with their migration out of the material were compared to those of commercially available citric acid based plasticizers. Our results show that similar or better results were obtained with these new PLA plasticizers.

We report the use of biobased plasticizers prepared from citric acid in poly(vinyl chloride) (PVC). The use of citric ester plasticizers is well known for PVC. However, these are known to leach out of the plastic material over time. Currently, this problem is resolved by the acetylation of the tertiary hydroxyl group of citric acid through environmentally polluting processes. An alternative strategy consists of the reductive removal of the tertiary hydroxyl group, resulting in propane-1,2,3-tricarboxylic acid. Esters of this compound lead to plasticizers that have not been tested in PVC yet. In this work, the syntheses of citrate esters, acetylated citrate esters, and esters of propane-1,2,3-tricarboxylic acid are evaluated based on their sustainability using the CHEM21 metric toolkit and lab-scale data. Next, the different esters of propane-1,2,3-tricarboxylic acid were blended in PVC. Their influence on the thermal, i.e., glass-transition temperature (T-g), and mechanical (Young's modulus, stress, and strain) properties of PVC along with their migration out of the PVC material were compared to that of commercially available citric acid-based plasticizers. Our results show that similar or better results were obtained with these green plasticizers, while their synthesis showed a high degree of sustainability.

Electrophilic amination (EA) involving transition metal-catalysed C-H activation of the arene has recently emerged as a promising method to directly construct aryl C(sp2)-N bonds. In EA, a leaving group (LG) is installed on nitrogen to overcome thermodynamic and kinetic barriers, as well as a polarity mismatch. However, many literature reports are limited to arenes carrying large directing groups and/or nitrogen coupling partners with extensive LGs. Many reactions also require additives (ligands, bases), often in superstoichiometric amounts. In addition, mechanistic information is often scarce. Herein we disclose a PdII-catalysed, AgI-mediated electrophilic amidation of simple arenes with O-acetyl acetohydroxamic acid (AcNHOAc). In contrast with previously reported systems, the reaction neither requires a ligand, nor superstoichiometric amounts of additives. Yields up to 50% were achieved, with up to 76% meta-selectivity. The catalytic system was optimized and the main yield-limiting factors were determined. Furthermore, we propose a mechanism only involving PdII species, in which coordination of AcNHOAc occurs before C-H activation. The mechanism is supported by experimental data from H/D exchange measurements, in situ XAS, FTIR, UV-Vis and NMR spectroscopy.

Post-consumer poly(lactic acid) (PLA) is recycled to high value monomers, either acrylic acid (AA) or lactide (LAC), using a phosphonium ionic liquid as the active solvent, in the presence or absence of an acid cocatalyst.

Tricarballylate esters are considered as an appealing class of biobased plasticizers. This work focusses on the production of tricarballylate esters from citrate esters through a one-pot sequential dehydration-hydrogenation process, in order to circumvent the undesired decarboxylation side reaction in the synthesis of tricarballylic acid directly from citric acid. High yields up to 93 % of different tricarballylate esters were obtained with a self-synthesised bifunctional 0.2 wt % Pd/Nb2O5.nH(2)O catalyst employed in methylcyclohexane as inert solvent.

We report the production of biobased plasticizers for PVC starting from citric by a two-step process comprising dehydration-hydrogenation followed by a Fischer esterification.

Graphical representation of Lewis acid catalyzed ammonolysis of polyamide 66.

Recently, a reaction sequence was developed for the production of tricarballylic acid, an interesting plasticiser precursor, from citric acid by using a H-Beta zeolite and Pd/C catalyst. Although yields of 85% of tricarballylic acid were obtained, citric acid elicited Al leaching from the zeolite framework, resulting in loss of activity. In this work, Nb2O5.nH(2)O was found to be a stable and performant catalyst for this reaction, and a strong involvement of the hydroxyl group of citric acid with the Nb2O5.nH(2)O surface was observed by C-13 MAS NMR. Next, Pd/Nb2O5.nH(2)O catalysts were synthesized via a low temperature reduction method to preserve the acidity of the Nb2O5.nH(2)O support; the nature of the Pd phase was examined by XAS. In presence of a 0.6 wt% Pd/Nb2O5.nH(2)O catalyst, yields over 90% of tricarballylic acid were obtained over multiple runs. Finally, this catalyst was also suitable for the dehydration-hydrogenation of other monohydroxy carboxylic acids. (C)& nbsp;2022 Elsevier Inc. All rights reserved.

Long-chain polyamides (LCPAs) are depolymerized by ammonolysis of the secondary amide bonds into building blocks for new polymer synthesis. Research on the ammonolysis of PA is quite limited and often proposes harsh reaction conditions with homogeneous catalysts. Here, we describe a heterogeneous catalytic system based on Nb2O5. Reactions were performed at a relatively low temperature of 200 degrees C in cyclopentyl methyl ether (CPME) as a green solvent and with limited addition of NH3 and H-2. The ammonolysis of secondary amides was extensively studied, initially with N-hexylhexanamide as a model compound. Since ammonolysis is an equilibrium reaction, it was eventually coupled to a hydrogenation process, with addition of a RuWOx/MgAl2O4 hydrogenation catalyst, in order to achieve complete depolymerization. Industrial LCPA samples were successfully and completely depolymerized to alpha, omega-diamine monomers and oligomers, resulting in product distributions of 62% primary amines and 36% secondary amines. The catalytic system was proven to be very robust against a variety of contaminants, e.g., fillers, other plastics, and additives. Only sulfur-containing compounds poison the Ru-catalyst and have to be removed completely.

In presence of a solid acid H-Beta zeolite and Pd/C catalyst, citric acid was converted to tricarballylic acid via a one-pot sequential dehydration-hydrogenation process with a yield up to 85% and a selectivity exceeding 90%.