Steric Control of Site Selectivity in the Pd-Catalyzed C–H Acetoxylation of Simple Arenes

This report describes the use of an oxidant and a ligand to control site selectivity in the Pd(OAc)₂-catalyzed C–H acetoxylation of simple arenes. The use of MesI(OAc)₂ as the terminal oxidant in combination with acridine as the ligand results in primarily sterically controlled selectivity. In contrast, with Pd(OAc)₂ as the catalyst and PhI(OAc)₂ as the oxidant, electronic effects dominate the selectivity of arene C–H acetoxylation

Selective Process Steps for the Recovery of Scandium from Jamaican Bauxite Residue (Red Mud)

We report the development of a process allowing the selective, sustainable recovery of scandium (Sc) with 75% efficiency from Jamaican bauxite residue (red mud), a waste product from aluminum production. The process design is inspired by green chemistry principles and focuses on establishing highly selective process steps (sulfation, leaching, and precipitation) in order to minimize costs and waste produced. In addition to scandium oxide, the chosen approach produces mixed rare earth oxides as a side product, thus isolating an average of 88% of all rare earth elements contained in red mud. Furthermore, in light of predicted supply shortages of the critical material Sc and the need to establish cost-effective bauxite residue remediation techniques, a systematic Monte Carlo-based economic performance assessment framework is developed in order to evaluate the economic prospects of the proposed process system in the presence of irreducible uncertainty

Value Analysis of Neodymium Content in Shredder Feed: Toward Enabling the Feasibility of Rare Earth Magnet Recycling

In order to facilitate the development of recycling technologies for rare earth magnets from postconsumer products, we present herein an analysis of the neodymium (Nd) content in shredder scrap. This waste stream has been chosen on the basis of current business practices for the recycling of steel, aluminum, and copper from cars and household appliances, which contain significant amounts of rare earth magnets. Using approximations based on literature data, we have calculated the average Nd content in the ferrous shredder product stream to be between 0.13 and 0.29 kg per ton of ferrous scrap. A value analysis considering rare earth metal prices between 2002 and 2013 provides values between $1.32 and$145 per ton of ferrous scrap for this material, if recoverable as pure Nd metal. Furthermore, we present an analysis of the content and value of other rare earths (Pr, Dy, Tb)

Nondirected, Cu-Catalyzed sp³ C–H Aminations with Hydroxylamine-Based Amination Reagents: Catalytic and Mechanistic Studies

This work demonstrates the use of hydroxylamine-based amination reagents RSO₂NH-OAc for the nondirected, Cu-catalyzed amination of benzylic C–H bonds. The amination reagents can be prepared on a gram scale, are benchtop stable, and provide benzylic C–H amination products with up to 86% yield. Mechanistic studies of the established reactivity with toluene as substrate reveal a ligand-promoted, Cu-catalyzed mechanism proceeding through Ph-CH₂(NTsOAc) as a major intermediate. Stoichiometric reactivity of Ph-CH₂(NTsOAc) to produce Ph-CH₂-NHTs suggests a two-cycle, radical pathway for C–H amination, in which the decomposition of the employed diimine ligands plays an important role

Cost Analysis as a Tool for the Development of Sc Recovery Processes from Bauxite Residue (Red Mud)

Process development for the recovery of rare earth elements (REEs) from production wastes is generally seen as one strategy to address potential supply shortages for these critical materials. However, very few reported process systems are both technologically feasible and economically viable. Herein, we propose a strategy which considers comprehensive cost analysis in the presence of irreducible uncertainty as a core strategy introduced early on at the process design stage for the recovery of scandium (Sc) from bauxite residue (red mud). The latter represents an important process example of REE recovery from what is typically considered a waste material. In particular, using both a classical and a probabilistic framework for cost model development and assessment, cost is considered as a key design parameter in addition to selectivity and yield to design processes primed for industrial applications. We further show that such an approach affords significantly enhanced prospects of economic viability to the proposed process system when comparatively evaluated against reported ones, thus promising to drive environmental remediation of red mud through recovery of a valuable material (Sc₂O₃) under enhanced environmental and economic performance profiles

Accessing Diverse Azole Carboxylic Acid Building Blocks via Mild C–H Carboxylation: Parallel, One-Pot Amide Couplings and Machine-Learning-Guided Substrate Scope Design

This manuscript describes a mild, functional group tolerant, and metal-free C–H carboxylation that enables direct access to azole-2-carboxylic acids, followed by amide coupling in one pot. This demonstrates a significant expansion of the accessible chemical space of azole-2-amides, compared to previously known methodologies. Key to the described reactivity is the use of silyl triflate reagents, which serve as reaction mediators in C–H deprotonation and stabilizers of (otherwise unstable) azole carboxylic acid intermediates. A diverse azole substrate scope designed via machine-learning-guided analysis demonstrates the broad utility of the sequence. Density functional theory calculations provide detailed insights into the role of silyl triflates in the reaction mechanism. Transferrable applications of the protocol are successfully established: (i) A low pressure (CO2 balloon) option for synthesizing azole-2-carboxylic acids without the need for high-pressure equipment; (ii) the use of 13CO2 for the synthesis of labeled compounds; (iii) isocyanates as alternative electrophiles for direct C–H amidation; (iv) and the use of the developed chemistry in a 24 × 12 parallel synthesis workflow with a 90% library success rate. Fundamentally, the reported protocol expands the use of heterocycle C–H functionalization from late-stage functionalization applications toward its use in library synthesis. It provides general access to densely functionalized azole-2-carboxylic acid building blocks and demonstrates their one-pot diversification

Cellulase-Inspired Solid Acids for Cellulose Hydrolysis: Structural Explanations for High Catalytic Activity

This work presents a detailed structure–activity analysis of a polymeric solid acid catalyst used in cellulose hydrolysis. In contrast to previous work, our studies show that the high catalytic activity is likely not due to hydrogen bonding between C–Cl moieties at the polymer surface and cellulose fibers. Instead, we report that such C–Cl bonds hydrolyze readily under polymer functionalization conditions to produce C–OH groups on the exterior of the solid acid beads. Furthermore, continued C–Cl to C–OH substitution under cellulose or cellobiose hydrolysis conditions releases HCl from the resin, which contributes to cellulose hydrolysis. Overall, the presented studies stress the need for detailed, quantitative analysis of polymer structures and spatial distribution of functional groups in order to correctly interpret the catalytic results obtained with polymer-based solid acids