Gillesds

Green resin adhesives: Owing to increasingly prominent environmental problems, the development of alternatives to petroleum based phenol-formaldehydes (PFs) is imperative. Herein, various methods for lignin modification and the use of modified lignin as a substitute for phenol in the preparation of PF adhesives are reviewed. In particular, industrial applications and prospects of modified lignin in PF are introduced.

Abstract

Traditionally, phenols used to prepare phenol-formaldehyde (PF) resin adhesives are obtained from phenolic compounds and various chemicals, which are extracted from petroleum-based raw materials. Lignin, a sustainable phenolic macromolecule in the cell wall of biomass with an aromatic ring and a phenolic hydroxyl group similar to those of phenol, can be an ideal substitute for phenol in PF resin adhesives. However, only a few lignin-based adhesives are produced on a large scale in industry, mainly because of the low activity of lignin. Preparing lignin-based PF resin adhesives with exceptional achievements by modifying lignin instead of phenol is an efficient method to improve the economic benefits and protect the environment. In this review, the latest progress in the preparation of PF resin adhesives via lignin modification, including chemical, physical, and biological modifications, is discussed. In addition, the advantages and disadvantages of different lignin modification methods for adhesives are compared and discussed, and future research directions for the synthesis of lignin-based PF resin adhesives are proposed.

The CBG aluminium-dihydride (I) is used as a catalyst for reducing esters with good tolerance of reducible functionalities. Furthermore, it was demonstrated that compound I catalyzed the hydroboration of epoxides into Markovnikov-branched products. The earth-abundant, non-toxic, and inexpensive Al-based catalysts are attractive and alternatives to expensive transition and lanthanide-based metal catalysts.

Abstract

In this work, the molecular aluminium dihydride complex bearing an N, N’-chelated conjugated bis-guanidinate (CBG) ligand is used as a catalyst for reducing a wide range of aryl and alkyl esters with good tolerance of alkene (C=C), alkyne (C≡C), halides (Cl, Br, I and F), nitrile (C≡N), and nitro (NO₂) functionalities. Further, we investigated the catalytic application of aluminium dihydride in the C−O bond cleavage of alkyl and aryl epoxides into corresponding branched Markovnikov ring-opening products. In addition, the chemoselective intermolecular reduction of esters over other reducible functional groups, such as amides and alkenes, has been established. Intermediates are isolated and characterized by NMR and HRMS studies, which confirm the probable catalytic cycles for the hydroboration of esters and epoxides.

Deoxygenative transformations of alcohols and their derivatives are often challenging due to the thermodynamic penalty associated with the cleavage of the C−O bond. This Review includes preparative protocols and their mechanistic aspects for the activation and functionalization of C−O bonds, detailing direct and indirect electrosynthetic methods, as well as photoelectrochemical strategies.

Abstract

Alcohols and their derivatives are ubiquitous and versatile motifs in organic synthesis. Deoxygenative transformations of these compounds are often challenging due to the thermodynamic penalty associated with the cleavage of the C−O bond. However, electrochemically driven redox events have been shown to facilitate the C−O bond cleavage in alcohols and their derivatives either through direct electron transfer or through the use of electron transfer mediators and electroactive catalysts. Herein, a comprehensive overview of preparative electrochemically mediated protocols for C−O bond activation and functionalization is detailed, including direct and indirect electrosynthetic methods, as well as photoelectrochemical strategies.

Highly active and selective catalysts pave the way for the production of bioplastics with tailor-made properties. Comonomers can be used to alter the properties of the prominent bioplastic PLA. Besides the variation in the microstructure, a treasure not yet fully uncovered lies within the combination of different monomer classes in multimechanistic polymerizations.

Abstract

Bioplastics are one of the answers to environmental pollution and linear material flows. The most promising bioplastic polylactide (PLA) is already replacing conventional plastics in a number of applications. The properties of PLA, however, do not fit for all potential application areas, but they can be altered by the introduction of comonomers. The copolymerization of lactide (LA) with other lactones like ϵ-caprolactone (CL) has been established for several years. Nevertheless, controlling copolymerizations remains a challenge due to the high complexity of the system. Copolymerization of LA with other monomer classes is much less investigated, but has the chance to overcome the limitations in material properties that occur when only lactones are used. The crucial factor for all copolymerizations is the catalyst. It dominates the reaction kinetics and determines the resulting microstructure. In this review, copolymerization catalysts for LA are presented divided into catalysts for the synthesis of lactone block copolymers, lactone random copolymers, and multimechanistically synthesized copolymers. The selected catalysts are highlighted either owing to their industrially applicable polymerization conditions or their non-standard mechanism.

Nature, Published online: 27 July 2022; doi:10.1038/d41586-022-02084-1

Synlett
DOI: 10.1055/a-1890-8503

Direct functionalization of heterocycles is an advanced strategy for diversifying privileged and biorelevant heterocycle-containing molecules. Particularly, use of the most abundant transition metal, iron, as a catalyst makes this process highly cost-effective and sustainable. Recently, some progress has been realized towards the direct functionalization of heterocycles under iron catalysis. Herein, we present the developments in the C–H bond functionalizations and related reactions of various heterocycles by abundant iron salts. This Synpacts is categorized into different sections based on heterocycles being functionalized, and each section is discussed based on the type of reaction catalyzed by iron.1 Introduction2 Functionalization of Indoles2.1 Alkylation2.2 Alkenylation2.3 Other Reactions3 Oxindoles and Isatins3.1 C–C Bond Formation3.2 C–Heteroatom Bond Formation4 Pyridines and Furans5 Functionalization of Azoles6 Summary and Outlook
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Nature, Published online: 27 July 2022; doi:10.1038/s41586-022-04993-7