The quantification of Lewis acidity is accomplished by a deuterated quinolizidine probe utilizing 2H NMR spectroscopy. The chemical shifts of the 2H NMR signals for aluminum, boron, titanium, and zinc halides are reported. The rate constants for Lewis acid catalyzed reactions were determined by utilizing UV/Vis spectroscopy for Diels–Alder and Povarov reactions under pseudo‐first‐order conditions. The magnitude of the 2H NMR chemical shifts correlates with the rate constants of the organic transformations for many Lewis acids investigated in the same order, whereas some deviations are identified.
The development of a system for the operationally simple, scalable conversion of polyhydroxylated biomass into industrially relevant feedstock chemicals is described. This system includes a bimetallic Pd/Re catalyst in combination with hydrogen gas as a terminal reductant and enables the high-yielding reduction of sugar acids. This procedure has been applied to the synthesis of adipate esters, precursors for the production of Nylon-6,6, in excellent yield from biomass-derived sources.
Round and round the olefin goes! A cobalt‐catalyzed 1,4‐hydrobutadienylation of a 1‐aryl‐substituted 1,3‐diene with 2,3‐dimethyl‐1,3‐butadiene yields 1,3,6‐triene derivatives in excellent yield and chemoselectivity. The application of a bulky ligand (SchmalzPhos) leads to the selective formation of a single regio‐ and stereoisomer.
This article reports on the applications of electrochemistry for the generation of radicals as neutral, cationic, and anionic intermediates and their use in preparative reactions for the formation of carbon–carbon and carbon–heteroatom bonds. The focus of this article is on electrochemical oxidation reactions of enol ethers, ketene acetals, and electron‐rich aromatic compounds. Furthermore, recent advances in the electrochemically induced synthesis of four‐membered ring systems and biaryl compounds are covered. The oxidative carbon–carbon bond formation by Kolbe electrolysis concludes the section dealing with oxidative transformations. The section describing reductive processes consists of indirect electrochemical reduction of alkylhalides and thioesters, as well as the reductive interconversion of functional groups described recently.
Converting agriculture to produce energy as well as food has become an important and well-funded global research goal as petroleum reserves fall and fuel prices rise. But the use of crop biomass-both grain and other plant parts-as a raw material for bioenergy production may compete with food and feed supplies and remove valuable plant residues that help sustain soil productivity and structure and avoid erosion. Agricultural research can mitigate these trade-offs by enhancing the biomass traits of dual-purpose food crops, developing new biomass crops for marginal lands where there is less competition with food crops, and developing sustainable livestock management systems that are less dependent on biomass residuals for feeds. Agronomists will need to define the minimum thresholds of crop residues for sustainable production in particular farming systems, especially in low-yield rainfed systems (that produce less than 5-6 metric tons of grain and straw per hectare), and to establish the level of additional residues that may be removed for other purposes, including biofuel production. Enhanced root growth offers another avenue for maintaining soil organic matter. Agricultural research can also help improve the energy efficiency of biomass crops, enhancing their value as renewable energy sources with low net carbon emissions. CROP-BREEDING OPTIONS TO ADDRESS BIOFUEL NEEDSAgricultural biofuels are currently based on the generation of ethanol from sucrose or starch derived from vegetative biomass or grain, on biodiesel from the more direct use of vegetable oils and animal fats. Ethanol has a high octane rating and can be blended in low proportions with gasoline for direct use in normal internal combustion engines.Further down the line, there is enormous potential to develop cellulose-based bioenergy systems. Plant biomass is an abundant and renewable source of hydrocarbons, and crops can generate more cellulose per hectare than sucrose or starch. Plant breeders should aim for high-density biomass production (for example, 15 tons per hectare in maize) rather than competing with crop residues or forest production for supplying materials to cellulosic biorefineries. Preliminary research shows significant genetic variation among maize and sorghum (brown midrib mutants) cultivars for cellulose and lignin content, suggesting that breeders can select for the increased quality of maize and sorghum stover for ethanol conversion. Breeders can also develop cultivars whose biomass lends itself readily to breakdown by fungi, improving ethanol production efficiency.Breeders can increase cellulose or hemicellulose production by making photosynthesis or nitrogen metabolism more efficient, but they must also select for enhanced water-and nutrient-use efficiency under resource-conserving systems that provide an overall energy savings and cut emissions of carbon dioxide and pollutants. Growing biofuel crops on lands not suitable for food production-for example, those affected by drought, salt, or temperature stresses-would substantially...
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.