China 
Africa 
Explore chapters and articles related to this topic
Green Catalysis, Green Chemistry, and Organic Syntheses for Sustainable Development
Published in Miguel A. Esteso, Ana Cristina Faria Ribeiro, A. K. Haghi, Chemistry and Chemical Engineering for Sustainable Development, 2020
Divya Mathew, Benny Thomas, K. S. Devaky
Lewis acid catalysis is of great interest in organic synthesis.17 But the Lewis acids have a higher affinity toward water rather than toward the substrates, and hence, the presence of even a minute amount of water may stop the reaction. Consequently, Lewis acids have restricted application in organic synthesis. However, undeniably, water is a safe, harmless, and environmentally benign solvent.18 From a viewpoint of green chemistry, nevertheless, it is desirable to use water instead of organic solvents as a reaction solvent. Rare earth metal triflates can be used as water-stable Lewis acids in water-containing solvents, for instance, Sc(OTf)3 and Yb(OTf)3. Furthermore, Lewis acid–surfactant-combined catalyst has also been developed without using any organic solvents. The first example of Lewis acid-catalyzed reaction is the hydroxymethylation of silyl enol ethers by commercial formaldehyde in aqueous solution. Moreover, Yb(OTf)3 is found to be the most effective catalyst among various Ln(OTf)3 tested for the aldol reaction because the catalytic amount of Yb(OTf)3 can drive the reaction to completion. Furthermore, Yb(OTf)3 can activate aldehydes other than formaldehyde with silyl enol ethers in aqueous solvents. Some important types of Lewis acid catalysts are discussed here.
Application of chiral polybinaphthyl-based Lewis acid catalysts to the asymmetric organozinc additions to aldehydes
Published in Y. Yagci, M.K. Mishra, O. Nuyken, K. Ito, G. Wnek, Tailored Polymers & Applications, 2020
Lewis acid catalysis is an important synthetic method in organic chemistry and has found very broad applications in natural product and drug syntheses [1]. In recent years, enormous progress has been made on the use of chiral ligand-based Lewis acid catalysts for asymmetric organic reactions [1–3]. However, compared to some late transition metal-based catalysts, Lewis acid catalysts are generally used with a much larger quantity in a reaction. In a number of cases, a stoichiometric or even excess amount of Lewis acid catalysts is necessary. The larger amount required is due to the high sensitivity of Lewis acid complexes towards air, moisture and impurity. Because it is often quite expensive to prepare the chiral ligands used in asymmetric Lewis acid catalysis, recovery and reuse of these compounds are highly desirable. Therefore, using easily recoverable polymer based chiral catalysts becomes a very attractive process for the asymmetric Lewis acid catalysis.
Science of Colloidal Processing
Published in Mohamed N. Rahaman, Ceramic Processing, 2017
The incorporation of a single polar group to the end of a polymer chain can help to strengthen the anchoring to the particle surface, by the formation of hydrogen bonds (in aqueous solvents) or coordinate bonds (in aqueous or nonaqueous liquids). A useful way to describe these polar interactions is by the Lewis acid–base concept or the more general donor-acceptor concept [39]. In the original form of the concept, a Lewis acid is defined as a substance capable of accepting a pair of electrons from another species, while a Lewis base is a substance capable of donating a pair of electrons. A basic functional group, for example, attaches itself to acidic functional sites on the particle surface, while an acidic functional attaches itself to basic functional groups. The resulting polymer-coated surface has a brush-like structure, with the chains attached at one end, while the nonadsorbing chain protrudes into the solvent (Figure 6.21d). Polymers used in this way are often short-chain polymers. An example is oleic acid, used as a dispersant in nonaqueous solvents. The oxygen atom in the −OH group of the −(CO)OH group can form a coordinated bond with a Lewis acid site (e.g., an electron-deficient metal atom) on the particle surface.
Tire-track resistance performance of acrylic resin emulsion coatings for colored asphalt pavements
Published in Road Materials and Pavement Design, 2022
Wen-rui Yang, Kai Zhang, Jiao Yuan, Hui-ying Li, Zhong-min Feng
van der Waals first discovered noncharged atoms and molecules in the presence of noncovalent interactions. In the process of separating two molecules or atoms (i-i) in a vacuum, the dispersion function can be expressed as Formula (1) (Tan & Guo, 2013). where A is the Hamaker constant, which is characterised by the value of the van der Waals attraction energy; q is the number of molecules in the unit volume; and β is the van der Waals interaction constant between the molecules of the substance. When two or more different substances interact with each other (i-j), the total Hamaker constant is determined by the following function: Therefore, to calculate the nonpolar LW component of the interface energy between two materials, the surface free energy parameters of each material can be calculated with Formula (3): where and are two types of nonpolar LW components, which are also known as dispersion components. Polar Lewis acid–base (AB) interaction
Hydrophobic chemical treatment of aggregate surfaces to re-engineer the mineral/bitumen interface and improve bitumen adhesion
Published in Road Materials and Pavement Design, 2021
Stephen Bagshaw, Tim Kemmitt, Sam Brooke, Mark Waterland, Larry Fertel
As part of on-going research aimed at developing methods and technologies to understand, then to combat these failure mechanisms, the issue of chip adhesion at the aggregate surface/bitumen (S/B) interface, has been investigated. The major challenge for adhesion of bitumen to aggregates is that the two systems are chemically poorly compatible at the molecular level. Roading aggregates are hydrophilic, low surface area mineral solids. In all cases, aggregates prefer to adsorb water onto their surfaces rather than organic compounds, such as those found in bitumen. The fact that the surface chemistries of different aggregates can be acidic (silicates) or basic (carbonates) in nature, does not obviate that basic premise (Read & Whiteoak, 2003; Rice, 1958; Weigel & Stephan, 2018). It should be noted, that the terms acidic and basic in the chemistry context invoked here, describe the Lewis acid/base theory of nucleophile/electrophile and their respective interactions with the mineral surface, rather than any particular effect on solution pH and this concept plays an important role with regard to the chemistry of the surface. The outcome is therefore well known that, if water can infiltrate the aggregate/bitumen interface, then both chemically and energetically, it will do so and will cause the bitumen and aggregate to separate (Bagampadde, Isacsson, & Kiggundu, 2005; Fromm, 1974; Sachin, Mallesh, & Shareef, 2017; Zhang, Airey, Grenfell, & Apeagyei, 2017).
Magnetic hybridized Fe3O4/HKUST-1 composite modified with graphite oxide to remove thiophene from model fuels
Published in Petroleum Science and Technology, 2019
Mingyan Chen, Jie Liu, Yucheng Liu, Yue Ding, Jie Chen, Bing Yang, Lili Ma, Lingli Li
For the mechanism of adsorbent desulfurization, three aspects can be considered:(1) the pore structure of Adsorbent. Since the average pore size of MH and MGH are 4.96 nm and 3.86 nm, thiophene (5.6 7.7 Å) can be easily enter the pore of the adsorbent and combine with the adsorption site. (2) Lewis acid-base interaction. Since Cu2+in HUSKT-1 belongs to Lewis acid, and thiophene is alkali compounds, the thiophene is adsorbed on the adsorbent by acid-base interaction (Jhung, Khan, and Hasan 2012). (3) The π-complexation between thiophene and adsorbents. Some electrons from the π-orbitals of sulfur atom in thiophene ring to the vacant s-orbital of Cu2+ to form the σ bond, and the electrons from d-orbital of Cu2+ to the π*-orbital of thiophene to form anti-bonding π-orbitals for removing the thiophene (Wang et al. 2006).