Catalysts/catalysis surfactant-type

Lewis acids as water-stable catalysts have been developed. Metal salts, such as rare earth metal triflates, can be used in aldol reactions of aldehydes with silyl enolates in aqueous media. These salts can be recovered after the reactions and reused. Furthermore, surfactant-aided Lewis acid catalysis, which can be used for aldol reactions in water without using any organic solvents, has been also developed. These reaction systems have been applied successfully to catalytic asymmetric aldol reactions in aqueous media. In addition, the surfactant-aided Lewis acid catalysis for Mannich-type reactions in water has been disclosed. These investigations are expected to contribute to the decrease of the use of harmful organic solvents in chemical processes, leading to environmentally friendly green chemistry. 

This type of catalyst was named Lewis acid-surfactant combined catalyst (LASC), and was expected to possess the characters of both a Lewis acid and a surfactant. Sc(DS)3 showed quite high activity in aldol reactions in water without using any organic solvents (Scheme 12.63). A kinetic study on the initial rate of this reaction revealed that the reaction in water is about 130 times faster than that in dichloromethane. It was assumed that hydrophobic reaction environments were created by combining Sc(DS)3 and substrates under the conditions, and that they were concentrated in water to realize efficient catalysis. Interestingly, under neat conditions, the reaction proceeded much slower to give the desired adduct in a much lower yield. 

Abstract Broad principles of Solid-Liquid calorimetry together with some illustrative examples of its use in the field of catalysis are presented here. The first use is related to the determination of surface properties of catalysts, adsorbents and solid materials in contact with liquids. In particular, it is shown how to evaluate the capacity of a given solid to establish different types of interaction with its liquid environment or to calculate its specific surface area accessible to liquids. The second use includes the measurement of the heat effects accompanying catalytic reactions and the related interfacial phenomena at Solid-Liquid and Liquid-Liquid interfaces. Examples of competitive ion adsorption from dilute aqueous solutions, as well as the formation of surfactant aggregates either in aqueous solution or at the Solid-Liquid interface are considered in view of potential applications in Environmental Remediation and Micellar Catalysis. 

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