Abstract
It is a dream that future synthetic chemistry can mimic living systems to process multistep cascade reactions in a one-pot fashion. One of the key challenges is the mutual destruction of incompatible or opposing reagents, for example, acid and base, oxidants and reductants. A conceptually novel strategy is developed here to address this challenge. This strategy is based on a layered Pickering emulsion system, which is obtained through lamination of Pickering emulsions. In this working Pickering emulsion, the dispersed phase can separately compartmentalize the incompatible reagents to avoid their mutual destruction, while the continuous phase allows other reagent molecules to diffuse freely to access the compartmentalized reagents for chemical reactions. The compartmentalization effects and molecular transport ability of the Pickering emulsion were investigated. The deacetalization-reduction, deacetalization-Knoevenagel, deacetalization-Henry and diazotization-iodization cascade reactions demonstrate well the versatility and flexibility of our strategy in processing the one-pot cascade reactions involving mutually destructive reagents.
Highlights
Living systems can process multistep cascade chemical transformations to produce complex molecules.[1]
Particle-stabilized emulsions [called Pickering emulsions, oil-in-water (o/w) or water-in-oil (w/o)] might make the dream come true,[32−38] because the whole system is divided into numerous separate droplets that can serve as microcompartments and even protocells.[39−42] in Pickering emulsions, the oil and water phases are sufficiently mixed leading to a high area of oil-water interface available for chemical reactions.[43−48] It has recently been found that such a micro-mixing enables organic-aqueous biphasic reactions to proceed efficiently through the auto-diffusion of reactant molecules, and the reaction efficiency is as high as that achieved with vigorous stirring.[49]
In a control experiment, mixing two mixtures that were the same as a1 and a2 Pickering emulsions in composition but not emulsified, led to a suspension that rapidly changed to red color (Figure 2, a4), which is a result of acid-base reactions
Summary
Living systems can process multistep cascade chemical transformations to produce complex molecules.[1]. The reactant A in the continuous (oil) phase can freely move through auto-diffusion, and is converted to the intermediate B upon meeting the acid at the droplet interface, which is subsequently transformed to the final product C after meeting the base-contained droplets located in the neighboring layer In this scenario, the whole Pickering emulsion reaction system is just like a living system, which can spatially position diverse cells in different regions, compartmentalize the mutually destructive enzymes or molecules in the different cells but allow for the free diffusion of other molecules located outside the cells for biochemical reactions if needed
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