Enhancing the catalytic activity of hydronium ions through constrained environments
نویسندگان
چکیده
The dehydration of alcohols is involved in many organic conversions but has to overcome high free-energy barriers in water. Here we demonstrate that hydronium ions confined in the nanopores of zeolite HBEA catalyse aqueous phase dehydration of cyclohexanol at a rate significantly higher than hydronium ions in water. This rate enhancement is not related to a shift in mechanism; for both cases, the dehydration of cyclohexanol occurs via an E1 mechanism with the cleavage of Cβ-H bond being rate determining. The higher activity of hydronium ions in zeolites is caused by the enhanced association between the hydronium ion and the alcohol, as well as a higher intrinsic rate constant in the constrained environments compared with water. The higher rate constant is caused by a greater entropy of activation rather than a lower enthalpy of activation. These insights should allow us to understand and predict similar processes in confined spaces.
منابع مشابه
Tailoring nanoscopic confines to maximize catalytic activity of hydronium ions
Acid catalysis by hydronium ions is ubiquitous in aqueous-phase organic reactions. Here we show that hydronium ion catalysis, exemplified by intramolecular dehydration of cyclohexanol, is markedly influenced by steric constraints, yielding turnover rates that increase by up to two orders of magnitude in tight confines relative to an aqueous solution of a Brønsted acid. The higher activities in ...
متن کاملCatalytic alcoholysis of epoxides using metal-free cucurbituril-based solids.
Metal-free cucurbit[7]uril (CB7) solid-state assemblies promote acid-catalysed alcoholysis of aliphatic and aromatic epoxides under mild conditions to give β-alkoxy alcohols, which are important intermediates for the synthesis of a vast range of compounds such as bioactive pharmaceuticals. The catalytic process is heterogeneous and the catalyst can be reused in consecutive runs without any reac...
متن کاملHazelnut shell as a valuable bio-waste support for green synthesis of Ag NPs using Origanum vulgare leaf extract: Catalytic activity for reduction of methyl orange and Congo red
In this work the Origanum vulgare leaf extract was used to green synthesis of Ag nanoparticles (NPs) supported on Hazelnut shell as an environmentally benign support. The Ag NPs/Hazelnut shell as an effective catalyst was prepared through reduction of Ag+ ions using Origanum vulgare leaf extract as the reducing and capping agent and Ag NPs immobilization on Hazelnut shell surface in ...
متن کاملHazelnut shell as a valuable bio-waste support for green synthesis of Ag NPs using Origanum vulgare leaf extract: Catalytic activity for reduction of methyl orange and Congo red
In this work the Origanum vulgare leaf extract was used to green synthesis of Ag nanoparticles (NPs) supported on Hazelnut shell as an environmentally benign support. The Ag NPs/Hazelnut shell as an effective catalyst was prepared through reduction of Ag+ ions using Origanum vulgare leaf extract as the reducing and capping agent and Ag NPs immobilization on Hazelnut shell surface in ...
متن کاملBiosynthesis of Ag Nanoparticles at Ziziphus Jujuba Kernel Substrate using Tilia platyphyllos Extract: Catalytic Activity for Reduction of Organic Dyes
For the first time the extract of the plant of Tilia platyphyllos was used to green synthesis of Ag nanoparticles (NPs) supported on Ziziphus jujuba kernel as an environmentally benign support. Ag NPs/ Ziziphus jujuba kernelas an effective catalyst was prepared through reduction of Ag+ions using Tilia platyphyllos extractas the reducing and capping agent and Ag NPs immobilization...
متن کامل