Heterogenization of Ketone Catalyst for Epoxidation by Low Pressure Plasma Fluorination of Silica Gel Supports.

Lucia D'Accolti,Nicoletta De Vietro,Francesco Fracassi,Angelo Nacci,Fiorenza Fanelli,Caterina Fusco

doi:10.3390/molecules22122099

Abstract

Low pressure plasma was used for preparing heterogeneous organocatalysts 2-(A)-(C) suitable for dioxirane-mediated epoxidations. Heterogenization was accomplished by adsorption of the methyl perfluoroheptyl ketone (2) on fluorinated supports (A)-(C) deriving from the treatment of commercial C8-silica gel in low pressure plasma fed with fluorocarbons. Catalyst 2-(C) proved to be the most efficient one, promoting epoxidation of an array of alkenes, including unsaturated fatty esters like methyl oleate (10) and the triglyceride soybean oil (11), with the cheap potassium peroxymonosulfate KHSO5 (caroate) as a green oxidant. Notably, the perfluorinated matrix gives rise to the activation of caroate, generating singlet oxygen. Materials were characterized by infrared Attenuated Total Reflectance spectroscopy (ATR-FTIR), X-ray Photoelectron Spectroscopy (XPS ) and Emission Scanning Electron Microscope (FESEM).

Highlights

Fluorous chemistry is a well-known methodology that involves the use of perfluorinated solvents and/or perfluorinated reagents to facilitate catalyst or reaction products recovery [1]
Well-known benefits of this strategy can be found into the increased reaction rates of alkene epoxidation with H2 O2 performed into perfluoroalcohols (e.g., 2,2,2-trifluoroethanol or 1,1,1,3,3,3hexafluoro-2-propanol, HFIP) [2], or with perfluorinated ketones/caroate [3]
Representative examples are given by perfluoro-tagged gold nanoparticles immobilized on Fluorous Silica Gel (FSG) as suitable catalysts for oxidation of alkenes with H2 O2 [7], or immobilized fluorinated flavins useful for promoting the photocatalytic oxidation of benzyl alcohols [8]

Summary

Introduction

Fluorous chemistry is a well-known methodology that involves the use of perfluorinated solvents and/or perfluorinated reagents to facilitate catalyst or reaction products recovery [1]. Conventional organic reagents incorporating perfluorinated tags can react in fluorous solvents (e.g., perfluorohexane) and are extracted into organic phases, or can be supported on fluorous solid matrixes behaving as heterogeneous reactants or catalysts [1,2]. The use of perfluorinated solvent suffers from the limitation of the prohibitive costs for large-scale applications. To overcome this drawback, Fluorous Silica Gel (FSG) systems, that can be used directly as a catalyst [4], or as solid supports to heterogenize perfluorinated catalytic species by means of fluorous interactions [5,6] are most useful. Representative examples are given by perfluoro-tagged gold nanoparticles immobilized on FSG as suitable catalysts for oxidation of alkenes with H2 O2 [7], or immobilized fluorinated flavins useful for promoting the photocatalytic oxidation of benzyl alcohols [8]

Methods

Discussion

Conclusion