Water as a catalytic switch in the oxidation of aryl alcohols by polymer incarcerated rhodium nanoparticles

Abstract

One of the major goals in the oxidation of organic substrates, and especially for alcohol oxidation, is the use of molecular oxygen as the oxidant under mild conditions. Here we report the synthesis and testing of Rh polymer incarcerated catalysts, using a metal so far not used for alcohol oxidation reactions, in which the catalytic activity towards aryl alcohol oxidation, for substrates like 1-phenylethanol and benzyl alcohol, is switched on by the addition of water as co-solvent in toluene. This is done by using air as oxidant at atmospheric pressure, in one of the mildest reaction conditions reported for this class of reaction. The promoting effect of water to higher conversions was observed also for rhodium over alumina supported catalysts, which were used as a benchmark allowing in all cases high conversion and selectivity to the ketone or the aldehyde within a short reaction time. The effect of water was explained as a medium capable to promote the oxidation of the alcohol to the ketone in a biphasic system assisted by phase transfer catalysis. This is particularly relevant for alcohols like 1-phenylethanol or benzyl alcohol that are not soluble in water at room temperature, and for which alternative oxidation routes are needed, as well as to switch on the catalytic activity of metal nanoparticles in a facile and green manner for the activation of molecular oxygen. Aliphatic alcohols like 1-octanol and 3-octanol were also tested, still showing Rh based catalysts as promising materials for this reaction if toluene only was used as solvent instead.2

Sensing aromatic pollutants in water with catalyst-sensitized water-gated transistor

“…This will require detailed consideration of specific reactive pathways though, note e.g. the breakdown of phenol is by peroxide decomposition while oxidation of alcohols like benzyl alcohol is via hydrogen abstraction (Weston et al 2017). Potentiometric response signals surface adsorption only, without distinguishing later reactive pathways, and can only be applied for substrates with a 'free' dipole.…”

Liquid Phase, Aerobic Oxidation of Benzyl Alcohol over the Catalyst System (Pt/TiO2+H2O)

“…Understanding the role of water in the oxidation of organic substrates is particularly important given that water is also a product in these reactions. Interestingly, water has been reported to enhance the catalytic activity in alcohol oxidation . Here, we explore the role of water on the oxidation of benzyl alcohol over Pt/TiO 2 .…”

“…An ideal solvent should facilitate contact between the reagents, in addition to being inherently safe to handle, eco‐friendly, readily available and cheap. Hence, water is considered as an ideal green solvent …”

“…The addition of water to the reaction mixture may results in gain in activity beyond that expected from a solvent‐effect and is even observed when water does not solubilize the substrate completely . Multiple effects have been invoked to rationalize this effect, i. e. the concentration of organic substrate in micro‐droplets, the extraction of products and/or intermediates, or water as a catalyst, acting as a Lewis base or Brønsted acid, or affecting the adsorption behavior of substrates on the catalyst surface . Understanding the role of water in the oxidation of organic substrates is particularly important given that water is also a product in these reactions.…”

Investigation of Polymer-Filler Interactions Using Functionalized Nanoparticles

“…x/ mol% X Bd St X Mn / 10 4-16) was also used as comonomer for later O-etherification. [107,131] The advantage of this approach is, that the copolymer can be functionalized with a variety of anchor groups. Terpolymerizations were conducted with a constant ratio of butadiene under variation of the styrene-to-comonomer ratio.…”