Spatio-temporal detachment of homogeneous electron transfer in controlling selectivity in mediated organic electrosynthesis.

In electrosynthesis, electron transfer (ET) mediators are normally chosen such that they are more easily reduced (or oxidised) than the substrate for cathodic (or anodic) processes; setting the electrode potential to the mediator therefore ensures selective heterogeneous ET with the mediator at the electrode, rather than the substrate. The current work investigates the opposite, and counter intuitive, situation for a successful mediated electroreductive process where the mediator (phenanthrene) has a reduction potential that is negative to that of the substrate, and the cathode potential is set negative to both ( < M < ). Simulations reveal a complex interplay between mass transport, the relative concentrations of the mediator and substrate as well as the heterogeneous and homogeneous rate constants for multiple steps, which under suitable conditions, leads to separation of the homogeneous chemistry in a reaction layer detached from the electrode.

Cathodic Radical Cyclisation of Aryl Halides Using a Strongly-Reducing Catalytic Mediator in Flow.

Electro-reductive radical cyclisation of aryl halides affords the corresponding hetero- and carbo-cycles in an undivided flow reactor equipped with steel and carbon electrodes using an organic mediator. A dissolving metal anode is not needed, and the mediator can be employed in a sub-stoichiometric amount (0.05 equiv), increasing the practical utility of cathodic radical cyclisation.

Cubane Electrochemistry: Direct Conversion of Cubane Carboxylic Acids to Alkoxy Cubanes Using the Hofer-Moest Reaction under Flow Conditions.

The highly strained cubane system is of great interest as a scaffold and rigid linker in both pharmaceutical and materials chemistry. The first electrochemical functionalisation of cubane by oxidative decarboxylative ether formation (Hofer-Moest reaction) was demonstrated. The mild conditions are compatible with the presence of other oxidisable functional groups, and the use of flow electrochemical conditions allows straightforward upscaling.

Flow Electrolysis Cells for the Synthetic Organic Chemistry Laboratory.

Electrosynthesis has much to offer to the synthetic organic chemist. But in order to be widely accepted as a routine procedure in an organic synthesis laboratory, electrosynthesis needs to be presented in a much more user-friendly way. The literature is largely based on electrolysis in a glass beaker or H-cells that often give poor performance for synthesis with a very slow rate of conversion and, often, low selectivity and reproducibility.

Electrochemical Deprotection of para-Methoxybenzyl Ethers in a Flow Electrolysis Cell.

Electrochemical deprotection of p-methoxybenzyl (PMB) ethers was performed in an undivided electrochemical flow reactor in MeOH solution, leading to the unmasked alcohol and p-methoxybenzaldehyde dimethyl acetal as a byproduct. The electrochemical method removes the need for chemical oxidants, and added electrolyte (BFNEt) can be recovered and reused. The method was applied to 17 substrates with high conversions in a single pass, yields up to 92%, and up to 7.

N-Heterocyclic Carbene-Mediated Microfluidic Oxidative Electrosynthesis of Amides from Aldehydes.

A flow process for N-Heterocyclic Carbene (NHC)-mediated anodic oxidative amidation of aldehydes is described, employing an undivided microfluidic electrolysis cell to oxidize Breslow intermediates. After electrochemical oxidation, the reaction of the intermediate N-acylated thiazolium cation with primary amines is completed by passage through a heating cell to achieve high conversion in a single pass. The flow mixing regimen circumvented the issue of competing imine formation between the aldehyde and amine substrates, which otherwise prevented formation of the desired product.

N-Heterocyclic Carbene-Mediated Oxidative Electrosynthesis of Esters in a Microflow Cell.

An efficient N-heterocyclic carbene (NHC)-mediated oxidative esterification of aldehydes has been achieved in an undivided microfluidic electrolysis cell at ambient temperature. Productivities of up to 4.3 g h(-1) in a single pass are demonstrated, with excellent yields and conversions for 19 examples presented.

TEMPO-mediated electrooxidation of primary and secondary alcohols in a microfluidic electrolytic cell.

A general procedure for the 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-mediated electrooxidation of primary and secondary alcohols modified for application in a microfluidic electrolytic cell is described. The electrocatalytic system utilises a buffered aqueous tert-butanol reaction medium, which operates effectively without the requirement for additional electrolyte, providing a mild protocol for the oxidation of alcohols to aldehydes and ketones at ambient temperature on a laboratory scale. Optimisation of the process is discussed along with the oxidation of 15 representative alcohols.

Electrodeposited lead dioxide coatings.

Lead dioxide coatings on inert substrates such as titanium and carbon now offer new opportunities for a material known for 150 years. It is now recognised that electrodeposition allows the preparation of stable coatings with different phase structures and a wide range of surface morphologies. In addition, substantial modification to the physical properties and catalytic activities of the coatings are possible through doping and the fabrication of nanostructured deposits or composites.

Nickel based electrocatalysts for oxygen evolution in high current density, alkaline water electrolysers.

A number of nickel based materials are investigated as potential oxygen evolution catalysts under conditions close to those met in modern, high current density alkaline water electrolysers. Microelectrodes are used to avoid distortion of voltammetric data by IR drop even at the high current densities employed in such water electrolysers. High surface area nickel metal oxides prepared by cathodic deposition and mixed oxides prepared by thermal methods are considered.

The influence of support and particle size on the platinum catalysed oxygen reduction reaction.

A range of platinum deposits, equivalent thicknesses (delta) 0.2-2.5 nm, have been synthesised on carbon and reduced titania (TiO(x)) supports using physical vapour deposition on (10 x 10) arrays of electrodes.

The influence of Pt particle size on the surface oxidation of titania supported platinum.

A range of reduced titania (TiO(x)) supported platinum electrocatalysts have been synthesised using physical vapour deposition on arrays of electrodes. Surfaces with equivalent thicknesses of platinum in the range 0.2-2.

Combinatorial approach to the study of particle size effects in electrocatalysis: synthesis of supported gold nanoparticles.

A high-throughput method for physical vapor deposition has been applied to the synthesis of libraries of supported gold particles on amorphous substoichiometric TiO(x)() and carbon supports. The TiO(x)() substrate stoichiometry can be varied or kept constant across a supporting sample, and subsequent deposition of particle sizes on supports are controlled through the nucleation and growth process. TEM measurements indicate nucleation and growth of Au particles takes place, with the smallest particles initially observed at 1.

A combinatorial approach to the study of particle size effects on supported electrocatalysts: oxygen reduction on gold.

A novel high-throughput technique has been developed for the investigation of the influence of supported metal particle size and the support on electrocatalytic activity. Arrays with a gradation of catalyst particle sizes are fabricated in a physical vapor deposition system that also allows selection of the support material. Simultaneous electrochemical measurements at all electrodes in the array, together with determination of the actual particle size distribution on each of the electrodes by transmission electron microscopy (TEM), then allows rapid determination of the activity as a function of catalyst center size.

Mesoporous palladium-the surface electrochemistry of palladium in aqueous sodium hydroxide and the cathodic reduction of nitrite.

The voltammetry of nanostructured palladium layers electrodeposited from a hexagonal liquid crystal phase onto platinum microdiscs show well defined peaks for the adsorption/desorption of hydrogen and surface oxidation/reduction in 2 M NaOH. These peaks are more clearly resolved than at smooth palladium and reveal the complications associated with hydrogen adsorption/desorption on palladium in aqueous alkaline solutions. The reduction of nitrite at the nanostructured palladium is also reported and it is shown that it occurs via a mechanism involving a chemical reaction between adsorbed hydrogen and adsorbed nitrite ion.