Direct vs Indirect Grafting of Alkyl and Aryl Halides

Abstract

The direct and indirect electrochemical grafting of alkyl and aryl halides (RX, ArX) on carbon, metal and polymer surfaces is examined. Their electrochemical reduction occurs at highly negative potential in organic solvents and very often produces carbanions because the reduction potentials of RX and ArX are more negative than those of their corresponding radicals. Therefore, direct electrografting of alkyl and aryl radicals generated from RX and ArX is not easy to perform. This obstacle is overcome using aryl radicals derived from the 2,6-dimethylbenzenediazonium salt (2,6-DMBD), which do not react on the electrode surface due to their steric hindrance but react in solution by abstracting an iodine or bromine atom from RX (X=I, Br) or ArI to give alkyl or aryl radicals. As a consequence, alkyl and aryl radicals are generated at very low driving force by diverting the reactivity of aryl radicals derived from an aryl diazonium salt; they attack the electrode surface and form strongly attached organic layers. This strategy applies to the chemical modification of polymers (polyethylene, polymethylmethacrylate) by alkyl halides under heating.

Designing Molecularly Imprinted Polymer-Modified Boron-Doped Diamond Electrodes for Highly Selective Electrochemical Drug Sensors

“…When an electron is injected into the linker molecule, the C–halogen bond is cleaved, and the corresponding alkyl or aryl radical is formed. Of the halogen atoms, the iodides are the most easily reduced, followed by the bromides and chlorides . Additionally, the molecule requires an amide structure to evaluate the linker modification using XPS and an acryl group to polymerize the monomers onto the electrode via the linker molecule.…”

“… During the first cycle of CV in the solution of N -(4-iodophenyl)­acrylamide in acetonitrile, the reduction current peak is observed at approximately −1.20 V (vs Ag/AgCl). This peak is due to the formation of aryl radicals and their anchorage onto the electrode substrate. , Approximately 100 scans of CV are required for complete attachment of the aryl iodides to the electrode surface, and the modification of the molecular linker layer should progress, based on the decrease in the reduction current peak according to the number of CV scans. Thus, in this study, electrochemical modification may proceed via the cleavage of the C–I bond in a concerted one-electron reaction, the formation of dangling bonds on the electrode, and covalent bonding between the linker molecules and the BDD electrode.…”

“…Of the halogen atoms, the iodides are the most easily reduced, followed by the bromides and chlorides. 32 Additionally, the molecule requires an amide structure to evaluate the linker modification using XPS and an acryl group to polymerize the monomers onto the electrode via the linker molecule. Therefore, N-(4iodophenyl)acrylamide may be adequate as a linker molecule, which may be electrochemically grafted onto the electrode surface and contribute to MIP polymerization.…”

Amine-Functionalized Diamond Electrode for Boosting CO2 Reduction to CO

“…A widely applied method is electrografting of an aryl diazonium salt 22 or aryl halide. 23 In this method, an aryl diazonium salt or aryl halide is electrochemically reduced to afford an aryl radical followed by covalent immobilization onto the electrode surface, which completes in a short reaction time and does not require an inert atmosphere. 24 We have previously reported the surface functionalization of BDD electrodes by the electrochemical method: highly sensitive detection of influenza viruses utilizing the molecular layer of the sialic acid-mimic peptide 25 and the controlled molecular decoration simply by tuning the reaction conditions.…”

“…For carbon electrodes, functional molecules can be modified via formation of C–C bonds. A widely applied method is electrografting of an aryl diazonium salt or aryl halide . In this method, an aryl diazonium salt or aryl halide is electrochemically reduced to afford an aryl radical followed by covalent immobilization onto the electrode surface, which completes in a short reaction time and does not require an inert atmosphere .…”