The scalable production of high-quality nanographite by organic radical-assisted electrochemical exfoliation.

One of the promising ways to produce graphene is the technology of graphite splitting or exfoliation, both by physical or mechanical and chemical, including electrochemical methods. The product of electro exfoliation is nanographite, which is transformed into multigraphene at the subsequent stage of liquid-phase mechanical and ultrasonic disintegration. This approach demonstrates a successful method of obtaining multigraphene from available graphite raw materials. Since, already at a potential of 1.23V, during the electrolysis of water on a graphite anode, the hydroxyl anion is discharged with the formation of a very active hydroxyl radical oxidizer, it is not surprising that when the graphite electro exfoliation process is overvolted at 10V, graphite oxidation products are formed. In order to control the defectiveness of the graphene lattice by oxidation products, we carried out processes of graphite exfoliation in the presence of both a number of reducing agents ascorbic acid, sodium borohydride, hydrazine hydrate, and in the presence of industrial antioxidants radical traps (2,2,6,6-tetramethylpiperidine-1-il)oxyl (TEMPO), (2,2,6,6-tetramethyl-4 oxo-piperidine-1-yl)oxyl (IPON), a mixture of 5,8,9-bis isomers[(2,2,6,6-tetramethyl - 4 oxo-piperidine-1-yl)]-{5,8,9-[1,1’- bi(cyclopentylidene)]-2,2’,4,4’- tetraene}(YARSIM-0215). It should be noted, that the best result of preventing the oxidation of nanographite in electro exfoliation technology in our studies is the ratio of carbon to oxygen (C/O) about 69.

Universal Chain-End Coupling Conditions for Brominated Polystyrenes, Polyacrylates, and Polymethacrylates

Atom transfer radical coupling (ATRC), performed with or without radical traps, has allowed for high extents of coupling (Xc) for a variety of brominated polymers, yet structurally different polymeric chain ends require unique reagents and reaction conditions. Inspired by a similar study that focused on universal conditions for the controlled polymerization of different monomers using atom transfer radical polymerization (ATRP), this work focuses on developing a single set of conditions (or conditions with as little variation as possible) that will achieve extents of coupling greater than 80% or end-brominated chains of polystyrene (PSBr), poly(methyl methacrylate) (PMMABr), and poly(methyl acrylate) (PMABr). The radical traps α-phenyl-tert-butylnitrone (PBN), 2-methyl-2-nitrosopropane (MNP), and nitrosobenzene (NBz) were chosen in this study, along with copper catalysts, reducing agents, and nitrogen-based ligands. Ultimately, a single set of effective reaction conditions was identified with the only difference being the radical trap used: MNP was effective for coupling PSBr and PMABr while NBz was necessary to achieve similarly high extents of coupling for PMMABr.

Sequential C–F bond functionalizations of trifluoroacetamides and acetates via spin-center shifts

Defluorinative functionalization of readily accessible trifluoromethyl groups constitutes an economical route to partially fluorinated molecules. However, controllable replacement of one or two fluorine atoms while maintaining high chemoselectivity remains a formidable challenge. Here we describe a general strategy for sequential C–F bond functionalizations of trifluoroacetamides and trifluoroacetates. The reaction begins with activation of a carbonyl oxygen atom by a 4-dimethylaminopyridine-boryl radical, followed by a spin-center shift to trigger the C–F bond scission. A chemoselectivity-controllable two-stage process enables sequential generation of difluoro- and monofluoroalkyl radicals, which are selectively functionalized with different radical traps to afford diverse fluorinated products. The reaction mechanism and the origin of chemoselectivity were established by experimental and computational approaches.

Oxidative Ring Expansion of Cyclobutanols: Access to Functionalized 1,2-Dioxanes

Cyclobutanols undergo an oxidative ring expansion into 1,2-dioxanols by using Co(acac)₂ and triplet oxygen (³O₂) as radical promoters. The formation of an alkoxy radical drives to the regioselective break of the strained ring with stabilization of a new radical on the most substituted side. The radical traps then oxygen to form 1,2-dioxanols. The reaction is particularly effective on secondary cyclobutanols but can work also on tertiary alcohols. Further acetylation generates peroxycarbenium species under catalytic Lewis acid conditions, which react with neutral nucleophiles. Many original 1,2-dioxanes, which would be difficult to prepare by another method, were then obtained with a preferred 3,6-<i>cis</i>-configuration. This method provides an interesting access to the total synthesis of many natural endoperoxides.

Oxidative Ring Expansion of Cyclobutanols: Access to Functionalized 1,2-Dioxanes

Cyclobutanols undergo an oxidative ring expansion into 1,2-dioxanols by using Co(acac)₂ and triplet oxygen (³O₂) as radical promoters. The formation of an alkoxy radical drives to the regioselective break of the strained ring with stabilization of a new radical on the most substituted side. The radical traps then oxygen to form 1,2-dioxanols. The reaction is particularly effective on secondary cyclobutanols but can work also on tertiary alcohols. Further acetylation generates peroxycarbenium species under catalytic Lewis acid conditions, which react with neutral nucleophiles. Many original 1,2-dioxanes, which would be difficult to prepare by another method, were then obtained with a preferred 3,6-<i>cis</i>-configuration. This method provides an interesting access to the total synthesis of many natural endoperoxides.

A General Approach to Deboronative Radical Chain Reaction with Pinacol Alkylboronic Esters

The generation of carbon-centered radicals from air-sensitive organoboron compounds via nucleohomolytic substitution at boron is one of the most general methods to generate non-functionalized and functionalized radicals. Due to their reduced Lewis acidity, the very popular, air-stable, and readily available alkylboronic pinacol esters are not suitable substrates for this process. Herein, is reported their <i>in situ</i> conversion to alkylboronic catechol esters by boron-transesterification with a substoichiometric amount of catechol methyl borate (MeO–Bcat) telescoped onto a wide array of radical chain processes. This simple one-pot, radical-chain, deboronative protocol allows for the conversion of pinacol boronic esters into iodides, bromides, chlorides, and thioethers. The process is also suitable the formation of nitriles and allylated compounds via C–C bond formation using sulfonyl radical traps. Finally, a particularly mild protocol for the protodeboronation of pinacol boronic esters is given. The power of combining radical and classical boron chemistry, is illustrated with a highly modular 5-membered ring formation using a combination of a three-component coupling reaction and a protodeboronative cyclization.

A General Approach to Deboronative Radical Chain Reaction with Pinacol Alkylboronic Esters

The generation of carbon-centered radicals from air-sensitive organoboron compounds via nucleohomolytic substitution at boron is one of the most general methods to generate non-functionalized and functionalized radicals. Due to their reduced Lewis acidity, the very popular, air-stable, and readily available alkylboronic pinacol esters are not suitable substrates for this process. Herein, is reported their <i>in situ</i> conversion to alkylboronic catechol esters by boron-transesterification with a substoichiometric amount of catechol methyl borate (MeO–Bcat) telescoped onto a wide array of radical chain processes. This simple one-pot, radical-chain, deboronative protocol allows for the conversion of pinacol boronic esters into iodides, bromides, chlorides, and thioethers. The process is also suitable the formation of nitriles and allylated compounds via C–C bond formation using sulfonyl radical traps. Finally, a particularly mild protocol for the protodeboronation of pinacol boronic esters is given. The power of combining radical and classical boron chemistry, is illustrated with a highly modular 5-membered ring formation using a combination of a three-component coupling reaction and a protodeboronative cyclization.

Synthesis and evaluation of new heteroaryl nitrones with spin trap properties

A new series of heteroaryl nitrones were synthesized and evaluated as free radical traps due to the results showed in our previous report.