Green Regio- and Enantioselective Aminolysis Catalyzed by Graphite and Graphene Oxide under Solvent-Free Conditions

The graphite-catalyzed ipso-functionalization of arylboronic acids in an aqueous medium: metal-free access to phenols, anilines, nitroarenes, and haloarenes

An efficient, metal-free, and sustainable strategy has been described for the ipso-functionalization of phenylboronic acids using air as an oxidant in an aqueous medium. A range of carbon materials has been tested as carbocatalysts. To our surprise, graphite was found to be the best catalyst in terms of the turnover frequency. A broad range of valuable substituted aromatic compounds, i.e., phenols, anilines, nitroarenes, and haloarenes, has been prepared via the functionalization of the C-B bond into C-N, C-O, and many other C-X bonds. The vital role of the aromatic π-conjugation system of graphite in this protocol has been established and was observed via numerous analytic techniques. The heterogeneous nature of graphite facilitates the high recyclability of the carbocatalyst. This effective and easy system provides a multipurpose approach for the production of valuable substituted aromatic compounds without using any metals, ligands, bases, or harsh oxidants.

Allylic and Allenylic Dearomatization of Indoles Promoted by Graphene Oxide by Covalent Grafting Activation Mode

The site-selective allylative and allenylative dearomatization of indoles with alcohols was performed under carbocatalytic regime in the presence of graphene oxide (GO, 10 wt % loading) as the promoter. Metal-free conditions, absence of stoichiometric additive, environmentally friendly conditions (H₂ O/CH₃ CN, 55 °C, 6 h), broad substrate scope (33 examples, yield up to 92 %) and excellent site- and stereoselectivity characterize the present methodology. Moreover, a covalent activation model exerted by GO functionalities was corroborated by spectroscopic, experimental and computational evidences. Recovering and regeneration of the GO catalyst through simple acidic treatment was also documented.

Bio-reduction of Graphene Oxide: Catalytic Applications of (Reduced) GO in Organic Synthesis

This work is based on various bio-reduction of graphene oxide into reduced graphene oxide and their applications in organic synthesis and group transformations. Graphene oxide, with abundant oxygencontaining functional groups on its basal plane, provides potential advantages, including excellent dispersibility in solvents and the good heterogeneous catalyst. This manuscript reviews various methods of synthesis of graphene and graphene oxide and a comparative study on their advantages and disadvantages, how to overcome disadvantages and covers extensive relevant literature review. In the last few years, investigation based on replacing the chemical reduction methods by some bio-compatible, chemical/impurity-free rGO including flash photo reductions, hydrothermal dehydration, solvothermal reduction, electrochemical approach, microwave-assisted reductions, light and radiation-induced reductions has been reported. Particularly, plant extracts have been applied significantly as an efficient reducing agent due to their huge bioavailability and low cost for bio-reduction of graphene oxide. These plant extracts mainly contain polyphenolic compounds, which readily get oxidized to the corresponding unreactive quinone form, which are the driving force for choosing them as bio-compatible catalyst. Currently, efforts are being made to develop biocompatible methods for the reduction of graphene oxide. The reduction abilities of such phytochemicals have been reported in the synthesis and stabilization of various nanoparticles viz. Ag, Au, Fe and Pd. Various part of plant extract has been applied for the green reduction of graphene oxide. Furthermore, the manuscript describes the catalytic applications of graphene oxide and reduced graphene oxide nanosheets as efficient carbo-catalysts for valuable organic transformations. Herein, important works dedicated to exploring graphene-based materials as carbocatalysts, including GO and rGO for organic synthesis including various functional group transformations, oxidation, reduction, coupling reaction and a wide number of multicomponent reactions have been highlighted. Finally, the aim of this study is to provide an outlook on future trends and perspectives for graphene-based materials in metal-free carbo-catalysis in green synthesis of various pharmaceutically important moieties.

Highly regioselective ring-opening of epoxides with amines: a metal- and solvent-free protocol for the synthesis of β-amino alcohols

We herein report a metal- and solvent-free acetic acid-mediated ring-opening reaction of epoxides with amines. This process provides β-amino alcohols in high yields with excellent regioselectivity. Importantly, this epoxide ring-opening protocol can be used for the introduction of amines in natural products during late-stage transformations.

A Metal-Free Carbon-Based Catalyst: An Overview and Directions for Future Research

Metal-free carbon porous materials (CPMs) have gained the intensive attention of scientists and technologists because of their potential applications, ranging from catalysis to energy storage. Various simple and facile strategies are proposed for the preparation of CPMs with well-controlled sizes, shapes, and modifications on the surface. The extraordinary tenability of the pore structure, the environmental acceptability, the unique surface and the corrosion resistance properties allow them to be suitable materials for a large panel of catalysis applications. This review briefly outlines the different signs of progresses made towards synthesizing CPMs, and their properties, including catalytic efficiency, stability, and recyclability. Finally, we make a comparison of their catalytic performances with other nanocomposites, and we provide an outlook on the expected developments in the relevant research works.

Graphene Oxide Promotes Site-Selective Allylic Alkylation of Thiophenes with Alcohols

The graphene oxide (GO) assisted allylic alkylation of thiophenes with alcohols is presented. Mild reaction conditions and a low GO loading enabled the isolation of a range of densely functionalized thienyl and bithienyl compounds in moderate to high yields (up to 90%). The cooperative action of the Brønsted acidity, epoxide moieties, and π-surface of the 2D-promoter is highlighted as crucial in the reaction course of the present Friedel-Crafts-type protocol.

Oxidized Carbon Black as an Activator of Transesterification Reactions under Solvent-Free Conditions

A metal-free procedure for oxidation of carbon black (CB), under mild and ecofriendly conditions, is described. The procedure, based on 5/1 w/w H₂O₂/H₂SO₄, when applied to high-surface-area CB, leads to oxidation contents (O/C = 0.66) comparable to those obtained for graphite with the more aggressive and metal-based Hummers method (O/C 0.63). Oxidized nanocarbons are able to activate transesterification reactions under solvent-free conditions. Activation of transesterification reactions is much more effective by oxidized CB than by graphene oxide.

Catalytic Activity of Oxidized Carbon Black and Graphene Oxide for the Crosslinking of Epoxy Resins

This article compares the catalytic activities of oxidized carbon black (oCB) and graphene oxide (eGO) samples on the kinetics of a reaction of diglycidyl ether of bisphenol A (DGEBA) with a diamine, leading to crosslinked insoluble networks. The study is mainly conducted by rheometry and Differential Scanning Calorimetry (DSC). Following the same oxidation procedure, CB samples are more efficiently oxidized than graphite samples. For instance, CB and graphite samples with high specific surface areas (151 and 308 m²/g), as oxidized by the Hummers' method, exhibit O/C wt/wt ratios of 0.91 and 0.62, respectively. Due to the higher oxidation levels, these oCB samples exhibit a higher catalytic activity toward the curing of epoxy resins than fully exfoliated graphene oxide.

Recent advances in organic reactions catalyzed by graphene oxide and sulfonated graphene as heterogeneous nanocatalysts: a review

Over the past decade, the application of carbocatalyst systems has been preferred over that of homogeneous catalytic systems because of their advantages such as physical and thermal stability of the catalysts in successive reaction runs and reusability.