The chemistry of copper is extremely rich because it can easily access Cu0, CuI, CuII, and CuIII oxidation states allowing it to act through one-electron or two-electron processes. As a result, both radical pathways and powerful two-electron bond forming pathways via organmetallic intermediates, similar to those of palladium, can occur. In addition, the different oxidation states of copper associate well with a large number of different functional groups via Lewis acid interactions or π-coordination. In total, these feature confer a remarkably broad range of activities allowing copper to catalyze the oxidation and oxidative union of many substrates.

Oxygen is a highly atom economical, environmentally benign, and abundant oxidant, which makes it ideal in many ways.1 The high activation energies in the reactions of oxygen require that catalysts be employed.2 In combination with molecular oxygen, the chemistry of copper catalysis increases exponentially since oxygen can act as either a sink for electrons (oxidase activity) and/or as a source of oxygen atoms that are incorporated into the product (oxygenase activity). The oxidation of copper with oxygen is a facile process allowing catalytic turnover in net oxidative processes and ready access to the higher CuIII oxidation state, which enables a range of powerful transformations including two-electron reductive elimination to CuI. Molecular oxygen is also not hampered by toxic byproducts, being either reduced to water, occasionally via H2O2 (oxidase activity) or incorporated into the target structure with high atom economy (oxygenase activity). Such oxidations using oxygen or air (21% oxygen) have been employed safely in numerous commodity chemical continuous and batch processes.3

However, batch reactors employing volatile hydrocarbon solvents require that oxygen concentrations be kept low in the head space (typically <5–11%) to avoid flammable mixtures, which can limit the oxygen concentration in the reaction mixture.4,5,6 A number of alternate approaches have been developed allowing oxidation chemistry to be used safely across a broader array of conditions. For example, use of carbon dioxide instead of nitrogen as a diluent leads to reduced flammability.5 Alternately, water can be added to moderate the flammability allowing even pure oxygen to be employed.6 New reactor designs also allow pure oxygen to be used instead of diluted oxygen by maintaining gas bubbles in the solvent, which greatly improves reaction rates and prevents the build up of higher concentrations of oxygen in the head space.4a,7 Supercritical carbon dioxide has been found to be advantageous as a solvent due its chemical inertness towards oxidizing agents and its complete miscibility with oxygen or air over a wide range of temperatures.8 An number of flow technologies9 including flow reactors,10 capillary flow reactors,11 microchannel/microstructure structure reactors,12 and membrane reactors13 limit the amount of or afford separation of hydrocarbon/oxygen vapor phase thereby reducing the potential for explosions.

Enzymatic oxidizing systems based upon copper that exploit the many advantages and unique aspects of copper as a catalyst and oxygen as an oxidant as described in the preceding paragraphs are well known. They represent a powerful set of catalysts able to direct beautiful redox chemistry in a highly site-selective and stereoselective manner on simple as well as highly functionalized molecules. This ability has inspired organic chemists to discover small molecule catalysts that can emulate such processes. In addition, copper has been recognized as a powerful catalyst in several industrial processes (e.g. phenol polymerization, Glaser-Hay alkyne coupling) stimulating the study of the fundamental reaction steps and the organometallic copper intermediates. These studies have inspiried the development of nonenzymatic copper catalysts. For these reasons, the study of copper catalysis using molecular oxygen has undergone explosive growth, from 30 citations per year in the 1980s to over 300 citations per year in the 2000s.

A number of elegant reviews on the subject of catalytic copper oxidation chemistry have appeared. Most recently, reviews provide selected coverage of copper catalysts14 or a discussion of their use in the aerobic functionalization of C–H bonds.15 Other recent reviews cover copper and other metal catalysts with a range of oxidants, including oxygen, but several reaction types are not covered.16 Several other works provide a valuable overview of earlier efforts in the field.17 This review comprehensively covers copper catalyzed oxidation chemistry using oxygen as the oxidant up through 2011. Stoichiometric reactions with copper are discussed, as necessary, to put the development of the catalytic processes in context. Mixed metal systems utilizing copper, such as palladium catalyzed Wacker processes, are not included here. Decomposition reactions involving copper/oxygen and model systems of copper enzymes are not discussed exhaustively. To facilitate analysis of the reactions under discussion, the current mechanistic hypothesis is provided for each reaction. As our understanding of the basic chemical steps involving copper improve, it is expected that many of these mechanisms will evolve accordingly.

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Aerobic Copper-Catalyzed Organic Reactions

The coordination chemistry of pyrazole-derived ligands

The three-dimensional structure of plastocyanin, a ‘blue’ or ‘Type 1’ copper-protein, has been determined at a resolution of 2.7 A. The copper atom has a highly distorted tetrahedral coordination geometry. It is coordinated by a cysteine thiol group, a methionine thioether group, and two histidine imidazole groups.

X-ray crystal structure analysis of plastocyanin at 2.7 Å resolution

Sensors and switches from supramolecular chemistry

Spectrometric Identification of Organic Compounds

Synthesis and characterization of Schiff bases from chitosan and salicylaldehyde derivatives

Synthesis, characterization, and spectroscopic studies of tetradentate Schiff base chromium(III) complexes

Chitosan is a linear polysaccharide obtained from the deacetylation of chitin. The physico-chemical properties of chitosan dependent on the average degree of acetylation () and of the average molar mass (). Several applications of chitosan have been proposed in the literature, mainly in water treatment, cosmetic and drug manufacturing, food additives, semipermeable membranes and development of biomaterials. In this work, three commercial chitosan samples were characterized by proton nuclear magnetic resonance (1H NMR), infrared spectroscopy (IR), conductimetric titration and thermal analysis (TG and DSC) in order to compare commercial chitosans from different supplies. The average viscosimetric molecular weight Mv was estimated from the intrinsic viscosity. The results confirmed remarkable differences in relation to the mean degree of acetylation () (or desacetylation, ). The thermal analysis data permitted to follow the dehydration, decomposition, and glass transition temperature (Tg).

/pdf/caracterizacao-de-quitosanas-comerciais-de-diferentes-27gtjemp88.pdf

Caracterização de quitosanas comerciais de diferentes origens

Letter: Redox properties of copper-thiaether complexes. Comparison to blue copper protein behavior.

An oxovanadium-salen complex (N,N � -ethylene-bis(salicylideneiminato) oxovanadium) thin film deposited on a graphite–polyurethane electrode was investigated with regard to its potential use for detection of l-dopa in flow injection system. The oxovanadium(IV)/oxovanadium(V) redox couple of the modified electrode was found to mediate the l-dopa oxidation before its use in the FIA system. Experimental parameters, such as pH of the carrier solution, flow rate, sample volume injection and probable interferents were investigated. Under the optimized FIA conditions, the amperometric signal was linearly dependent on the l-dopa concentration over the range 1.0 × 10 −6 to 1.0 × 10 −4 mol L −1 (Ianodic A) = 0.01 + 0.25 [l-dopamol L −1 ]) with a detection limit (S/N = 3) of 8.0 × 10 −7 mol L −1 and a sampling frequency of 90 h −1 was achieved. For a concentration of 1.0 × 10 −5 mol L −1 l-dopa, the R.S.D. of nine consecutive measurements was 3.7%.

Edward R. Dockal

Papers

Synthesis and characterization of Schiff bases from chitosan and salicylaldehyde derivatives

Synthesis, characterization, and spectroscopic studies of tetradentate Schiff base chromium(III) complexes

Caracterização de quitosanas comerciais de diferentes origens

Letter: Redox properties of copper-thiaether complexes. Comparison to blue copper protein behavior.

An electrochemical sensor for l-dopa based on oxovanadium-salen thin film electrode applied flow injection system