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.

/pdf/aerobic-copper-catalyzed-organic-reactions-3ctljpvivz.pdf

Aerobic Copper-Catalyzed Organic Reactions

Low dielectric constant polymers for microelectronics

A lattice model for dense polymer solutions and polymer mixtures in three dimensions is presented, aiming to develop a model suitable for efficient computer simulation on vector processors, with a qualitatively realistic local dynamics. It is shown that the bond fluctuation algorithm for a suitable set of allowed bond vectors has the property that due to the excluded volume constraint no crossing of bonds by local motions can occur, and entanglement restrictions thus are fully taken into account. For athermal binary (AB) symmetrical polymer mixtures, the dependence of both self‐diffusion coefficient and interdiffusion coefficient on polymer density is obtained, simulating a thin film geometry where a film of polymer A is coated with a film of polymer B. For one density, the dependence of the interdiffusion coefficient on an attractive energy between unlike monomers is also studied. For weak attraction an enhancement of interdiffusion proportional to this energy occurs. For strong attraction, however, a rather immobile tightly bound AB layer forms in the interface which hampers further unmixing.

Interdiffusion and self‐diffusion in polymer mixtures: A Monte Carlo study

A brief analysis is presnted of the current understanding of substituent perturbations in monosubstituted benzenes as determined by substituent induced carbon chemical shifts. A critical tabulation of the four substituent chemical shifts is given for c. 700 monosubstituted benzenes.

13C substituent effects in monosubstituted benzenes

Partial table of contents: Introduction, Theory, and Methods. 13C NMR Spectral Characteristics. Aliphatic Compounds. Aromatics. Organic Functional Groups. Ions, Radicals, and Complexes. Polymers. Relaxation Studies. Biomolecules. Special Techniques and Applications. Appendix. Index.

https://science.sciencemag.org/content/sci/180/4082/141.full.pdf

Carbon-13 nuclear magnetic resonance spectroscopy

We have used forward recoil spectrometry to measure the mutual diffusion and tracer diffusion coefficients, D and D*, in the miscible polymer blend of deuterated polystyrene (d-PS):poly(xylenyl ether) (PXE). Using the “fast theory” of mutual diffusion, D is related to the D*, degree of polymerization N, and volume fraction φ of the individual blend components by, D = 2 φ (1-φ) [D* PS N PS + φD* PXE N PXE ](χ S -χ), where χ and χs are tne Flory interaction parameter of the blend and its value at the spinodal. From the measured values of the D*’s and D at a volume fraction φ=0.55 of d-PS, the interaction parameter χ=0.112-62/T was estimated as a function of temperature T(K). At low T, D was much larger than D*’s due to the large negative value of χ whereas at high T, D becomes less than the D*’s as χ becomes positive (thermodynamic slowing down). Similar measurements show that χ is not markedly composition-dependent in the d-PS:PXE blends.

Mutual diffusion in the miscible polymer blend: polystyrene:poly (xylenyl ether)

Etude par spectroscopie de recul avant pour le systeme miscible polystyrene+poly(dimethyl-2,6 phenyleneoxyde-1,4)

Fast mutual diffusion in polymer blends

Temperature dependence of neutron scattering behavior and resultant thermodynamics of mixing of poly(2,6-dimethyl-1,4-phenylene oxide) in polystyrene

The tracer diffusion coefficient D* of small concentrations of tagged linear polymers seems well understood on the basis of the reptation model1–6, but the mutual diffusion coefficient D which characterizes diffusion at higher concentrations remains controversial7–17. Such diffusion is important in blends of miscible, yet chemically dissimilar, polymers where it controls the kinetics of phase separation and the welding of polymer interfaces. The controversy centres on predicting D from the D*s of the components of the blend. While the 'slow theory'7,8 predicts that D is controlled by the diffusion of the slower-moving component, 'fast theory'9,10 says it is controlled by the diffusion of the faster-moving one. Here we report experiments in which we measure the mutual diffusion coefficient as we increase the tracer diffusion coefficient of the faster-moving component in the blend by decreasing its molecular weight. The strong increase in D we observe demonstrates that the 'fast theory' prediction is correct.

Fast macromolecules control mutual diffusion in polymer blends

Reptation in polymer blends

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