Roles of water for chemical reactions in high-temperature water

The marine environment has proven to be a very rich source of extremely potent compounds that have demonstrated significant activities in antitumor, antiinflammatory, analgesia, immunomodulation, allergy, and anti-viral assays. Although the case can and has been made that the nucleosides such as Ara-A and Ara-C are derived from knowledge gained from investigations of bioactive marine nucleosides, no drug directly from marine sources (whether isolated or by total synthesis) has yet made it to the commercial sector in any disease. However, as shown in this review, there are now significant numbers of very interesting molecules that have come from marine sources, or have been synthesized as a result of knowledge gained from a prototypical compound, that are either in or approaching Phase II/III clinical trials in cancer, analgesia, allergy, and cognitive diseases. A substantial number of other potential agents are following in their wake in preclinical trials in these and in other diseases.

Marine Natural Products and Related Compounds in Clinical and Advanced Preclinical Trials

Supercritical water oxidation (SCWO) technology presents important environmental advantages for the treatment of industrial wastes and sludges. The homogeneous reaction that takes place between the oxidizable materials and oxygen, at temperatures and pressures above the critical point of the water (647.3 K and 22.12 MPa), is well known. Specific equations of state for water and aqueous mixtures, gases, and organics have been developed. The process is not having the expected industrial development. Some new plants have been closed by corrosion and operational problems related with high temperature, high pressure, and oxidative atmosphere inside of the equipments. To overcome these technical difficulties more research focused on solving operational problems is necessary. This article presents an overview of the technical aspects of the supercritical water oxidation process. Reactors design, construction materials, corrosion, salts precipitation problems, and industrial applications are discussed. © 2006 American Institute of Chemical Engineers AIChE J, 2006

Supercritical water oxidation: A technical review

Over the last 15 years electron transfer activation has emerged as a valuable concept for accomplishing novel reactions and has found widespread application in the selective transformation of increasingly complex molecules. This review presents in a conceptualized manner the vast number of radical cation reactions obtained after chemical, electrochemical, and photoinduced one-electron oxidation. To familiarize the reader with the concepts of electron transfer a simple and straightforward classification of radical cation reactions has been devised to allow the presentation of a manifold of reactions in a readily understandable manner. Whenever possible, thermochemical and kinetic data are provided.

Understanding Reactivity Patterns of Radical Cations

Hot compressed water (HCW, here water above 200 °C) owns interesting properties The impact of the unique properties is discussed exemplary for the thermal degradation of tert-butylbenzene and the oxidation of methanol Both reactions have been conducted not only in HCW but also in other high-pressure media and from the comparison the impact of the special properties of HCW can be settled In addition the degradation of glycerol, a model substance for carbohydrates and biomass in HCW was studied This reaction shows a strong dependence on the properties of HCW The examples picture an increased specific impact of HCW with rising polarity of the reactants and intermediates The studies also points to higher importance of microscopic properties for understanding reactions in HCW than assumed in the past

Hot compressed water as reaction medium and reactant. 2. Degradation reactions

An interesting and intriguing aspect of supercritical fluid solutions is their microscopic inhomogeneities. The most well-known of these are the long-range densities fluctuations that occur in a pure fluid at conditions close to the critical point. However, there are also short-range inhomogeneities around dissolved solutes in supercritical fluids, which are frequently referred to as local density augmentation and local composition enhancements. Many questions have arisen about the potential influences that short-range solvation and long-range density fluctuations might have on complex chemical reaction schemes. In attempts to answer these questions, researchers have sought to study the effect of supercritical fluid solvents on simple unimolecular and bimolecular reactions. In doing so, the reactions themselves have become probes of the molecular structure and the influence of solvation on reactivity in supercritical fluids (SCFs). In this paper, the authors attempt to review those studies that involve simple reactions as probes of molecular structure and its effect on reactivity in SCFs. The paper discusses (1) the potential ways for solvation in supercritical fluids to affect reactivity and (2) the reactions that probe solvation in supercritical fluids, including diffusion-controlled reactions, kinetically-controlled reactions, equilibrium reactions, SCF solvent cage effects, and other important reactions and directions.

Homogeneous Organic Reactions as Mechanistic Probes in Supercritical Fluids.

Dichlorocarbene is the cornerstone of singlet carbene reactivity. Moss has thoroughly characterized carbenic selectivity in cyclopropanation reactions. The reactivity of any singlet carbene (:CXY) may be standardized by comparison of its reactivity toward a standard set of alkenes with that of chlorocarbene (:CCl{sub 2}). Amazingly, however, the absolute kinetics of this important reactive intermediate have not been measured to date. This is primarily due to the lack of a suitable photolabile precursor. Herein, they report a clean photolytic source of :CCl{sub 2} and the first absolute rate constants for reaction of :CCl{sub 2} with olefins in solution.

Absolute kinetics of dichlorocarbene in solution

We describe here the design of self-destructive electron acceptors, radical anions of which undergo rapid fragmentation on the micro- to nanosecond time scale, yielding PET systems with quantum yields approaching unity

Design of self-destructive electron acceptors. Highly efficient cleavage of C-C bonds in photogenerated radical anions

Laser flash photolysis of the hydrogen abstraction reaction of triplet benzophenone ({sup 3}BP) from 2-propanol and 1,4-cyclohexadiene in supercritical ethane and fluoroform was investigated. Bimolecular rate constants based on bulk concentrations decrease with an increase in pressure along both isotherms studied. These results corroborate previous studies in CO{sub 2} that show increased reaction rates due to enhanced local compositions of cosolvent around the {sup 3}BP solute. Analysis of the results includes prediction of the thermodynamic pressure effect on the rate constant, which suggests an increase in the rate constant with pressure, as well as the effects of increased local cosolvent concentrations about {sup 3}BP. Spectroscopic measurements of the local composition of 2-propanol about a solute in supercritical CO{sub 2} are used to explain the apparent discrepancy between experiment and prediction, providing reasonable evidence that the local environment can influence kinetically controlled reactions in supercritical fluids.

Solvation effects on reactions of triplet benzophenone in supercritical fluids

Kinetic Evidence for Chlorine Atom Complexes in "Noncomplexing" Solvents.

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