Water as reaction medium

We have developed an efficient and practical method for clean oxidation of starch (21-23) resulting in the oxidation of primary alcohol function in Ce position and the cleavage of vicinal diols in C2 and C3 position (Figure 30.2). We used small amounts of cheap iron tetrasulfophthalocyanine catalyst, pure water as reaction medium and H2O2 as clean oxidant to achieve a one-pot conversion of starch resulting in the introduction of aldehyde and carboxyl functions in polymer chains. The iron content... 

There is significant interest in enzymes as they have proven to be powerful and environment-friendly natural catalysts for the polymerization of water-soluble monomers that can function under milder reaction conditions than those used in traditional free radical polymerization techniques. Hence, the combination of SCCO2 and water as reaction medium is a significant advancement made by Villarroya et al. 

Solvothermal process is now becoming a powerful technique for preparing nanomaterials. It is analogous to hydrothermal synthesis, except that non-aqueous solvents replace water as reaction medium. From the chemical reaction point of view, solvents in supercritical conditions play a significant role in reaction and crystallization. New materials, especially those having metastable phases and special nanostructures, can be obtained under mild conditions. By sealing the reaction system in an autoclave, the reactants and products prevent effectively from oxidation, hydrolysis and volatilization, and the reaction and crystallization can be realized synchronously. 

Water as Reaction Medium. Being transparent to the near-ultraviolet spectrum of sunlight, pure water can serve as an inert medium in which pesticide transformations take place. For example, Henderson and Crosby (28) have shown that suspensions of the chlorinated hydrocarbon insecticide dieldrin (I), although essentially insoluble in water, undergo a photocondensation reaction to give photodieldrin (II) (Equation 2). 

There are some drawbacks associated with this methodology. L-Proline is poorly soluble in many organic solvents and requires the use of polar organic solvents such as DMSO or DMF. Unfortunately the use of water as reaction medium results in the formation of racemates. Furthermore, relatively high catalyst loadings are... 

Kruse, A. and E. Dinjus. 2007. Hot compressed water as reaction medium and reactant— Properties and synthesis reactions. Journal of Supercritical Fluids. 39, 362. 

In 1931 Diels and Alder used water as reaction medium for the cycloaddition of furan and maleic anhydride. This work was revised in 1948 by Woodward and Baer and some years later by De Koning. ... 

The first mechanistic study on the benefits of a combination of Lewis acid catalysis and water as reaction medium for a Diels-Alder reaction appeared in 1995. Cu(DS)2 micelles (DS dodecyl sulfate) catalyze the cycloaddition of 3-(para-substituted... 

On a final note, it is hoped that the contents of this book will serve to rectify some of the misconception that persist about the inadequacy of water as reaction medium, and that water will soon become a not only viable but also attractive option to the synthetic chemist in the planning of new synthetic processes. 

The use of water as reaction medium is not new. The oxidation of arenes with KMn04 in alkaline aqueous medium is a very old reaction [2]. Also, H2O2 in water, in the presence or absence of catalyst, is a more frequently used oxidant owing to its peculiarities, such as low relative molecular mass, stability and solubility in many organic solvents. It is economical and environment-friendly since it forms water as a secondary product [3]. 

As an example let us consider the case of the dimethylformamide (DMF). If it is used in reactions evolving in anhydrous media, it will be mandatory to control the level of water on the ppm level. The specification regarding the water content will be of coinse loosened if DMF is used in the chemical step including water as reaction medium. 

The exploitation of biotechnologies for the utili2ation of CO2 as source of carbon is an interesting approach to developing new, environmentally friendly synthetic technologies based on CO2. In principle, both carboxylation and reduction reactions can be carried out, under mild conditions and using water as reaction medium, that would greatly improve the environmental quality of new processes with respect to those actually on stream [56, 58). 

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