Reactions in Water

Dear Colleagues,

Whereas the single water molecular has no perculiar properties apart from being very small, it is the aqueous liquid, with its highly dynamic three-dimensional hydrogen-bond network, that has many unique properties. All living systems are critically dependent on the presence of water, both as a medium and as a reagent. In physical-organc chemistry it is often the medium of choice, in part because of its high dielectric constant that avoids ion pair formation and the associated kinetic complexities. Although being the ultimate green solvent, in synthetic chemistry water has for a long time not been popular for two main reasons: (1) the limited solubility of  many apolar substrates and (2) the instability of  a variety of functional groups in aqueous media.

In the past three decades there have been many new developments. Kinetic studies, performed at low substrate concentrations, showed that hydrophobic effects had highly interesting effects both on the reactivity of apolar substrates in water as well as on the stereochemistry of these reactions. Particularly pericyclic reactions have been examined in considerable detail. A second breakthrough came from the group of Sharpless. In contrast with traditional beliefs, it was found that the limited solubilities of organic substrates can be turned into an advantage. A number of transformations, conducted in heterogeneous aqueous suspensions, showed high yields, often improved reaction rates and favorable stereochemistry. Such “on-water reactions” opened many novel possibilities for powerful synthetic protocols in water and for mechanistic investigations.

“Reactions in Water” remains a highly challenging topic for further investigation of the secrets that the aqueous medium has to offer to present day scientists in the area. I kindly invite my colleagues to submit their novel results to the Special Issue of Molecules. We are eagerly awaiting your contributions!

Dr. Jan B.F.N. Engberts
Guest Editor