“On Water”: Unique Reactivity of Organic Compounds in Aqueous Suspension

Abstract

Water, the medium of choice: Many reactions, such as Claisen rearrangements (see scheme), are dramatically accelerated when performed in aqueous suspension (“on water”) relative to organic solvents or even neat conditions. Low miscibility of organic compounds with water is not detrimental: in fact, it facilitates the isolation of products.

Microwave-Promoted Synthesis of 4-Arylpyrimidines by Pd-Catalysed Suzuki–Miyaura Coupling of 4-Pyrimidyl Tosylates in Water

“…19 In our case, it is noteworthy that water not only had no adverse effect on this Pd-catalyzed process, but indeed proved to be the best solvent for these coupling reactions. As recognized before for several organic reactions involving hydrophobic reagents, 20 this enhanced reactivity may be ascribed to hydrophobic aggregation of the reactants in water. Having established water as the solvent of choice, and microwave heating at 100 °C for 1 hour as the optimal reaction conditions, the effect of different palladium catalysts was next investigated.…”

On the Role of Water in Heterogeneous Catalysis: A Tribute to Professor M. Wyn Roberts

“…Roberts [4] drew attention to Marcus' model [37] explaining Sharpless' observation [38] of rate enhancements in oil/water suspensions and two further Fig. 4 Schematic illustration of the predominant reaction pathways for CO oxidation with and without H 2 O. Reproduced from Ref.…”

Microscopic structure and dynamics of air/water interface by computer simulations—comparison with sum-frequency generation experiments

“…Certain atmospheric reactions, 6 such as those involved in ozone depletion, are known to be catalyzed by the ice surface on cloud particles. Study of the air/water interface is also important for understanding more complicated organic/water interfaces 5 that have recently begun to attract interest for its potential for rate acceleration 7 of organic reactions and green chemistry in emulsions. For example, interest in catalytic effects of dangling OH's has also been extended to their role in catalysis of different organic reactions by metal oxides enriched in surface OH groups.…”