Organic synthesis in water

Article By:

Lindström, U. Marcus Department of Chemistry, McGill University, Montreal, Quebec, Canada.

Last reviewed:2008

DOI:https://doi.org/10.1036/1097-8542.YB080160

Water is the most abundant molecule on Earth and the universal solvent in which the chemistry of the life processes has developed over billions of years. Its unique chemical and physical properties have fascinated scientists for a long time. The connection between water's deceptively simple molecular structure and its influence as a solvent on biological reactions remains one of the greatest scientific challenges. In sharp contrast to the general academic interest in water, the modern chemist rarely uses or even considers water as a medium for synthetic organic reactions. Students working on all levels of organic chemistry are trained to use anhydrous reaction conditions. The diligent synthetic chemist keeps glassware, syringes, reagents, and solvents free from traces of water. The reason behind the lack of interest in using water as a reaction solvent can be traced back to the beginning of the twentieth century when new synthetic methods based on organometallic reagents were introduced. These methods were extremely powerful but often required inert conditions because of the high reactivity of the carbon-metal bond. Throughout the better part of the last century, synthetic methods were developed for use primarily in anhydrous organic media. It was not until the early 1980s that the use of water was reevaluated when it was found that the rate and selectivity of the important and useful Diels-Alder reaction could be greatly enhanced in water compared to the same reaction in an organic solvent. The interest in water as solvent was further invigorated in the 1990s with the introduction of the concept of “green” chemistry, which addresses the environmental impact of chemicals and chemical processes. Water, being cheap, safe, nontoxic, and environmentally benign, was soon recognized as perhaps the ultimate green solvent. In view of the potential reward of replacing hazardous organic solvents with water, researchers took up the academic challenge of developing new synthetic methods that were compatible with the aqueous medium. This article highlights two recent important developments in this area: the discovery of metal-based catalysts that operate in water, and new insights into the influence of aqueous biphasic reaction conditions on reaction rates.

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