Water - The Green Solvent for organic chemists

Dr. B. Gopalan

Water as a solvent is not only inexpensive & environmentally benign but also shows completely different reactivity to Organic solvents. Organic reactions in water are varied and have many applications such as, in the synthesis of biologically active compounds from carbohydrates & the chemical modification of biomolecules.

Aqueous reactions could be the answer to the future of organic chemistry. The types of organic reactions in water are broad including pericyclic reactions, reaction of carbanion & carbocation equivalents, reactions of radicals & carbenes, transition-metal catalyses and oxidations-reductions.

The upside of Water as a green solvent are a) Non toxic (liquid + vapour), b) Non flammable, c) Abundantly available (better availability than organic solvent in less developed countries), d) Inexpensive.

The downside are a) Corrosion, b) Heat sink, c) High boiling point {Water-based reactions are energy intensive}, d) Solubility of organic matter is generally poor, e) Reaction range is narrower than organic solvents, f) A vital resource to be conserved & protected {100 litres of water is needed to dye 1 Kg of fibre} and g) Expands when freezes.

Several recent advances in organic reactions in water & in near critical water would be delineated in detail.