Water/Organic Solvent Systems for Reaction Between Organic Substrates and Inorganic Reagents

Choosing Reaction Solvents

Aqueous acetonitrile and aqueous 1-propanol are two separate solvent systems which should be considered for reactions between organic substrates and inorganic reagents. To separate these reaction mixtures into two phases; an essentially aqueous one to extract the inorganic residuals  and the second to take up the organic products,T.Hori and T.Fujinaga [Talanta, 32, 8(2), 735-743, 1985] have developed a method that appears more practical than adding salts. This involves adding chloroform in the case of aqueous acetonitrile and cyclohexane in the case of aqueous 1-propanol. These additions of a third solvent component appear to be preferable to the usually large amount of a salt (impurities in which may cause undue contamination); also, the volume and composition of the organic phase can be predicted from phase diagrams and the overall composition of the solvent mixture. Volume-fraction diagrams are especially easy to use. Furthermore, equilibrium is attained in solvent mixtures more rapidly than in salting-out systems.

Reactions that require an aqueous-organic solvent are usually candidates for the application of phase transfer catalysis and this should be the first option because of cost and waste destruction considerations.