1-Butanol: Extraction Solvent for Removing Quite Polar Organic Substances from Dilute Aqueous Solutions

Ethyl acetate is the most polar organic solvent organic chemists use regularly in extractions from large volumes of water. 1-Butanol is more polar but still only partially miscible with water. It follows that it should be more effecient for taking up polar solutes from water. There is a further advantage. 1-Butanol distils with water as a lower boiling azeotrope and the azeotropic composition separates into layers upon cooling, allowing, as we shall propose, solvent recycling.

 According to the CRC Handbook of Chemistry and Physics 55^th Edition, at atmospheric pressure, the azeotrope boils at 93.0°C and separates on cooling into an upper phase that is, by volume, 71.5% of the total distillate. This layer is 79.9% by weight 1-butanol and 20.1% water.

The azeotropic behaviour varies little, whether the pressure is atmospheric or as low as 30 mm. of mercury. At 30 mm. pressure, this azeotrope boils at just 29.0°C. Again, two phases separate on cooling with the butanol rich upper phase constituting 59.0% by volume. The phase contains 79.9% by weight 1-butanol.

Despite these advantageous properties, this solvent is not popular, perhaps because this predominantly organic phase still contains 20.1 water weight % and would require special drying to get back pure 1-butanol. It would be interesting to see what the effect would be of adding 35 g of sodium chloride to 5 liters of this mixture of 1-butanol and water. I would not be surprised if most of the 1 liter of water separated as a brine!

My suggestion is to use the composition of the upper phase in the azeotrope’s distillate, which is 79.9%/20.1% 1-butanol/water by weight, as the original extraction phase for recovering polar organics from a dilute aqueous reaction mixture. First you would mix in about 35 g of salt for each liter of dilute aqueous solution to reduce partitioning of butanol into the material to be treated. Then you would perform multiple extractions on this mixture with this butanol-water composition. These would t be combined and distilled down to a convenient volume for product recovery by heating under 30 mm. vacuum to distil that azeotrope which comes over at the very moderate temperature of 29.0°C. After the distillate phases separate, the 59.0% percent by volume that constitutes the upper phase in the receiving vessel is of exactly the correct composition to be recycled as original extraction mixture in the next product batch!

This 79.9/20.1% 1-butanol/water composition might become so useful that it could end up commercially available!