Recently, I'm working on a project involving the use of n-butanol and ethyl acetate for phytochemical extraction. However, I'm confused with regards to the polarity of these 2 solvents, based on the information on the internet , the polarity index of n-butanol is 4.0 and ethyl acetate is 4.4. As far as I know, the higher the polarity index, the greater the polarity. However, based on literature, it was stated that n-butanol is more polar than ethyl acetate. Can you clarify which is actually true? I'd appreciate your help in this matter.
Dear Charles,
That is a good question. What happens is that the polarity index is just an approximation of solvent properties. There are several: Hildebrand solubility parameter, Snyder polarity index, Hansen solubility parameters, etc. All are indirect ways of looking at the termodynamics of the solution, and are just an indication of what may happen in terms of solubility. Hansen solubility parameters, for example, try to account for hydrogen bonds, polar and London forces between molecules. If you are interested, start with Wikipedia and then proceed to the second link:
http://en.wikipedia.org/wiki/Hansen_Solubility_Parameters
http://cool.conservation-us.org/coolaic/sg/bpg/annual/v03/bp03-04.html
Check this image and locate your solvents:
http://prodimages.vertmarkets.com/image/b09b5729/b09b5729-a835-11d3-9a74-00a0c9c83afb/original/md2.jpg
You will see that n-butanol is not very polar (in the sense of dipolar bonding), but that it is higly capable of hydrogen bonding; while ethyl acetate is about the same polarity, but poorer in terms of hydrogen bonding. There is one Hansen parameter missing, which is associated with dispersion forces, which are about the same for both solvents.
Now to the practical extraction: if you want to dissolve a target molecule from a plant matrix, there are two things you must also worry about: interaction of the solute with other substances (e.g. carbohydrates, proteins and lipids in the material), and the need to permeate or dissolve complex structures such as cell walls and membranes. All considered, I guess that you will need experimental data as much as the theoretical basis here.
Good luck!
Interesting question! Well, n-butanol has shown the strong hydrogen bonding, while ethyl acetate is poorer in H-bonding. Resulting, n-butanol is more polar in comparison with ethyl acetate...means n-butanol>ethyl acetate. Thanks
- Badges
- Science topic