# Separation techniques for different organic compounds

Select the best (most appropriate, easiest, fastest) separation technique for each pair of compounds shown below:

Separation techniques:

1. evaporation under reduced pressure
2. column chromatography
3. water-diethyl ether extraction
4. acid-base extraction

This requires knowledge of what compounds are separated most efficiently/appropriately by what separation technique. Since I did the labs separately I can only attempt to try to meld the concepts together.

Pair 1 is a carboxylc acid and chlorodiene. Both are polar.
Pair 2 is an ether and hydrocarbon. One is polar the other nonpolar.
Pair 3 looks to be an ester and cyclodiene. One is polar and the other slightly polar.

My attempt:

Based on the acid I'd use acid-base on pair 1.
Pair 2, since one is polar and the other nonpolar, seems like it needs liquid-liquid extraction (water-diethyl ether extraction)
Pair 3 are polar. Unsure of this one. They'd be slow on a column. Evaporation is based on a low boiling point.

Dipentylether, $\ce{C5H11-O-C5H11}$, has a much higher molar mass than n-hexane, $\ce{C6H12}$. As a rule of thumb, you can assume that the compound with the higer molar mass will have a much higher boiling point. (There will be exceptions when strong interactions between molecules come into play, such as in the case of hydrogen bonds. But this isn't the case here!) If you look up the boiling points (bp) for both compounds, you'll see that our rule of thumb is supported here. The bp of n-hexane is 68 °C, that of the much heavier ether is > 180 °C. Consequently, distillation (under reduced pressure) is the way to go here.
There is an $\ce{OH}$ group in the the first molecule. Here, the term polar is justified! Think about the typical setup of column chromatography. The stationary phase is usually silica (or aluminium oxide), while the mobile phase typically consists of mixtures of not-so-polar organic solvents. Compound 1 can strongly interact with the silica through hydrogen bonding, while compound 2 is an unsubstituted aromatic hydrocarbon. Separation by colunm chromatography is a very promising method for this pair.