[karen0215]

Separate cis- and trans- 2,3-dipheny propenoic acids
by using buffer solution of pH 5.2, ether, concentraed HCl.

Given pKa of cis-form is 6.1 and that of trans-form is 4.8.

The anwser was given but i don't know why they are separated in this way (step 3)
Could you explain it to me?

ans:
1. Add the buffer solution to the aqueous layer. Cis- form will be precipitate.Filter the mixture to obtain it.
2. Add concentrated HCl to the filtrate to regenerate trans-form
3. Use ether to extract it. It can be obtained by evaporating the solution and then followed by crystallization.

I think that after adding conc. HCl, the regenerated trans-compound will be precipitated out.
So I don't know why step 3 is needed.

[Helper0863]

Step 3 is needed because trans compounds are known to be more soluble in aqueous solution (water) than cis compounds.  Therefore, ether is required to extract it.