1)when benzoic acid and quinine is dissolved in CH2Cl2 and added 2M NaOH, what is the organic layer and what is the aqueous layer?

Question

a)and by adding another 2M NaoH to the organic layer, what is the new aqueous layer and organic layer?

b)from (1), if we add CH2Cl2 to the aqueous layer, what is the new organic layer and aqueous layer? and if we then add HCl to the aqueous layer, what is the product?

Answer 1

1) the aqueous layer will contain sodium salt of benzoic acid (sodium benzoate) while quinine will be dissolved in the organic layer.

a) new aqueous layer will still contain sodium benzoate, and the organic, quinine. the purpose of adding another 2M NaOH to the organic layer is to have any remaining unreacted benzoic acid to react with the additional NaOH added, which i think is to purify the organic layer so that it only contains the required component at the end, if you eventually need to carry out the recrystallisation of the quinine and benzoic acid.

b) same as part a), except that now you are getting any quinine that might've gone into the same flask as the aqueous phase and you need to have them separated...have the aqueous layer purified in the same manner as you did for the organic. lastly, the addition of HCl to the aqueous layer sees the recovery of (impure) benzoic acid in the form of white ppt, as well as sodium chloride.

[i noticed that this question has been asked some time ago but i think there may be others who would be searching for answers related to this question, hence for the following. my answers are based on the expt i did previously. hope this helps. pls do check with other sources too. thks :)]

Answer 2

additional notes:
- dichloromethane (CH2Cl2) is the organic solvent in which quinine dissolves; like dissolves like.
- NaOH (aq) reacts with benzoic acid to form sodium benzoate and water (acid-base reaction).