I\'m having a hard time making sense of this lab procedure interms of the reacti

Question

I'm having a hard time making sense of this lab procedure interms of the reaction equations...and how things went down. Here'swhat happened... Took unknown mixture of 500mg of a carboxylic acid (it wasdetermined that my particular species was salicylic acid) andincluded was 2mL of a neutral compound. Used several portions of pet ether to transfer to a seperatoryfunnel and added 10mL of 5% aqueous sodium hydroxide to the sepfunnel. shaked it, vented it. Then we allowed the layers to separate and drained off thebottom layer into an erlenmeyer flask. Repeated extractionprocedure on remaining pet ether layer using another 10mLNaOH. Then, to the extracted material we added a 6M HClsolution until the pH was about 2. Still with me? Placed this solution in an ice bath to allow crystals (thecarboxylic acid) to form. Then we filtered this crystal solid, washed it, dissolved andrecrystalized it. Based on melting points my crystals turned out tobe Salicylic acid. So.....what just happened in terms of reactionequations!? I'm having a hard time making sense of this lab procedure interms of the reaction equations...and how things went down. Here'swhat happened... Took unknown mixture of 500mg of a carboxylic acid (it wasdetermined that my particular species was salicylic acid) andincluded was 2mL of a neutral compound. Used several portions of pet ether to transfer to a seperatoryfunnel and added 10mL of 5% aqueous sodium hydroxide to the sepfunnel. shaked it, vented it. Then we allowed the layers to separate and drained off thebottom layer into an erlenmeyer flask. Repeated extractionprocedure on remaining pet ether layer using another 10mLNaOH. Then, to the extracted material we added a 6M HClsolution until the pH was about 2. Still with me? Placed this solution in an ice bath to allow crystals (thecarboxylic acid) to form. Then we filtered this crystal solid, washed it, dissolved andrecrystalized it. Based on melting points my crystals turned out tobe Salicylic acid. So.....what just happened in terms of reactionequations!?

Explanation / Answer

I'm not going to draw the whole structure of salicylic acid, butthe main focus of it is the carboxylic acid group so I willrepresent the rest of salicylic acid with an "R". When NaOH is added to the separatory funnel, it deprotonates thecarboxylic acid. RCO2H + OH-1 RCO2-1 + H2O The carboxylate anion remains dissolved in the aqueous layer sinceit is ionic. The rest of the organic impurity is extracted out inthe organic layer. Finally you are able to "get back" the carboxylic acid byacidification with conc. hydrochloric acid and then allowed torecrystallize through vacuum filtration. RCO2-1 + H+ RCO2H

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