EK #995-1000 Organic Chemistry 1001 Extraction of Tea Components

[mtravis2190]

Hello all,

The question I'm stuck on in EK has to do with extraction of three different components of tea.

Caffeine is isolated from the other components found in tea by extraction with sodium hydroxide. I've attached the structures with this post. The top left is caffeine, middle is carboxylic acid, and the rightmost is tannin.

I understand 995 and 996, but the others are giving me some trouble.

Q 995. After the addition of sodium hydroxide to the tea solution and extraction with dichloromethane, what components are present in the organic layer?
I. Caffeine
II. Carboxylic acids
III. Tannins
Answer-I

Q. 996. After the addition of sodium hydroxide to the tea solution and extraction with dichloromethane, what components are present in the aqueous layer?
I. Caffeine
II. Carboxylic acids
III. Tannins
Answer-II and III

Q.997. If the tea solution were extracted without the sodium hydroxide present, what components would be present in the aqueous phase after the extraction?
I. Caffeine
II. Carboxylic acids
III. Tannins
Answer-I

Q.998. If the tea solution were extracted without the sodium hydroxide present, what components would be present in the organic phase after the extraction?
I. Caffeine
II. Carboxylic acids
III. Tannins
Answer- II and III

Q.999. If the tea solution were extracted with sodium bicarbonate instead of sodium hydroxide, what components would be present in the organic phase after the extraction?
I. Caffeine
II. Carboxylic acids
III. Tannins
Answer- I and III

Q.1000. If the tea solution were extracted with sodium bicarbonate instead of sodium hydroxide, what components would be present in the aqueous phase after the extraction?
I. Caffeine
II. Carboxylic acids
III. Tannins
Answer- II

THANK YOU!

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[inasensegone]

Hello all,

The question I'm stuck on in EK has to do with extraction of three different components of tea.

Caffeine is isolated from the other components found in tea by extraction with sodium hydroxide. I've attached the structures with this post. The top left is caffeine, middle is carboxylic acid, and the rightmost is tannin.

I understand 995 and 996, but the others are giving me some trouble.

Q 995. After the addition of sodium hydroxide to the tea solution and extraction with dichloromethane, what components are present in the organic layer?
I. Caffeine
II. Carboxylic acids
III. Tannins
Answer-I

Q. 996. After the addition of sodium hydroxide to the tea solution and extraction with dichloromethane, what components are present in the aqueous layer?
I. Caffeine
II. Carboxylic acids
III. Tannins
Answer-II and III

Q.997. If the tea solution were extracted without the sodium hydroxide present, what components would be present in the aqueous phase after the extraction?
I. Caffeine
II. Carboxylic acids
III. Tannins
Answer-I

Q.998. If the tea solution were extracted without the sodium hydroxide present, what components would be present in the organic phase after the extraction?
I. Caffeine
II. Carboxylic acids
III. Tannins
Answer- II and III

Q.999. If the tea solution were extracted with sodium bicarbonate instead of sodium hydroxide, what components would be present in the organic phase after the extraction?
I. Caffeine
II. Carboxylic acids
III. Tannins
Answer- I and III

Q.1000. If the tea solution were extracted with sodium bicarbonate instead of sodium hydroxide, what components would be present in the aqueous phase after the extraction?
I. Caffeine
II. Carboxylic acids
III. Tannins
Answer- II

THANK YOU!

First of all, your post did not include any pictures of molecules so I whipped up the same structures real quick and attached a picture below. Second of all, EK 1001 explanations suck, so I'm not surprised that you didn't get much out of their explanations. Anyway, here are the molecules as provided in EK 1001:

I want to preface this by saying that EK 1001 again shows its laziness by not indicating the length of the carboxylic acid. This is actually important because short chain carboxylic acids are miscible in water. Once the chain grows in length, then its solubility is more heavily affected by basicity of the solvent. Anyway, enough of my diatribe...

OK, so since you understand 995 & 996, I'll start with 997: Since there is no NaOH present, this is basically like asking "what happens if you mix these molecules in simply water and organic solvent?" Well, Caffeine is shown as having a positive charge on the protonated Nitrogen, so therefore it is highly polar. Like dissolves like, so it will wind up in the polar water solvent. The other 2 molecules do not exhibit any charge, so EK's logic is that they would not be dissolved in the polar solvent, and would instead be dissolved in the non-polar solvent. Again this is why I take issue with these questions. Depending on how much of these other molecules (tannin and COOH) are present, and how long their chains and non-polar components are, they may very well be soluble in a polar solvent. Tannin is shown as having 3 hydroxyl groups, and as I stated before, small chain COOH's are miscible in water. Anyway, I suppose you are to assume that they have substantial non-polar regions, and this is why they are non-polar overall and would wind up in the non-polar solvent. The same logic can be applied to the other questions...

998: This question is the flip-side of 997, so following EK's logic, the tannin and COOH would be in the organic (non-polar) solvent because they are allegedly non-polar.

999: Sodium bicarbonate is a weak base so it will interact with caffeine and the COOH, thus turning them into neutral caffeine (non-polar) and the carboxylate (polar and charged) salt, respectively. EK is accurate in saying that the bicarbonate is not a strong enough base to deprotonate the phenol (hydroxyl groups) of the tannin, so the tannin will remain in the organic layer. Again, the caffeine has been deprotonated so now it is neutral and will thus be in the organic layer as well. This is similar to the diazole ring in the amino acid Histidine which can be similarly protonated. If those terms are foreign, don't worry about it, I can almost guarantee you that they won't be on your MCAT.

1000: This is just the flip side of 999, so, since the caffeine and the tannin are in the organic layer, the COOH must be in the aqueous phase after extraction.

After looking at these problems and EK's weak-as$ explanations, I feel like they got progressively more lazy and just squeezed out those 1001 questions. Quality > Quantity doesn't really seem to apply here...

 

[mtravis2190]

Oh my apologies! I didn't realize I didn't upload them! WOW! Thank you for so much detail! I really appreciate your time for helping me make sense of this stuff! Thanks a lot!