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I have to seperate phenacetin and caffeine using a seperation funnel and varying the pH (by varying the pH the coupounds are protonated depending on their pKa and go into the water phase). But the problem is both coumpounds are weak bases. It seems to me that it is nearly impossible to seperate these compounds in this way... and we are not allowed to use other methods to do so.

Anyone an idea how to seperate them with a seperation funnel?

These are the solubilities of both compounds:
phenacetin: 1 in 1300 water, 1 in 15 alcohol, 1 in 14 chloroform, 1 in 90 ether
caffeine: 1 in 46 water, 1 in 66 alcohol, 1 in 50 aceton, 1 in 5,5 chloroform, 1 in 530 ether

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Draw both structures and think!

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I've done so already more than 10 times and I really don't know... there must be an error in my way of thinking. 
Can you give me a hint please?

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Ok, this is what I thought (sorry for my bad English, it's not my mother tongue)

- Phenacetin: the proton goes off the N and the negative charge is stabilized over the aromatic ring and the carbonyl. But a pKa of 2,2 means that it is a quite strong acid, but I thought that phenacetin is a weak base. Moreover an amide has a pKa of 14 when it is considered as an acid (so it is a very weak acid). Why is then the pKa of this amide 2,2?
Someone said to me that phenacetin would rather pick up another proton (because it is a weak base) and that we get a positive charge on the N. I find this a strange idea...
The problem is where the pKa's belong to. Does it belong to the acid/base or to the conjugated acid/base?
So what is now the right solution for this problem, I really don't know anymore.

- Caffeine: I found a pKa of 10,4 for this one, but that means that it is a rather stronge base and I'm almost sure that it is a weak base.
The person who told me about the pKa's thought that this pKa of 10,4 was wrong and that it should be something around pKa 1 (so a weak base and strong conjugated acid).
What do you think about it?

I'm not asking this to get an easy an quick answer on my questions, I 've really been thinking a lot about this. Ik thought I understood the theory behind the pKa's, but this problem is quite a strange one in my opinion.

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Nobody who can help me? 

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To separeate both chemicals you need to find such a condition one chemiical is completely insoluble (impossible in your case) or chemical will be separated into two phases. What about chloroform and basic water solution?