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Topic: Differences in solubility of diasteromeric salts ...  (Read 6031 times)

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Offline sun725

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Differences in solubility of diasteromeric salts ...
« on: December 06, 2016, 03:50:37 PM »
Hi,

At the moment I have a project regarding: Differences in solubility of diasteromeric salts and isolating one enantiomer from a racemic mixture. We are working with (RS)-2(4'-isobutylphenyl)propionic acid (ibuprofen)

However, there is a question I have really hard time figuring out and it says:

How does the number equivalents og KOH(potassium hydroxide) influence the outcome of this experiment.

Hoping for an explenation on this. Thanks a lot.

Online Babcock_Hall

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Re: Differences in solubility of diasteromeric salts ...
« Reply #1 on: December 06, 2016, 07:28:31 PM »
It is a forum rule that you must show your attempt or give your thoughts before we can help you.  I'll give you a small hint, however.  Don't overthink this problem.

Offline Dan

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Re: Differences in solubility of diasteromeric salts ...
« Reply #2 on: December 07, 2016, 02:24:40 AM »
How does the number equivalents og KOH(potassium hydroxide) influence the outcome of this experiment.

In addition to the post above, you should post the details of the experiment so that we know what it was.
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Offline sun725

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Re: Differences in solubility of diasteromeric salts ...
« Reply #3 on: December 07, 2016, 05:04:58 PM »
Thanks for answering.
The exercise is called: Separation of enantiomers by formation of a diasteromic salt.
To explore differences in solubility of diasteromeric salts and use it to isolate one enantiomer from a racemic mixture. The racemic mixture here is
RS)-2(4'-isobutylphenyl)propionic acid (ibuprofen).

And the question I was asked: How does the number equivalents og KOH(potassium hydroxide) influence the outcome of this experiment

What I think is that adding KOG would make the mixture more soluble, also that the relationship between should be 2:1 other wise it wouldn't be possible to isolate.

That's my attempt and I'd love to know more... Thanks again.

Online Babcock_Hall

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Re: Differences in solubility of diasteromeric salts ...
« Reply #4 on: December 07, 2016, 06:00:11 PM »
We are still missing a key piece of information; there has to be something forming the salt besides ibuprofen.

Offline discodermolide

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Re: Differences in solubility of diasteromeric salts ...
« Reply #5 on: December 07, 2016, 11:35:50 PM »
Adding KOH will just give you the potassium salt of ibuprofen and you still have the mixture of enantiomers, not a mixture of diastereoisomers.
So as Babcock asked, what have you forgotten to include in your question?
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Offline sun725

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Re: Differences in solubility of diasteromeric salts ...
« Reply #6 on: December 08, 2016, 02:54:03 PM »
Hi,

I think what I'm missing here is adding a base which in this situation is
(S)-(a)-Phenylethylamine...?

Offline discodermolide

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Re: Differences in solubility of diasteromeric salts ...
« Reply #7 on: December 08, 2016, 03:45:22 PM »
OK, now we are getting somewhere.
So what happens if you use KOH, I assume after the separation of the diastereoisomeric salts?
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Online Babcock_Hall

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Re: Differences in solubility of diasteromeric salts ...
« Reply #8 on: December 08, 2016, 05:49:45 PM »
I would interpret the question to mean what if you included 0, 1, 2, ... equivalents of KOH during the separation.  However, I am not sure.

Offline Dan

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Re: Differences in solubility of diasteromeric salts ...
« Reply #9 on: December 09, 2016, 02:05:00 AM »
Sun725, until you post a full experimental procedure, it is not clear what the question means and people are having to guess. Post the procedure.
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Offline sun725

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Re: Differences in solubility of diasteromeric salts ...
« Reply #10 on: December 11, 2016, 01:53:56 PM »
@Dan,

I posted every single detail written on the assignment therefor I don't know what to add anymore.

The questions directly stated: Discuss how the number equivalents of KOH influences the outcome of this experiment.


Offline sun725

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Re: Differences in solubility of diasteromeric salts ...
« Reply #11 on: December 11, 2016, 02:28:42 PM »
I would interpret the question to mean what if you included 0, 1, 2, ... equivalents of KOH during the separation.  However, I am not sure.

It might be right ...
As stated before they directly say: Discuss how the number equivalents of KOH influences the outcome of this experiment.

Offline AWK

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Re: Differences in solubility of diasteromeric salts ...
« Reply #12 on: December 11, 2016, 03:49:57 PM »
In optimized procedure 1 mole of KOH is used for 2 moles of ibuprophen and a bit more than 1 mole of phenylethylamine. It gives food for thought.
« Last Edit: December 11, 2016, 04:01:33 PM by AWK »
AWK

Offline sun725

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Re: Differences in solubility of diasteromeric salts ...
« Reply #13 on: December 11, 2016, 05:51:28 PM »
In optimized procedure 1 mole of KOH is used for 2 moles of ibuprophen and a bit more than 1 mole of phenylethylamine. It gives food for thought.

Okay, I was close to that earlier, however I missed adding the phenylethylamine.

Offline Dan

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Re: Differences in solubility of diasteromeric salts ...
« Reply #14 on: December 12, 2016, 02:18:27 AM »
@Dan,

I posted every single detail written on the assignment therefor I don't know what to add anymore.

The questions directly stated: Discuss how the number equivalents of KOH influences the outcome of this experiment.

What is missing is the experimental procedure - i.e. what you actually did, which reagents were mixed, in what ratios, and in what order etc.
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