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Topic: Solubility  (Read 2079 times)

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Offline Nekromantis

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Solubility
« on: August 12, 2013, 12:29:59 PM »
Hi,

I have a question. Anilin is insoluble in water but benzylamine is soluble in water. Why?

I think that the main thing is pKa.
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Ph.D student of organic chemistry from Poland
Speciality: Ionic Liquids, Chiral Ionic Liquids, Diels-Alder reaction

Offline salteen

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Re: Solubility
« Reply #1 on: August 12, 2013, 12:33:40 PM »
pKa is a good hypothesis.  What's the difference in pKa between benzylamine and aniline, and how would this affect their solubility?
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Offline Nekromantis

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Re: Solubility
« Reply #2 on: August 12, 2013, 12:41:19 PM »
pKa water: 15.7
pKa aniline: 30.6
pKa benzylamine: 9.33

Because pKa aniline is higher than pKa of water so aniline is insoluble in water?
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Offline salteen

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Re: Solubility
« Reply #3 on: August 12, 2013, 12:49:59 PM »
To be clear, it's the pka value of the conjugate acid (i.e. protonated form) of each amine which plays a role here.  Your values below are mixed up.

The pka of benzylammonium ion (PhCH2NH3+) is 9.33.  You want to compare this to the pka of the anilinium ion (PhNH3+).  Not the pka of aniline, which is indeed ~30.
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Offline Nekromantis

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Re: Solubility
« Reply #4 on: August 12, 2013, 01:02:52 PM »
So what kind of answer should be ?
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Ph.D student of organic chemistry from Poland
Speciality: Ionic Liquids, Chiral Ionic Liquids, Diels-Alder reaction
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