What does solubility in NaOH mean?

[kfcman289]

I had a practice MCAT question that was discussing the solubility of phenol and benzyl alcohol in NaOH and NaHCO3. The passage said that phenol would dissolve in NaOH but that benzyl alcohol wouldn't. Additionally, the passage said that neither phenol or benzyl alchohol would dissolve in NaHCO3. Can someone explain why one alcohol would dissolve in a base but not another? And what happened to like dissolves in like?

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[Medix450]

I believe it has to do with acid/base reactions. NaHCO3 isn't a strong enough base, and so phenol and benzyl alcohol wouldn't dissociate enough to dissolve.

 

[Teleologist]

I believe it has to do with acid/base reactions. NaHCO3 isn't a strong enough base, and so phenol and benzyl alcohol wouldn't dissociate enough to dissolve.

Sounds about right. Alcohols are weak acids; phenol technically isn't an alcohol but it's still a weak acid. Hydroxide ion is several orders of magnitude stronger than HCO3(-) as a base.

 

[The Brown Knight]

Yup the above explanations are perfect; just wanted to add a bit:
The reason phenol dissolves in hydroxide and not benzyl alcohol is that the conjugate base of phenol, phenoxide, is awesomely resonance stabilized by the ADJACENT phenyl ring. Benzyl alcohol has a methylene (--CH2--) group separating the phenyl ring and the anionic oxygen in the conjugate base and hence prevents resonance stabilization of the conjugate base. Hence phenol is stronger acid than benzyl alcohol and hence the latter doesn't dissolve in either.

 

[Teleologist]

Yup the above explanations are perfect; just wanted to add a bit:
The reason phenol dissolves in hydroxide and not benzyl alcohol is that the conjugate base of phenol, phenoxide, is awesomely resonance stabilized by the ADJACENT phenyl ring. Benzyl alcohol has a methylene (--CH2--) group separating the phenyl ring and the anionic oxygen in the conjugate base and hence prevents resonance stabilization of the conjugate base. Hence phenol is stronger acid than benzyl alcohol and hence the latter doesn't dissolve in either.

You mean the electron-withdrawing phenyl group spreads out the negative charge density from the oxygen with the neg. formal charge.

 

[The Brown Knight]

You mean the electron-withdrawing phenyl group spreads out the negative charge density from the oxygen with the neg. formal charge.

Yup, and they do it AWESOMELY lol with the conjugated double bond system and all!

 

[kfcman289]

I believe it has to do with acid/base reactions. NaHCO3 isn't a strong enough base, and so phenol and benzyl alcohol wouldn't dissociate enough to dissolve.

You mean the electron-withdrawing phenyl group spreads out the negative charge density from the oxygen with the neg. formal charge.

But why couldnt a strong base like NaOH deprotonate the benzyl alcohol?

 

[Teleologist]

But why couldnt a strong base like NaOH deprotonate the benzyl alcohol?

Probably because the deprotonated benzyl oxide ion isn't stable.