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Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: onthisday420 on February 06, 2019, 09:27:16 PM

Title: Protonation of an alcohol for extraction
Post by: onthisday420 on February 06, 2019, 09:27:16 PM
Hey guys,

I'm studying for the mcat and there is a question that I'm not sure about in my review book. The question is as follows:

A non-polar tertiary alcohol is treated with 60% sulfuric acid and then extracted with hexane. Will it stay in the aqueous layer or organic layer? I would think the aqueous solution because the alcohol would be protonated at such a low pH and, as an ionic species, would, therefore, stay in aqueous solution. Am I missing something here?

Thanks
Title: Re: Protonation of an alcohol for extraction
Post by: chenbeier on February 07, 2019, 04:47:50 AM
I think acccording Nernst you will get a distribution between polar and non poar solvent.
Title: Re: Protonation of an alcohol for extraction
Post by: kriggy on February 08, 2019, 04:40:06 AM
Think about some reaction that can occur when tertiary alcohols react with acids
Title: Re: Protonation of an alcohol for extraction
Post by: onthisday420 on February 08, 2019, 05:04:15 PM
What do you mean? I figured it would either be protonated or deprotonated and so it would be soluble in polar or non-polar solvents respectively. I don't think the question is much deeper than that.
Title: Re: Protonation of an alcohol for extraction
Post by: wildfyr on February 09, 2019, 10:07:05 AM
Kriggy is telling you that such a compound may react under these conditions. So it's not just about partitioning.
Title: Re: Protonation of an alcohol for extraction
Post by: onthisday420 on February 09, 2019, 12:26:06 PM
Trust me, the MCAT is not asking about side reactions of tertiary alcohols and sulfuric acid. The level of organic chemistry we have to know is pretty rudimentary. I appreciate the help though.
Title: Re: Protonation of an alcohol for extraction
Post by: sjb on February 09, 2019, 01:23:43 PM
Quote from: onthisday420 on February 09, 2019, 12:26:06 PM
The level of organic chemistry we have to know is pretty rudimentary.

I'd argue this is rudimentary though - I certainly remember this coming up at secondary school level chemistry, pre-university courses...
Title: Re: Protonation of an alcohol for extraction
Post by: kriggy on February 10, 2019, 06:06:02 AM
Quote from: onthisday420 on February 09, 2019, 12:26:06 PM
Trust me, the MCAT is not asking about side reactions of tertiary alcohols and sulfuric acid. The level of organic chemistry we have to know is pretty rudimentary. I appreciate the help though.

Its not a side reaction, its pretty fast reaction. Also, do you think the protonated alcohol, R-OH2+ is stable?
Title: Re: Protonation of an alcohol for extraction
Post by: onthisday420 on February 11, 2019, 02:34:15 AM
Ah I see you're talking about an elimination reaction. There's no way you could have known this because I didn't tell you, but the tertiary alcohol was dicofol. There is no elimination reaction that could occur here. I should be more attentive though. Thanks. With that in mind though what would you say would happen?

Quote from: kriggy on February 10, 2019, 06:06:02 AM
Quote from: onthisday420 on February 09, 2019, 12:26:06 PM
Trust me, the MCAT is not asking about side reactions of tertiary alcohols and sulfuric acid. The level of organic chemistry we have to know is pretty rudimentary. I appreciate the help though.

Its not a side reaction, its pretty fast reaction. Also, do you think the protonated alcohol, R-OH2+ is stable?
Title: Re: Protonation of an alcohol for extraction
Post by: AWK on February 11, 2019, 03:59:54 AM
Quote from: onthisday420 on February 09, 2019, 12:26:06 PM
Trust me, the MCAT is not asking about side reactions of tertiary alcohols and sulfuric acid. The level of organic chemistry we have to know is pretty rudimentary. I appreciate the help though.
That is true
http://mcat-review.org/organic-chemistry.php
Your question probably comes from "Separation and Purification" chapter.
But even then questions should be realistic. Sulfuric acid cause elimination of water from tertiary alcohols even at room temperature. Other alcohols with such concentrated sulfuric acid will form esters of type R-O-SO3H, at least partially. In SN1 mechanism, that MCAT involves, E1 elimination reactions are (in fact) side reactions.