Deprotonation of alcohols to give alkoxides
Description: Treatment of alcohols with bases give their conjugate bases, called alkoxy ions (alkoxides)
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Why is in the last example no reaction?
Hi – kind of a silly trick question. The first step is deprotonation of the alcohol to give the alkoxide RO(-) and the second step is treatment of this with acid to give back the neutral alcohol (ROH). Although I can see how this could be ambiguous to the point that the final answer could be PhOH2(+)
Hi James thankyou for your reply
actually i am trying an electrochemical ring forming reaction. where the electrons on the hydroxyl group in salicylicaldehyde (after it is deprotonated) can donate its electron to a near by oxidised nitrogen atom in the same molecule, forming a heterocyclic ring. actually the salicylaldehyde is pretreated with phenylhydrazine forming a schiff base.
what base should i use to deprotonate the hydroxyl hydrogen from salicylaldehyde (acetonitrile solvent)? can i use ammonia?
With salicylaldehyde and ammonia, what’s more likely to happen is formation of the imine. What kind of reaction are you trying to perform with deprotonated salicylaldehyde?
There was a question on one of my practice exams that asked “which base will not fully deprotonate an alkyl alcohol?”
So I take it is NaOH because of the pKa similarity, but I don’t really understand what it means to “not fully deprotonate”
Hey Sarah – thanks for writing. I think a better way of writing it is “to not irreversibly deprotonate”. In other words, once the acid base reaction occurs, there is no equilibrium between the new acid [the conjugate acid of the base] and the new base [conjugate base of the acid]
For example in the reaction
CH3OH + NaOH —> CH3O- + H2O
there can still be an acid-base reaction between the base [CH3O-] and acid [H2O] formed in this reaction [in other words it is in equilibrium]
but in the reaction
CH3OH + CH3Li —> CH3O- + CH3-CH3
there is no acid base eaction between the base [CH3O-] and acid [CH3CH3] formed here – it is an irreversible acid-base reaction.
I agree that “completely deprotonated” is confusing because of course in any individual reaction the molecule is completely deprotonated. The issue is wherther ALL of the molecules are irreversibly deprotonated.
Does that make sense?
James
I do not understand the equation CH3OH + CH3Li —> CH3O- + CH3-CH3. Is it balanced? It would seem that CH3OH deprotonated would yield CH4 as the other product.
It would definitely not be balanced! It should be CH4!
In Example 2, you have a potassium ion above your reaction arrow, yet you have a sodium ion in your products. It is completely irrelevant for the reaction, just different spectator, but just thought you should know.
Fixed, thank you!
FYI James, example 2 is supposed to have K+ as a product, not Na+.
Fixed, thank you!