enter image description here

Can anyone please help me come up for a curved arrow mechanism for the reaction pictured? I'm familiar with the mechanism for the general acid catalyzed dehydration of butanol, where the arrow comes off a hydrogen bonded O on the sulfuric acid to the hydrogen on butanol to the oxygen and the following steps for that reaction are pretty simple too but I can't for the life of me come up with a curved arrow mechanism for this side reaction.

Currently, I think the butanol takes a hydrogen from the sulfuric acid (arrow from butanol O to Sulfuric acid H to O), followed by the removal of the hydronium atom from the butanol chain (arrow from sulfuric acid O to carbon on butanol chain to the O on butanol chain), followed by maybe a combination of butanol and the synthesized butanol sulfate???? I'm really not sure any help would be greatly appreciated.


Edit: This is the final mechanism I came up with. Is this right? enter image description here

  • 5
    $\begingroup$ In the fourth step your curly arrows are not right. The proton transfer in the first step is correct, though, so you certainly do know how to draw it correctly. $\endgroup$
    – orthocresol
    Aug 3 '20 at 7:57
  • $\begingroup$ Also, proton transfer from protonated ether could be to another alcohol molecule as well. $\endgroup$ Aug 3 '20 at 8:08
  • $\begingroup$ @orthocresol Bisulphate is not a very strong base, due to I- effect and reverse d-orbital hyperconjugation. So should it attack the proton for deprotonarion, or will some other stronger base like water deprotonate? $\endgroup$ Aug 3 '20 at 8:33
  • $\begingroup$ @ADITYAROYCHOWDHURY I don't know what "reverse d-orbital hyperconjugation" means, but I'm pretty sure that no such thing exists. You don't need, and shouldn't use, d-orbitals to describe the bonding in sulfate ion (or its protonated forms). $\endgroup$
    – orthocresol
    Aug 3 '20 at 8:53
  • 1
    $\begingroup$ @ADITYAROYCHOWDHURY I don't make any claim as to which species deprotonates which. Truthfully, I don't think it matters much; as long as the thing gets deprotonated, it doesn't really matter what molecule does it. But yes, water, and the alcohol itself as Mathew suggests, are stronger bases than HSO4-, so yes it is probably better to use water to deprotonate. I do take issue, though, with you talking about d-orbitals of sulfur. That is an outdated theory of bonding which is not really true at all. $\endgroup$
    – orthocresol
    Aug 3 '20 at 10:27

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