A problem I was recently working on poses the following scenario:

A student realizes that protonation of an alcohol makes the -OH into a better leaving group. Therefore, he suggested the following reaction between 1-propanol, sulfuric acid, and trimethylamine. However, this process does not yield the product predicted here. Why not?

enter image description here

The only reason I can think of deals with the leaving group, which I usually only see in tertiary alcohols/SN1 reactions. Therefore, I supppose that since the reaction proceeds via an SN1 mechanism, the carbocation formed in this case (which is primary) would not form at an appreciable rate --> reaction would not proceed to form product predicted.

Is this line of reasoning correct or is there a better reason why the predicted reaction does not occur? Any ideas will be highly appreciated.

  • $\begingroup$ @AdvilSell The diagrams were provided in the question. I am not sure what the question makers used to make the diagrams. $\endgroup$ – Ethiopius Mar 7 '19 at 18:29

Here the reason is not $S_N1$. In fact the $S_N1$ mechanism is quite difficult to observe with $1$-propanol. The main problem is the sulfuric acid, which not only protonates the alcohol but also protonates the trimethylamine, which is a strong base also. Therefore, being protonated, its nucleophilicity is greatly diminished and the reaction can't occur. The protonation and consequent loss of nucleophilicity of trimethylamine is the main reason.


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