The reaction of the compound in picture with potassium tert-butoxide, pyridine, diethanolamine and 4-toluenesulfonyl chloride group leads to the formation of an azacrown.

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It seems that the OH groups of the ether molecule and That of the diethanolamine group react with water elimination to form the azacrown. But then what is the role of the other reagents?

What is the exact reaction mechanism? Please be detailed and show electron movements and type of reaction(e.g.- SN1, E1cB etc.) , if possible.


The reaction scheme you have given is probably not complete. It has all the reagents you need, but is crucially missing the fact that those four compounds are not mixed together all at once.

Simple dehydration of two alcohols to give an ether, as you have described, is very difficult to selectively accomplish. Often it is only useful when you are trying to make a symmetric ether from two molecules of the same alcohol. Otherwise, it is very difficult to control which OH group reacts with which OH group.

In this case, you want to be able to distinguish the -OH groups on the starting material from the -OH groups on diethanolamine. That is why you need the first step of pyridine and tosyl chloride (above the arrow). This converts the -OH groups in the starting material into -OTs groups, which are much better leaving groups.

In the second step, you add t-butoxide and diethanolamine. t-Butoxide, a bulky alkoxide ion, is acting as a base here. The most acidic proton in the mixture is the -OH protons on diethanolamine, and these therefore get deprotonated.

A double $\mathrm{S_N2}$ reaction yields your product.

  • 2
    $\begingroup$ The reason you want to do it this way is that you want to try to form the A-B product instead of A-A or B-B, which is what you would get if you just started trying to form bonds via "water elimination." $\endgroup$ – Zhe Oct 20 '16 at 18:02
  • $\begingroup$ What are the SN2 reactions? $\endgroup$ – Shoubhik Raj Maiti Oct 21 '16 at 4:43

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