My question is quite easy to solve.
The question simply asked to find the final product of the reaction shown below, which I did. enter image description here

But the my question lies in the catalyst.
What is the role of the catalyst ? And, why is it used in traces ?
Also what is benzene doing there ?

I have understood the heat symbol. It simply facilitates the conversion of the alcohol formed to an alkene

  • 3
    $\begingroup$ Benzene is just the solvent. pTsOH protonates the carbonyl group to activate it to attack by the amine. It is used in trace amounts because it is regenerated at the end of the reaction. $\endgroup$
    – Waylander
    Jun 1 at 9:28
  • $\begingroup$ Some thing wrong in your product's structure. Oxygen cannot eliminate under this condition. $\endgroup$ Jun 1 at 14:39
  • 1
    $\begingroup$ @MathewMahindaratne please go through the following page and update your knowledge : orgsyn.org/demo.aspx?prep=CV5P0808 $\endgroup$ Jun 1 at 14:44
  • 2
    $\begingroup$ @om joglekar: I don't have to update my knowledge. You start with morpholine and end up with pyrrole derivative. You should get your brain checked first before advising others about their brain. $\endgroup$ Jun 1 at 14:53

TsOH is a relatively strong organic acid (Source: Wikipedia). It is used to protonate the carbonyl oxygen and make the carbon atom more electrophilic, thus facilitating nucleophilic addition of the amine.

Benzene acts as a solvent in this case. It can dissolve the less polar cyclohexanone. Also, since benzene is a non-polar solvent, strong mineral acids (like H2SO4) cannot be used as it will not dissolve in benzene. Hence TsOH is chosen.

  • 6
    $\begingroup$ It is worth noting that benzene forms an azeotrope with water so the water produced by the reaction can be removed e.g. by Dean-Stark reflux to drive the reaction to completion. Benzene however, is not used these days because of its high carcinogenicity, toluene is the safer choice. $\endgroup$
    – Waylander
    Jun 1 at 10:02
  • 3
    $\begingroup$ My experience with this reaction is that a catalyst is not mandatory. While the Org. Syn. prep. (orgsyn.org/demo.aspx?prep=CV5P0808) employs p-TsOH, this one doesn’t ( prepchem.com/cyclohexanone-morpholine-enamine-ii/.) $\endgroup$
    – user55119
    Jun 1 at 12:29

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