Olympiad question - To work out the remainder of the intermediates in this synthesis

Here I have a Chemistry Olympiad question I'm doing that outlines the synthesis of Ritalin. So far I've worked out A, Anion B -, and compound C. You can see my workings, as I've attached them here too.

Nucleophilic substitution with the nucleophile $\ce{C#N-}$ produces A: enter image description here

A proton is taken away from the $\alpha-\ce C$ to deprotonate it to form Anion B -: enter image description here

Anion $\ce{B-}$ acts as a nucleophile and substitutes $\ce{Cl}$ to produce C: enter image description here

But how would I work out the structures of D, E and F?

I'm not familiar with all the mechanisms/reactions of nitriles and am unsure how to proceed.


1 Answer 1

  1. In A and B, you should probably draw the C-C single bond in the nitrile longer, it's a bit difficult to see at the moment.

  2. The nitrile is sequentially hydrolysed to an amide and then to an acid.

  3. Treatment with $\ce{ROH/H+}$ is a rather obvious Fischer esterification.

enter image description here

You can arguably work all of this out from first principles: the nitrile carbon is electrophilic, and is therefore susceptible to nucleophilic attack by water. The reaction mechanism is given here. On top of this, the IR peaks strongly support the presence of amide and acid functional groups in D and E respectively.

With that said, I'd argue that there is always going to be an element of "I just know this because I read about it/was taught it before". The very fact that you said "I'm not familiar with the mechanisms/reactions of nitriles" indicates this - if you had happened to read a textbook chapter on nitriles, then you would probably have seen this, since it is one of the most fundamental reactions of nitriles. You would also have to read up about the IR wavenumbers - otherwise it's just gibberish.

  • $\begingroup$ Thank you very much. In my A-level syllabus the reactions of nitriles are very limited and are not found in my textbooks - this is why I'm working through Olympiad papers, so I can familiarise myself with a wider range of Chemistry and ways to solve questions like this, as I've received an interview for Chemistry at Oxford. Ive seen you're an undergraduate and would very much appreciate some advice on the interview, I'm just doing Olympiad papers right now to improve. $\endgroup$ Nov 19, 2016 at 23:17
  • 3
    $\begingroup$ IR is gibberish, of course. */obligatory IR rant ;)* $\endgroup$
    – Jan
    Nov 19, 2016 at 23:25
  • $\begingroup$ @MichaelHarding feel free to pop into chat, I'm there often. $\endgroup$ Nov 19, 2016 at 23:26
  • $\begingroup$ @Jan re: IR BOOM! $\endgroup$ Nov 20, 2016 at 2:19
  • $\begingroup$ Just as a point of interest, pyridine's pKa is 5.25, acetic acid's is 4.75. So, in E, that acidic proton should probably be more closely associated with the nitrogen than with the oxygen (I'd assume no matter where the proton is, there's going to be some cyclic intramolecular H-bonding). $\endgroup$ Nov 20, 2016 at 19:05

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