Question

Synthesis of 5,5-diphenylhydantion (Dilantin)

#1. Suggest an appropriate solvent for taking the NMR of Dilantin, considering its physical state.

#2. Provide a mechanism for the step in the synthesis that is labeled "protonation and loss of water".

#3. Draw a significant (not involving the benzene rings) resonance form for Dilantin. Very briefly explain which resonance form is likely more stable.

#4. Draw a concerted mechanism for the rearrangement of benzil to benzilic acid.

Answer 1

1. This is a bucherer bergs reaction. Bergs described a synthesis of some 5-substituted hydantoins by treatment of aldehydes or ketones with potassium cyanide, ammonium carbonate, and carbon dioxide under several atmospheres of pressure at 80⁰ C. So You may use water as solvent.

2. The mechanism is in the picture (You may see there even the answer for question 4).

3. The most stable resonance form would be the one where the less charges appear and the farthest they are in the molecule. That's why the second structure I drew is the more stable. Only two charges, while the second one, has 4 charges, it's very unstable in that form.

4. This question I answered as general from benzil to benzilic acid, however, the rearrangement for this molecule it's in question 2. The whole mechanism.