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396 Chapter 20 CARBOXYLIC ACID DERIVATIVES :0: O. C NH₂ + NH₂ : NH : NH OH C + OH :0. :0. OH₂ O: Phthalimide Then O NaOH :NH :N: + Na :NBr -NaBr O O Now what? There's no hydrogen on the N anymore, so how can you get to an intermediate N-haloamidate that can rearrange to the isocyanate? C R NBr 0=C=N R N-Haloamidate Isocyanate The answer: The reaction takes place in strong base, so use hydroxide in addition-elimination. :0: :0:- OH C -OH NBr OH NBr A N Br C O Now you are in business. Continue exactly as in Section 20-7. O O C COH OH (See Exercise 20-22) N=C=0 = NH₂ 56. Self-explanatory. 57. From A: 2. (CH₃)₂NH (makes 3. then H₂O. From B: 1. 2. 3. NaOH (Hofmann rearrangement. loses and makes simple amine), 4. 2 NaOH methylations of amine nitrogen). Notice that B had an extra carbon that the Hofmann rearrangement removed.