1 (541)

Prévia do material em texto

478 Chapter 25 HETEROCYCLES: HETEROATOMS IN CYCLIC ORGANIC COMPOUNDS (c) Paal-Knorr HCCH CHCH product CH₃ CH₃ CH₃ CH₃ CH₃ H (d) CH₃ S 42. The only structural difference is the presence of a methyl group on a caffeine nitrogen, which in theobromine contains a hydrogen. Fortunately, this hydrogen should be usefully acidic because the nitrogen containing it lies between two carbonyl groups. Recall (Section 21-5) that the similarly placed hydrogen in 1,2-benzenedicarboximide (phthalimide) has a of about 8. Thus, 1. deprotonate with base (NaOH should be more than adequate) and 2. alkylate with 43. (a) I hope you haven't forgotten how to do this. Melamine's approximate formula weight is 36 (three C) + 6 (six H) + 84 (six N) = 126, of which 84 is nitrogen. Thus, % N = (84/126) 100% = 67%. Clearly even a fairly small amount of melamine as an adulterant in any food product will increase the % N analysis, giving the impression that more protein is present than actually is the case. (b) The reaction is a nucleophilic aromatic substitution via the addition-elimination mechanism (Recall Section 22-4): + H3N: :N N: :N N: :N N: -CI- CI N: CI N: CI N: CI NH₂ NH₂ Repeat sequence :N N: twice more :N N: CI N: CI H₂N N: NH₂ Melamine This process is favored by the presence of three electronegative nitrogen atoms in the ring as well as the chlorine substituents, all of which help stabilize the negative charge of the intermediates. 44. CH₃CCH₃ CH₃CH₂O C + C Double Claisen C condensation OCH₂CH₃