Ch_322b_20.11

Ch_322b_20.11 - Reactions of Amines The chemistry of amines...

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Unformatted text preview: Reactions of Amines The chemistry of amines is determined by the nonbonding electron pair on nitrogen. Amines are bases and nucleophiles. The amino group as a substituent on a benzene ring is a powerful activating group and ortho-para director in electrophilic aromatic substitution: NH 2 : E + NH 2 : E ortho and para N: + H + N: N-H + base + R-X N-R + + X- nucleophile Diazonium Ions: Reaction of Primary Amines with Nitrous Acid Nitrous acid, HNO 2 , is unstable and is prepared in the reaction mixture from a nitrite salt and a mineral acid such as HCl or HBr in the presence of the amine. overall chemistry RNH 2 + NaNO 2 + 2 HX H 2 O sodium nitrite R-N N: X- + diazonium salt unstable + NaX + 2 H 2 O A Mechanism for Diazotization of Primary Amines Na + :O N=O : : : :- sodium nitrite + H-OH 2 + H-O N=O : : : : + NaX nitrous acid : : The unstable nitrous acid is formed by protonation of the nitrite ion. formation of nitrosonium ion H-O N=O : : : : + H-OH 2 + : H-O N=O : : : H + : N=O : : : + + H 2 O nitrosonium ion nitrosation of amine R-NH 2 : + N=O : : : + R-N- N=O : : : H H + N-nitrosoamine dehydration of N-nitrosoamine A series of deprotonation and reprotonation steps leads to dehydration:...
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Ch_322b_20.11 - Reactions of Amines The chemistry of amines...

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