Ch_322b_20.06

Ch_322b_20.06 - Aminium Salts Protonation of primary,...

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Aminium Salts Protonation of primary, secondary or tertiary amines produces aminium salts . Aminum salts are weak acids (K a ). As conjugate acids of the free base amines (K b ), the conjugate relationship applies where pK a + pK b = 14. The aminium salts of aliphatic amines (pK b ~5) have pK a values ~9 (close to phenols). The aminium salts of aryl amines (pK b ~10) are about as acidic as carboxylic acids, pK a ~4. RNH 2 + HX RNH 3 X + - R 2 NH + HX R 2 NH 2 X + - R 3 N + HX R 3 NH X + - aminium salts . . . . . . In all of the above aminium salts, there is one or more H attached to the tetravalent nitrogen. Aminium salts are not basic because there is no nonbonding electron pair on the nitrogen atom.
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When there are four R groups (alkyl or aryl) attached to the nitrogen, the function is called a quaternary ammonium ion. N R''' R R' R'' + X - a quaternary ammonium salt Quaternary ammonium salts are prepared by the exhaustive N-alkylation of amines: R-NH 2 : R'X (-HX) X -
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This note was uploaded on 10/20/2009 for the course CHEM 322BL at USC.

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Ch_322b_20.06 - Aminium Salts Protonation of primary,...

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