Amines and Related Nitrogen Compounds

In this chapter, we will discuss the last of the major families of simple organic compounds—the amines. Amines are relatives of ammonia that abound in nature and piay an important role in many modern technoiogies. Exampies of important amines are the painkiller morphine, found in poppy seeds, and putrescine, one of several polyamines responsible for the unpleasant odor of decaying fiesh. A diamine that is largely the creation of humans is 1,6-diaminohexane, used in the synthesis of nylon. Amine derivatives, known as quaternary ammonium salts, also touch our daily lives in the form of synthetic detergents. Several neurotoxins also belong to this family of compounds. They are toxic because they interfere with the key role that acetylcholine, also a quaternary ammonium salt, plays in the transmission of nerve impulses. 

In this chapter, we will first describe the structure, preparation, chemical properties, and uses of some simple amines. Later in the chapter, we will discuss a few natural and synthetic amines with important biological properties. 

8 Reaction of Amines with Strong Acids Amine Salts A WORD ABOUT... Alkaloids and the Dart-Poison Frogs 

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Amines are organic bases derived from ammonia. 

Amines are organic derivatives of ammonia. They may be primary, secondary, or tertiary, depending on whether one, two, or three organic groups are attached to the nitrogen. The nitrogen is sp3-hybridized and pyramidal, nearly tetrahedral. 

Primary and secondary amines form intermolecular N-H--N bonds. Their boiling points are higher than those of alkanes but lower than those of alcohols with comparable molecular weights. Lower members of the series are water-soluble because of N-H-0 bonding. 

Amines can be prepared by SN2 alkylation of ammonia or 1° and 2° amines. Aromatic amines are made by reduction of the corresponding nitro compounds. Amides, nitriles, and imines can also be reduced to amines. 

Amines are weak bases. Alkylamines and ammonia are of comparable basicity, but aromatic amines are much weaker as a result of delocalization of the unshared electron pair on nitrogen to the ortho and para carbons of the aromatic ring. Amides are much weaker bases than amines because of delocalization of the unshared electron pair on nitrogen to the adjacent carbonyl oxygen. Amides are stronger Bronsted acids than amines because of the partial positive charge on the amide nitrogen and resonance in the amidate anion. 

Amines react with strong acids to form amine salts. The pKas of amine salts are related to the base strength of the corresponding amines. Alkylammonium salts have pKas of 9-10 while arylammonium salts have pKas of 4-5. The fact that these salts are usually water-soluble can be exploited in separating amines from neutral or acidic contaminants. Chiral amines can be used to resolve enantiomeric acids, through the formation of diastereomeric salts. 

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