Amines

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Overview:

Amines introduces the first of the nitrogen-containing groups. In this unit structure, nomenclature, physical properties, preparations, reactions, and both chemical and spectroscopic analysis are included.

The relationship between the familiar structure of ammonia and the subsequent structure of amines provides an introduction to both the structure and the classification of amines. The naming of amines includes the common names as well as the systematic (IUPAC) names students should know. Aromatic names are included.

The section on physical properties of amines addresses the usual properties of boiling points and solubilities with emphasis on the ability or inability to form hydrogen bonds. The sharp difference in the boiling points of first, second, and third degree amines having the same molecular weights are explained, as are the differences in water solubility. The solubility increase resulting from salt formation is treated as a way of making aqueous solutions of otherwise insoluble amines. Structural features impacting Lewis basicity are discussed and explained. The basicity of aqueous solutions is addressed by using equilibrium problems involving Kb as a means of stressing the distinctly basic nature of these solutions.

Reduction reactions, substitution reactions, the Gabriel Synthesis, the Hofmann rearrangement and reduction of azides are treated in the section on preparation of amines. Reductive amination involving Schiff's bases is only one of the reduction methods described. Reduction of nitros, amides, and nitriles is also included. The mechanism for the SN2 reaction of phthalimide with alkyl halides (the Gabriel Synthesis) is shown. It is strongly advised that the student have completed the unit on substitution vs. elimination reactions prior to undertaking the study of amines. The intricacies of the Hofmann rearrangement of amides is discussed in detail. The reduction of azides is treated so that the student understands the many possibilities which arise from thinking of this reaction when developing syntheses.

The reactions of amines addressed include the Hinsberg, electrophilic aromatic substitution, nitrosation, and the Hofmann elimination. The Hinsberg is carefully developed as an appropriate test tube test to determine the degree of amine encountered. Electrophilic aromatic substitution recalls the activating nature of the aromatic amine. The formation of diazzonium salts as an intermediate pathway for the formation of numerous other types of compounds is addressed. The problems encountered when second degree amines are treated to nitrosation is addressed with the view that organic students must be aware of the dangers of many of the compounds with which they work. The E2 mechanism for Hofmann elimination using quaternaries is discussed.

The unit on amines concludes with discussion of chemical analysis. Not only is chemical analysis discussed, but the spectral analyses using IR, NMR, and CMR with amines is covered.

 

 

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