Aldehydes and Ketones

Overview:

Aldehydes and Ketones addresses carbonyl structure, nomenclature, and physical properties of these two related families. In a special topics section, the characteristics and usage of some of the small aldehydes and ketones are addressed. Preparation of aldehydes and ketones, their reactions, and chemical and spectroscopic analyses are also included.

The unit begins with developing an understanding of the nomenclature of carbonyls, especially the common naming and numbering system derived from acids. From nomenclature, the study progresses to the physical properties of aldehydes and ketones. These properties are reinforced with the introduction of four commonly used carbonyls: formaldehyde, acetaldehyde, acetone, and methylethyl ketone. The properties, sources, uses, and dangers of these popular compounds are discussed.

The preparation of aldehydes addressed include oxidation of alcohols with pyridinium chlorochromate, alkenes with ozone, the hydroboration-oxidation reaction with terminal alkynes using disiamylborane, then the chlorination followed by hydration of the toluenes. Other preparations of aldehydes discussed include dithiane with alkyl halides and reduction of acid chlorides.

Preparations of ketones are approached initially from similar oxidation reactions. However there are a number of preparations for ketones that may not have a counterpart in aldehydes: Friedel-Crafts acylation, Keto-enol tautomerism that is reviewed from alkenes, a variation on the Grignard using several organometallics, preparation from nitriles, and preparation from carboxylic acids.

The reactions of carbonyls for both aldehydes and ketones follow a similar path. The reactions in a strong base address the issue of relative strengths of bases as well as how to produce the stronger base within an easily reproducible laboratory method. The mechanism for this important process is extensively animated to show the changes in molecular geometry that occur during the course of the reaction and to project how the reactive particles might behave. The reactions of aldehydes and ketones with Schiff’s bases produce a variety of compounds that may be easily identified by their melting points and sometimes by their appearance. They look somewhat like colorful chrysanthemums. The Schiff’s bases noted are oximes, hydrazones, phenylhydrazones, semicarbazones, and immines.

Other reactions of carbonyls are addressed: reactions in a strong acid, oxidation, reduction (using Clemmensen, Wolff-Kishner, 9-BBN, sodium borohydride, and lithium aluminum hydride), the Grignard addition, and reaction with water. Other, name reactions are introduced and noted for their use in simple test-tube tests: Tollens silver mirror, Fehlings, and Iodoform to be specific. The steps in the iodoform reaction: oxidation, halogenation, and cleavage are addressed in such a manner as to clarify the key structures that will allow this reaction.

The unit concludes with a section on chemical and spectroscopic analysis.