5.2 Reactions of Alcohols

LEARNING GOALS

After   Chapter 5.2,    you will    be  able    to:

Predict the reaction    of  primary and secondary   alcohols    with    strong  oxidizing   agents

Recall  the reagent(s)  used    to  oxidize primary alcohols    to  aldehydes

Explain the purpose of  a   mesylate    or  tosylate    group

Describe    the process for protecting  an  aldehyde    or  ketone

The main reactions that we will see on the MCAT for alcohols include oxidation, preparation of
mesylates and tosylates, and protection of carbonyls by alcohols.

OXIDATION REACTIONS

Oxidation of alcohols can produce several products. Primary alcohols can be oxidized to aldehydes,
but only by pyridinium chlorochromate (PCC), a mild anhydrous oxidant, as shown in Figure 5.6.
This reactant stops after the primary alcohol has been converted to an aldehyde because PCC lacks
the water necessary to hydrate the otherwise easily hydrated aldehyde. With other oxidizing agents,
aldehydes are rapidly hydrated to form geminal diols (1,1-diols), which can be easily oxidized to
carboxylic acids.

Figure 5.6. Oxidation   of  a   Primary Alcohol to  an  Aldehyde    by  Pyridinium  Chlorochromate

(PCC)

Secondary alcohols can be oxidized to ketones by PCC or any stronger oxidizing agent. Tertiary
alcohols cannot be oxidized because they are already as oxidized as they can be without breaking a