Organic Chemistry: Concepts and Applications - Headley Allan D. 2020
An Overview of the Reactions of Organic Chemistry
6.5 Oxidation Reactions
Based on one of the definitions that was learned in general chemistry, oxidation is the supply of oxygen and/or the removal of hydrogen and electrons from molecules. Oxidation reactions are the opposite of reduction reactions, which are discussed in Section 6.4. Oxidizing agents typically are reagents that have oxygen atoms. Thus, the following molecules are good oxidizing agents: Na2Cr2O7, KMnO4, OsO4, and O3 (ozone) since they all contain oxygen. In organic chemistry, we will frequently encounter oxidation reactions in which there is also a removal of a hydrogen atom from molecules. Shown below are examples of oxidation reactions, in which oxygen is added (or a change in oxidation state of oxygen is achieved) in going from the reactant to the organic product, and at the same time, a hydrogen atom is removed as shown in the reactions in Reactions.
(6-20)
(6-21)
(6-22)
Note that in the oxidation of alcohols, the hydrogen that is bonded directly to the carbon that has the —OH group (indicated in red) is lost. Thus, based on this observation, a tertiary alcohol is not expected to undergo oxidation.
Also notice that the hydrogen that is removed during the oxidation of an aldehyde is the hydrogen that is bonded to the carbonyl carbon. Thus, a ketone is not expected to be oxidized since it does not have a hydrogen atom bonded to the carbonyl carbon, as shown below.
A very practical application of oxidation reactions is to detect the presence of alcohol for drivers suspected to be intoxicated, also known as driving while intoxicated of alcohol (DWI). In this test, Na2Cr2O7 is used as an oxidizing agent, which has an orange color, and after it oxidizes ethanol to acetic acid, it changes to green, the reaction is given in Reaction (6-23).
(6-23)
Problem 6.7
i. Give the oxidation products for the following reactions.
ii. Give the organic reactant that is needed to give the following oxidation products shown for the reactions below.
Note that the last question of Problem 6.7 is intended to get students to think critically about these reactions by reversing the thinking process and coming up with possibilities for reactants to give a desired organic product.