Organic Chemistry - "Change", Part 17, Alcohols

 Greetings,

This post is an introduction to reactions of alcohols. Alcohols, by themselves, or as a neutral aqueous solution, are not among the more reactive organic compounds. This is related to the fact that the -OH functional group does not leave the molecule very readily (is a poor leaving group).  However, alcohol reactions can be induced by the use of certain reagents.

Two Examples - Protonation and Oxidation

1. Addition of an Acid: When an acid is added to an alcohol, the oxygen of the hydroxyl group readily bonds to a proton from the acid. This produces a water molecule (with a positive charge) in place of the original -OH group. Water is a much better leaving group (than -OH), so water comes off of the molecule leaving a positive charge on the carbon atom (that -OH was bonded to). The result is a carbocation, which can readily convert into an alkene by loss of a proton from the adjacent carbon.

2. Oxidation: For a primary alcohol, oxidation produces an aldehyde. Depending on the reagents used, further oxidation to a carboxylic acid may occur. Oxidation of a secondary alcohol (-OH carbon bonded to two other carbons) produces a ketone. Oxidation occurs when oxidizing agents, such as KMnO4, are added.

Future posts will expand on the two general examples, discussed above.

That's all for this post.  As always, thank you for reading!