Objectives After completing this section, you should be able to identify the four types of reaction which a carboxylic acid can undergo. Study Notes You may wish to review Section 17.4 which discusses reduction of carbonyl compounds to form alcohols and Sections 20.2–20.4 which highlights the acidity of carboxylic acids, which is important to salt formation and substitution of the hydroxyl hydrogen. Nucleophilic acyl substitution (Chapter 21) and alpha substitutions (Chapter 22) are discussed later in more detail. Four Categories of Carboxylic Acid Reactions Carboxylic acid reactions are typically classified into four major categories: As carboxylic acids are easily deprotonated, they readily form a carboxylate salt which can then potentially be reacted with an electrophile to complete a substitution of the hydroxyl hydrogen. Nucleophilic acyl substitution reactions allow substitution of the hydroxyl group which leads to several carboxylic acid derivatives (e.g. acid halides, esters, amides, thioesters, acid anhydrides etc.). We will see these reactions in more detail in Chapter 21. Like other carbonyl compounds, carboxylic acids can be reduced by reagents such as LiAlH 4 . While the proton on the carbon alpha to the carbonyl group is not as acidic as the hydroxyl hydrogen, it can be removed leading to substitution at the alpha position. The scheme summarizes some of the general reactions that carboxylic acids undergo. Exercise \(\PageIndex{1}\) Show how the following transformation can be performed. Multiple steps may be required. Answer Exercise \(\PageIndex{2}\) Show how the following transformation can be performed. Multiple steps may be required. Answer