Chapter 7: Carboxylic Acid Derivatives

Carboxylic Acid Derivatives explores the chemical behavior and transformations of carboxylic acid derivatives, which are functional groups where a heteroatom replaces the hydroxyl group of a carboxylic acid. The reactivity of these species follows a predictable hierarchy based on the stability of their leaving groups, ranging from highly reactive acid halides and acid anhydrides to less reactive esters and amides. A central principle in their chemistry is the nucleophilic acyl substitution mechanism, which typically involves a nucleophilic attack on the carbonyl carbon followed by the restoration of the double bond and expulsion of a leaving group. Additionally, bases like pyridine are essential for sequestering acidic byproducts in these transformations. While hydrogen and carbon nucleophiles—such as Grignard reagents and lithium aluminum hydride—frequently attack twice to produce alcohols, other nucleophiles generally result in a single substitution to form a new derivative. Synthesis strategies often focus on moving down the reactivity ladder, though moving up is possible by first converting a derivative back into a carboxylic acid. Key reactions discussed include the preparation of acid halides using thionyl chloride, the Fischer esterification for synthesizing esters, and the hydrolysis of various derivatives under acidic or basic conditions, such as saponification. The chapter also integrates nitriles into this category due to their equivalent oxidation state, explaining their hydration into amides. Finally, it highlights methods to bridge the gap between carboxylic acid derivatives and ketones or aldehydes, utilizing selective reagents like lithium dialkyl cuprates or Baeyer-Villiger oxidation to control the final oxidation state of the product.