Chapter 17: Alcohols, Esters and Carboxylic Acids

Alcohols, Esters and Carboxylic Acids explores the structure, synthesis, and key reactions of three vital organic functional groups: alcohols, esters, and carboxylic acids. Alcohols, defined by the hydroxyl group, are classified as primary, secondary, or tertiary based on the attachment points of the carbon atom bonded to the -OH group. Their physical properties, such as higher boiling points and miscibility with water, are explained by the strong intermolecular forces arising from hydrogen bonding. Discussing their acidic nature, the text clarifies that ethanol acts as a weaker acid compared to water because the electron-donating inductive effect of the alkyl group stabilizes the negatively charged oxygen in the resulting alkoxide ion, making it a stronger base and less likely to donate a proton. Methods for producing alcohols include the industrial hydration of ethene (using steam and a phosphoric(V) acid catalyst) and laboratory preparations like the reduction of aldehydes (to yield primary alcohols) or ketones (to yield secondary alcohols), nucleophilic substitution of halogenoalkanes, and the hydrolysis of esters. The characteristic reactions of alcohols include complete combustion to carbon dioxide and water, substitution with hydrogen halides to form halogenoalkanes, and the reaction with active metals like sodium, which breaks the oxygen-hydrogen bond to produce a metal alkoxide salt and hydrogen gas. A key set of reactions involves oxidation, which serves as a method to distinguish between alcohol classes: primary alcohols can be gently oxidized to aldehydes or vigorously oxidized under reflux to carboxylic acids; secondary alcohols are oxidized only to ketones; and tertiary alcohols remain resistant to oxidation using acidified potassium dichromate(VI) solution. Alcohols also participate in esterification, a condensation reaction with carboxylic acids using a strong acid catalyst to form fruity-smelling esters and water. Esters can be broken down by hydrolysis, which is reversible under acidic conditions, but irreversible when using a soluble base (alkali hydrolysis), yielding an alcohol and the salt of the carboxylic acid. Finally, the chapter addresses carboxylic acids, explaining that they are weak acids that undergo typical acid reactions with alkalis, reactive metals, and carbonates to form carboxylate salts. Carboxylic acids can be synthesized through the oxidation of primary alcohols or the acid hydrolysis of nitriles, and they can be reduced back to primary alcohols using lithium tetrahydridoaluminate. The chapter begins with an emphasis on making ethanol as a renewable biofuel through the fermentation of sugar extracted from crops like sugar cane.