acidocatalizzate

Acidocatalizzate, or acid-catalyzed reactions, are chemical transformations in which an acid catalyst accelerates the reaction by increasing the electrophilicity of substrates or by stabilizing reaction intermediates. The term encompasses both Brønsted acid catalysis, where a proton is donated, and Lewis acid catalysis, where a Lewis acid accepts electron density to activate substrates.

Mechanisms commonly involve protonation of carbonyl or alcohol groups to form more reactive intermediates, generation of carbocations, or increased leaving-group ability. Protonation often makes carbonyl compounds more susceptible to nucleophilic attack, while dehydration and acetalization proceed via protonated intermediates. Lewis acids, by accepting electron density, polarize substrates such as carbonyls, alkenes, or epoxides, enabling various rearrangements and additions.

Typical examples include Fischer esterification (carboxylic acids reacting with alcohols under acidic conditions to form esters and water), acetal or ketal formation from aldehydes/ketones and diols or alcohols, and the acid-catalyzed hydrolysis of esters. Acid catalysis also underlies many rearrangements and polymerization processes, as well as the ring-opening and hydration of epoxides.

Catalysts range from mineral acids like sulfuric acid to Lewis acids such as aluminum chloride, boron trifluoride, or metal salts. Solid acid catalysts—zeolites, sulfated metal oxides, and sulfonic-acid resins—are used to improve selectivity and enable easier separation and recycling, contributing to greener processes.

Limitations include catalyst corrosivity, sensitivity to water, and competing side reactions like rearrangements or polymerization. Reaction conditions must balance reactivity, selectivity, and safety, particularly on an industrial scale.