A brown bottle with a red cap labeled “Formaldehyde, Stabilized, ≥99%.” The label includes hazard symbols indicating flammability and health risks, as well as a Sigma-Aldrich logo. The background is plain white.

In organic chemistry, an aldehyde is an organic compound featuring a functional group represented by the structure R−CH=O, also known as a formyl group, excluding the "R" side chain. Aldehydes are characterized as having a carbon oxygen double bond, and a single carbon containing functional group. Aldehydes are versatile compounds with applications in synthetic chemistry, biology, and various industries. They contribute not only as building blocks in the synthesis of various compounds but also as solvents, perfume ingredients, and intermediates in the production of dyes and pharmaceuticals. Additionally, they are used as monomers in the formation of condensation polymers like Bakelite and Formica, used in plastics. Their significance extends to industries such as food, cosmetics, and chemical manufacturing, where they serve as solvents, starting materials, and reagents.

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Aldehydes as Building Blocks

Aldehydes remain consistently appealing as fundamental building blocks due to their facile reactivity with various nucleophiles. This inherent reactivity expands the scope of synthetic opportunities, facilitating the efficient synthesis of complex molecules like vanillin, formaldehyde, and polyformaldehyde with applications in pharmaceuticals, agrochemicals, polymers, and other fine chemicals.

Aldehydes in Fragrance and Flavors Industry

Aldehydes are prized compounds known for their pleasant odors. In the flavor and fragrance industries, aldehydic compounds offer several advantages, including intense aroma, versatility, and long-lasting effects. Their ability to enhance floral and fruity accords makes them invaluable to perfumers and flavorists. These compounds contribute to the creation of fragrances with strong and unique olfactory impressions. Additionally, aldehydes serve as fixatives in perfumery, prolonging the scent's longevity. In the flavor industry, aldehydes play a crucial role in adding authenticity and complexity to food and beverage products, helping recreate natural flavors.


Benzaldehyde, known for its aromatic properties, exhibits a distinctive bitter almond taste and odor. This compound has been identified in the volatile fractions of various sources, including mushrooms, medlar seeds, and cheese. Commonly referred to as bitter almond oil, benzaldehyde finds widespread use in the cosmetics and flavor industries. Its natural origin lies in amygdalin, a glycoside present in apricots, bitter almonds, apples, cherries, and similar sources. Commercial production of benzaldehyde involves liquid-phase chlorination and oxidation of toluene. Alternative methods reported for its synthesis include the oxidation of benzyl alcohol, hydrolysis of benzal chloride, and carbonylation of benzene.


Acetaldehyde is an organic, colorless, flammable liquid, significant in various industrial applications. It can be commercially produced from the liquid-phase oxidation of ethylene or obtained as a co-product from the oxidation of saturated hydrocarbons like propane or butane. This production versatility contributes to its availability for diverse applications.
In industry, acetaldehyde is an important solvent, widely used as an intermediate for synthesizing a broad range of compounds. Its role as a chemical intermediate is notable, particularly in acetic acid production.

Biologically, acetaldehyde is a product of ethanol metabolism in the liver, with the capability to bind covalently to various proteins, thereby altering liver function and structure. It finds applications in the enzymatic synthesis of fatty acids, showcasing its role in biological processes. Also, acetaldehyde has been employed in plasma polymerization for the deposition of reactive aldehyde groups onto substrates, demonstrating its innovative applications.

Additionally, acetaldehyde is an important volatile flavoring compound found in Sherry-like wines and many fruits. It is primarily used as a flavoring ingredient in milk products, fruit juices, and soft drinks, enhancing the sensory profiles of these products.

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