alcools

Alcools, or alcohols, are a class of organic compounds characterized by one or more hydroxyl (-OH) groups bonded to a carbon atom. The general formula for simple aliphatic alcohols is CnH2n+1OH; when the hydroxyl is attached to an aromatic ring the compounds are called phenols, which are chemically distinct.

Classification: Based on the carbon bearing the hydroxyl group, alcohols are categorized as primary, secondary, or tertiary. Primary alcohols have the OH on a carbon bonded to at most one other carbon (examples include methanol and ethanol); secondary alcohols have the OH on a carbon bonded to two carbons; tertiary alcohols have the OH on a carbon bonded to three carbons. Aromatic alcohols such as phenol are not classified as aliphatic.

Properties and reactivity: Alcohols are polar due to the OH group and form hydrogen bonds, giving higher boiling points than hydrocarbons of similar molecular weight and, for smaller alcohols, miscibility with water. They act as weak acids, with pKa values around 15–18, and can be deprotonated to form alkoxides. Oxidation of primary alcohols yields aldehydes and then carboxylic acids, while secondary alcohols yield ketones; tertiary alcohols are generally resistant to oxidation. Alcohols can participate in dehydration to give alkenes and can react with carboxylic acids to form esters (Fischer esterification) or with alkyl halides to form ethers (Williamson ether synthesis).

Production and occurrence: Ethanol is produced mainly by fermentation of sugars, while methanol is produced from synthesis gas. Other alcohols are produced via petrochemical routes or through fermentation and biomass processing. They occur naturally in trace amounts in plants and foods.

Applications and safety: Alcohols are widely used as solvents, intermediates, and fuels. Ethanol is consumed in beverages and used as a biofuel; many alcohols serve as precursors to esters and ethers. They are generally flammable; methanol and some higher alcohols are highly toxic and require careful handling and storage.