Dehydraatioreaktio

Dehydraatioreaktio, also called dehydration reaction, denotes a chemical process in which a molecule loses a small molecule, typically water, to form a new bond or a more unsaturated product. In organic synthesis, dehydration refers most commonly to the removal of water from alcohols to give alkenes, often catalyzed by strong acids.

Under acid catalysis, the alcohol is protonated, water departs to form a carbocation, and elimination of a proton yields an alkene. Tertiary and some secondary alcohols follow an E1 mechanism with carbocation rearrangements; primary alcohols more often proceed via E2 or with special catalysts. Reaction conditions typically require heat and catalytic acid (for example concentrated sulfuric acid or phosphoric acid) and sometimes molecular sieves to scavenge water. Regioselectivity is described by Zaitsev’s rule: the more substituted alkene is usually formed.

Another common context is dehydration of inorganic hydrates, where heating removes crystal water from salts, producing anhydrous compounds with higher melting points. In carbohydrate chemistry, dehydration reactions can generate furan derivatives or unsaturated compounds under acidic conditions, and may occur in the degradation of sugars.

Applications of dehydration reactions include synthesis of alkenes for further functionalization, preparation of polymers, and analysis of dehydration pathways in biochemistry and geology. The term emphasizes the net loss of water and the formation of a new, often unsaturated, product.