acetaldehyde or ethanal, CH₃CHO, colorless liquid aldehyde, sometimes simply called aldehyde. It melts at -123°C;, boils at 20.8°C;, and is soluble in water and ethanol. It is formed by the partial oxidation of ethanol; oxidation of acetaldehyde forms acetic acid. Acetaldehyde is made commercially by the oxidation of ethylene with a palladium catalyst (see Wacker process). It is used as a reducing agent (e.g., for silvering mirrors), in the manufacture of synthetic resins and dyestuffs, and as a preservative. When treated with a small amount of sulfuric acid it forms paraldehyde, (CH₃CHO)₃, a trimer, which is used as a hypnotic drug.