aldehydes

[Contraction from Med Lat. alcohol dehydrogenatus =alcohol deprived of hydrogen.] Chem. Aldehydes are formed by the oxidation of alcohols, and are re-converted into alcohols by the action of nascent hydrogen; by further oxidation they are converted into acids. They differ from alcohols in having two atoms le of hydrogen, which are removed from the carbon atom containing the radical HO' (hydroxyl) connected to it in the alcohol; thus the aldehyde monatomic radical is (O=C-H)'. The carbon atom having two bonds united to an atom of oxygen, and another to an atom of hydrogen, the fourth is united to a monatomic hydrocarbon radical, or hydrogen, From monatomic alcohols only one aldehyde can be formed; from a diatomic alcohol there may be formed a diatomic aldehyde containing the radical (OCH)' twice, or an alcohol aldehyde, or acid aldehyde thus, glycol alcohol could yield IMG:content-0338.png:[merged small][merged small][merged small][merged small][merged small][ocr errors][merged small][merged small][merged small] CH3 HCO 1 Chemistry: C2H4O = or C2H30.H. Aldehyde is a colourle , limpid, suffocating smelling liquid, boiling at 22°; it is soluble in alcohol, water, and ether; its sp. gr. is 08 at 0°. It is readily oxidized into acetic acid; when heated with caustic potash it forms a resin called aldehyde resin. Heated with AgNO3 (nitrate of silver), the silver is deposited as a bright mirror, and the liquid contains silver acetate. Nascent hydrogen converts it into alcohol. Chlorine converts it into C2H2O.CI (acetyl chloride). When treated with H(CN) (hydrocyanic acid), it yields olanine , C3H7NO (amido-propionic acid). Aldehyde forms a crystallic compound with ammonia, called aldehyde ammonia, C2H4O. NH3, which forms transparent colourle crystals; these melt at 76° and distil at 100°. Aldehyde forms a crystallic compound with NaHSO3 (acid sodium sulphite). It forms polymeric modifications, paraldehyde and metaldehyde . It is prepared by the action of chlorine and weak alcohol, or by a mixture of MnO2 (binoxide of manganese) and H2SO4 (sulphuric acid), or again by distilling a mixture of pota ium acetate and formate. It unites with aniline to form diethidene - dianiline and water. * ǎl'-děn, pa. par. Holden. [See HALDE.] ( William of Palerne, Skeat's ed., 1875.)