Online Encyclopedia


Online Encyclopedia
Originally appearing in Volume V01, Page 532 of the 1911 Encyclopedia Britannica.
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C6H5CHO. The aldehydes are characterized`by their great chemical re-activity. They act as reducing agents, silver nitrate in the presence of ammonia being rapidly reduced to the condition of metallic silver. They are easily oxidized to the corresponding fatty acid, in many cases simply by exposure to air. Nascent hydrogen reduces them to primary alcohols, and phosphorus pentachloride replaces the carbonyl oxygen by chlorine. They form many addition compounds, combining with ammonia to form aldehyde ammonia s of the type R•CH(OH)•NH,. . These are colourless crystalline compounds, which are most readily prepared by passing ammonia gas into an ethereal solution of the aldehyde. With sodium bisulphite they form the so-called bisulphite compounds R•CH(OH)•SO3Na, which are readily resolved into their components by distillation with dilute acids, and are frequently used for the preparation of the pure aldehyde. With hydrocyanic acid aldehydes form the cyanhydrins R•CH(OH)•CN. They react with hydroxylamine and phenylhydrazine, with the formation of aldoximes and hydra-zones. (For the isomerism of the aldoximes see OXIMES). The hydrazones are crystalline substances which are of value in the characterization of the aldehydes. Both oximes and hydrazones, on boiling with dilute acid, regenerate the parent aldehyde. The hydrazones are best prepared by mixing the aldehyde with phenylhydrazine in dilute acetic acid solution, in the absence of any free mineral acid. Semioxainazid, NH2•CO•CO•NH•NH2, has also been employed for the identification of aldehydes (W. Kerp and K. Unger, Berichte, 1897, 30. p. 585)• Aldehydes are converted into resins by the action of caustic alkalies. On heating with alcohols to loo° C. they form acetals, and they also form condensation products with para-amido-di-methyl-aniline (A. Cahn, Berichte, 1884, 17, p. 2939). They react with the zinc alkyls to form addition products, which are decomposed by water with formation of secondary alcohols (K. Thurnlach, Ainalen, 1882, 213, p. 369) thus: Zn(C2H3)z H2O CH3•CHO CH3•CHCO2ZnC2H6 CH3-CH End of Article: C6H5CHO

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