C6H5CHO

This article appears in Volume V01, Page 532 of the Encyclopedia Britannica.

Encyclopedia Britannica - Main :: BUN-CAL

C6H5CHO .
The aldehydes are characterized`by their

great

GREAT

chemical re-activity. They act as reducing agents, silver nitrate in the presence of ammonia being rapidly reduced to the

condition

CONDITION (Lat. condicio, from condicere, to agree upon, arrange; not connected with conditio, from condere, conditum, to put together)

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 RCH(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 RCH(OH)SO3Na, which are readily resolved into their components by

distillation

DISTILLATION (from the Lat. distillare, more correctly destillare, to drop or trickle down)

with dilute acids, and are frequently used for the preparation of the pure aldehyde.
With hydrocyanic acid aldehydes form the cyanhydrins RCH(OH)CN. They react with

hydroxylamine

HYDROXYLAMINE, NH2OH

and phenylhydrazine, with the formation of aldoximes and hydra-zones. (For the

isomerism

ISOMERISM

of the aldoximes see

OXIMES

OXIMES

). The hydrazones are crystalline substances which are of value in the characterization of the aldehydes. Both

oximes

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

MINERAL

acid. Semioxainazid, NH2COCONHNH2, 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

CAUSTIC (Gr. rcavvraubs, burning)

alkalies. On

heating

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
CH3CHO CH3CHCO2ZnC2H6 CH3-CHThe reaction is a general one for all aldehydes with zinc methyl and zinc ethyl, but not with the higher zinc alkyls. V. Grignard (Comptes Rendus, 1900 et seq.) showed that aldehydes combine with magnesium alkyl iodides (in absolute ether solution) to form addition products, which are decomposed by water with the
OCformation of secondary alcohols, thus from acetaldehyde and magnesium methyl iodide, isopropyl alcohol is obtained.
Ho

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