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BENZALDEHYDE (oil of bitter almonds),...
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See also:BENZALDEHYDE (oil of See also:bitter almonds), See also:C6H5CHO , the simplest representative of the aromatic See also:aldehydes. It was first isolated in 1803 and was the subject of an important investigation by J. v.See also:Liebig in 1837( Annalen,1837,2 2, p• r) . It occurs naturally in the See also:form of the See also:glucoside See also:amygdalin (C2nH22NO11), which is See also:present in bitter almonds, cherries, peaches and the leaves of the See also:cherry See also:laurel; and is obtained from this substance by See also:hydrolysis with dilute acids: C20H22NOn+2H20 = HCN+2CsH,206+C6H5CHO. It occurs See also:free in bitter almonds, being formed by an See also:enzyme decomposition of amygdalin (q.v.). It may also be prepared by oxidizing benzyl See also:alcohol with concentrated nitric See also:acid; by distilling a mixture of See also:calcium benzoate and calcium formate; by the condensation of chlor-oxalic ester with See also:benzene in the presence of See also:aluminium chloride, the ester of the ketonic acid formed being then hydrolysed and the resulting acid distilled: C61-I6+Cl•CO•COOC2H5 = C6H5CO•000C,H5+FIC1, C6H5CO•000H = CsH5CHO+See also:CO2; by the See also:action of anhydrous hydrocyanic acid and hydrochloric acid on benzene, an aldime being formed as an intermediate product: CsHs-+-ICN+HC1= C6HSCH:NH•HCI, Benzaldine hydrochloride C6FI5CH : NH•HC1+See also:H2O = NFI,CI+C6H5CHO ; and by the action of See also:chromium oxychloride on See also:toluene dissolved in See also:carbon bisulphide (A. Etard, Berichte, 1884, 17, pp. 1462, 1700). Technically it is prepared from toluene, by converting it into benzyl chloride, which is then heated with See also:lead nitrate: C6H5CH2C1+Pb(NO3)2 = 2NO2+PbC1.OH +C6H5CHO, or, by See also:conversion into benzal chloride, which is heated with See also:milk of See also:lime under pressure: C2112CHCl2+CaO = CaC12+C6HSCH0. E. See also:Jacobsen has also obtained benzaldehyde by See also:heating benzal chloride with glacial acetic acid: (751.3mm). It is only slightly soluble in See also:water, but is readily volatile in See also:steam. It possesses all the characteristic properties of an aldehyde; being readily oxidized to benzoic acid; reducing solutions of See also:silver salts; forming addition products with See also:hydrogen, hydrocyanic acid and See also:sodium bisulphite; and giving an oxime and a See also:hydrazone. On the other See also:hand, it differs from the aliphatic aldehydes in many respects; it does not form an addition product with See also:ammonia but condenses to hydrobenzamide (C6H5CH)3Nz; on shaking with alcoholic potash it undergoes simultaneous oxidation and reduction, giving benzoic acid and benzyl alcohol (S. See also:Cannizzaro); and on warming with alcoholic See also:potassium See also:cyanide it condenses to See also:benzoin (q.v.). The oxidation of benzaldehyde to benzoic acid when exposed to See also:air is not one of See also:ordinary oxidation, for it has been observed in the See also:case of many compounds that during such oxidation, as much See also:oxygen is rendered " active " as is used up by the substance undergoing oxidation; thus if benzaldehyde is See also:left for some See also:time in contact with air, water and indigosulphonic acid, just as much oxygen is used up in oxidizing the See also:indigo See also:compound as in oxidizing the aldehyde. A. v. See also:Baeyer and V. Villiger (Berichte, 1900, 33, pp. 858, 2480) have shown that benzoyl hydrogen peroxide C6H2•CO.O.OH is formed as an intermediate product and that this oxidizes the indigo compound, being itself reduced to benzoic acid; they have also shown that this peroxide is soluble in benzaldehyde with See also:production of benzoic acid, and it must be assumed that the oxidation of benzaldehyde proceeds as shown in the equations: C6H5CHO+02 =C6H5CO.O.OH, C6 H 5C O.O.O FI +C6 H 5C H O = 2 C6 H 5000H. Further see G. Bodlander, See also:Ahrens Sammlung, 1899, iii. 47o; W. P. Jorissen, Zeit. fiir phys. Chem., 1897, 22, p. 56; C. Engler and W. See also:Wild, Berichte, 1897, 30, p. 1669. The oxime of benzaldehyde (CSHSCH: N•OH), formed by the addition of See also:hydroxylamine to the aldehyde, exhibits a characteristic behaviour when hydrochloric acid See also:gas is passed into its ethereal See also:solution, a second modification being produced. The former (known as the a or benz-See also:anti-aldoxime) melts at 34–350 C.; the latter ((3 or benz-syn-aldoxime) melts at 130 C. and is slowly transformed into the a form. The difference between the two forms has been explained by A. Hantzsch and A. See also:Werner (Berichte, 1890,23, p.11) by the See also:assumption of the different spatial arrangement of the atoms (see STEREO-See also:ISOMERISM). On See also:account of the readiness with which it condenses with various compounds, benzaldehyde is an important synthetic reagent. With See also:aniline it forms benzylidine aniline C6H5CH:N•C6H5, and with See also:acetone, benzal acetone CsHSCH:CH•CO•CH3. Heated with anhydrous sodium acetate and acetic anhydride it gives cinnamic acid (q.v.); with See also:ethyl bromide and sodium it forms triphenyl-carbinol (See also:C6H5)3C•OH; with dimethylaniline and anhydrous See also:zinc chloride it forms leuco-See also:malachite See also:green C6H5CH[C6H4N(See also:CH3)212; and with dimethylaniline and concentrated hydrochloric acid it gives dimethylaminobenzhydrol, C6H5CH(OH)C6H4N(CH3)2. Heated with See also:sulphur it forms benzoic acid and stilbene: 2C,H60+S =C6HSO00H+C6H1CHS, 2C6H6CHS =2S+C14I112. Its addition compound with hydrocyanic acid gives mandelic acid C6H6CH(OH)•000H on hydrolysis; when heated with sodium succinate and acetic anhydride, phenyl-iso-crotonic acid C6H5CH : CH•CH2COOH is produced, which on boiling is converted into a-naphthol C10H7OH. It can also be used for the See also:synthesis of See also:pyridine derivatives, since A. Hantzsch has shown that aldehydes condense with aceto-acetic ester and ammonia to produce the homologues of pyridine, thus: R R ROOC•CH2 CHO See also:CH2.COOR ROOC•C—CH—C•COOR I + + I = u II +3H20. Additional information and CommentsThere are no comments yet for this article.
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