AROMATIC ALDEHYDES, KETONES, AND GLYCOLS.

ALDEHYDES, CH2-7.COH.

Benzaldehyde, Benzoic Aldehyde, Bitter Almond Oil,

1031. This aldehyde results from the action of the ferment emulsine or synaptase on amygdalin, a glucoside (§ 74) contained in bitter almonds; it is also obtained by the oxidation of benzyl alcohol with dilute nitric acid; from heating benzylic dichloride, C¡Í ̧.CHC1, with water, or metallic oxides or sulphuric acid to about 50°, and by the dry distillation of a mixture of salts of benzoic and formic acids (comp. § 386):

(CH5.CO.O),Ca + (HCO.O),Ca = 2CaCO3 + 2CH.COн. The crude product obtained by the distillation of the fermented bitter almond meal contains hydrocyanic acid, from which it may be separated by shaking with ferric chloride and milk of lime, or by addition of CH.CH.OH

hydric sodic sulphite, yielding the compound

O.SO,Na

which is

then decomposed by sodic hydrate and the oil distilled. It is a colourless liquid boiling at 180°, of pleasant odour and high refracting power. Its sp. gr. 1·0504 at 15°. It dissolves in thirty times its weight of water, and in alcohol and ether in all proportions.

=

Benzilidene dichloride, benzal chloride, CH,.CHCl, isomeric with the dichlor-toluènes (§ 1012) and chlor-benzyl chloride (§ 1028), is formed by the continued action of chlorine on boiling benzyl chloride. It is a liquid boiling at 206°, giving benzaldehyde on heating with water, sulphuric acid, or metallic oxides. On heating with argentic acetate, the diacetate is formed. The corresponding bromide cannot be distilled without decomposition.

Benzilidene sulphide, CH,.CHS, obtained by the action of benzylidene dichloride on alcoholic potassic sulphide :

CH5.CHCl2+ K2S = 2KC1 + CH5.CHS,

crystallises from alcohol in colourless plates, melting between 68° and 70°, above which temperature they decompose. On treating an alcoholic solution of benzoic aldehyde with ammonic sulphide, a white amorphous body, softening at 90°-95° and insoluble in alcohol, is obtained. Analysis gives a formula C,H,S, but whether this substance (thio-picramil) corresponds to a polyaldehyde or to benzoin (which see) is not settled.

Concentrated aqueous ammonia converts benzoic aldehyde into hydrobenzamide (§§ 424 and 939):

3C6H5.CHO+ 2NH3 = 30H2 + (C6H5.CH)3N2,

which crystallises in colourless octahedræ, insoluble in water, by long boiling with which it is slowly converted into the aldehyde and ammonia. By heating to 130° it is converted into a powerfully basic isomeric body, amarine, which, since it gives a diethyl compound, is perhaps C21H16(NH)2. The same body also results when ammonia gas is passed into alcoholic benzoic aldehyde. It gives difficultly soluble monacid salts, e.g. C21 H1N2.HNO3.

Amarine on distillation yields an isomeric compound, lophine, C21 H1N2, also obtainable by heating di- and tri-benzylamine. It crystallises from alcohol in needles and melts at 270°, also giving monacid salts, e.g. 2C21 H18N2.HCl + OH2.

Substitution Products from Benzoic Allehyde.

1032. Chlorinated benzoic aldehydes are produced by heating the chlor-substitution products of benzilidene dichloride with water to a high temperature; e.g. parachlor-benzilidene dichloride, boiling point 234°, yields parachlor-benzaldehyde :

CH ̧¤1„CHC12 + OH2 = 2HCl + CH,C.CHO,

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an oil distilling at 170° without decomposition. The di- and tri-chloraldehydes may be similarly obtained; they are solids melting at 68° and 111° respectively.

Orthochlor-benzoic aldehyde is obtained from salicylic aldehyde by the action of phosphoric chloride, the intermediate product, orthochlorbenzilidene dichloride, b.p. 227°-230°, being decomposed by water. It boils at 210°.

Nitro-benzoic aldehyde, CH (NO2)COH, is prepared by dropping benzoic aldehyde carefully into cold fuming nitric acid; it forms colourless needles, m.p. 50°.

1033. Salicylic aldehyde, orthohydroxy-benzaldehyde :

CH(OH).COH,

occurs in different varieties of spirea, &c., from which it may be obtained by distillation with steam, also by the oxidation of saligenin and salicin with a mixture of potassic dichromate and sulphuric acid (3 parts salicin, 3 parts K2Cr2O7, 36 parts OH, 44 parts SO, H2). It is a colourless, aromatic oil, sp. gr. 1.173, solidifying at boiling at 196°, slightly soluble in water.

20,

Salicyl aldehyde combines the characters of an aldehyde with those of a phenol. It gives an intense violet coloration with iron salts, and forms compounds with strong bases, eg. CH1(OK).COH. An alcoholic copper solution gives a fine green precipitate of

From these reactions it has been improperly termed an acid, as in the case of phenol. It gives crystalline compounds with alkaline sulphites, and substitution products with chlorine, bromine, and nitric acid, &c.

秘

gode oitained from the cambium để comiteroga wool, is elunly related to vanilline It crystallises in weilute gronze of prisma, weting at 1857. Emulsin decomposes its wpurona wolution into grape sugar and emiferyl alcohol, CH,0, misiting at 74%. This latter is apparently an ethyl derivative of vaniline, was on heating with dilute sulphuric acid and potassic dichromates it is oxidized to aestic aldehyde and vanilline.

Homologues of Benzaldehyde.

1035. Paratoluic aldehyde, CHO = C,H,(CH3).CHO, is obtained by the dry distillation of a mixture of calcic paratoluate and formate, as a colourless liquid boiling at 204.

Phenyl acetic aldehyde has been similarly obtained as a gelatinous

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Cumic aldehyde, or cuminol, C10H12O = C6H1(C3H7).CHO, occurs, together with cymene, in Roman caraway oil, from which it is separated by shaking with hydric sodie sulphite as a crystalline compound, which after washing with alcohol can be decomposed with sodic carbonate. Cumic aldehyde is a colourless oil of agreeable odour; it boils at 236-237°, and is decomposed by alcoholic potash into cumin alcohol (§ 1030) and potassic cumate. Gentle oxidising agents convert it into cumic acid; chromic acid oxidises it to terephthalic acid.

1036. The ketones of the above formula contain an aromatic and an alkyl nucleus united to each other by means of CO. They are prepared by the dry distillation of a mixture of the calcic salts of an aromatic and a fatty acid (comp. § 435). The group CnH2 can evidently be united to the CO.CnH2n+1 group either by a carbon atom of the benzene nucleus or by the nucleus CnH2n in combination with the latter.

2n'-7

They unite with nascent hydrogen, yielding aromatic pinacones and secondary aromatic alcohols; on oxidation they invariably give benzoic acid.

1037. C.H.O. Phenyl-methyl ketone, or acetophenone:

CH5.CO.CH3,

is formed by the dry distillation of a mixture of calcic benzoate and

acetate :

(C6H5.CO.O)2Ca + Ca(O.CO.CH3)2 = 2CaCO3 + 2C6H5.CO.CH3, and by the action of benzoyl chloride on zinc dimethyl :

2C6H5.CO.Cl + Zn(CH3)2 = ZnCl2 + 2C6H5.CO.CH3.

It crystallises in large plates, melts at 14°, and boils at 200°; it gives a crystalline compound with hydric sodic sulphite:

C6H5OH
CH,..O.SO,Na

Nascent hydrogen converts it into secondary phenethyl alcohol; chromic and sulphuric acids oxidise it to carbonic and benzoic acids. When heated and treated with chlorine it is converted into chlor-acetoxybenzene, CH5.CO.CH,Cl, a crystalline body, melting at 41° and boiling at 246°.

1038. Two isomers of the formula C,H10O are known.

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1. Phenyl-ethyl ketone, CH5.CO.C2H, (propio-phenone), is formed by the dry distillation of calcic benzoate and propionate, and by the action of benzoyl chloride on zinc ethyl. It is a colourless oil, boiling at 208°-210°, which does not combine with alkaline hydric sulphites. Chromic acid oxidises it to benzoic and acetic acids, and by treatment of its aqueous alcoholic solution with sodium amalgam secondary phenylpropyl alcohol is formed, and in addition a pinacone :

CH5.C(OH).C2H ̧

C6H5.C(OH).C2H ̧

which crystallises from alcoholic solution in spear-shaped crystals, melting at 120°.

2. Benzyl-methyl ketone, CH5.CH2.CO.CH3, obtained from calcic acetate and phenyl acetate, is liquid, boils at 214°-216°, unites with hydric sodic sulphite, and yields benzoic and acetic acids on oxidation.

1039. Four isomers of the formula C10H120 have been prepared. 1. Phenyl-propyl ketone, CH5.CO.CH, is obtained as an oil, boiling at 220°-222°, on the dry distillation of calcic benzoate and butyrate; on oxidation it yields benzoic and propionic acids.

2. Phenyl-isopropyl ketone, CH5.CO.CH(CH3)2, prepared by distillation of calcic benzoate and isobutyrate, boils below 217° and gives benzoic, acetic, and carbonic acids on oxidation.

3. Benzyl-ethyl ketone, CH5.CH2.CO.C2H5, obtained by action of phenyl-chloracetyl on zinc diethyl, boils at 225°-226°, and gives benzoic and propionic acids when oxidised.

4. Phenethyl-methyl ketone, C6H5.CH2.CH.CO.CH3. Ethylic sodaceto-acetate (§ 786), when treated with benzylic chloride, is converted into ethylic benzyl aceto-acetate:

which on saponification gives alcohol, a carbonate, and phenethylmethyl ketone. This latter is an oil boiling at 235°-236°, and giving a crystalline compound with hydric sodic sulphite:

CH.CH2.CH2OH
CH3. SO Na H2O.

Chromic acid oxidises it to benzoic, carbonic, and acetic acids.
1040. Phenyl-isobutyl ketone:

C, H, O = CH.CO.CH..CH(CH3)2,

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is obtained by the dry distillation of calcic benzoate and isovalerate; it boils at 225°-226°, and yields benzoic and isobutyric acids on oxidation.

AROMATIC GLYCOLS.

1041. Only a single true aromatic glycol has yet been obtained with certainty.

Tollylene glycol, xylene glycol, or paraphenylene dicarbinol, CH10O2 = C6H,(CH2.OH)2. Paraxylene, when treated with chlorine gas at 140°, gives tollylene dichloride, CH(CH2Cl)2, melting at 100°, or with bromine yields tollylene dibromide, CH1(CH2Br)2, in plates melting at 145°-147°. When these haloids are heated at 180° with 30 times their weight of water, they are converted into the glycol tollylene dihydrate, CH,(CH2.OH)2, which crystallises in needles melting at 112°-113°, and is readily soluble in water. Tollylene diiodide, CH4(CHI), obtained by heating the glycol with hydriodic acid, forms fine needles, melting at 170° with decomposition and readily soluble in chloroform.

The halogen compounds react with potassic acetate at 140°, forming tollylene diacetate, crystalline plates, and when treated with alcoholic potassic hydrate give the monethyl ether of tollylene glycol,