Volume 1
A dictionary of applied chemistry / by Sir Edward Thorpe, assisted by eminent contributors.
- Thomas Edward Thorpe
- Date:
- 1912-1913
Licence: Public Domain Mark
Credit: A dictionary of applied chemistry / by Sir Edward Thorpe, assisted by eminent contributors. Source: Wellcome Collection.
17/776 page 5
![Wurtz, Ann. Chirn. Phys. [3] 48, 70 ; Geuther, Annalen, 126, 63). To prepare acetal by Wurtz’s method, 2 parts alcohol are added to a mixture of 3 parts man¬ ganese dioxide, 3 parts sulphuric acid and 2 parts water, and, after the effervescence first produced has subsided, the whole is heated at 100° until 3 parts Have distilled over. The product is then fractionally distilled, and two portions, one boiling below 80° and the second boiling at 80°-95°, are collected.1 Each fraction is treated with solution of calcium chloride and the ethereal layer which separates is distilled. The product contains aldehyde and ethyl acetate in addition to acetal; to remove these it is shaken with con¬ centrated aqueous potash, the brown liquid separated from the aqueous layer is distilled, and the distillate shaken with calcium chloride. It is then heated with twice its volume of con¬ centrated aqueous soda in sealed tubes at 100° for 24 hours, separated from the soda, distilled, the distillate again rectified: the fraction 100°- 105°, which constitutes the greater portion, is acetal. In addition to its formation as a by-product in the oxidation of alcohol, acetal can also be obtained from a mixture of acetaldehyde (1 vol.) and absolute alcohol (2 vols.) (1) by heating with acetic acid vol.) for 12 hours at 100° (Geuther, Annalen, 126, 63); (2) by cooling in a freezing mixture, passing dry hydrogen chloride to satu¬ ration, and decomposing the resulting mono- chlorether with sodium ethoxide (Wurtz and Erapolli, Compt. rend. 67, 418 ; Annalen, 108, 223); or (3) by cooling a mixture of equal volumes to —21°, and passing a current of pure hydrogen phosphide for 24 hours (Engel and Girard, Compt. rend. 92, 692 ; J. 1880, 694). Acetal is a colourless liquid with agreeable odour: b.p. 104°, and sp. gr. 0-821 at 22-4° (Stas, Annalen, 64, 322); b.p. 103-7°-104-3° at 744-4 mm., and sp. gr. 0-8314 at 20°/4° (Briihl, Annalen, 203, 25). It is soluble in 18 vols. of water at 25°, and the solubility increases as the temperature rises. Acetal is miscible in all proportions with alcohol and ether, does not reduce ammoniacal silver solution, and is un¬ altered on exposure to air; platinum black, however, oxidises it first to acetaldehyde and subsequently to acetic acid. Acetal does not give the iodoform reaction until shaken with a few drops of hydrochloric acid, whereby the acetal is hydrolysed to alcohol and aldehyde. Derivatives.—Mono-, di-, and trichloracetal are obtained as intermediate products in the preparation of chloral by passing chlorine through 80 p.c. alcohol (Lieben, Ann. Chim. Phys. [3] 52, 313 ; Patemo, Compt. rend. 67, 765). According to Krey (J. 1876, 475), a better yield of these derivatives is obtained if a mixture of 2 parts absolute alcohol, 3 parts manganese dioxide, 3 parts sulphuric acid, and 2 parts water is heated until § of the liquid has distilled over and chlorine is passed through the well- cooled distillate until it shows signs of turbidity. In either case the product is washed with water, dried over calcium chloride, and submitted to fractional distillation. The fraction £0°-120° 1 The b.p. is given as in the original paper, but, inas¬ much as b:p. of acetal is 104°, it seems probable that 95° is a misprint for some higher temperature—say 105°. contains chiefly aldehyde and compound ethers, 120°-170° chiefly monochloracetal, 170°-185° di- chloracetal (Lieben, l.c.), and the fraction boiling above 185° contains trichloracetal (Paterno, l.c.). These compounds may then be obtained in the pure state by repeated fractionation. A better method of obtaining monochloracetal is by passing chlorine through well-cooled 94-99 p.c. alcohol until the chlorinated product has a sp.gr. 1-02-1-03 at 25°. Half the original volume of alcohol is added and the mixture heated a few hours at 50°-60°. The free acid is removed by calcium carbonate; the oil washed with water, dried and fractionated. The proportion of di- and tri- chloro-derivatives formed depends on the amount of chlorine added (Eritsch, Annalen, 279, 288). Monochloracetal CH2C1.CH(0C2H6)2 (Lieben, Annalen, 146, 193 ; Paterno, Mazzara, Ber. 6, 1202; Klien, J. 1876, 336 ; Natterer, Monatsh. 3, 444 ; 5, 497 ; Wislicenus, Annalen, 192, 106 ; Frank, Annalen, 206, 341) is a colourless liquid, ! having an aromatic ethereal odour ; b.p. 155° ; j sp.gr. 1-0418 at 0°, 1-026 at 15° (Klien): 156°- 158° (Autenrieth, Ber. 24, 159). When heated with bleaching powder it yields di- and tri- I chloracetal, chloroform, and chlorinated acetal¬ dehyde (Goldberg, J. pr. Cheni. [2] 24, 107). Dichloracetal CH(T2-CH(OC2H6)2 (Jacobsen, Ber. 4, 217 ; Pinner, Ber. 5, 148 ; Annalen, 179, 34; Krey, l.c.; Paterno, Annalen, 149, 372; 150, 134); b.p. 183°-184° ; sp.gr. 1‘1383 at 14°. | When treated with hydrocarbons it forms com- ; pounds of the type CHX2-CC12 (Fritsch, Annalen, j 279, 219; Wiechell, Annalen, 279, 337 ; Butten- ; berg, Annalen, 279, 324). Trichloracetal CC13-CH(0C2H6)2 (Byasson, Bull. Soc. chim. 32, 304 ; Wurtz, Frapolli, J. 1872/438); b.p. 197°; 204-8° at 758-7 mm. j Patemo, Pisati J. 1872, 303); sp. gr. 1-2813. J When heated with concentrated sulphuric acid it yields chloral. Trichloracetal C6HnCl302. Obtained by the action of chlorine on alcohol (Lieben, Paterno, Krey, l.c.); crystallises in monoclinic needles resembling caffeine ; m.p. 89°. Monobromacetal (Pinner, Ber. 5, 149 ; Wis¬ licenus, Annalen, 192, 112 ; Fischer a. Lund- t steiner, Ber. 25, 2551 ; Freundler a. Ledru, I Compt. rend. 1905, 140, 794); b.p. 81°-82° at 27-28 mm. (Freundler). According to F. a. L. a ! cheap method of making monobromacetal is by I brominating paraldehyde at 0° with constant ! shaking ; mixing with absolute alcohol, and after standing 12 hours pouring into an ice-cold sol. i of potassium carbonate. The separated oil is dried and fractionated in vacuo. Monoiodoacetal, b.p. 100° at 10 mm.; sp. 1-4944 at 15° (Hesse, Ber. 1897, 30, 1438). ACETALS (Wurtz, Ann. Chim. Phys. [3] 48, 370). The acetals are a group of compounds formed by the combination of 1 mol. of an alde¬ hyde with 2 mols. of an alcohol, and the elimina¬ tion of the elements of 1 mol. of water. They are generally obtained as by-products in the pre¬ paration of aldehydes by the oxidation of the corresponding alcohols, the aldehyde at the mo¬ ment of formation uniting with the alcohol, and this tendency to combine is much increased if acetic acid is present (Geuther, Annalen, 126, 65), or if pure hydrogen phosphide is passed through the cooled mixture of aldehyde and](https://iiif.wellcomecollection.org/image/b31355080_0001_0017.jp2/full/800%2C/0/default.jpg)
