PROPIONIC AND BUTYRIC ALDEHYDS. 347 passes over with the more volatile portion; whilst the acetal is separated from the portion which distils between 176° and 200°, by agitating it with caustic potash to remove the aldehyd and compound ethers, and then rectifying from chloride of calcium, as above directed. Acetal forms a colourless liquid, of an agreeable characteristic odour, and a flavour resembling that of hazel nuts. It is soluble in about 6 parts of water, but its solubility diminishes as the temperature rises; it is soluble in all proportions in alcohol and ether. Aqueous solutions of the alkalies, if excluded from the air, do not decompose acetal. (Stas. Ann. de Chimie, III. xix. 151.) Oxidizing agents transform it first into aldehyd, and then into acetic acid. Acetal may be regarded as a combination of aldehyd with ether; 3 molecules of alcohol concurring to the production of 1 molecule of acetal :— Wurtz, however, views it as glycol in which 2 atoms of hydrogen are displaced by 2 of ethyl; and by distilling wood spirit with oxide of manganese and sulphuric acid he has obtained a corresponding compound [E,H,(EH),,], in which 2 equivalents of methyl have taken the place of the 2 of hydrogen in glycol: this is a liquid which boils at about 185° (85° C.), of sp. gr. 0853, with a vapour density of 3'475. 2 3 6 (1252) 3. Propionic Aldehyd (E2H ̧Ð). Sp. gr. of liquid 079; of vapour 2169; Rel. wt. 29.-The aldehyds which still remain to be noticed are comparatively unimportant. Propionic aldehyd was found by Guckelberger amongst the products furnished by distilling albuminous substances with a mixture of sulphuric acid and black oxide of manganese. It passes over mixed with acetic and butyric aldehyds, as well as with the oil of bitter almonds (benzoyl hydride). Propionic aldehyd is a limpid liquid of an ethereal odour; it is soluble in water, alcohol, and ether, in all proportions. It boils between 131° and 149° (55° and 65° C.), and becomes slowly acid when exposed to the air, yielding propionic acid. 8 (1253) 4. Butyric Aldehyd (¤ ̧H ̧Ð; Sp. gr. of liquid 0·8) is obtained during the same process as the foregoing compound. It is a colourless liquid which is very sparingly soluble in water, but is freely dissolved by alcohol and ether. It has an ethereal pungent odour and a burning taste, and becomes rapidly converted into butyric acid by exposure to the air. It forms with ammonia the crystalline compound characteristic of the aldehyds, 348 BUTYRAL, VALERIC, AND OTHER ALDEHYDS. and when heated with a solution of nitrate of silver, gives a brilliant mirror of reduced metal. It boils between 154° and 163° (68° and 73° C.). Butyral (Sp. gr. of liquid at 71°, 0·821; of vapour 2·61; Rel. wt. 36) was the name given by Chancel to a compound isomeric with the foregoing body, obtained by the distillation of dry calcic butyrate when exposed to the air, it absorbs oxygen, and becomes rapidly converted into butyric acid. It, however, yields no compound with ammonia, and does not reduce the nitrate of silver. 5 (1254) 5. Valeric Aldehyd, or Valeral (ЄH1). Sp. gr. of liquid 0·82; of vapour 2'96; Rel. wt. 43 ; Boiling pt. 205° (96° C.).— This compound may be obtained in various ways. One of the best consists in oxidizing fousel oil by means of a mixture of sulphuric acid and potassic dichromate: 37 parts of the dichromate dissolved in warm water and placed in a retort, are to be gradually mixed with 49 parts of oil of vitriol, previously diluted with an equal bulk of water; 33 parts of fousel oil are then to be carefully added: the aldehyd distils over without the necessity for applying heat. If the distillate be mixed with a saturated solution of hydro-sodic sulphite (NaHSO), the compound of acid sulphite of sodium and valeric aldehyd crystallizes readily, and may be purified by recrystallization from alcohol. If these crystals be mixed with a solution of potassic carbonate, and distilled, valeric aldehyd passes over, and may be dried over chloride of calcium. This aldehyd is a highly mobile, limpid, colourless liquid, with a burning taste and a pungent, penetrating odour; its vapour takes fire easily. It is insoluble in water, but soluble in alcohol and in ether. By oxidation it is converted rapidly into valeric acid. 6. Caproic Aldehyd is scarcely known. 14 (1255) 7. Enanthylic Aldehyd, or Enanthol (E,H1). Sp. gr. of liquid o8271 at 63°; of vapour 4'17; Rel. wt. 57; Boiling pt. about 312° (156° C.).—This aldehyd is furnished by the destructive distillation of castor oil. In order to purify the crude distillate, it is agitated with baryta water, which retains the volatile acids; the oil, which rises to the surface on standing, is submitted to distillation, and is then dried by digestion on chloride of calcium. Water dissolves it sparingly. It rapidly absorbs oxygen from the air, and becomes converted into oenanthylic acid. (1256) 8. Caprylic Aldehyd (H). Sp. gr. of liquid 0818; Rel. wt. 64; Boiling pt. 340° (171° C.).—This is a powerfully refract THE KETONES, OR ACETONES. 349 ing colourless liquid, with an odour of banana, and a burning taste. It is insoluble in water, and exhibits very little tendency to become oxidized; but it forms a crystalline compound with the acid sulphite of potassium, and it reduces nitrate of silver, producing a beautiful mirror-like deposit of the metal. It is easily obtained by the dry distillation of sodic caprylate. 9. Pelargonic Aldehyd has not been examined. (1257) 10, 11, and 12, Rutic, Euodic, and Lauric Aldehyd. These substances appear to be among the constituents of oil of rue. Gerhardt considered that this oil consisted mainly of rutic aldehyd, but G. Williams appears to have shown that euodic aldehyd (so named from súdng, sweet smelling) (H; Sp. gr. of liquid 08497; of vapour 587; Rel. wt. 85; Freezing pt. 44°6; (7° C.); Boiling pt. 415°4 (213° C.) is its most abundant component. Oil of rue has a somewhat viscid consistence; it possesses the strong disagreeable odour of the plant, and an acrid, bitterish, somewhat aromatic taste. Nitric acid acts rapidly upon oil of rue, and furnishes different products according to the degree of concentration of the acid; by the prolonged action of the concentrated acid, pelargonic acid (H,H) and the lower homologues of the group of acids to which it belongs are obtained; by moderating the action of the nitric acid, rutic acid (HE10H1902) is procured. Essence of rue does not absorb oxygen very rapidly, nor is it easily converted when heated with caustic potash into the rutate of this base; but it combines readily with the acid sulphites of the alkali-metals, and forms with them crystallizable compounds which correspond with those formed with the other aldehyds. (b) The Ketones, or Acetones. (1258) The ketones constitute a class of compounds closely related to the aldehyds. When the calcium or barium salt of any of the volatile monobasic acids (the molecules of which contain two atoms of oxygen) is submitted to dry distillation, the acid undergoes decomposition, and amongst the volatile products which come over, is a body which has been termed the ketone of the acid; the new body which is formed bears the same relation to the acid from which it is obtained that acetone does to acetic acid. The general properties of this class of compounds may be illustrated by a description of acetone, which has been examined with care. 350 3 6 ACETONE. 6 (1259) Acetone (¤ ̧н ̧‡‚ or С ̧Н ̧O2). Sp. gr. of liquid 0*792 ; of vapour 2002; Rel. wt. 29; Boiling pt. 133° (56° C.).—When calcic acetate is mixed with an excess of quicklime, and submitted to distillation, calcic carbonate is formed, whilst the residues from two molecules of acetic acid coalesce, and a volatile inflammable liquid passes over, to which the formula €,H ̧ has been assigned : 6 When the vapours of acetic acid are transmitted through a heated porcelain tube they are resolved into acetone, carbonic anhydride, and water; 2€,H,0 ̧=€Ð ̧+н ̧Ð+¤ ̧H ̧; but a better mode of preparing acetone than either of the foregoing ones consists in distilling crystallized acetate of lead with half its weight of quicklime. Acetone is a colourless liquid, with an agreeable ethereal odour, and a pungent taste. When heated it gives off an inflammable vapour, which burns with a clear white flame. When heated with caustic potash, it yields at a moderate temperature a mixture of potassic acetate and formiate, with liberation of hydrogen : At a higher temperature potassic carbonate and marsh gas are the result:- Acetone. Potassic carb. Marsh gas. 2 €H, ¤ ̧Н ̧Ð + 2 = Ꮊ Ꮋ Ꮎ + 2 ᏦᎻᎾ = K, €Ꮎ, + 2 When acetone with water is acted upon by an amalgam of sodium, it combines with two atoms of nascent hydrogen, H2+H2 becoming Є,H,, which is Friedel's secondary alcohol, Є(ЄH2),H,HO (p. 179), isomeric with tritylic alcohol. 3 6 2 3 8 Gerhardt and Chancel consider acetone as a species of aldehyd, in which an atom of hydrogen is displaced by its equivalent of methyl :-* * Some doubt still exists as to the true nature of the ketones. Kane at one time regarded acetone, which has been more thoroughly examined than any of the others, as a sort of alcohol (CH,O,HO; C = 6 and 0=8), which he termed mesitic alcohol; it is metameric with allylic alcohol. By distilling it with sulphuric acid he obtained a compound having the composition CH,O, which corresponds to the ether of such an alcohol, and is metameric with allylic THE KETONES, OR ACETONES. Ethylic aldehyd, Є,H,, H, being acetyl hydride, and 2 3 Acetone, being €2H ̧, ¤H, or acetyl methylide. 3 351 Acetone, however, does not admit of direct oxidation like an aldehyd, and this is a well-marked difference between this body and the aldehyds, which it otherwise so much resembles. The ketones, like the aldehyds, have the power of forming crystalline compounds with the acid sulphites of potassium and sodium, but they do not react upon aniline. Any view which is adopted for acetone would be extended to the other members of this group, which are all homologous with it; thus : Acetone = 3 6 5 10 3 3 5 2 ¤ ̧н, or ЄН ̧, ¤H,, acetyl methylide 14 41 The experiments of Williamson show that a series of intermediate double or mixed ketones may be formed by distilling mixtures of equivalent quantities of the homologous salts of calcium; for example, by distilling a mixture of acetate and valerate of calcium in equivalent proportions, the compound H12 (=¤¿н‚¤‚¤H2) is formed :— Calcic acetate. : Freund has also succeeded in obtaining acetone and propione synthetically, by decomposing acetyl chloride by means of zincmethyl and zinc-ethyl; thus:— Limpricht, in pursuing this subject, found that by mixing calcic formiate in equivalent proportion with calcic acetate, with calcic valerate, with calcic oenanthylate, or with calcic caprylate, and distilling, the corresponding aldehyds, viz., acetic, ether. He also produced other bodies corresponding to iodide and chloride of ethyl. Acetone forms with sulphuric acid a double acid (2 HO,CH ̧O,S2O). But this sulpho-acid is dibasic, unlike the true vinic acids; moreover, acetone cannot be recovered from it when it is decomposed by the hydrated alkalies; whilst all the true alcohols may be reproduced from the vinic sulpho-acids when they are decomposed in this manner by the alkalies; and he has recently published some additional experiments upon the subject (Journ. Chem. Soc., 1866.) |