PROPERTIES OF THE ETHERS.

207

of ethyl in the alcohol and that of hydrogen in the acid change places, and hydrochloric ether and water are produced by double decomposition; or the reaction may be expressed by saying,—in the formation of the ethers of the hydracids the alcohols lose hydroxyl (HO), and receive in its place an atom of chlorine, bromine, or iodine,—the hydracid ether and water being produced; as for example:

(Є,Н¿)H→+(H)Cl=(¤‚H¿)Cl+(H)HO.

In some instances it is found advantageous to act upon the alcohol with the corresponding compound of phosphorus, which is prepared at the moment by reaction in the presence of the alcohol; as for instance, in the preparation of hydrobromic ether :Ethylphosphoric acid.

Alcohol.

Ethyl bromide.

In many instances it is best to act upon the anhydrous alcohol with the tribromide or triiodide of phosphorus, and simply to wash the product with water.

Advantage is taken of the facility with which the hydracids act upon the alcohols, in order to prepare compound ethers with acids of comparatively feeble chemical activity. If, for example, it be desired to obtain ethers of the fatty acids, such as palmitic ether, the palmitic acid is dissolved in alcohol, and a current of hydrochloric acid is transmitted, whilst the alcohol is gently heated. After the reaction has terminated, the product is washed with hot water, and the palmitic ether being insoluble in water, is readily separated from the mixture. It appears that hydrochloric ether is first formed, and this afterwards undergoes double decomposition when heated with the fatty acid :

The ethers of the dibasic acids, when converted into vapour, yield only one volume of vapour for each atom of ethyl (¤‚Í¡) which they contain: so that if two volumes of vapour be taken as the representative of the molecule of those compounds, the molecular formula of the oxalic, carbonic, and succinic ethers must be taken as containing one atom of the dibasic acid and two atoms of ethyl; the formula of carbonic ether being written [(Є,H.),Є0,].

(1140) Chemical Properties of the Ethers.-The simple ethers,

208

OCCURRENCE OF COMPOUND ETHERS READY FORMED.

5

and the compound ethers of the monobasic acids, may generally be volatilized without undergoing decomposition; but their boiling point rises about 39° (21°.6 C.) for each addition of the hydrocarbon (EH). A similar observation may be applied to the boiling point of compound ethers of different alcohols derived from the same acid, as well as to that of ethers derived from the same alcohol, though containing different but homologous acids. The ethers are generally sparingly soluble in water, but they are readily dissolved by alcohol and by ordinary ether. None of the simple ethers have as yet been detected ready formed in the vegetable kingdom, but the compound ethers appear to be not unfrequently present in fruits and some other parts of plants, which occasionally owe their fragrance to these bodies. The oil of winter-green is a methyl salicylate (CH,,,H,,), and as Cahours has shown, it may be artificially produced by the reaction of oxide of methyl upon salicylic acid. Many of the artificial essences sold by the perfumers and confectioners consist of compound ethers dissolved in alcohol; for it is a remarkable circumstance, that the pure ethers often have a repulsive odour, which is very different from that which they possess when largely diluted with alcohol. The so-called pear oil, or essence of Jargonelle pear, is an alcoholic solution of amyl acetate, Є,H,,H,2. Apple oil is a similar preparation of amyl valerate, Є,H,,,H,. Pine-apple oil is simply butyric ether (Єн ̧‚¤‚Í‚Ð ̧), diluted with alcohol (Hofmann, Ann. de Chimie, III. xxxiv. 325). Essence of melons is the ethyl compound of one of the acids of cocoa-nut oil. Essence of quinces is dilute pelargonic ether, Є,H,,,H12; and the peculiar odour of wine is found to be due to an ether, termed by Liebig and Pelouze, who discovered it, ananthic ether (from oivos, wine), and which, according to Fischer, is a mixture of rutic and caprylic ethers. This ether is stated to be the basis of Hungarian wine oil, which has been sold at a very high price for flavouring brandy.

2 52

5

5

3

5 9

9 17

(a) Ordinary Ether-Theory of Etherification.

(1141) ETHER: Ethylic or Vinic Ether, sometimes improperly called Sulphuric Ether, (H), or (C,H,,O), = 74: Sp. gr. of liquid at 32°, 07365; of vapour 2.586; Rel. wt. 37; Boiling pt. 95° (35° C.).

Preparation. Formerly ether was prepared by mixing two measures of alcohol and one measure of sulphuric acid, and distilling until it began to blacken; then a quantity of alcohol, equal to half that originally used, was added to the residue in the retort, and the distillation was again proceeded with until the ether ceased

PREPARATION OF ORDINARY ETHER.

209

to come over. The method at present in general use for the preparation of ether is that known as the 'continuous process' of Boullay. It consists in mixing together two measures of alcohol (sp. gr. 0830) and one measure of concentrated sulphuric acid; the mixture is submitted to distillation in a capacious retort, which must be connected with an efficient condenser. Through the tubulure of the retort a tube is introduced, which is in communication with a reservoir of alcohol, designed to maintain a supply of spirit sufficient to keep the amount of liquid at a uniform level in the retort, during the course of the subsequent distillation. The temperature is then rapidly raised so as to maintain the mixture in steady ebullition. The liquid which passes over consists almost entirely of ether and water, mixed with a small portion of alcohol, which has distilled over unchanged.

This process may go on without interruption until a quantity of alcohol, about 30 times as great as that originally taken, has become converted into ether. Isethionic acid is gradually formed in the residue.

Mitscherlich distilled a mixture of one part of absolute alcohol with two parts of sulphuric acid, consisting of five parts of oil of vitriol diluted with one part of water (H2SO, + H2O; sp. gr. 178 nearly), the original volume of liquid in the retort being maintained by a gradual supply of absolute alcohol; he found that for every 100 parts of alcohol consumed, about 65 of ether, 17 of water, and 18 of undecomposed alcohol were obtained: the quantity of alcohol which distils depending upon the rapidity with which the operation is conducted; the more quickly it is performed the larger being the quantity of alcohol. When absolute alcohol is used, for every 65 parts of ether obtained, 15'4 of water should be produced, the slight excess observed depending upon the presence of traces of water in the alcohol. With a more dilute alcohol the proportion of water which passes over is greater, the excess corresponding with the amount present in the alcohol. The temperature most favourable to the formation of ether is from 284° to 290° (140° to 143° C.). At a temperature of 320° (160° C.) the disengagement of sulphurous anhydride mixed with olefiant gas and oil of wine commences. If a sulphuric acid

much more dilute than one of sp. gr. 1632 (H2SO4+2H2O) be employed, the excess of water gradually distils over with the alcohol, which undergoes little change until the liquid has become sufficiently concentrated to allow the boiling point to rise to 284°, after which ether is formed as usual. Alcohol may also be converted into ether by heating it with phosphoric, arsenic, and per

210

ETHER ITS PROPERTIES.

chloric acids, as well as by means of stannic chloride, chloride of zinc, fluoride of boron, and by several other processes which will be further considered when the theory of etherification is passed under review (1142).

In order to purify the crude ether, it should be agitated with an equal bulk of water, containing of its weight of caustic soda in solution; the water combines with the alcohol, and the soda neutralizes any sulphurous acid that may have distilled over: the liquid separates into two layers, the upper one of which consists of ether holding a little water in solution. The ether may be freed from water by allowing it to stand for a day or two upon quicklime, or upon chloride of calcium: it is then to be rectified by the heat of a water-bath, and condensed in vessels kept cool with ice-cold water.

Properties. Pure ether is a very limpid, colourless, transparent, volatile liquid, of high refracting power; it possesses a powerful, penetrating, and peculiar odour, and a taste at first fiery but afterwards cooling: if taken internally it produces stimulating and intoxicating effects. Its vapour, when inhaled, at first occasions exhilaration, speedily followed by complete insensibility to pain; owing to this property it was at one time extensively administered during surgical operations, to diminish the sufferings of the patient; but its employment for this purpose has been nearly superseded by the use of chloroform, the effects of which are more speedy and certain, and are attended with less excitement to the system. Ether has a sp. gr. of 0.724 at 55°, and it is usually stated to freeze at -24° (-31° C.). It is probable, however, that the specimen which gave this result was not pure, as, according to Mitchell, it may be exposed to a cold of -146° (-99° C.) without becoming solid. From its great volatility, and the consequent depression of temperature furnished by its rapid evaporation, it is frequently employed for producing cold artificially. Ether is dissolved freely by alcohol, but sparingly by water. When agitated with an equal bulk of water, it dissolves about 6 of its volume of water, while the water takes of its bulk of ether. Ether is employed to some extent as a solvent for fatty bodies, and is used in the proximate analysis of organic matters for separating the fats or oils which they contain, from other substances which are not soluble in ether. Iodine, sulphur, and phosphorus are dissolved by ether. Ammoniacal gas, and nitric oxide, are also freely absorbed by it: certain metallic salts are likewise dissolved by it; among these are platinic chloride, and ferric chloride with stannic chloride it forms a volatile crystalline com

I

8

ETHER-PRODUCTS OF ITS DECOMPOSITION.

211

pound 2[(Є2H.),],SnCl ̧; and a similar compound containing titanium may likewise be procured. Mercuric chloride and trichloride of gold are also freely soluble in ether; these two compounds may be separated from their solutions in water, by agitation with ether, and they rise with it to the surface when left

at rest.

Ether is highly inflammable, and as it is also very volatile and furnishes a vapour of considerable density, care must be taken not to pour it out in the vicinity of a flame; many serious accidents have arisen from a neglect of this precaution. In certain proportions its vapour forms an explosive mixture with air or oxygen. When burned with a sufficient supply of oxygen it produces only water and carbonic anhydride. Its flame is more luminous than that of alcohol, and it deposits charcoal on cold bodies which are introduced into it. When passed through ignited porcelain tubes filled with fragments of porcelain it is decomposed; charcoal is deposited, and aldehyd is found among the products. If the temperature be not too high, a large quantity of acetylene (¤‚H2; 1208) is obtained, mixed with olefiant gas. If burned at a lower heat with insufficient access of air, it yields a mixture of aldehyd with acetic acid and acetal; but aldehyd is the predominating ingredient. This formation of aldehyd is easily explained, since the substitution of one atom of oxygen for two of hydrogen in one molecule of ether, furnishes the elements of two molecules of aldehyd, the hydrogen combining with another atom of oxygen, and being eliminated in the form of water:

If ether be kept in vessels partially filled with air, it gradually absorbs oxygen, and acetic acid is formed. When treated with concentrated sulphuric acid, ordinary ether becomes converted into ethylsulphuric acid; and if this liquid be boiled, sweet oil of wine mingled with sulphurous anhydride passes over; the mixture blackens considerably, and ethionic and isethionic acids are formed in the retort.

Nitric acid acts powerfully upon ether with the aid of heat, forming carbonic, acetic, and oxalic acids.

If ether be saturated with hydrochloric acid and distilled, hydrochloric ether is the product; and the effects of hydrobromic and hydriodic acid are analogous, though the bromide and iodide of ethyl are less easily produced. Chlorine acts violently upon ether, converting it into various substitution compounds (1174),