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pared from the respective olefines (CnH2n) by heating with concentrated hydriodic acid (§ 163). At higher temperatures the secondary compounds easily decompose again into the olefine and hydriodic acid.

All these iodides turn brown on exposure to light, from separation of iodine, a paraffin being formed at the same time:

2CnH2n+1I = I2 + CnH2n+2•

190. Methylic iodide, CHI, is a colourless, sweet-smelling liquid, nearly insoluble in water, boils at 44°-45°, and has sp. gr. 2·199.

191. Ethylic iodide, CH3.CH2I, can be prepared as follows: A mixture of one part phosphorus with four parts absolute alcohol is placed in a retort connected with an inverted condenser, and ten parts of iodine, either solid or dissolved in alcohol, gradually added. Phosphorous iodide is formed with evolution of heat, which immediately reacts on the alcohol, the liquid generally entering into spontaneous ebullition. It is finally gently heated on the water bath for an hour, and the product distilled off. The distillate is then shaken with water to remove alcohol, and the separated iodide dried over calcic chloride and distilled.

Ethylic iodide is a colourless, strongly refractive liquid of pleasant sweetish taste, of sp. gr. 1·946 at 16° and boiling at 72°.

192. Propylic Iodides.—Normal propylic iodide, CH3.CH2.CH2.I, has sp. gr. 1782 at 0° and boils at 102°.

Isopropylic iodide, CH3.CHI.CH3, is usually prepared from glycerine by means of iodine and amorphous phosphorus. Propylene and allylic iodide are formed and are converted into isopropylic iodide by excess of hydriodic acid :

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It boils at 89° and has at 0° sp. gr. 1.735; it is not miscible with

water.

193. Butylic Iodiles, C,H,I.-Normal primary butylic iodide, CH3.CH2.CH2.CH,I, obtained from the normal primary alcohol, boils at 129°, and has sp. gr. 1·643 at 0°.

Normal secondary butylic iodide, CH3.CH2.CHI.CH,, results, by

a similar reaction to that for isopropylic iodide, by heating erythrite with hydriodic acid:

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It boils at 117-118°, and has sp. gr. 16 at 20°. It is converted into the normal secondary alcohol by treatment with moist argentic oxide.

CH3

Primary isobutylic iodide, CH>CH.CH,I, obtained from fermentation butylic alcohol, has sp. gr. 1.592 at 22°, and boils at 120.5°.

Tertiary isobutylic iodide, or trimethyl-carbin iodide:

CH

CHCI-CH

3

31

is most easily prepared from isobutylene and hydriodic acid. boiling point is 99°.

194. Amylic Iodides.-Normal primary amylic iodide :

CH3.CH2.CH2CH2.CH2I,

boils at 155°; sp. gr. 1·5435 at 0°.

a Normal secondary amylic iodide, CH3.CH2.CH2.CHI.CH 3,

boils at 146°.

a Primary isoamylic iodide, CH3>CH.CH.CH,I, fermentation amylic iodide, prepared from fusel oil, boils at 147°, and has sp. gr.

1.511 at 11°.

CH3

Secondary isoamylic iodide, CH3>CH.CHI.CH3, prepared from isoamylene and hydriodic acid, boils at 128°-130°.

195. Hexylic Iodules.-Normal primary hexylic iodide :

CH3CH2CH2.CH.CH2.CH2I.

Boiling point 179.5; sp. gr. 1·4115 at 17·5°.

a Normal secondary hexylic iodide, CH3CH2CH2CH2.CHI.CH 3, prepared from mannite and hydriodic acid:

CH(OH) + 11HI = 6H2O + 512 + C6H13I,

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boils at 167.5°, and has sp. gr. 1.4477 at 0°.

B Normal secondary hexylic iodide, CH3.CH2CH2.CHI.CH2.CH3, is prepared by heating the product of the reaction of bichlorether upon zinc ethyl:

CH2CI

CH2.C2H5

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It is a liquid of high boiling point.

The iodide of primary fermentation hexylic alcohol, probably CH3>CH.CH.CH.CH,I, distils between 172° and 175°.

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196. Of the higher homologues may be mentioned

Normal primary octylic iodide:

CH3.CH2.CH2.CH2.CH2.CH2.CH2.CH2I,

boiling at 220°–222°.

Cetylic iodide, C16H33I, prepared from cetylic alcohol by means of phosphoric iodide, is a solid body, which, after recrystallisation from alcohol, fuses at 22°.

. METALLIC ALCOHOLATES, CnH2n+1.OM.

197. The hydroxylic hydrogen of alcohols is only replaced directly, with evolution of hydrogen gas, by the most strongly positive metals, and then always with less energy than in the action of the metal upon water. The metallic alcoholates so formed are solid bodies, in great part readily soluble in alcohol, are capable of standing high temperatures without decomposition, but are very readily decomposed by water. If a metallic alcoholate be treated with water, it is converted into hydrate, with considerable evolution of heat. Unless, however, the water be in great excess the decomposition is not complete, and can be represented by the general equation:

CnH2n+1.ONa+ xHOH = уC, H2n+1.OH+yNaOH

n

+(x-3)CnH2n+1ONa + (x-y)HOH,

in which y, by employment of equal molecules of the ingredients, is invariably considerably greater than x.

The decomposition is naturally diminished by addition of alcohol, as in reverse action, on bringing together the strongest metallic bases and alcohols, some amount of metallic alcoholates are formed:

KOH + CnH2n+1.OH=CH2n+1.OK + 2H2O + (x-2)KOH

+(-2)CnH2n+1.OH.

≈H2O

The alcoholates can never be obtained pure by this last reaction; but their formation is placed beyond doubt by some of the reactions of the solutions of strong metallic hydrates in absolute alcohol, as, for instance, the formation of'metallic alkylic carbonates on passing carbonic anhydride.

These compounds are scarcely known in the case of the heavy metals, except those of aluminium and zinc, which latter result from the slow oxidation of zinc alkyls by atmospheric oxygen:

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2Zn O.CH3

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+ O2

=

O.CH3 2Zn O.CH3

as solid bodies, readily converted by water into alcohols with separation of zincic hydrate :

O.CH3 + 2HOH =
+2HOH Zn(OH)2 + 2HO.CH3.

Zu O.CH3

They are decomposed by acids and halogen compounds with still greater readiness than by water.

The best known member of the series is

198. Sodic ethylate, C2H5.O.Na = CH3.CH2.O.Na. This is readily obtained by placing one part of bright metallic sodium in ten parts of quite anhydrous alcohol. Hydrogen is given off violently, and so much heat is evolved that either the vessel must be cooled or else the metal added in small quantities and slowly. The whole of the alcohol cannot be converted into its sodium derivative by this means. In order to obtain a pure product, when all action has ceased, the excess of alcohol is removed by distillation from a water bath; a white crystalline mass remains, which is a compound of one molecule of sodic ethylate with two molecules of alcohol, C2H,.ONa, 2C,H,.OH. Either by long exposure in a vacuum or by heating to 200° in a current of hydrogen, this compound is resolved into alcohol, which volatilises, and a white, very voluminous residue of sodic ethylate, CH.ONa, which is not decomposed by a temperature of 290°.

ETHERS OR OXIDES OF THE ALCOHOL RADICALS.

CnH2n+1.O.CnH2n+1 and CnH2n+1.0.CmH,

2m+1.

199. The ethers are compounds of two alcohol radicals with one oxygen atom; they can be regarded as alcohols whose hydroxylic hydrogen atom has been replaced by an alcohol radical. They can be divided into two groups, the first or simple ethers containing two similar alcohol radicals, whilst in the second, the so-called mixed ethers, two dissimilar alcohol radicals are united together by oxygen. In this way many more ethers are possible than alcohols. The general

formula of the ethers:

CnH2n+1.0.CmHm+1 = Cn+mH2n+m+20=CnH2n+20 (if n+m=n'), being identical with that of the alcohols, numerous cases of metamerism must occur between members of the two classes of bodies.

200. Methods of Preparation. All ethers can be prepared by action of metallic alcoholates upon the haloid compounds of the alcohol radicals. Of the first the sodium compounds are best employed; of the last, the easily decomposable iodides; the action then starting without application of heat, but can be accelerated and finished by heating.

If a sodic alcoholate be heated with the iodide of the same alcohol radical, a simple ether is formed:

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2n+1 = NaI + C12H 2n+1.0.CnH2 or (CnH2n+1)20;

2n+1

whilst the derivatives of different alcohol radicals give mixed ethers, it being, as regards the end product, a matter of indifference which alcohol radical is employed as the sodium oxyderivative and which as the haloid salt:

CnH2n+1.ONa + ICmH2m+1 = NaI + CnH2n+1.0.CmH2 2m+11 or CnH2n+1.I + CmH2m+1.ONa : = NaI + CnH2n+ 1.0.CmH

2m+1.

As a rule the sodic alcoholate is not employed pure, but dissolved in an excess of the alcohol. The ether must in every case be purified by distillation.

The only cases where good yields are obtained by this process are the mixed methyl ethers, prepared from methylic iodide and sodic alcoholates; the higher homologous iodides so reacting with the alcoholates as in great part to produce olefines :

CnH2n+1I + NaO.CmH2m+1 = NaI + HO.CmH2m+1 + CnH2n.

Those salts of alcohol radicals with acids, which are not volatile without decomposition, and better the acid than the neutral salts, yield ethers and free acids when heated with alcohol to high temperatures:

and

CnH2n+1.HSO4 + CnH2n+1.OH = H2SO4 + (CnH2n+1)20

CnH2n+1.HSO4 + CmH2m+1.OH= H2SO4 + CnH2n+1.0.CmH2m+1.

Monethylic sulphate, for instance, when heated with ethylic alcohol to about 140°, decomposes into diethylic oxide and sulphuric acid:

C2H5.HSO4 + C2H¿.OH = H2SO4 + (C2H5)2O.

The simple ethers can also be prepared by heating the haloid compounds of the alcohol radicals with the anhydrons oxides of basic metals, most readily by employment of iodides and argentic oxide :

2CnH2n+11+ Ag2O= Ag2I, + (CnH2n+1)2O.

The method most frequently employed for preparing the simple ethers consists in heating the respective alcohols with sulphuric acid. Bearing in mind only the ingredients and the final products, the reaction may be represented by the equation:

2CH2n+1.OH + H2SO1 = (CnH2n+1)2O+ H2SO4 + OH2,

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in which the process appears as the splitting off of a molecule of water, from two molecules of alcohol, by the dehydrating power of the sulphuric acid-a view which was formerly held. As a matter of fact it is quite different, being essentially the same as the second method mentioned above. During the preparation of ether by heating an alcohol with sulphuric acid, it is found that water distils over before the ether, although the latter may have a lower boiling point; and, further, a very small quantity of sulphuric acid can decompose a very

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