252

COMPOUNDS OF ZINC WITH THE ALCOHOL RADICLES.

3. Action of organo-zinc compounds upon the haloid compounds of the metals, as in the preparation of mercuric-dimethyl by the action of zinc-methyl upon corrosive sublimate :—

4. Displacement of the metal in the organo-metallic compound by another more positive metal, as when sodium-ethyl is formed from zinc-ethyl by the action of sodium upon the zinc compound :

In order to illustrate the properties and mode of formation of these singular compounds, a description will now be given of a few of the organo-metallic bodies into the formation of which zinc, mercury, arsenic, and antimony enter.

(a) Compounds of Zinc with the Alcohol Radicles.

(1182) The properties of the compounds formed by zinc with the alcohol radicles are very remarkable; they furnish a good illustration of the organo-metallic compounds of a dyad metal, and these substances are further interesting in connexion with the process of isolating the alcohol radicles themselves.

ZINC-METHYL [Zn(CH3)2. Sp. gr. of vapour 3'291; Rel. wt. 475] is a very volatile, colourless, transparent, and highly mobile liquid, with a penetrating, peculiar, and insupportable odour, and boiling between 122° and 140° (50° and 60° C.). It is immediately decomposed by oxygen, chlorine, and iodine, forming compounds which are rather unstable. If placed in contact with atmospheric air, it takes fire instantaneously, burning with a beautiful greenish-blue flame, and forming white clouds of zinc oxide; in contact with pure oxygen it burns with explosion, and the presence of a small quantity of its vapour in combustible gases gives them the property of spontaneous inflammability on admixture with oxygen. When thrown into water, zinc-methyl decomposes this liquid with explosive violence, attended with flame; and if the reaction be moderated, so as to prevent any intense elevation of temperature, the sole products of the decomposition are zincic oxide and methyl hydride (marsh gas);

ZINC-METHYL-ZINC-ETHYL.

253

Zn(CH3)2+2 H ̧O=2(ЄH„H)+ZnO,H,O. Ether dissolves zincmethyl freely.

Frankland has shown that, owing to the intense attraction of zinc-methyl for oxygen and chlorine, it is possible in certain cases to employ it for effecting the substitution of methyl for oxygen and for chlorine.

In order to obtain zinc-methyl in a state of purity, methyl iodide is sealed up with an excess of dry granulated zinc, in a strong glass tube, drawn out to a capillary end, and exposed to a temperature of from 300° to 320° in an oil-bath, until all the methyl iodide has disappeared. A mass of white crystals, consisting of a compound of zinc-methyl with zinc iodide, and a colourless, mobile liquid, which is zinc-methyl, are thus formed, and at the same time a considerable quantity of gaseous methyl is produced and confined. One portion of the methyl iodide is

converted into zinc iodide and methyl,

whilst another portion yields zinc iodide and zinc-methyl,

2 CH2I + 2 Zn = ZnI2+ Zn(CH3)2

The zinc-methyl may be obtained by breaking off the capillary extremity, and allowing the included gaseous methyl to escape, and the liquid contents are separated from the solid ones by distillation at a gentle heat in an atmosphere of dry hydrogen.

(1183) ZINC-ETHYL, [Zn(E,H ̧),], or (C2H.,Zn),=123'5. Sp. gr. of vapour 4'259; of liquid 1182 at 64°; Rel. wt. 617; Boiling pt. 244° (118° C.). (Frankland, Phil. Trans. 1855.)—This compound is a colourless, transparent, mobile liquid, which refracts light strongly, and is possessed of a peculiar, powerful, but not disagreeable odour. It is not solidified by a cold of -8° (-22° C.). It may be distilled without change in vessels filled with carbonic anhydride, or with hydrogen. Zinc-ethyl is less inflammable than zinc-methyl, but its attraction for oxygen is sufficiently intense to cause it to take fire as soon as the liquid is brought into contact with that gas, or with atmospheric air, when it burns with a brilliant blue flame, fringed with green, and forms dense white clouds of zincic oxide. If a cold piece of glass, or of porcelain, be held in the flame, it becomes coated with a deposit of metallic zinc, surrounded by a white ring of the oxide of this metal. If the oxidation be allowed to take place more

254

ZINC-ETHYL-PREPARATION.

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slowly, zinc-alcohol (zinc-ethylate) Zn(Є,H),,, is the principal product; and this mode of the formation of zinc-alcohol by the direct combination of zinc-ethyl with oxygen, is certainly very remarkable. Ether dissolves it freely without change, but water immediately decomposes zinc-ethyl; hydrated zinc oxide and the gaseous ethyl hydride (Є,H,H), being the result :— Zn(¤‚H ̧)1⁄2 + 2 H2O=2 €2H2H+ZnO‚H2O.

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5

2

:

Iodine, bromine, and chlorine, decompose zinc-ethyl with great violence; if the action be moderated, iodide, bromide, or chloride of zinc is formed, whilst the corresponding compound of ethyl with the halogen is produced; in the case of iodine, the reaction may be thus represented :—

Zn(¤ ̧H ̧), +2 I2 = 2 €2H2I+ZnI ̧.

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2 5

A similar effect is produced if zinc-ethyl be heated with powdered sulphur, the double sulphide of zinc and ethyl being formed.

Preparation.-Zinc-ethyl is obtained by heating anhydrous ethyl iodide (diluted with an equal volume of anhydrous ether* to regulate the reaction) with twice its weight of well-dried granulated zinc. The mixture is introduced into a sealed glass tube, and heated in a closed vessel to about 266° (130° C.) for twelve or eighteen hours. When large quantities are required, the safest plan is to conduct the operation in a strong metallic vessel, or species of digester. A full description of this apparatus is given by Frankland in his paper. If the materials employed for the preparation of the zinc-ethyl are really anhydrous, very little permanent gas is produced, but if moisture be present, a quantity of ethyl hydride is formed. After the apparatus has become cool, the permanent gas, if any, is allowed to escape; and the zinc-ethyl is distilled from the materials employed in its preparation, in vessels filled with carbonic anhydride, or hydrogen. Particular modes of manipulation are required during the distillation and purification of the product, in order to prevent the access of air, which would oxidize and destroy the compound. For details upon these points, the reader is referred to the memoir already cited.

(1184) Sodium-ethyl.-Wanklyn found that if a piece of sodium be sealed up in a tube (previously filled with coal gas) with about 10 times its weight of zinc-ethyl, in the course of a

In order to deprive this mixture completely of moisture, it is agitated with about one-twentieth of its weight of phosphoric anhydride.

+ Pebal, however, conducts the operation in ordinary glass retorts filled with carbonic anhydride.

SODIUM-ETHYL-ZINC-AMYL.

255

few days the sodium is dissolved, a deposit of metallic zinc takes place, and a viscid liquid is formed :

3 [Zn(EH)2]+Na,=2 [Na€,H,,Zn(Є2H ̧),]+Zn.

This liquid consists of a solution of a compound of sodiumethyl and zinc-ethyl [Na€,H,,Zn(E,H,),] dissolved in an excess of zinc-ethyl, and when exposed to a temperature of 32° beautiful crystals of this compound are deposited; they fuse at about 80° (27° C.). Attempts to procure sodium-ethyl in an isolated state were unsuccessful. When the foregoing double compound is heated, an evolution of gas occurs, and an alloy of sodium and zinc, free from carbonaceous residue, is left. When exposed to the air the crystals instantly take fire, burning explosively with a yellow flame. Water decomposes them with evolution of pure ethyl hydride. The reaction with carbonic anhydride is especially remarkable, sodic propionate being formed, which combines with the zinc-ethyl, and may be obtained in a separate form by decomposing the compound with water. The reaction which gives rise to the formation of the propionate appears to be the following:

This reaction is extremely interesting, since it points out a method of forming the fatty acids by substitution from carbonic acid. Sodium-methyl has been found in like manner to yield sodic acetate, and sodium-amyl would probably furnish sodic caproate. It is remarkable that a series of monobasic acids are thus obtained from the dibasic carbonic acid.

A compound of zinc-ethyl with potassium-ethyl may be obtained by means analogous to those adopted for procuring the sodium compound; and there can be no doubt that corresponding compounds of the other alcohol radicles could be procured.

(1185) Zinc-amyl, (Zn(E,H,1),].-This body is obtained by decomposing amyl-iodide with zinc in a sealed tube, at a temperature of 356° (180°). It forms a colourless, transparent liquid, which emits fumes, and absorbs oxygen rapidly when exposed to the air; but it does not take fire spontaneously. Water decomposes it into hydrated zinc oxide and amyl hydride :

Zn(¤ ̧H11)2+2 H2O=2¤¿H12H+ZnO,H ̧Ð.

5 11

(b) Compounds of Mercury with the Alcohol Radicles.

(1186) This series is also furnished by a dyad metal. All its members may be compared in constitution with corrosive sublimate; as for instance :

(Mercuric methiodide) mercuric-methyl iodide

(Mercuric methhydrate) hydrated mercuric

methyl oxide

(Mercuric metho-nitrate) mercuric-methyl nitrate Hg

(CI

Hg

Cl

Hg CH2

Mercuric-amyl chloride

The organo-mercurial compounds, when first discovered, were obtained either by acting upon the iodide of the alcohol radicle by means of mercury in sunlight, when direct combination takes place, Hg+ЄH,I, for instance, becoming HgЄH,I; or by acting by means of corrosive sublimate upon the zinc compound of the alcohol radicle, as for instance:

Zn(Є2H ̧),+HgCl2=Hg(Є,H,),+ZnCl2 ;

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simple exchange of the two metals taking place if the compounds are presented to each other in equivalent proportions; but if the mercuric chloride be in excess the reaction takes the following form; Zn(Є2H)2+2 HgCl2=2 (Hg‚¤2H ̧Cl) +ZnCl2.

Frankland and Duppa have recently (J. Chem. Soc., 1863, 415) found that mercuric dimethyl, diethyl, or diamyl, may be obtained in quantity by the easier method of decomposing the iodide of the corresponding alcohol radicle by means of sodium amalgam in the presence of acetic ether; and the mercury compounds thus obtained can be employed as sources whence zinc ethyl, aluminum-ethyl, and other inflammable compounds of this class may be procured more easily than by methods hitherto used. Inhalation of the vapour of these compounds cannot be too carefully avoided. It acts as a cumulative poison, and gradually and completely destroys the powers of thought by a specific action on the brain.

(1187) Mercuric Dimethyl (Mercuric Methide), [Hg(EHg),]. Sp. gr. of liquid 3'069; of vapour 8.29; Rel. wt. 115; Boiling pt. 200°-205°. (about 96° C.).—In order to prepare this compound 10 parts of methyl iodide and one part of acetic ether are