Silicon ethyl-triethylate, or ethylic orthosilico-propionate:

C2H5

Si=(OC2H5)3

When purified by fractional distillation the compound is obtained as an ethereal liquid of agreeable odour, boiling at 159°, insoluble in water, though slowly altered by it. By heating with three molecules of acetic chloride to 180° it forms

Silicon ethyl-trichloride, Si(C2H5)Cl3, a liquid boiling between 90° and 110°:

Si(C2H5)(O.C2H5)3 + 3C2H2O.Cl = 3C2H5.O.C2H2O + Si(C2H5)Cl3, which is slowly converted by water into

Silicon ethyl-oxyhydrate, Si(CH3)O.OH:

This latter compound forms an insoluble white powder; on heating in air it smoulders, leaving carbonaceous silicic anhydride. It is dissolved by potassic hydrate, probably forming the salt Si(CH3)O.OK. In its constitution this weak acid corresponds to propionic acid, and is therefore designated silico-propionic acid:

347. Zinc methyl and sodium act only with great difficulty on ethylic orthosilicate. The mixture must be heated for a long time, finally to 300°, when, according to the equation:

2Si(OC2H5)4 + Zn(CH3)2 + Na2 = 2NaO.C2H5 + Zn
+2Si(CH3) (C2H5O)39

silicon methyl-triethylate is formed. This boils at 145°-151°, and on treatment with hydriodic acid is converted into silicon methyl-oxyhydrate:

Si(CH3)(C2H5O)3 + 3HI= 3С2HыI + H2O + Si(CH3)O.OH. This latter compound is insoluble in water, smoulders on heating in air, has the properties of a weak acid, and, on account of the analogy of its constitution to that of acetic acid, is termed silico-acetic acid.

TIN COMPOUNDS OF THE ALCOHOL RADICALS.

348. Tin unites with two, three, or four alcohol radicals, but only the bodies of the last group :

occur as simple molecules, whilst the tri and di derivatives occur as radicals in combination with other elements, or united with a further quantity of themselves, forming complex molecules:

so that the tin in all these compounds behaves as a tetrad.

The ethyl compounds have been most investigated.

349. The tin ethyl compounds can be conveniently prepared by action of ethylic iodide upon the alloy prepared by fusing together sodium and tin. This latter is powdered and placed in a flask provided with an inverted condenser, covered with the iodide, and the reaction started by application of a gentle heat. Once commenced, it proceeds with such energy that the flask must be cooled by immersion in water. When the temperature falls the reaction is completed by

heating.

Different compounds are obtained according to the amount of sodium in the alloy and to the proportion of the different ingredients present.

By employment of an alloy very poor in sodium, and an excess of ethylic iodide, stan-diethyl diiodide, Sn(C2H5)212, and stan-triethyl iodide, Sn(C2H5),I, are mainly formed, the latter being formed in larger quantity the larger the amount of sodium in the alloy. If the amount of sodium reaches 20 % there are obtained only the free radicals distan-tetrethyl, Sn2(C2H5), and distan-hexethyl, Sn(C2H5). These latter are extracted from the mixed products, which contain sodic iodide and excess of zinc, by means of ether, and are obtained mixed together on evaporation of the filtered solution in an atmosphere of carbonic anhydride. They can be separated by means of alcohol, in which distan-hexethyl is scarcely soluble, whilst distantetrethyl is readily dissolved.

On distilling the reaction-mass directly from the sand bath the distan-hexethyl passes over nearly unaltered, but distan-tetrethyl decomposes into tin and stan-tetrethyl, which volatilises. The two bodies in the distillate can be separated by fractional distillation.

Pure tin in the shape of tin filings only acts on ethylic iodide at high temperatures or in sunlight. Stan-diethyl diiodide is the main product:

Sn+2C2H,I= Sn(C2H5)2I2.

Stan-tetrethyl is most conveniently prepared by careful mixing of two molecules of zinc ethyl with one molecule of stannic chloride and afterwards distilling:

SnCl,+2Zn(C2H5)2 = 2ZnCl2 + Sn(C2H5).

The halogen compounds of the radicals poorer in ethyl also yield stan-tetrethyl when treated with zinc ethyl:

Sn(C2H5)2I2+Zn(C2H5)2 = ZnI2 + Sn(C2H5)4.

350. The alcohol radicals united to tin can be easily replaced one after another by halogens. If, for instance, stan-tetrethyl be treated with a molecule of iodine, it yields ethylic iodide and stan-triethyl iodide :

Sn(C2H) + I2 = C2H¿I + Sn(C2H5)зI.

2

This by more iodine is converted into stan-diethyl diiodide:

Sn(C2H ̧)3I + I2 = C2H¿I + Sn(C2H5)2I2.

This latter on heating with iodine is converted into stannic iodide : Sn(CH3)2I2 + 212 = 2C2H2I + SnI ;

but so far attempts to prepare a stan-ethyl triiodide in this way have not met with success. Hydrochloric acid converts stan-tetrethyl into stan-ethyl chlorides and ethane :

Sn(C2H5) + HCl = Sn(CH3)3Cl + C2H6

4

5/3

Sn(CH)3Cl + HCl = Sn(C2H3)2Cl2 + C2H6.

Stan-diethyl Compounds.

351. Stan-diethyl, or distan-tetrethyl, Sn(C2H5). As mentioned above, distan-tetrethyl is separated from the distan-hexethyl formed at the same time by means of alcohol; from this solution it is precipitated by water as a colourless, thick, oily liquid of 1.558 sp. gr. From the air it absorbs oxygen, and similarly unites with the halogens to form stan-diethyl dihaloids; e.g.

It is not volatile without decomposition; on heating it is converted, with separation of tin, into stan-tetrethyl, which distils over:

The diiodide can be obtained directly by the action of ethylic iodide on

poor sodium zinc alloy, as also from zinc filings and ethylic iodide on heating or exposure to the action of sunlight :

Stan-diethyl diiodide crystallises in colourless needles, melting at 44.5° and subliming on stronger heating. In water it is but little soluble, more readily in alcohol, readily in ether.

Stan-diethyl dichloride is best prepared by dissolving stan-diethyl oxide in hydrochloric acid and evaporation of the solution. It forms colourless needles, melting at 85°, boiling unaltered at 220°, and even sublimes on slightly heating. The vapour density is 8.553.

Both halogen compounds yield distan-tetrethyl when treated with zinc :

2Sn(C2H5)2Cl2 + 2Zn =2ZnCl2 + Sn2(C2H5)4.

In an aqueous solution of the dihaloids ammonia gives a precipitate of

Stan-diethyl oxide, Sn(C2H3)2O:

a white powder insoluble in water, alcohol, and ether, soluble in acids forming salts. The dinitrate, Sn(C2H5)2(O.NO2)2, crystallises in prisms; the sulphate, Sn(C2H5)2SO4, in plates.

is a thick liquid, insoluble in alcohol, but readily soluble in ether, boiling at 265°-270° with partial decomposition.

It can be obtained from stan-triethyl iodide by action of sodium: 2Sn(C2H5)I+Na2 = 2NaI + Sn2(C2H5)6.

:

Its sp. gr. at 0° = 1.4115, its vapour density = 14.70.

It is unaffected by the air. Its odour, like that of all stan-triethyl compounds, is peculiarly penetrating.

On passing chlorine into a solution of distan-hexethyl in chloroform, stan-diethyl dichloride is obtained, according to the equation :

Sn2(C2H5)6 + 3Cl2 = 2Sn(C2H5)2Cl2 + 2C2H¿Cl;

whilst iodine, when carefully added in the cold, gives stan-triethyl iodide:

Sn2(C2H5)6 + I2 = 2Sn(C2H5)3I.

Stan-triethyl chloride, Sn(C2H5),Cl, is obtained most readily by action of hydrochloric acid on the oxide (compare § 350). It is an oily liquid, boiling at 209°, of sp. gr. 1-428, and solidifying in crystals at 0°. Its vapour acts violently on the mucous membrane.

Stan-triethyl iodide, Sn(CH3)2I, is prepared directly by aid of tin alloy poor in sodium, and is obtained in a state of purity by the fractional distillation of the product. It is a colourless oil of 1.85 sp. gr., boiling at 231°. It is miscible in all proportions with alcohol and ether.

If a solution of the halogen compound be decomposed by argentic oxide or potassic hydrate and distilled,

Stan-triethyl hydrate, Sn(C2H5)3.OH, passes over along with the water vapour. It crystallises in brilliant colourless prisms, which melt at 43° and distil at 272°. It sublimes slowly at ordinary temperatures. It is only slightly dissolved by water, but readily by alcohol and ether. It reacts strongly alkaline, and absorbs carbonic anhydride from the air. If heated for a long time to near its boiling point it evolves water and leaves the anhydride

Stan-triethyl oxide, [Sn(CH3)3]20:

2Sn(C2H5)3.OH = H2O + [Sn(C2H5)3].O.[Sn(C2H5)3], which by action of water again yields the hydrate.

The salts of stan-triethyl are mostly crystallisable, and can be prepared directly.

The sulphate, [Sn(C2H5)3]2SO4, crystallises in brilliant colourless prisms, which are more soluble in cold than in boiling water. The nitrate, Sn(CH3)3.O.NO2, is difficult to crystallise.

If stan-triethyl iodide be heated to 200° with dry sodic ethylate, Stan-triethyl ethylate, Sn(C2H5)3(OC2H5), distils over as a colourless, unpleasant-smelling liquid, of 1-2634 sp. gr. at 0°, boiling at 1900-192°. It is formed according to the equation :

Sn (C2H5)3 + Na.O.C2H, NaI + Sn (C2H5)3

I

=

O.C2H5

and decomposes with water to ethylic alcohol and stan-triethyl hydrate (§ 344).

353. Stan-tetrethyl, Sn(C,H5). The method of preparation and most important reactions of this body have already been given. It is a colourless liquid of faint ethereal odour and somewhat metallic taste, boiling at 181°. Its sp. gr. is 1·187 at 13°, the vapour density 8.021.

354. Several of the methyl compounds of tin have been prepared; they resemble the corresponding ethyl compounds.

Stan-tetramethyl boils at 78°, has at 0° sp. gr. 1-3138 and a vapour density of 6:00. Stan-trimethyl iodide, Sn(CH3)3I, is liquid, smells like mustard oil, boils at 170°, and has sp. gr. 2·1432 at 0°. Treated with sodium it does not yield distan-hexmethyl, but is decomposed according to the equation

4Sn(CH3)I + 2Na2 = 4NaI + Sn + 3Sn(CH3).

Stan-trimethyl hydrate, Sn(CH3)4.OH, forms colourless prisms, very slightly soluble in water. It reacts strongly alkaline, and readily