Page:Encyclopædia Britannica, Ninth Edition, v. 16.djvu/207

Rh METHYL 197 is distilled with lime ; the volatile bases are absorbed in hydrochloric acid ; the hydrochloric solution is evaporated ; and the sal-ammoniac which conies out at first is, as far as possible, fished out. The last mother-liquor is evaporated to dryness, and in this form represents commercial trimethylamine hydrochlorate. It is this product which serves for the preparation of methyl chloride (vide siipra), the process being founded upon the fact that a concentrated solution of the salt, when heated, breaks up 3HC1. N(CH 3 ) 3 into 2N(CH 3 ) 3 of free trimethylamine + NH 2. CH 3 HC1 of hydrochlorate of monomethylamine and 2CH 3 C1 of methyl chloride. These processes are being carried out industrially by Vincent in France. But this base trimethylamine seems destined to do more than provide us with a new refrigerat ing agent. The attempt has been made it would appear, with success to utilize it for the preparation of pure carbonate of potash from native chloride of potassium, just as ordinary ammonia, in the famous ammonia-soda process, serves for the conversion of common salt into soda- ash. Methyl Cyanides. There are two distinct bodies which, by com position and by synthesis, are both CH 3 + NC ; they are named &quot; acetonitrile &quot; (formerly called simply cyanide of methyl) and isocyanide of methyl or methylcarbamine respectively. Acetonitrile was discovered by Dumas in 1847. It may be pre pared by the distillation of a mixture of methylsulphate and of cyanide of potassium ; but is obtained more easily and in a purer state by distilling acetamide with phosphoric anhydride. Acetate of ammonia may be used instead of the amide, but it does not work so well. CH 3 .CO.O(NH 4 ) Acetate of NH 3 -A (say). CH 3. CO. (NIL) CH 3. CN Acetamide Nitrile = A-H 2 0. =A-2H 2 0. It is a colourless liquid of a pungent aromatic odour, with specific gravity 805 at 0&quot;, and boils at 82 0. When heated with aqueous potash (at the wrong end of a condenser) it breaks up with for mation of ammonia and acetate of potash. Whence we conclude that the methyl is combined more directly with the carbon of the cyanogen, thus : N {C CH 3 } + 2H 2 = NH 3 + CH 3. COOH. Acetic acid. This conclusion is supported by the action on the nitrile of nascent hydrogen, which leads to the formation of ethylamine, thus (Men- dius) : NC CH 3 + 4H = H 2 N CH 2 CH 3. Ethylamine. In either case we pass from a monocarbon to a dicarbon body, virtually from methyl to ethyl alcohol. The isocyanide is prepared by heating iodide of methyl with cyanide of silver (CH 3 I ; 2N CAg) and ether in a sealed-up tube to 130 to 140, to produce the crystalline body AgNC + NCCH 3 (and Agl). The double cyanide, when distilled with some water and cyanide of potassium, breaks up into its components, the NCAg forming (NC) 2 AgK ; and the cyanide of methyl distils over. It is a colourless liquid, characterized by quite an unbearably irritating and sickening smell. The specific gravity is 756 at 14, the boiling point 59^ C. It combines with hydrochloric acid into a crystalline salt which is readily decomposed by water into methylamine and formic acid. Whence we conclude that in this case the cyanogen is tied to the methyl by its nitrogen ; thus : C{N CH 3 }+2H 2 = H.COOH + NH 3 .CH 3. Formic acid. Methylamine. The methyl here remains methyl, being separated by an N from the cyanogen-carbon, which latter passes into formic acid. We must not close this section without at least referring to the methyl phosphincs, as being a set of bodies related to PH 3 (phosphine) as the methylamines are to NH 3 (ammonia), and similar to these in their chemical character, in so far as they are bases. The points of difference between the two series are of pretty much the same sense as those between the two prototypes. Thus, for instance, whilo trimethylamine N(CH 3 ) :j is a strong base, but inert to oxygen gas, trimethylphosphine is a relatively feeble base, but in contact with air greedily absorbs oxygen with formation of an oxide P(CH 3 ) 3 0, the like of which in the nitrogen series has no existence. Sulphur Compounds of Methyl. Substances analogous to methyl- alcohol and methyl-ether respectively can be obtained by the dis tillation of methyl sulphate of potassium with strong solutions of the potassium sulphides KHS and K 2 S respectively. The body CH 3. SH is known as methyl-mercaptane, the other (CH 3 ).,S as sulphide of methyl. Both are very volatile stinking liquids. Sulphide of methyl claims a special interest as being the starting point for the preparation of an important class of bodies called trymethyl sulphine compounds. The sulphide (CH 3 ) 2 S readily unites with the iodide CH 3 I into crystals of iodide of trimethyl sulphine, (CH 3 ) 3 S. I, a substance which is closely analogous in its chemical character to the iodide of tetramethyl-ammonium. Moist oxide of silver, for instance, converts it into a strongly basic hydrate, S(CH 3 ) 3. OH, which in its avidity for acids almost beats its analogon in the nitrogen family. An investigation of its salts was published by Crum Brown and Blaikie. Methyl Arsenides. Arseniferous bases constituted like mono- or di-methylamine (bodies such as AsH 2 CH 3, analogous to NH 2 . CH 3 ) do not seem to exist. What we do know of are (1) a trimethyl- arsine and the iodide and the hydroxide of tetramethylarsonium, -As(CH 3 ) 3, As(CH 3 ) 4 I, and As(CH 3 ) 4 OH, bodies discovered by Cahours and Riche ; (2) a whole series of monomethylic bodies, As(CH 3 )X 2 (where X = C1, Br, orX 2 =0,S), discovered by Baeyerin 1857 ; (3) the kakodyle compounds, a series of bodies, As(CH 3 ) 2. X or As(CH 3 ) 2. X 3, which were discovered and investigated by R. Bunsen in 1842. This great investigation marks an epoch in the history of organic chemistry, and our article would not be complete without at least a short summary of its results. Bunsen started in his investiga tion with a liquid which had been obtained by Cadet as early as 1760, by the dry distillation of equal parts of white arsenic and anhydrous acetate of potash, and which nobody cared to investigate because it emits fumes which have an indescribably sickening smell and an intensity of poisonous action, compared with which that of white arsenic itself appears insignificant. It was reserved for Bunsen to attack this awful substance and force it to give an account of itself. According to Bunsen, Cadet s liquid is substantially an oxide, (AsC 2 H 6 ) 2 0, which has strongly basic properties, readily exchang ing its for C1 2, &c. To obtain the pure substance, the liquor is distilled with corrosive sublimate and hydrochloric acid, which in the first instance yields the pure muriate of the base As(CH :i ) 2 Cl, in the form of a liquid volatile above 100 into vapours which take fire spontaneously in air. From this chloride of kakodyle the pure oxide is obtained by distillation with caustic potash. The pure oxide emits no fumes; its specific gravity is 1 462; it boils near 150. A mixture of its vapour with air detonates at 50 C. From the chloride again, Bunsen obtained the free radical kakodyle, (AsC 2 H 6 ) 2, by treatment with metallic zinc in a special apparatus, so constructed that all the several operations involved could be carried out without bringing the contents in contact with air, a necessary precaution, because kakodyle is a liquid which takes fire in air spontaneously even at ordinary temperatures. Pure kakodyle is a heavy colourless liquid boiling at about 170 C., and freezing at - 6. When exposed to oxygen or chlorine it suffers destructive combustion ; but on slow access of air it is oxidized into its oxide, (AsC 2 H 6 ) 2 0, and kakodylic acid; with chlorine water it unites into the chloride which it came from ; it also unites directly with sulphur and other elements ; in short, it is exactly to kako dyle compounds what potassium is to potash and potash salts, &quot;a true organic element,&quot; as Bunsen himself put it. This dis covery of Bunsen s was greeted with an enthusiasm which it is difficult in these days to realize. With us now, a radical is intrinsically a fiction ; it was different in 1842. By the isolation of kakodyle the &quot;radical&quot; notion suddenly rose from an unproved hypothesis to the rank of a theory based on experiment. Still, however much our theoretical notions may shift, Bunsen s research will stand as a piece of monumental scientific work. Kakodylic acid. As. . (CH 3 ) 2. OH, is most conveniently pre pared from the oxide by addition of water and oxide of mercury, H 2 + 2HgO supplying the H 2 + 3 required for l(AsC 2 H 6 ) 2 0. This is a crystalline monobasic acid, soluble in water. Unlike the kakodylides of the As. X 3 type, it has no smell, and is no very violent poison. It takes six grains of it to kill a rabbit. Metallic Mcthides. Examples of these are Sb(CH 3 ) 3 ; Sb(CH 3 ) s ; Mg(CH 3 ) 2 ; Zn(CH 3 ) 2 ; Pb(CH 3 ) 4 ; A1(CH 3 ) 3 ; Sn(CH 3 ) 4. To give an idea of the chemical character of this interesting class of bodies we choose zinc-methyl as a representative example, and state briefly the chief points of its chemical history. This body was discovered by Frankland in 1849. It is prepared by boiling iodide of methyl over granulated zinc in a flask connected with an inverted condenser, and so contrived otherwise that the contents are protected against access of moisture and oxygen. Under these circumstances the two in gredients gradually unite into a non-volatile and solid compound IZn. (CH 3 ). W r hen this body is heated with more of iodide of methyl, it undergoes decomposition, with formation of iodide of zinc and of dimethyl gas, I Zn CH 3 + CH 3 I = ZnI 2 + (CH 3 ) 2 , which reaction to some extent takes place unavoidably in the pre paration of the zinc salt, however great an excess of metal may be taken. What survives needs only to bo subjected to dry distillation (in the absence of air) to yield a distillate of zinc-methyl : 2I-Zn CH 3 = ZnI 2 + Zn(CH 3 ).j.