hydrosulphide, or by some other suitable reducing agent, 2 atoms of oxygen being removed, whilst 2 atoms of hydrogen are introduced into the compound (1360) :— Hydrocarbon (nH2n-6) Nitro-substitute (EnH2n-7NO2) Base (En Han-N) These bases of the aniline series belong to the class of amidogen bases (1375), I atom of hydrogen having been displaced by the hydrocarbons, H.; Є,H,; ЄH,, &c., but they still retain 2 atoms of hydrogen in a form susceptible of displacement by an equal number of atoms of the alcohol radicles (p. 523). b. Pyridine Bases (ЄH-5)""N. n (1368) A series of bases, however, exists, each member of which is metameric with one of those belonging to the aniline group: but in the alkalies of this class, none of the hydrogen admits of displacement by the alcohol radicles; consequently they must be regarded as belonging to Hofmann's subdivision of nitrile bases (1375). They boil at a lower temperature than the corresponding bases of the aniline series. These compounds have been principally investigated by Anderson, and by Greville Williams. They are furnished by the destructive distillation of a bituminous shale from Dorsetshire; and many of them are also contained in the products of the distillation of bones, and of pit-coal. The following table exhibits the metameric pairs of the aniline and pyridine groups : The bases of the pyridine series correspond to ammonia in which the 3 atoms of hydrogen have been displaced by 1 atom of ARTIFICIAL BASES-PYRIDINE-PICOLINE. 5 5 513 a triad hydrocarbon, such as (Є2H2)''' or (Є,H,)"", equivalent to 3 atoms of hydrogen: none of the hydrogen in these hydrocarbons admits of displacement by the alcohol radicles, but Anderson has succeeded in obtaining from the pyridine series some remarkable bases into the composition of which platinum enters. These bases have the closest connexion with those obtained by the action of ammonium on the chlorides of platinum (973). The two platinum bases from pyridine are: 5 3 Platinopyridine = [(¤ ̧H2),Pt]N ̧. In the first of these compounds 4 atoms of hydrogen in 2 atoms of the hydrocarbon ЄH,, appear to have been displaced by one atom of platinum, which here performs the function exerted by it in the platinic compounds; whilst in the second compound the 2 atoms of hydrogen in a single atom of the hydrocarbon are displaced by the atom of platinum, the metal here discharging the function exercised by it in the platinous compounds. Picoline yields similar compounds with platinum. When the alkaloids of the pyridine group are treated with ethyl iodide, compounds are formed belonging to the class of ammonium bases (1375). Anderson has thus obtained ethylopyridium iodide [(H.)'''(Є2H¿)'N,I] and ethylopicolium iodide [(EH,)''' (Є,H)'N,I]. The hydrated oxides, procured by acting upon these compounds with oxide of silver, are not volatile, and are strongly basic. 5 (1369) Pyridine [(Є,H ̧)"'N=79]; Sp. gr. of liquid 0·9858; of vapour 292; Rel. wt. 39'5; Boiling pt. 242° (117° C.).-This base is a colourless oil with a pungent smell; it is soluble in water in all proportions. It precipitates the oxides of iron, zinc, manganese, and aluminum from their salts, and forms a blue solution with the salts of copper when added in excess. Its simple salts crystallize with difficulty, but many of its double salts -particularly its double chlorides with platinum, gold, and copper-form well-defined crystals with facility. Pyridine may be extracted from Dippel's oil (a product of the destructive distillation of bones) by treating it with hydrochloric acid, and distilling the hydrochloric solution with lime. The volatile bases which come over are submitted to fractionated distillation, collecting separately those parts which come over at about 240°. (1370) Picoline [(Є,H,)"''N = 93]; Sp. gr. of liquid 0955; of vapour 329; Rel. wt. 46'5; Boiling pt. 275° (135° C.).— This base is the one best known of the series to which it belongs. 514 PICOLINE-PARAPICOLINE. It is usually extracted from coal tar or from Dippel's oil by a process similar to that employed for pyridine, collecting separately those portions of the distillate which come over at about 270°. The name picoline was suggested by the word pix, pitch. Picoline is a colourless, very mobile, oily liquid, of a penetrating odour. It is gradually volatilized by exposure to the air, and it does not, like aniline, become brown under these circumstances. By this fact, as well as by its lower boiling point and smaller density, picoline is at once distinguished from aniline. Picoline is soluble in water in all proportions. It is not coloured violet by chloride of lime, and is not affected by the addition of chromic acid to its solutions. The salts of picoline crystallize with difficulty, and many of them are deliquescent. The hydrochlorate forms deliquescent prisms. Parapicoline (EH1N; Sp. gr. of liquid 1077).—The effect of heating picoline for several hours with from th to 4th of its weight of sodium is remarkable. A hard, dark brown resinous mass is obtained, which, when freed from the excess of sodium, and thrown into water, is gradually decomposed. An alkaline liquid is obtained containing soda and unchanged picoline, and a viscid dark-coloured oily base collects at the bottom. If this be washed and carefully distilled until the temperature rises to 380° (193° C.), the water and picoline are expelled with a little ammonium carbonate. On continuing the distillation in a current of hydrogen at a temperature which must not be allowed to exceed 400°, and rectifying the product a second time with similar precautions, a pale yellow viscid oily base, with a persistent characteristic empyreumatic odour, is obtained; it becomes brown by exposure to air. It is insoluble in water, but soluble in alcohol, ether, and the fixed and essential oils. With cupric sulphate it gives an emerald green precipitate, soluble in hydrochloric acid, with which it forms a double salt. The salts of parapicoline exhibit but little tendency to crystallize. The principal point of interest is the fact that it is a polymeride of picoline, presenting the closest analogy with nicotylia. Owing to the facility with which it undergoes decomposition at temperatures near its boiling point, it has not been practicable to ascertain the density of its vapour, but there can be little doubt that the base is diatomic, saturating 2 atoms. of a monobasic acid, and that a quantity of it represented by the formula given above would yield 2 volumes of vapour. The attempts made by Anderson to reconvert parapicoline into picoline were unsuccessful. (Edinb. Phil. Trans. xxi. 580.) Both picoline and parapicoline are isomeric with aniline. ARTIFICIAL BASES-QUINOLINE. 515 c. Quinoline Series of Bases (EH-11)""'N. (1371) In addition to the members of the aniline and pyridine series, coal tar contains a third series of bases of which quinoline Three bases of this class are at is the most important member. present known, viz. :— They combine with the hydriodic ethers, and form compounds corresponding to ammonium; quinoline, for instance, yields with iodide of ethyl an iodide of ethylo-quinolium [(E,H,)"',H,,N,I]. These compounds, therefore, like those of the pyridine group, belong to the class of nitrile bases. (1372) Quinoline, or Leukol [(E,H,)""N=129]; Sp. gr. of liquid 1·081; of vapour 4'519; Rel. wt. 64'5; Boiling pt. 462° (239° C.). —This alkali is readily obtained by decomposing cinchonia with caustic potash: the resinous mass which is separated under the name of quinoidine, during the preparation of the salts of quinia, also yields it by similar treatment. Fragments of the caustic potash are placed in a tubulated retort, moistened with a few drops of water, and powdered cinchonia is added in small quantities at a time; on applying heat, the new base passes over, accompanied by free hydrogen; if the product be redistilled, an aqueous solution of ammonia with portions of the base pass over first, and the latter portions consist of nearly pure quinoline, which may be rendered anhydrous by a second rectification, after it has stood some days upon chloride of calcium. Quinoline is a colourless oil of high refracting power; it has a disagreeable penetrating odour, and a bitter acrid taste. It remains liquid at -4°. When heated it burns with a smoky flame. When exposed to the air it becomes slowly converted into a resinous mass. If dropped upon paper it leaves a greasy stain, which quickly disappears. It is dissolved sparingly by water, but it is soluble in all proportions in alcohol, ether, wood spirit, and carbonic disulphide, as well as in the fixed and essential oils. The nitrate, the oxalate, and the acid chromate of quinoline crystallize with facility; many double salts of quinoline, 516 BASES DERIVED FROM THE ALCOHOLS. such as those which it forms with platinum, gold, palladium, and cadmium, may be obtained in beautiful crystals. The platinum salt is nearly insoluble in water. Greville Williams, by boiling I part of quinoline for ten minutes with 1 of amyl iodide, obtained a mass of crystals which he dissolved by boiling with 6 parts of water, and then mixed with excess of ammonia and boiled for an hour: he thus separated a resinous substance which is readily soluble in alcohol, and furnishes a splendid, though fugitive, blue dye. 2. Bases obtained by the action of Ammonia upon Derivatives of the Alcohols. (1373) ALLUSION has been already made (p. 77) to the remarkable manner in which the hydrogen in ammonia may be displaced by the hydrocarbons which are supposed to form the radicles of the alcohols; and in consequence of this kind of substitution, compounds are produced in which the basic character of the ammonia is fully preserved, and a new series of highly interesting bodies is obtained. The first bases of this description were procured by Wurtz, who found that when the cyanic ether, or its polymeride, the cyanuric ether of any of the alcohols, or the corresponding urea (1163), was distilled with caustic potash, a volatile base was obtained homologous with ammonia, but containing the radicle of the alcohol corresponding to the compound subjected to distillation; for example: Hofmann (Phil. Trans., 1850) found shortly afterwards that these bases may also be produced directly from ammonia, by acting upon this alkali by means of the hydriodic or the hydrobromic ethers of the different alcohols. He obtained this result by enclosing, in a long sealed tube, a mixture of a concentrated alcoholic solution of ammonia, and the bromide, or the iodide derived from the alcohol which he wished to examine. When this mixture was heated for some hours in a water-bath, combination occurred, and a hydrobromate or hydriodate of the new base was formed. When, for instance, ethyl iodide is made to act upon a solution of ammonia, the following change occurs : |