Metallic radicles

Metallic Radicles.—The organic matter in the compound is destroyed either (a) by heating to redness for some time in contact with air in a quartz or porcelain crucible, or (b by oxidising with a mixture of cone, nitric and sulphuric acids. After decomposition is complete, the residue is examined by the usual tests for inorganic radicles. In (a) volatile radicles such as mercury, arsenic and ammonium will be lost. 

Aqueous solutions of calcium chloride, ferric chloride or silver nitrate give precipitates or colorations with certain organic acids which are valuable for the detection of these acids. It is important to use neutral solutions of the acids which at the same time do not contain metallic radicles likely to react with the reagents added. Thus the addition of calcium chloride to a solution of lead acetate may produce a precipitate of lead chloride. A neutral solution, which should be of about 10% concentration, prepared as follows, usually avoids such complications —... 

The ammonium theory.—In the ammonium theory of H. Davy, A. M. Ampere, and J. J. Berzelius, it was assumed. that the ammonium compounds contain a metallic radicle, NH4 (4.31,38), which may replace potassium, sodium, etc., in different salts. When ammonia unites with hydrogen chloride, the NH4-radicle is formed which unites with chlorine to form ammonium chloride in the same way that potassium united with chlorine forms potassium chloride. The ammonium theory thus corresponds with the ethyl theory of J. J. Berzelius, and J. von Liebig. The nitrogen is assumed to be quinquevalent, and this is in harmony with the work of V. Meyer and M. T. Lecco, A. Ladenburg, and W. Lossen on the quaternary ammonium baseb, and with the isomorphism of the ammonium and the potassium salts. 

The action is referable to the effect of the ionisation of the water in the presence of one of its salts a weak acid such as hydrocyanic is dissociated to an extent so slight as to be comparable in dissociation with water itself. Under such conditions an appreciable competition will occur between the acid of the salt and the water for possession of the metallic radicle. 

An interesting form of isomerism, dependent on the formation of such cations, is exhibited by chromic salts, which usually exist in at least two modifications, the one green and the other violet or dark blue. In both varieties the chromium is in the same state of oxidation, but the non-metallic radicle, while apparently freely ionised in a violet solution, is only partly active in the green. Thus the chlorine in violet chromic chloride, CrQj.eHjO, is completely precipitated by the addition of a soluble silver salt, but in the ordinary green variety only one-third of See Vol. X. of this series. 

J. J. Colin and H. Gaultier de Claubry made observations in Gay-Lussac s laboratory on the action of iodine on organic substances, in which they discovered the blue colour formed by the action on starch. Vauquelin investigated the action of iodine on ammonia, iron, tin, mercury, and alcohol. In 1814 English chemists besides Davy were experimenting with iodine, giving details for its preparation. J. Murray (of Saffron Walden) asked whether iodine is the metallic radicle of chlorine , or a peculiar principle elaborated in plants. 

Oxidases catalyse oxidations in presence of free oxygen. Unlike the dehydrogenases, they are unable to use methylene blue, cytochrome or similar hydrogen acceptors, and they also differ in their sensitivity to inhibitors. Thus, urethane and related narcotics have no action on oxidases, but cyanide, carbon monoxide or hydrogen sulphide in concentrations as low as 0-01 M to O OOl M inhibit them completely. This is ascribed to the fixation of an active metallic radicle, usually Fe, in the oxidase effector mechanism. 

Of the synthetic reactions of the alkyl halides that with potassium cyanide, which enabled H. Kolbe to synthesise acetic acid from a methane derivative, has already been mentioned (cf. the preparations on pp. 137 and 254). Of the simpler syntheses that of Wiirtz may be mentioned here. Metallic sodium removes the halogen from two molecules and the two radicles combine. Thus, in the simplest case, ethane is formed from methyl bromide ... 

If water is excluded this potassium salt can be isolated in the form of orange-yellow crystals which, with benzil, yield the red solution sensitive to the action of air. The solution probably contains the potassium-benzil radicle which is also obtained by the addition of metallic potassium to benzil (Beckmann and Paul,2 Schlenk 3) ... 

Of the further results of the investigation of the carbon radicles, a field still actively cultivated, only the so-called metal ketyls will be mentioned. These addition products of the alkali metals to ketones are also intensely coloured (Schlenk), e.g. 

The number of radicles or atoms attached to the metal in the first zone is termed the co-ordination number, the value for which in the case of the cobalt-ammines is almost invariably six. 

The valency of the complex radicle is the same as that of the central metallic atom when the complex contains only ammonia, substituted ammonia, water, or other neutral group. For example, cobalt in eobaltie. salts is trivalent, and the cobalt complex with ammonia, Co(NI13)8 ", is likewise trivalent copper in cupric sulphate is divalent, and the copper complex, [Cu(NH3)4] , is also divalent. In the same wn.y [Co(NH3)5.H30] " and [Co(NII3)4.(II20)2] " are trivalent, as also [Co(NH3)2.en2]" and [Co.en3] ", where en represents cthyleucdiamine, CH NH2... 

The valency of the complex, therefore, is found by subtracting the number of acidic radicles from the total valency of the metal. Thus, [Co(NH3)4.(N02)2] has two acidic radicles, the valency of the central... 

In some instances the metal complex may become the anode instead of the cathode. The acidic radicles have, in this case, increased at the expense of ammonia until there is a greater number of acidic radicles in the complex than corresponds to the valency of the metallic atom thus [Co(NH8)s.(NO,)J. If valency is determined by the above method it is found, since cobalt is trivalent, and (N02)4 has a total valency of four, that the valency of the complex, namely, three minus four, has a unit negative value. The complex is thus anodic and unites with one atom of a monovalent metal or its equivalent. The complex radicle cited, therefore, united with potassium yields the substance [Co(NH.))2.(N02)4]K, or potassium tctranitrito-diammino-eobalt,. 

Ionisation Isomerism.—This type of isomerism is very common in the metal-ammines. If two or more different acidic radicles are present in a molecule of metal-ammine, the acidic radicles may be firmly fixed in the co-ordination complex or may be outside of this. If they are outside the complex they are easily ionised and easily freed by other acids if, on the other hand, they are within the complex they are not ionised and are difficult to free by other acids. This distribution of the acidic radicles in the complex, or outside of it, gives rise to ionisation isomerism. Tor example, the compound Co(NH3)5Br(S04) is known in two forms, one violet and the other red. The violet modification in aqueous solution contains —S04" ions, which may be precipitated by barium chloride. The red variety gives no — S04" ions in aqueous solution, and barium sulphate is not precipitated by barium chloride. These two substances, bromo-pentammino-eobaltic sulphate and sulphato-pentammino-eobaltic bromide, are ionisation isomers, and are represented as ... 

According to Werner s co-ordination theory, compounds containing the radicles A, B, C, D, united with metal atom, should give optical isomers, the groups combined with metal taking up the positions,... 

The trinitro-triammine cobalt has practically no conductivity.3 Werner s theory is further supported by the fact that by the introduction of a fourth molecule of ammonia into the triacido-triammine compound the solution becomes once more conducting, as one (N02) group is displaced from the co-ordination complex. The eobalt-ammino-compounds, therefore, containing fewer than three ammino-radicles, contain non-ionisable acidic radicle, and those containing more than three contain ionisable acidic radicles. The generalisation made in connection with the triammino-eompounds led, therefore, to the establishment of the constitution of other ammino-derivatives, and also to the constitution of some of the ammino-salts of divalent and tetravalent metals. 

The best known of these compounds is potassium cobalti-nitrite, [Co(N02)6]K3.1 This salt was originally regarded as a double salt of cobaltic nitrite with potassium nitrite, and represented by the formula Co(NQ2)3.3KNOa. Such a formula, however, does not represent the reactions of the substance, as the nitrite radicle is held firmly, and nitrous aeid is not liberated when the compound is treated with cold dilute acids, as it would be if it were a double salt as the formula indicates. Molecular conductivity measurements also indicate that it is a complex salt comparable with the metal-ammines. Many compounds of cobalt of this type are known. They may be regarded as the salts of the complex acid hexanitrito-cobaltic acid, [Co (N02)6]H3. 

Nickel, although closely resembling cobalt, shows much less tendency to form complex radicles, and there is no long series of stable ammino-nickel salts as in the case of cobalt. Further, the stable series of ammino-derivatives of cobalt are those in which the metal is trivalent, whereas in the case of nickel the niekelie salts are unknown, and the complex ammino-derivatives are additive compounds of nickelous salts. 

Aquo-ruthenium salts, therefore, cannot be washed with alcohol or water, as both reagents cause hydrolysis. They may, however, be washed with absolute ether or with acetone without causing any change. Like all aquo-ammino-metallic salts, these compounds may be caused to lose water, passing thereby into aeido-tetrammino-salts, where one acidic radicle enters the complex thus ... 

Platinum forms both platinous and platinie salts, in which the metal is divalent and tetravalent respectively. Both series of salts are capable of uniting with ammonia, forming complex ammines. The co-ordination number in the platinous series is four and in the platinie series six. The latter series correspond in many respects to the chromic and cobaltic ammino-salts, but as the metal is tetravalent, the maximum number of radicles outside the complex is four instead of three. Also, the ammino-bases from which the salts are derived are much more stable than those of chromium or cobalt. 

Different metal chlorides unite with one another to form double lasts. Just as the acidic and basic oxides unite together to form oxy-salts, so do the halides of an electropositive element (or radicle) unite with a halide of a less positive element (heavy metal or metalloid) to form double halides. So far as is known the alkali chlorides do not unite with one another to form double salts, nor do the halides of the same natural group form compounds with one another, but compounds of the alkali chlorides with the chlorides of the more electronegative chlorides are known. A comparison of nearly 500 double halides has been made by H. L. Wells (1901).1 He calls the one component—e.g. the alkali halide—the positive halide, and the other the negative halide. A. Werner calls the halide which plays the role of the basic oxide, the basic halide, and the other, the acid halide. A great many of the simple types of the double salts predominate. Writing the number of molecules of the positive halide first, and the negative halide second, salts of the 2 1 and 1 1 ratios cover about 70 per cent, of the list of known double halides, and 4 1, 3 1, 3 2, 2 3, and 1 2 represent over 25 per cent. Two halides sometimes unite in several proportions—for instance, six caesium mercuric halides have been reported where... 

When iodine is dissolved in hydriodic acid or a soln. of a metallic iodide, there is much evidence of chemical combination, with the formation of a periodide. A. Baudrimont objected to the polyiodide hypothesis of the increased solubility of iodine in soln. of potassium iodide, because he found that an extraction with carbon disulphide removed the iodine from the soln. but S. M. Jorgensen showed that this solvent failed to remove the iodine from an alcoholic soln. of potassium iodide and iodine in the proportion KI I2, and an alcoholic soln. of potassium iodide decolorized a soln. of iodine in carbon disulphide. The hypothesis seemed more probable when, in 1877, G. S. Johnson isolated cubic crystals of a substance with the empirical formula KI3 by the slow evaporation of an aqueous-alcoholic soln. of iodine and potassium iodide over sulphuric acid. There is also evidence of the formation of analogous compounds with the other halides. The perhalides or poly halides—usually polyiodides—are products of the additive combination of the metal halides, or the halides of other radicles with the halogen, so. that the positive acidic radicle consists of several halogen atoms. The polyiodides have been investigated more than the other polyhalides. The additive products have often a definite physical form, and definite physical properties. J. J. Berzelius appears to have made the first polyiodide—which he called ammonium bin-iodide A. Geuther called these compounds poly-iodides and S. M. Jorgensen, super-iodides. They have been classified 1 as... 

The ammonia-radicle theory.—The oldest hypothesis concerning the nature of the ammonia-compounds, and that adopted by A. L. Lavoisier, supposed ammonia to be an independent base or radicle, saturating acids, and forming salts. This theory has been likened to the etherin theory of J. B. A. Dumas and P. F. G. Boullay. The radicle is NHS sal-ammoniac is NH3+HCI etc. The theory makes no attempt to explain the nature of the other classes of ammonia-compounds nor does it explain the relation of ammonia to ordinary bases, which are metallic oxides, nor the differences between the ammoniacal salts from metallic sails of the same acid. Later on, the theory became associated with the mol. compound theory, so that sal ammoniac was represented by F. A. Kekule as an associated complex of ammonia and hydrogen chloride, in which the ammonia remained tervalent. These compounds were considered to be analogous to double salts, and to substances with water of crystallization. This view was supported by the ready dissociation of sal ammoniac by heat—a subject discussed in connection with ammonium chloride (2. 20, 16). H. Rose also emphasized the analogy between compounds of ammonia and of water in various salts as exemplified by the use of the term ammonia of crystallization. 

AuC13OH], etc.—the linkage between the metal and the acid radicle is not broken and virtually no gold ions are formed. If auric tetramminonitrate, [Au(NH3)4](N03)3, be treated with potassium chloride, auric tetramminochloride, [Au(NH3)4]C13, is probably first formed and, owing to the affinity between the outer sphere and the complex itself, ammonia is displaced and the series of auric amines, [AuCl(NH3)s]Cl2, [AuC12(NH3)2]C1, and [AuC13NH3], is produced. As a matter of fact, some of the combined chlorine passes out with the ammonia as ammonium chloride, and hydroxyl remains in the complex. This subject has been studied by F. Ephraim, A. Pieroni, E. Weitz, etc. 

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