GERMANIUM. XXII. T H E DIHALIDES O F GERMANIUM' BY F. M. BREWER AND L . M. D E N N I S ~
Introduction I n the chemistry of the fourth group of the periodic system very interesting variations in properties and behavior are to be found in those compounds in which the group elements are divalent. This applies particularly to germanium, tin, and lead. The outstanding anomaly of carbon monoxide has long been recognized as a problem whose solution will illuminate the whole field of chemical combination; but the explanation of the change from carbon and silicon, where divalency is so little in evidence, to tin and lead, where it would appear to be in many cases the more natural condition for the element, has probably a far greater fundamental significance. Germanium occupies the intermediate position and the preparation of its compounds in the divalent series is therefore a matter not only of immediate practical interest, for very few of them have hitherto been made, but also of considerable theoretical importance. Divalency in the case of carbon and silicon appears to be limited t o carbon monoxide, a doubtful monoxide of silicon, and the equally questionable existence of the monosulphides. The valency of carbon in the isocyanides raises the larger issue of tautomeric change, which is beyond the scope of this paper. What evidence there is for even the transient existence of a dihalide of carbon comes from the work of Lob.3 He decomposed the vapor of chloroform by means of a heated wire, and found perchlorethylene to be one of the main products of decomposition. He considered that this was best explained on the assumption that the primary reaction was in accordance with the equation CHC13 +CCle HCl
+
If such a compound does exist, it is subject to immediate polymerization and condensation reactions. Troost and Hautefeuille4describe substances which they designate as subfluoride and subchloride of silicon, but the existence of these compounds has not been confirmed. On the other hand, the dihalides of tin and lead are quite well known, and in the case of lead are distinctly more stable than the corresponding compounds in the tetravalent series. This development of a lower valency, and particularly one which differs by two from the normal group valency, is quite marked in elements of high atomic number, and its theoretical basis has been dis-
' Contribution from the Department of
Chemistry, Cornell t-niversity. This article is based upon part of the thesis presented to the Faculty of the Graduate School of Cornell Kniversity, by Frederick M , Brewer in partial fulfillment of the requirements of the degree of Doctor of Philosophy. 3 2. Electrochem., 7,907 (1901). Ann. Chim. Phys., (5),7,464 ( 1 8 j 6 ) .
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cussed by Grimm and Sommerfeld.’ The fact that the germanium dihalides have been but little investigated is attributable not only to the scarcity of the element itself, but also to the difficulty of isolating and handling what have since proved to be very reactive substances. I n the first of his two main articles on germanium Winkler2 stated that the dichloride is produced by the action of hydrogen chloride upon the metal or upon germanium monosulphide. He described it as a colorless liquid which fumes in the air, but he was really doubtful as to its identity, suggesting the possibility of it being the chloroform, GeHC13. I n his later paper3 he stated definitely that the product of these reactions was the chloroform, and not the dichloride. Winkler made the tetrabromide and tetra-iodide of germanium but he does not recount any attempt to prepare the lower halides. In the case of the fluoride, he found evidence of the formation of a difluoride in the reaction of hydrogen upon potassium fluogermanate. Actually his experiment denotes a reduced complex rather than a free difluoride. In preparing germanium tetra-iodide by the action of iodine vapor upon heated germanium Dennis and Hance4 obtained a small yield of a substance which proved to be germanous iodide. I t appeared in the form of yellow hexagonal crystals and was comparatively stable in air. They made no further investigation of the compound. Dennis, Orndorff, and Tabern5 prepared germanium chloroform by passing hydrogen chloride over the product that resulted when the vapor of germanium tetrachloride was passed over metallic germanium at high temperature. This product was presumably germanium dichloride. I t was rapidly attacked by moisture and by the oxygen of the air. The study of this substance was not completed at that time. The general methods which suggested themselves for the preparation of the dihalides were:( I ) The restricted action of halogenfi upon metallic germanium, ( 2 ) The reduction of the tetrahalides, (3) The dissociation of the tetrahalides, (4)The removal of the hydrogen halide from compounds of the chloroform type, and ( 5 ) Metathetical reactions.
Experimental Attempts to prepare Germanium Dichloride. (a) Metafhdzcal Reactions. hletallic germanium was prepared by the method of Dennis, Tressler and A small quantity of the finely divided germanium was heated with mercuric chloride in an inclined tube of hard glass in an atmosphere of nitrogen, Z. Physik, 36,36 (1926). J. prakt. Chem., 142,177 (1886). J. prakt. Chem., 144,177 (1887). 4 J. Am. Chem. S O C . , 2854 ~ ~ , (1922). Dennis, Orndorff and Tabern: J. Phys. Chem., 30,1049 (1926). 6
J. Am. Chem. SOC.,45,2033 (1923).
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F. 11. BREWER A S D L. M. D E N N I S
at a pressure of 1 5 mm. There was no evidence of the formation of germanium dichloride. When mercurous chloride was used, germanium tetrachloride formed and condensed on the walls of the tube. On further heating, mercury distilled up the tube, and where it condensed with the tetrachloride a yellow product was formed. The experiment indicated that a reduction of germanium tetrachloride by mercury takes place, but separation of th? products would be difficult. (b) Reduction of Germanium Tetrachloride. Instead of mercury, a 957c sodium amalgam was used as the reducing agent, the reaction being carried out in an atmosphere of nitrogen. A dark powder began to form in the cold upon the surface of t’he amalgam, and increased in amount on the application of heat. The final product was a black powder mixed with mercury and the residual amalgam. The powder appeared to be metallic germanium. Dilution of the tetrachloride with toluene did not affect the result. Similar products were also obtained with the use of aluminum amalgam at elevated temperature. Tin foil and tin amalgam had no effect upon the tetrachloride at its boiling point, nor was there any indication of reaction upon passing the vapor of the tetrachloride over heated tin amalgam. Magnesium ribbon, neither by itself nor in the presence of mercury, appeared to effect reduction when refluxed with germanium tetrachloride] nor was zinc dust any more effective. When germanium tetrachloride was refluxed with freshly cut sodium, a black coating formed on the surface of the metal. The action of metallic silver was next studied. Crystalline silver, made by direct electrolysis of a solution of silver nitrate, had no effect when refluxed with the tetrachloride, but a vigorous reaction occurred when the vapor of germanium tetrachloride was passed over the heated crystals. There was some indication that silver chloride had been formed in the reaction, but germanium dichloride was not found among the products of the reaction. Gomberg’sl “molecular silver” was then used. This gives a very fine product of higher reducing power and catalytic activity. Nevertheless, it appeared to have no effect upon germanium tetrachloride, nor did it catalyze its reduction by organic reducing agents. The statement of Dennis and Hance2 that germanium tetrachloride dissolves in acetone with the formation of a light orange-colored liquid made it appear possible that the acetone reduced the tetrachloride. It was found, however, that germanium tetrachloride could be refluxed with acetone for three days without any development of color. As the reduction may have been due to the presence of aldehyde in the acetone originally used, paraldehyde was added to the solution, which was again refluxed. The mixture eventually became pale yellow in color, but no solid could be isolated. Formaldehyde bubbled through liquid germanium tetrachloride at room temperature or at the boiling point of the tetrachloride was equally ineffective as a reducing agent. Ber., 39,3287(1906). J. Am. Chem. SOC.,44,307 (1922).
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(c) Reactions with Germanium Chloroform. There remained the possibility of preparing the dichloride from the chloroform. Laubengayer' had shown that hydrogen chloride reacts with metallic germanium to give a mixture of germanium chloroform and germanium tetrachloride which cannot be resolved into its components by fractionation. This mixture forms, nevertheless, by far the most convenient source of germanium chloroform. The two methods available for the preparation of the dichloride from the chloroform were thermal dissociation or purely chemical reactions. Experiments upon the thermal decomposition of the chloroform present the same difficulties as the reduction of germanium tetrachloride by germanium. If whatever dichloride that may be formed remains in the heated region where dissociation of the chloroform takes place, the dichloride is immediately decomposed into germanium and germanium tetrachloride. This was demonstrated by a repetition of Lob's experiment with chloroform vapor, using a rather simpler apparatus. A coil of fine platinum wire was sealed into a glass tube about one centimeter in diameter, which had a bulb attached a t either end. The chloroform-tetrachloride mixture was brought into one of these bulbs, and was made to pass slowly over the platinum by regulated cooling of the other bulb. The platinum was heated electrically, and a t a temperature just below red heat, first a few drops of liquid, and then a thin film of cream-colored solid, were deposited on the walls of the tube. As the temperature of the wire was raised, the solid dissociated and germanium and germanium tetrachloride were formed. It was then sought to remove the elements of hydrogen chloride from germanium chloroform or from a mixture of the chloroform and the tetrachloride, in the hope that germanium dichloride or a mixture of the di- and tetra-chlorides would result. The tetrachloride could then be separated by distillation. Moreover, if the agent that effected the removal of hydrogen chloride should form with it a volatile compound, or even by its presence alter the equilibrium GeHC13 GeCll HC1
e
+
it should be possible to obtain solid germanium dichloride in a pure state. The simplest compounds which fulfill this function are the unsaturated hydrocarbons, for they should be able to take up the elements of hydrogen chloride t o give the chloro-substituted paraffins, which are comparatively volatile. A slight distillation should then suffice to separate the dichloride from the reaction mixture. Toward the close of this investigation it was found that ethylene could thus be used for the preparation of germanium dibromide, and the application of thisreaction to the synthesis of the dichloride is now being studied. Another class of compounds which might be employed for the removal of hydrogen chloride are the substituted ammonia derivatives, but these are I
Dennis, Orndorff and Tabern: loc. cit.
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F. M. BREWER A N D L. M. D E N N I S
polar compounds and are as a rule insoluble in organic solvents; consequently success in effecting a satisfactory separation in this manner seemed remote. It was possible, however, that oxonium derivatives might serve the purpose. Ether takes up hydrogen chloride at low temperatures to form a definite hydrochloride and although this dissociates upon warming, it was hoped that by fractionation under extremely reduced pressure, there would not be sufficient dissociation to regenerate germanium chloroform. The reaction of ether upon a mixture of germanium chloroform and germanium tetrachloride proved to be more complicated than was expected. A mixture of the three substances was placed in a bulb which was joined to a receiver that could be cooled in liquid air. The contents of the bulb first separated into two liquid layers, both of which were colorless. Of these the upper was the more volatile, the lower developing a pale yellow tint during the gradual disappearance of the upper. When warmed to soo, the liquid became viscous, and changed in color from yellow to orange. Finally, on raising the temperature to 90°, a bright yellow solid was deposited and the liquid phase disappeared entirely. Analyses were carried out a t various stages of the distillation, but consistent results could not be obtained in successive experiments. The final product always yielded a much smaller percentage of chlorine than germanium dichloride would contain, and it seemed evident that treatment with ether not only breaks down the germanium chloroform, but that the reaction continues at the expense of the dichloride. Further study of the preparation of germanium dichloride was deferred for the time being.
Germanium Dzbromide. As Dennis and Hancel had succeeded in preparing a stable specimen of germanium di-iodide, it was thought that the dibromide might more easily be obtained than the dichloride, and that at the same time an investigation of its properties might indicate a technique for the isolation of the dichloride. I t was to be expected that the action of hydrogen bromide upon germanium would resemble that of hydrogen chloride, in which case a mixture of germanium bromoform and germanium tetrabromide would result, although there was always the possibility that by careful temperature control the dibromide might be produced in a pure state. Hydrogen bromide was prepared by the method of Recours,* the bromine, however, being covered with concentrated hydrobromic acid instead of with water. The gas, dried by passage through U-tubes containing fused calcium bromide, was led over germanium contained in porcelain boats in a hard glass tube which could be heated in an electric furnace. The reaction tube was connected with a U-tube receiver similar to that described by Dennis and Hance3 for their preparation of germanium tetrachloride. To avoid any oxidation of the product, the apparatus was filled with hydrogen bromide before heating was begun. Condensation of the product was effected by ice and salt. J. Amer. Chem. SOC.,44,2854 (1922). Compt rend., 110, 784 (1890). 3 J. Am. Chem. Soc.,44,304 ( 1 9 2 2 ) .
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Appreciable reaction began at about 400'. The run was concluded a t a somewhat higher temperature. The reaction proceeded slowly at the beginning, but a good yield was eventually obtained. As in the similar experiment with hydrogen chloride, if the passage of gas was slow, a certain amount of yellow solid, presumably the dibromide, was deposited in the forward end of the tube, but this could be completely removed as a volatile liquid by the action of more hydrogen bromide. The liquid product was colorless, but when air was admitted to the reaction tube after the conclusion of the experiment, the few remaining drops of liquid in it were converted to a sticky, yellow solid. A vacuum distillation apparatus' was then prepared for the fractionation of the liquid condensed in the receiver. In the first distillation, the pressure maintained in the system was not carried below 4 . 5 mm. and this was sufficient to distill only a portion of the main product into the vacuum system. The residue was reserved for further fractionation at lower pressures. While the distillation was in progress two layers separated out in the receiver bulb. One of these becane distinctly yellow. The fraction which distilled over evidently contained a large amount of free hydrogen bromide, since its zero vapor pressure was 1 5 7 . 5 mm. This was considerably higher than the vapor pressures of either the chloroform or tetrachloride, and therefore could hardly be expected to come from any of the bromine compounds of germanium, which should be even less volatile. The hydrogen bromide was therefore distilled off before the main fractionation was attempted. When one of the valves was opened, however, and liquid air was applied to a condensing bulb connected with it, only a minute quantity of liquid was found to have condensed in the bulb, while a cream-colored solid was deposited throughout the connecting parts of the apparatus. When the condensate in the bulb was again allowed to evaporate, it completely removed all of this deposit. From this it appeared that in the absence of an excess of hydrogen bromide, the germanium bromoform is dissociated into the dibromide and hydrogen bromide, and that the effect of the liquid air is to condense some of the more rapidly diffusing hydrogen bromide, thus disturbing the equilibrium and eventually depositing the dibromide. This was confirmed by later work. I t also became clear from this experiment that fractionation in the vacuum apparatus was not feasible, because it was impossible to keep the valves free from the deposit. The residue left from the first attempted fractionation of the mixture produced by the action of hydrogen bromide on germanium was kept for several days in a vessel sealed from the air, and a t the end of that period was observed to have deposited a few long, pale yellow crystals. As these did not melt below IOO', even though moist with residual mother liquor, they could not be crystals of germanium tetrabromide. Since it had been shown that fractionation tended to condense hydrogen bromide, and therefore presumably LaubengayerandCorey: J. Phys. Chem.,30,1043(1926).
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F. M. BREWER AND L. M. DENNIS
leave behind germanium dibromide, it seemed probable that these might actually be crystals of the desired compound. Some of them were eventually extracted from the receiver in which they had been held, and were washed rapidly with benzene and dried. They became sticky on exposure to the air, and on this account it was impossible to obtain the exact weight of a sample, but the ratio of germanium to bromine was determined. A11 analyses in connection with the dibromide were made by dissolving the sample, with or without the aid of hydrogen peroxide, making up the solution in a graduated flask to a known volume, determining bromine as silver bromide gravimetrically in one portion, and germanium by the method of Dennis and Johnson' in another. The atomic ratio of germanium to bromine in this preparation was I :1.93. The results of this analysis and the behavior of the crystals justified an attempt to prepare germanium dibromide by the continued fractionation of the mixture which contained presumably germanium bromoform and tetrabromide. The liquid was first subjected to pumping at ordinary temperatures. Later the temperature was raised to 90'. There formed a thin upper layer of yellow color which deepened in intensity with further pumping. The lower layer was colorless. As evaporation proceeded, the colorless layer disappeared and, on cooling, crystals were deposited from the yellow solution. The germanium tetrabromide was then pumped out, leaving a cream-colored crystalline deposit. Analysis of this product showed the ratio Ge:Br = I :2.04. A second preparation by this method gave the ratio 1:2.06. Although the samples were not pure, the analytical results left no doubt that the solid product was chiefly germanium dibromide. Attempts to fractionate the product by heating in an oil bath at 125' to 130' under reduced pressure were unsuccessful. The greater part of the substance melted and began to decompose, setting on cooling to a yellowieh brown mass which became pasty on exposure to the air. I t dissolved completely in acetone, but not to any appreciable extent in benzene. The preparation of the dibromide was next attempted by the action of zinc upon the mixture of germanium bromoform and germanium tetrabromide. Pure zinc was prepared by the electrolysis of a solution of zinc sulphate between a zinc anode and a copper cathode. It was then added to a solution of the bromoform-tetrabromide mixture in benzene. There was a vigorous reaction on warming, resulting in a yellow solution which turned cloudy on cooling because of the separation of an oil. The liquid showed remarkably strong reducing power. On repetition of the experiment without benzene, almost colorless crystals were deposited. These behaved like the dibromide hitherto prepared. An apparatus for the application of the zinc reaction was then constructed (Fig. I ) . This consists of a reservoir A for the liquid mixture, to which is joined adapter B from the generating tube. On the other side, A has an outlet tube C which is fused into a wide slip-joint D. E is the reaction vessel J. Am. Chem. SOC.,47,790 ( 1 9 2 j ) .
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and in this is placed a small quantity of zinc. I t has a side tube F to which is connected by a normal slip-joint, G, the manifold receiver H. This has its own side-tube with stop-cock for attachment to the vacuum system. The side-tube F of the reaction chamber is plugged prior to the experiment just in front of the stop-cock. The plug originally used was a mixture of asbestos fibre and glass wool, but pure cotton was eventually substituted. Its function is to retain the zinc crystals and insoluble products of the reaction. I n the first experiment with this apparatus, a sample of the bromoformtetrabromide mixture was run upon the zinc in presence of air, and was then frozen while the air was pumped out of the system. The zinc was warmed, and gas wm liberated. This was removed by cautiously opening the stop-
cock connecting the reaction vessel with the vacuum system from time to time. When the reaction had subsided, the apparatus was turned through 90°, so that the hot solution could run through the plug and stop-cock into the receiver H . The cloudy yellow suspension noticed in the reaction vessel gave a clear, greenish yellow filtrate. h much larger quantity of solid separated from the solution than had been the case in the thermal decomposition experiments, and it was distinctly crystalline in form. I n appearance and in behavior on fractionation, the yellow liquid closely resembled that obtained by the former method. The tetrabromide, which was removed by pumping, was in this case almost entirely free from bromoform, as was shown by its solidification at room temperature, and the lack of any colored products on hydrolysis. Qualitative analysis of the residue showed that it was free from zinc. The zinc which had been used in the reduction became coated with a black powder, which was apparently metallic germanium. Preliminary experiments revealed difficulties in sampling and analytical procedure, and the apparatus was therefore modified by the introduction of
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F. M. BREWER AND L. $1. DEXNIS
interchangeable slip-joints, but the principle of the method remained the same. Instead of a manifold receiver, the new receiver consisted of a single tube consisting of two slip-joints at right angles, as shown in Fig. z . The slip-joints made it possible to clean the apparatus and quickly re-assemble it. Two caps were made from portions of the slip-joints, and these were placed upon the sample tube after it had been detached from the apparatus. Analysis of the preparations made in this apparatus showed that if the dibromide is formed in crystals of appreciable size, it is extremely difficult to remove the tetrabromide which is occluded by them: the product contained only germanium and bromine, but the bromine was always in excess of that required for germanium dibromide. httempts to remove the tetrabromide by prolonged heating at 90' under reduced pressure caused some decomposition of the dibromide. httempts to wash it out with benzene or toluene removed both dibromide and tetrabromide without appreciably altering the ratio of germanium to bromine, and always left the sample contaminated with the solvent. For these reasons the tetrabromide was removed by rapid distillation, with consequent formation of small crystals which were then heated For analyto 90' for a short t,ime, and then pumped for a long period at 30'. sis, the minimum quantity of absolute alcohol was used for their solution, and great care taken to extract all of the germanium from the sulphide precipitate by the repeated application of ammonium hydroside. Analysis:Substance, 0.3286. Wt. of Ge02,0.1450 = 0.1006 Ge. JVt. AgBr = 0.5301 = 0 . 2 2 j j Br. Calculated Ge, 31.23 per cent., Br, 68.8j per cent. Found Ge, 30.61 per cent., Br, 68.69 per cent. Keight ratio Ge: Br = I : 2 . 2 4 . Atomic ratio = I : z . o ~ . The results show that while the determination of bromine in the product was accurate, there was loss of z nig. of germanium in the analysis. The data suffice, however, to establish the identity of the compound. Properties o j Germanium Dibroniide.-Prepared in the manner described above, germanium dibromide is a colorless, crystalline solid. If the crystallization is rapid, the crystals appear as very small, glistening plates; more gradual crystallization results in the formation of needles. When heated, the substance behaved like the product obtained by the thermal decomposition of the bromoform. It left a black residue and simultaneously there were formed drops of an oily liquid which afterwards volatilized. The full decomposition is probably represented by the equationz
GeBrs = Ge
+ GeBr4
The compound was not appreciably soluble in hydro-carbons (benzene, toluene) unless germanium tetrabromide was also present. It dissolved in alcohol and acetone to give colorless solutions of strong reducing power. The solution in acetone decolorized bromine water far more rapidly than the acetone itself. Water hydrolyzed the compound to the yellow hydrated germanous hydroxide, but an excess of water dissolved the product to give a solution showing all the characteristics of the germanous ion.
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Germanium dibromide absorbs bromine but the reaction is not vigorous. Heat is developed and the resulting product is germanium tetrabromide. Germanium dibromide unites with hydrogen bromide to form the bromoform. (See below). It is interesting to note that the solution of the dibromide in the tetrabromide is always yellow, whereas in the solid state both are colorless. If, as is probable, the color of the solution is due to the unsaturated nature of the dihalide, it must be assumed that the compound in the solid state is polymerized. This would not only bear out a relation to carbon which can form only the polymerized tetrachlorethylene in place of the dichlormethylene, but would also resemble the behavior of the definitely unsaturated carbon compounds, the triphenylmethyl series. These compounds develop a really intense color only in solution, in which they have been shown to have the dissociated, or unsaturated, constitution. Germanzum Bromoform. Hydrogen bromide was passed over a sample of germanium dibromide prepared in the vacuum apparatus, which for this experiment was equipped with a reservoir bulb for the gas. The chain was filled with hydrogen bromide at room temperature and atmospheric pressure. The gas was first condensed on the dibromide by means of solid carbon dioxide, but the union of the gas with the dibromide, except when the latter had been deposited in a very thin layer, was rather slow. The rate of reaction increased considerably on warming to 40'. h liquid, which was a t first rather cloudy but which cleared on standing in contact with hydrogen bromide, was formed in the receiver. By analogy to the chloroform it was expected that this liquid would prove to be the corresponding germanium bromoform. An attempt was made to distill this product into a weighed tube fitted with a stop-cock and slip-joint for attachment to the vacuum chain. During distillation at 90°, however, the distillate was observed to decompose throughout the system and to give a white deposit just as in the original fractionation carried out in the vacuum apparatus. When more hydrogen bromide was introduced from the reservoir, this white deposit disappeared and a liquid collected in the sample tube. This liquid remained clear at on even when the pressure was reduced to 1.9 mm. which was the value obtained for the oo vapor pressure of the compound. When the temperature rose to IO' the pressure was z mm. and the liquid was no longer clear. This cloudiness did not disappear when hydrogen bromide was admitted to the liquid at 10' but the turbidity vanished when the sample was warmed. When this clear product was heated to 80' the liquid again became turbid probably because of incipient thermal dissociation. Because of the extremely slow absorption of hydrogen bromide by the liquid, except over a very small range of temperature, it was impossible to obtain definite information concerning the equilibrium pressures by starting with the dissociation products. Analysis:-Since dissociation of the liquid was negligible a t ' 0 or lower temperatures, the sample was held at - IO' and the apparatus was evacuated
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F. M. BREWER A S D L. M. DENNIS
with a pump to remove any dissolved hydrogen bromide. The sample tube was then closed and was detached and weighed. If dissociation occurred when the sample tube came to room temperature, any evolved hydrogen bromide remained in t'he closed tube and the dissociation therefore did not vitiate the analytical results. Substance, 0.4015. Calcd. for GeHBra: Ge, 0.0930 = 23.16 per cent.; H , 0.0014 = 0.23 per cent; Br. 0.3071 = 76.51 per cent. Found: Ge, 0.0933 = 2 3 . 2 3 per cent; Br, 0.3068 = 76.41 per cent; H, by diff. = 0.36 per cent. The above analysis identifies the liquid as germanium bromoform, and its production in this manner is evidence tha,t the solid from which it was made was germanium dibromide. Melting Point:-Before the analysis was made, the sample tube was cooled to -60' and its contents was thus solidified. The melting point was found X second sample melted at -24'. to lie between - 25' and -24'. I t was observed that when bromine is passed through the liquid product that' results from the action of hydrogen bromide on germanium, a considerable amount of hydrogen bromide is evolved and there is formed a homogenous product showing the physical constants and chemical behavior of germanium tetrabromidc. This shows conclusively that when hydrogen bromide act,s upon germanium, a mixture of germanium tetrabromide and germanium bromoform results.
Germanium Di-iodide. Dennis and Hance' found that germmiurn di-iodide was formed as a product of the reaction between germanium and iodine and also by the dissociation of germanium tetra-iodide at temperatures above 440'. They described it as a yellow solid crystallizing in plat,es and belonging to the hexagonal syst,em. Their experiments indicated that it should prove a fairly simple matt,er either to effect dissociation of the tetra-iodide at high temperatures or Ge12 z I, towards the right,. to displace the equilibrium, GeIi The act,ion of germanium tetra-iodide upon germanium heated to various t,emperaturesbetween 3 70' and 600' gave a small yield of germaniumdi-iodide immediately in the neighborhood of the metal. Hydrogen iodide, acting upon germanium below 400°, gave germanium tetra-iodide as a finely divided, bright-yellow powder. On raising the temperature of t,he reaction tube, the hydrogen iodide dissociated and the subsequent course of the reaction was essentially that of free iodine upon the metal. Both hydrogen and acetylene reduced germanium tetra-iodide to some extent, but most' of the tetra-iodide volatilized before reduction had taken place. I n addition to the volatilixation of the tetra-iodide at low temperatures, all of these methods were unsatisfactory because of the equilibrium which exists between the two iodides and free iodine at the higher temperatures where the reaction velocity is appreciable.
+
J. .%m,Chem. Soc., 4 4 , 2 8 j 4 ( 1 9 2 2 )
GERMANIUM XXII
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Anhydrous stannous chloride and mercurous chloride reduce germanium tetra-iodide, but the final reaction product consists of mixtures of the tetrachloride, tetra-iodide and di-iodide of germanium together with stannic halides and mercuric halides respectively. I n the latter case, metallic germanium was also formed. I t was found that the germanium di-iodide which had been prepared in small quantity by the action of iodine vapor upon germanium was only slowly hydrolyzed by cold water. It therefore seemed probable that it would be stable in concentrated hydriodic acid, and consequently might be prepared by solution of hydrated germanium monoxide in that acid. A mixture of the hydrated monoxide and dioxide of germanium was prepared by adding ammonium hydroxide to the chloroform-tetrachloride mixture, and carefully heating the product. The hydrated oxides were dissolved in concentrated hydriodic acid and the tetra-iodide, which is only sparingly soluble in the concentrated acid, was separated from the solution by filtration. The filtrate, when cooled, deposited a large quantity of feathery, yellow crystals which did not resemble in any way the di-iodide previously prepared. Examination of this substance indicated that it was impure germanium iodoform. To avoid the formation of the iodoform, an excess of the mixture of the two hydrated oxides was caused to act upon concentrated hydriodic acid, the temperature being kept below 40'. The contents of the flask was then heated to 60" and was filtered. The clear, yellow filtrate deposited wellformed hexagonal plates which were washed with benzene to remove germanium tetra-iodide. Analyszs:-Calcd. for Ge12: Ge = 2 2 . 2 4 per cent.; I = 77.76 per cent. Subst., 0.4082, 0.3856. Found, Ge02, 0.1300 = Ge, 22.11 per cent; Ge02,0 . 1 2 3 9 = Ge, 2 2 . 3 0 per cent. Subst. 0,4074, 0. j705. Found, I, 0 . 3 1 4 4 = 77.37 per cent; 0.4417 = 7 7 . 4 2 per cent. Propertzes:-Germanium di-iodide is a yellow solid which crystallographically is very similar to lead iodide. I t is insoluble in hydrocarbons, but appears to dissolve slightly in chloroform and carbon tetrachloride. I t is soluble in concentrated hydriodic acid and can be recrystallized from this medium, except when both acid and di-iodide are present in high concentration. It is soluble in dilute acids and in water, the solutions having the reducing properties associated with the germanous ion. When exposed to the air, the diiodide is slowly hydrolyzed and germanium dioxide is formed. When preserved in a sealed tube the substance is quite stable. When heated in the air, Jt a t 210' is rapidly oxidized to a mixture of germanium odide. A sample was placed in a capillary tube which was evacuated and then sealed. When the tube was heated to 240°, a yellow sublimate filled the capillary, and at 265' sublimation was rapid. The color of the solid changed meanwhile from yellow to red. This shows that, a t higher temperatures, the di-iodide breaks down, forming germanium and germanium tetra-iodide.
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F. M. BREWER AND L. M. DENNIS
summary The preparation of germanium dibromide, germanium bromoform, and germanium di-iodide are described, together with attempts to prepare pure germanium dichloride. It is shown that the dihalides of germanium possess strong reducing power similar to the dihalides of tin, and that the germanium bromoform, and probably also the iodoform, are produced by the action of the halogen acid upon the corresponding dihalide of germanium. Ithaca, New York.
