are 15.5 and 35.6 ~ m . respectively. ~, On this basis we would expect the refractivity of UC12F2 to be somewhere near the mean of these values, or 27 ~ m . ~Therefore . the formula UClFB fits the observed refractivity much better than does UC12F2. X portion of the material weighing 448.7 mg. and containing (by microscopic estimation) a t least 95% of this mixed halide, the balance being entirely Uc14, was analyzed for total U, F and C1. The material was not found to be readily water soluble, but was dissolved in a strong, aqueous solution of KaOH to which H20z was added. Aliquot portions of this solution were checked for uranium content by a standard ceric titration, for fluorine by a triphenyl tin precipitation, and for chloride by a silver chloride gravimetric method. The results gave 371 mg. of U, 81 mg. of F, and 47.9 mg. of C1, or 70.6% U, 20.3% F, and 10.7% C1 (a total of 101.6y0). Table I compares these results with the theoretical values for the formulas indicated. TABI.E r
As found VCI?Fz CCII.':;
--.-..--\v u
' t . ,c CI
iO.6
10.7 20.44 10 73
08.61 72 03
F 20.3 10 95 17,25
The fluorine analysis, being the most uncertain, was rechecked by a different method on a new sam-
[CONTRIRUTIOS FROM
THE
ple taken from the same mixture. The basic solution was acidified, care being taken not to heat the acid solution and drive off any H F ; and from 1 liter of solution 10-ml. aliquots were steam distilled by the method of Huckaboy, Welch and Metler3 to separate the fluorine from the uranium. The distillate was then titrated against a standard thorium nitrate solution according to the method of Willard and Winter4 using a zirconium nitrate-alizarin indicator, with sodium fluoride as the primarq. standard. The results of these titrations indicated li-1970 F and thus tended to confirm the formula as UClF3. From these results, it seems most likely that previous analyses of the suspected UClzF2were made on mixtures of UC1F3 and UC14 in such proportions that the overall composition had a U : F: C1 mole ratio of closer to 1: 2 : 2. Acknowledgments.-The author wishes to express his gratitude to E. Staritzky of this Laboratory who made all of the optical measurements, to F. Ellinger and E. Staritzky for the X-ray data, and to R. D. Baker for many helpful discussions and suggestions. 13) W B. Hucknbay, E T. U'elch and A 1.. 1Ietlt.r. A I I O ;C. h t , ~ . , 19, I X (1947). '4) H. H . \villarii and 0. H . Winter, I i i d E i i g Chr.?ii , A ~ i i i . , 5, 7 (1933).
Los ALAMOS,KEW MEXICO
DEPARTMENT O F CHEMISTRY, C X I V E X S I T Y
O F PEXNSYLVAXIA]
The Formation and Decomposition of Trichloromonogermane and Germanium Dichloride1 BY
CH.ZRLES \Y.MOULTOX .4XD
JOHX
G. MILLER
RECEIVED OCTOBER 20, 1953 \.arious methods of preparing GeHC13 have been tested. The most efficient method appears t o be the reaction of gaseous IICl with GeS and a n improvement of this procedure has been obtained. Both GeHC13and GeCla have been found more unstable than indicated in the literature. GeHCI3 is apparently highly ionized in acidic aqueous solutions even at high hydrogen ion concentrations. GeClz has been prepared as residue of the low temperature distillation of GeHCI3. The dichloride has been shown t o decompose into polymeric subchlorides even a t low temperatures The results have been correlated ir. ith the observations of other workers
In efforts to prepare trichloromonogermane, GeHC13, in a high state of purity, we have been surprised t o find that this substance is even less stable than the literature would indicate.?-? Furthermore, it appears that the product of the dissociation of GeHC13, germanium chloride, when free of GeHC13and HC1, decomposes readily a t much lower temperatures than one would expect from earlier descriptions of this compound.2,5,6 Even a t temperatures in the neighborhood of -30°, GeHCI3 loses HC1 readily and when the (1) Taken from a dissertation submitted by Charles a'.Rloulton in partial fulfillment of t h e requirements for t h e P h . D . degree, University of Pennsylvania, 1955. ( 2 ) L. >I Dennis, . W. R . Orndorff and D . I,. T a b e r n , J . P h y s . C'izem., 30, 1049 (1926). (3) A . Tchakirian, Biill. soc. chim., [ 4 ] 5 1 , 846 ( 1 9 3 2 ) . (4) P. Venkateswarlu, R . C. llockler and XV. Gordy. J . Chem. P h r s . . 21, 1713 (1953). ( 5 ) I,. 11.Dennis and H. L . Hunter, THISJ O U R X A L , 5 1 , 11.51 (19201. (6) F. >I. Brewer and I.. 31. Dennis, J . P h y s . Cheirz, 31, 1526
(1927).
GeHC13 has been converted in this way to GeClz, the dichloride even a t these low temperatures decomposes into subchlorides of the type formed by Schwarz and Baronetzky' * a t high temperatures by the cracking of GeC14. The results of this study are of interest in relation to the recent findings of Schumb and Smythg who showed how readily and similarly Xg?O and 0 2 react with GeHCI3 to form GeC12, and who suggested that the silver oxide might act as a chemical acceptor for HC1 in this reaction. Earlier, Brewer dnd Dennis6 tried, with only partial success, to prepare GeC12 by chemical relnolal of HC1 from GeHC13 They were able, howver, to prepare GeBr? from GeHBrs on removal of HBr by physical means. (7) R (1952)
Schwarz and E Baronetzk,
(8) R S c h s a r z and E Baronetiky Z
\'TI{
P ~ e n s r i i n f l e i z ,39, 2 i G
LY
(1110
P
allsen! C h h m
215. 1
(1954) (9) VV' C Schumb a n d D h I Smyth, THISJ O U R X A L , ? I , 3001 (19.57)
J une 20, 1g,%
DECOMPOSITION O F TRICHLORONONOGERMANE AXD GERX4NIUM DICHLORIDE 2703
chamber. It may be t h a t the GeS becomes coated with decomposition products. The residue was noticeably lighter Materials .-Germa.nium metal and germanium dioxide in color than the starting material. When a furnace was were obtained from the Eagle-Picher Company. Qualitative used to heat the reaction tube, reaction was more rapid, b u t tests showed no arsenic was present in the dioxide. The there remained greater fractions of unreacted GeS. When n-heptane was a product of the Westvaco Chlorine Products these residues were removed by washing the reaction tube Corporation and was redistilled, only the portion boiling with sodium hydroxide solution, a gas with a pungent, phosa t 99.0-99.2” being retained. It was dried over silica gel. phine-like odor formed. If this gas was germane, it would T h e hydrogen chloride was Matheson Company anhydrous indicate the presence of material other than GeS in the resigas. due. Preparation of GeHCl,.-The Dennis-Orndorff-Tabern A large part of the residue may have been due t o impurities method2 was tried first and found unsatisfactory even after contained in the original GeS. We did not analyze this much effort was expended in constructing the apparatus in GeS, but Schumb and Smythg found as much as 20% chloa way to minimize the thermal decomposition of the GeCL ride in GeS prepared by the “Inorganic Syntheses” method. formed in the first stage of t h e method. T h e modification They also found t h a t these impurities did not react with of this method proposed by Schwarz and Baronetzky’ was H C l even at 50°, so t h a t no contamination of GeHCl;, also unsatisfactory; t h e same fundamental objection ap- should result from this source. A sample of the GeHClj plied, namely, t h a t at the temperature required for reaction prepared by this procedure was analyzed for Ge (as GeO2) between GeClr and Ge metal, the GeCL decomposed too and C1 (as AgCl), the average of duplicate determinations extensively. From the results described below, this de- yielding the Ge: C1 ratio 1: 3.04. composition is now seen to consist of not only the direct rePreparation and Properties of GeC12.-In the storage of formation of Ge and GeClr but also formation of subchlo- the GeHCls, it was noticed t h a t small amounts of a white rides which do not react with HCl. material, initially amorphous in appearance, were formed Among additional methods tried, two were based on the where the surface of the liquid GeHCI: contacted the walls of equilibrium between GeHC1, and its ionization products, a the storage ampoules. It was further observed in some proton and the GeC13- ion in acidic aqueous s o l ~ t i o n , ~ J ~cases - ~ ~ that on standing for several days this white deposit and on the lack of ionization of GeHCl3 in non-polar sol- had acquired a crystalline appearance. When the liquid vents.’3~’* Although Tchakirianlo has stated t h a t GeHCI3 was subsequently distilled from the ampoule a t low temdoes not distil from weakly acid aqueous solution, i t was perature, the color of this initially white deposit changed hoped t h a t the ionization which prevents distillation or ex- in the usual pattern observed for GeCL, becoming first traction of GeHC13 might be repressed by a higher concen- yellow and then orange. Similar behavior was observed tration of acid, especially in view of t h e fact that t h e solu- when one of the GeHC13 samples under its own vapor presbility of the closely related GeC14 is reduced practically to sure was chilled with liquid air; as evidenced by a slight zero in concentrated aqueous hydrochloric acid .16 Accordfoaming action, there occurred some distillation from the ingly, efforts were made to prepare GeHCls by forming the surface of the white wall deposit and portions of the decompound in aqueous solution saturated with HC1 at room posit then became light yellow-orange in color. On contemperature and either fractionally distilling the solution densing dried gaseous HCl into the bulb with a bath of or extracting with n-heptane, in which it was established liquid air, and subsequently pumping away the excess HCl that GeHC18 is soluble t o the extent of at least 1 g. per 10 while cooling the bulb with baths of Dry Ice-isopropyl alcoml. The efforts failed; no germanium appeared in the dis- hol and then of melting chlorobenzene, the remainder of the tillates or in the n-heptane layer. It is obvious t h a t Ge- white deposit disappeared. The white, apparently crystalHC13 remains soluble and highly ionized in aqueous solution line material had evidently reacted with hydrogen chloride, even up to high hydrogen ion concentrations. indicating t h a t i t was a form of GeC12. T h e portion which Good success mas obtained by reaction of hydrogen chloride had become discolored did not seem to be in the least afwith germxnium monosulfide.lB The GeS was prepared by fected by the HCl. the method of Foster” and dried in a n evacuated desiccator. T o obtain a repesentative sample of GeClt by physical The HC1 was dried over phosphorus pentoxide before pas- removal of HCl from GeHC13, the GeHC13 was distilled a t sage into the Pyrex glass apparatus, in which formation and several temperatures in a Pyrex glass apparatus containing purification of the GeHC13 took place. a removable collecting bulb which could be weighed in adIt was found t h a t it is not necessary to heat the GeS as vance. The GeHCls was placed in this bulb by condensaoriginally prescribed,16 for reaction with H C l takes place a t tion with a liquid air-bath and was then brought to a higher room temperature. Although slow initially, the reaction temperature in the range -24 t o -33”. In this range, is exothermic and soon reaches a convenient velocity if the provided by baths of melting carbon tetrachloride or liquid pressure of the hydrogen chloride is maintained in the range ammonia, it was pumped until all t h e liquid distilled from of 65 to 75 cm. of mercury. the bulb. During this slow distillation, HC1 was removed At the end of a run all of the volatile substances were sufficiently more rapidly than the GeHC13 by the pumping collected in one bulb of the apparatus by means of a liquid- so t h a t the GeCI2 accumulated in the GeHC13 in which it is air bath which was then replaced by one of Dry Ice-isosomewhat soluble and remained behind when the GeHC1: propyl alcohol (- 7S0),a large part of the hydrogen chloride had left the system. thereby being exoelled from t h e system thiough a mercury At higher temperatures the breakdown of GeHC1, was blow-off tubeJo Following this, a bath of melting chloro- more rapid, but the removal of the HCI was not as complete benzene (-40 ) was placed about the bulb, both HCl and so that less GeCL accumulated during the distillation. HgS then being expelled. The system was finally pumped Furthermore, even at - Z o o , the decomposition of the Geat this temperature for 1.5 t o 2 hours t o remove from the Cl2 to subhalide was rapid. product the remainder of these gases. I n this same apparaThe GeC12 deposits formed in the distillation a t -24 to tus, the purified GeHC13 was distilled into another storage -33’ were generally white in color with only occasional bulb and then into small ampoules by use of liquid air-baths. traces of yellow. Two such deposits were analyzed for Ge Retreatment of the remaining GeS with fresh H C l pro- and C1 and gave the same value, 2.11, for the atomic ratio duced a small additional amount of GeHC13, so t h a t the over- of C1 t o Ge. all yield was nearly 40%. After the second treatment there The residues of the distillation of GeHCly at room temperature were chlorine-deficient GeCL of widely varied comstill remained a considerable bulk of solid in t h e reaction position. On standing a t room temperature, these residues underwent rapid change in color from white through yellow t o (IO) A, Tchakirian, Com9t. rend., 204, 117 (1937). orange and red-orange, with accompanying lowering of the (11) D. A. Everest, J. Chent. Soc., 660 (1953). chlorine content. A volatile substance, apparently GeC14 (12) D. Cozzi and S. Vivarelli, M i k r o c h e m . Mikrochim. A d a , 40, from its physical properties, was given off during the decom1 (1952). position. (13) M. L. Delwaulle, J. P h y s . C h e m . , 56, 355 (1952). (14) M. I,. Delwaulle and F. Francois, Compt. r e n d . , 228, 1585 The further decomposition of one of these subhalides was studied at higher temperatures. This sample had been (1949). formed b y distillation of GeHCI3 a t room temperature and (15) E. R . Allison and J. H. Muller, THISJOURNAL, 5 4 , 2833 (1932). had been allowed t o stand for approximately eight days a t (16) L. M. Dennis and R. E. Hulse, i b i d . , 63, 3553 (1930). this temperature before analycis. Durirlg that time its (17) L. S. Foster, “Inorganic Syntheses,” Vol. 11, W. C. Fernelius, color had changed from white to red-orange. Sm‘ill dropi Editor, McGraw-Hill Book Co., I n c . , S e w York, h-.Y.,1946, p. 102.
Experimental
2704
CHARLES JV. MOULTON AND
JOHN
G. MILLER
Vol. 7s
of a clear colorless liquid, presumably Gec14, had formed and had condensed on the walls of the storage ampoule. This was pumped off and the ampoule was then opened under a n atmosphere of dry nitrogen and some of the solid material removed. for the thermal decomuosition studies.
this reaction, the fact's that dichlorogermane decomposes with evolution of hydrogen indicates that behavior for trichlorogermane not be ruled out. However, it is noteworthy that
c10.64. In the thermal studies of this subhalide the substance was heated under reduced pressure, volatile products being collected in a trap cooled b y a Dry Ice-isopropyl alcohol mixture. The heating was carried out with continuous pumping for periods of about 2 hours each at a series of increasing temperatures between 35 and 400'; after each period, dry nitrogen was admitted into the apparatus and the sample was reweighed. Apparently the decomposition takes place a t a rather constant rate above 35", for the small losses in weight were nearly the same a t each of the eighteen temperatures used above 35'. The trap collected very small quantities of a solid which melted t o a clear, colorless liquid on warming to room temperature; on addition of small amounts of distilled water, this liquid hydrolyzed t o a white precipitate. The color of the subhalide steadily darkened from the original red-orange to red-brown at about 75", dark brown between 200 and 300°, and finally brown-black a t 400". At about 150" a white deposit appeared on the unheated upper wall of the sample tube, and at 165" there also appeared a slight iridescence resembling a metallic mirror of extreme thinness. The extent of the first deposit increaieti with rising temperature, and it became yellow in part.
periods up to several years have not ihown the buildup of gas pressure expected from evolution of hydrogen. Concerning GeC12, it now appears that the amorphous form has only a transient existence when it is isolated a t room temperature. I n contact with trichlorogermane, amorphous GeClz seems to persist, but when the GeHC18 is removed, there ensues decomposition, the progress of which is visible in the succession of colors which appear. There is some indication that amorphous GeC12 alters into a crystalline modification. The deposits in which this was observed remained white in color as long as liquid GeHC13was present a t room temperature, but chilling the sample with liquid air effected decomposition, due to distillation of some volatile substance, probably GeC14,from the deposit. Schwarz and Baronetzky8 obtained a yellow, crystalline form of GeClZfrom thermal treatment of crystalline germanium monochloride. They stated that decomposition of crystalline GeClz begins a t 75", but that it can be produced from the monochloride within a temperature range of 210 to 1200" if it is removed sufficiently rapidly from the heater zone by appropriate apparatus design. Formation of a yellow, apparently crystalline sublimate, possibly identical with the crystalline germanium dichloride of these workers, was observed in this study when the red-brown subchloride of composition GeC10.64was heated to about 200". The non-stoichiometric compounds formed by decomposition of GeClz resemble the subchlorides described by Schwarz and Baronet~ky,',~ although in no case were those encountered in this research formed above room temperature. While the subchlorides met here showed signs of non-homogeneity, they are certainly not to be regarded as heterogeneous mixtures of metallic germanium and GeCh. This was demonstrated by dissolving the subchlorides in solvents such as benzene, dioxane or diethyl ether. In no case was the undissolved material elemental germanium. The observation that hydrogen chloride has no effect on these subchlorides further supports this finding. These materials are rather to be regarded as mixtures of polymeric substances similar in formation and nature to the chlorine-deficient silicon chloride^.^^'^^^^ Thermal decomposition causes continuous approach to the pure metal, presumably due to splitting, from an extended chain or network of small fragments which can then reunite to form germanium tetrachloride. I t is probable that the decomposition reaction usually written for GeCIz, 2 GeC12 = Ge f GeC14, does not lead immediately to metallic germanium, but always involves intermediate subhalides.
Discussion of Results The demonstrated instability of germanium dichloride accounts for a fundamental defect in the Dennis-OrndorfT-Tabern synthesis of trichlorogermane. On the other hand, the discovery that germanium monosulfide and hydrogen chloride react t o form GeHC13 satisfactorily without heating is of great advantage in this alternate procedure. Better yields of GeHC13can be obtained in this way, both because of the lowered decomposition of any GeC12which may form as an intermediate and because of lack of undesirable side reactions. The original temperature proposed l6 for this method was 150", but Schumb and Smythgrecently used it successfully a t a much lower temperature, 50". I t has been shown that trichlorogermane exhibits greater instability than hitherto noted. An equilibrium dissociation into germanium dichloride and hydrogen chloride now appears to be well established. i2t normal temperatures and under conditions which would not otherwise disturb the equilibrium, dissociation is slight in extent. But during distillation, dissociation is promoted by more rapid diffusion of hydrogen chloride than of GeHC13. I t is rather surprising that such behavior has not been reported earlier for GeHC13, especially since it was noted long ago6for GeHRra. Perhaps the solubility of GeClz in GeHC13 has hidden this dissociation from earlier observation. Dissociation must have significant consequences on attempts to purify GeHC13 by distillation, leading to samples which may be either enriched or deficient in hydrogen chloride. The instability of GeHC13must also raise some doubts concerning the vapor pressure values reported2for the substance. The report by D e l ~ a u l l eof~ ~ decomposition of GeHC13 in alcoholic solution, resulting in evolution of hydrogen, suggests that such a reaction might likewise occur for the pure state. Although little information is available concerning the nature of
PHILADELPHIA 4, PA (18) L. M. Dennis and P. R . Judy, THIS JOURNAL, 61, 2321 (1929). (19) K. A. Hertwig and E. Wiberg, 2. Nafurforsch., 6B,336 (1951). (20) R . Schwarz and A. Kbster, i b i d . , 7B, 57 (1952); 2. anorg. allgcm. Chem., 270 2 (1952).
