Mar., 1954
225
BORON BROMIDE WITH INORGANIC HALIDES : BINARY FREEZING POINT
BINARY FREEZING-POINT STUDIES FOR BORON BROMIDE WITH INORGANIC HALIDES BY ROBERTF. ADAMSKY AND CHARLES M. WHEELER, JR. Department of Chemistry, University of NEWHampshire, Durham, N . H . Received September 8, 1065
Freezing point and solubility data are presented for the binary systems boron bromide-aluminum bromide, boron bromidearsenic bromide, boron bromidestannic bromide and boron bromide-stannic iodide. All systems had simple eutectic points and there was no evidence of compound formation. Comparisons of ideal and experimental solubilities have been made and are interpreted with the aid of the internal pressure concept.
The number of molecular coordination compounds with boron bromide is far less than that reported for boron fluoride and boron chloride. Martin2 has reported compounds with R B P ~in whic,h the donor atoms belong to Group V (nitrogen, arsenic,, phosphorus), Group VI (oxygen and sulfur) and Group VI1 (chlorine and bromine). No element of Groups I, 11, I11 or IV has been found to act as a donor to boron bromide. This paper reports the results of cryoscopic and solubility studies of systems of boron bromide with some halides of Group I11 (aluminum bromide), Group IV (stannic bromide and stannic iodide) and Group V (arsenic bromide).
1
120 100 80 60 40 d 20 $ 0 -20 -40 - 60
’-
90 80 70 60 50 40 30 20 10 Mole % aluminum bromide. Fig. 1.-The aluminum bromide-boron bromide system.
Experimental
fU
Materials.-Boron bromide was prepared by metathesis of boron fluoride and anhydrous aluminum bromide.’ The boron bromide was shaken wit.h mercury, distilled and stored in all glass cont,ainers. The boron b r o m i e was redistilled immediately prior to its use, b.p. 90.6-91 The aluminum bromide (Matheson, Coleman and Bell) was twice divtilled yielding a pure white crystalline product which froze a t 97.0’. Stannic bromide was synthesized from the elements an! purified by two successive dist.illations, freezing point 30.2 Stannic iodide was prepared by reaction of granular tin with iodinc dissolved in carbon disulfide, the solvent being evaporat,ed after the reaction. The compound was purified by crystallization from benzene, freezing point 143.5 to 144.0’. Arsenic bromide was prepared from t8he elcnicnts and purified hy dislillat8ion,freezing point 30.8‘. Procedure.-The freezing point,r;:of t,he st,antiic iotlitlaboron bromide systems, a t stannic iodide concent raOions of 80 mole per cent. or greater, were obtained by t,he s e a M h b e (static) method of Collett and Johnston.‘ Stannic iodide solutions less than 30 mole per cent. and all other systems were studied by the freezing point method. The freezing points were determined by means of cooling curves using a copper-constantan thermocouple to determine temperatures. The thermocouple was calibrated against an electronic resist>ancethermometer. The freezing point cell was 20 cm. long X 2 cm. diameter fit,ted with a 24/40 joint. The cell cap carried a thermocouple well, a mercury seal wit,h a glass coil vertical mot,ion st8irrerand a glass stoppered addition tube. All determinations were made wit,h 10 to 15 cc. of solution. All additions were made in a “dry” box. The cooling curves were obtained over the entire composition range for each system studied with the exception of the part of the stannic iodidc system noted above.
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Results and Discussion The freezing point-composition diagrams for the four systems reported in this paper are given in Figs. 1, 2, 3 and 4. The solubilities of aluminum (1) Taken in part from the M.S. thesis of Robert F. Adamsky. (2) D. R. Martin, ChPm. Reus., 42, 581 (1948).
(3) L. F. Audrieth, ed., “Inorganic Syntheses.” Vol. 111, hloclrawHill Book Co., Inc., New York, N. Y..1950, p. 27. (4) A. R. Co!Iatt and J. Johnston, Tma JOURNAL, so, 70 (1926).
30 20 10
6
0
E,
-20 -30 - 40 -50
. -10 d
90 80 70 60 50 40 30 20 10 Mole % stannic bromide. Ng. 2.--Tlic stannic Ix-on&le-boron broiiiitle fiysteni. 1
1601
140 120 100 6 80 60 40 20
-
$ G
0L
-20
-41
-40
90 80 70 60 50 40 30 20 10 Mole % stannic iodide. Fig. 3.-The stannic iodide-boron bromide system.
bromide. stannic bromide. stannic iodide and arsenic bromide in boron b&$& are shown in Figs. 5-8 inclusive, plotted as the logarithm of the mole fraction of the halide us. the reciprocal of the absolute temperature. These plots were made t o
226
ROBERTF. ADAMSKY AND CHARLES M. WHEELER, JR.
VOl. 5s
=" I
-
-40 -50-1
-0.5
b
1 I
90 80 70 60 50 40 30 20 10 Mole % arsenic bromide. Fig. 4.-The arsenic bromide-boron bromide system.
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determine the deviation from ideal solubility after the method used by Hildebrand.s The ideal solubilities were calculated from the heats of fusion and heat capacities, where available, of the solutes.
o.a
- 1.5 36 38 40 42 44 46 i p x 104. Fig. 6.-The solubility of arsenic bromide in boron bromide: -, ideal; 0-0, experimental. 32
--0.6
34
and others7 whose conclusions were not in agreement with Kendall, Crittenden and Miller.* The latter workers reported a phase transformation 5 -1.0 near 70' for solid aluminum bromide. The stannic bromide-boron bromide system has a eutectic a t -52.5 f 0.5' and 18.3 mole per cent. bo stannic bromide. There is no compound formed in this system. The stannic iodide-boron bromide system forms -1.5 no compound and has a eutectic at -51.1 k 0.5' and 0.94 mole per cent. stannic iodide. The system arsenic bromide-boron bromide has a eutectic at 5.8 mole per cent. arsenic bromide, freezing at -54.1 f 0.5'. There was no evidence of compound formation in this system. In a previous -2.0 study of boron bromide reactions, TaribleQ observed that arsenic bromide was soluble in boron bromide, but that no reaction occurred at 18'. Our findings are consistent with those of Tarible, 24 28 32 36 40 44 48 and his observation may thus be extended to the I/T x 104. entire concentration range, Fig. 5.-The solubility of stannic iodide in boron bromide: It is apparent from the present phase studies __ , ideal; 0-0, experimental. that bromine in aluminum, stannic and arsenic The aluminum bromide-boron bromide system bromides and iodine in stannic iodide show no has a eutectic at -46.1 0.5' and 5.24 mole per tendency to coordinate with boron in boron brocent. aluminum bromide as A12Bra,with no evidence mide. Only one instance is reported in which broof compound formation. Aluminum bromide has mine is considered the donor atom, in the case of the been considered to be A12Br6 throughout this compound PBrs.BBrr.'0 I n contrast, Cueilleron,l' present work in view of the knowledge of its molec- in a study of the system Br2-BBr3, found that no ular state when no chemical reaction has occurred. maximum occurred, the system having a simple The cooling curves of pure aluminum bromide eutectic a t 80 mole per cent. BBr3 and -60.4. showed no phase transformation down to room His work indicated that free bromine apparently (7) J. D. Heldman and C. D. Thurmond, J . Am. Cham. Soc., 66, temperatures. This observation is in accord with and supports the reports of Burbage and Garrett6 427 (1944).
z-
*
( 5 ) J. H. Hildebrand and R. L. Scott, "The Solubility of NonElectrolytes," 3rd ed., Reinhold Publ. Corp., New York, N. Y.,1950, Chap. XVII. (6) J. J. Burbage and A. B. Qarrett, T H IJOURNAL, ~ 66, 730 (1902).
(8) J. Kendall, E. D. Crittenden and H. K. Miller, ibid., 46, 963 (1923). (9) J. Tarible, Compl. rend., 188, 204 (1901). (10) J. Tarible. dbid., 116, 1621 (1893). (11) J. Cueilleron, ibdd., 817, 112 (1943).
l
*
BORONBROMIDN WITH INOR~ANIC HALIDES : BINARYFREEZING POINT
Mar., 1954
227
amok
-0.2
-1.0
E
- 1.2
I
33 35 37 39 41 43 I / T x 104. Fig. %-The solubility of aluminum bromide in boron bromide: 0, ideal; 0, experimental. 29
38 40 42 44 46 I/T x 104. solubility of stannic bromide in boron bromide: -, ideal; 0-0, experimental. 34
36
31
cc. for boron bromide. This positive deviation is consistent with Hildebrand's observation that large differences in internal pressures, between solute and solvent, are generally reflected in dehas no tendency t o donate electrons to boron creased solubilities. The plot of tke experimental bromide to form a molecular compound. The data for these two solutes in Figs. 5 and G forms an data obtained in the present research indicates the S shaped curve, typical of solutions which have been same conclusion with respect to bromine as bromide. classified as regular by Hildebrand. Sufficient Of the three metal components used in this re- data are not available to allow calculations over a search, only arsenic has previously been considered wide temperature range to test this classification. to be a donor atom with boron in boron bromide. A comparison of the experimentally determined An investigation12 of the system boron bromide- solubility with the calculated ideal solubility for arsine gave evidence of a 1:1 complex between stannic bromide shows a negative deviation. The arsine and boron bromide. In the complex which internal pressure was calculated to be 77.5 cal./cc., was formed arsenic was considered to be the donor somewhat lower than the similar quantity for boron atom. In contrast, no tendency for coordination bromide. was shown by arsenic in arsenic bromide in this The experimental data for aluminum bromide research. corresDonded closely to the calculated ideal soluHildebrand6has shown that in'non-polar systems bility curve. The" latter curve was plotted by the relative values of the internal pressures of the calculating the heat of fusion for aluminum bromide two components are important factors in determin- at a number of different temperatures using availing the solubilities (or freezing point depressions) able heat capacity data. The internal pressure in the systems. Therefore a comparison of the value for aluminum bromide was found to be deviation from ideal solubility shown in Figs. 5-8 78.6 cal./cc. and the internal pressures of the added halides From the above comparisons, large differences seemed desirable. in internal pressures appear to be significant in Stannic iodide and arsenic bromide exhibited determining solubility relationships in these syspositive deviations from ideal solubility. Their tems. However, additional thermodynamic data, calculated internal pressure values are 135.8 and such as heat capacity of liquid boron bromide, are 120.5 cal./cc., respectively, compared to 80.5 cal./ needed for a more rigorous treatment of the solubility curves. (12) A. Stock, Ber., 84, 949 (1901): Fig. 7.-The
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