T H E PHOSGENO-ALUMINATES O F SODIUM, STRONTIUM AND BARIUM1 BY A. F. 0. GERMANN AND D. M. BIROSEL
It has been shown that the phosgene-soluble phosgeno-alumina tes may be prepared most easily by the neutralization of phosgeno-aluminic acid (COALCls) with phosgeno-bases2 (metallic chlorides). These bases are in general insoluble, so that after complete neutralization of the acid the soluble salt may be readily removed from the excess of base by decantation, and the salt purified by fractional crystallization. It was the object of the present investigation to extend our knowledge of phosgeno-salts by the preparation and characterization of some new members of the series, of which calcium phosgeno-aluminate is the only one so far defini,tely characterized3. Kendall, Cri ttenden and Miller4 have investigated the melting point curves of the binary systems formed between aluminium chloride and a number of metallic chlorides. They identified the double salts : KaCl.AlC13 and BaClz zA1C13,but did not investigate the systems with calcium or strontium chloride. Baud5 investigated a number of systems, one component of which was aluminium chloride, but Kendall points out that the method used by him is open to serious question. He reported a number of compounds not revealed by the fusion curves, and was unable to prepare the calcium compound prepared in phosgene solution by Germann and Gagos.
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Preparation of Materials Phosgene and aluminium chloride were purified as described in previous papers6. Sodium chloride was purified by precipitation from solution with hydrogen chloride gas, and dried by heating with the free flame in a platinum dish. The barium chloride used was the purest obtainable, and was dehydrated by heating to fusion in a platinum dish in a current of dry hydrogen chloride gas. Pure strontium chloride was dehydrated in the same way. Procedure. Slightly modified Faraday tubes were used as reaction tubes, like that illustrated in Figure I ; a I O mm. bore filling-tube near the arch, at A, being designed to permit the entrance of a weighing tube, for the introduction of weighed samples of the solid reagents, after which i t mas sealed to the apparatus containing the phosgene supply, and evacuated. Pure phosgene was then distilled in, and the tube finally sealed off a t A. The aluminium 1 From a thesis submitted to Stanford University by D. M. Birosel in partial fulfillment of the requirements for the degree Chemical Engineer. Germann and Timpany: J. Am. Chem. Soc., 47, 2275 (1925). 3Germann and Gagos: J Phys. Chem., 28, 965 (1924); Germann and Timpany: J. Phys. Chem., 29, 1423 (1925). J. Am. Chem. SOC.,45, 963 (1923). &Ann.Chim. Phys., ( 8 ) , 1, 8 (1904). 6 Germann and MoIntyre: J. Phys. Chem., 29, 102 (1925).
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A. F. 0. GERMANN AND D. M. BIROSEL
chloride dissolved immediately, while the other chloride reacted more slowly. The reaction was speeded up by maintaining the temperature of the leg con,taining the reagents in the neighborhood of 100'; in this way constant agitation of the solution was effected, due to boiling and distillation of the solvent .to the cooler leg. After a week or more of khis treatment, the solution was decanted from the excess of insoluble chloride into the other leg of the tube, pure solvent was distilled back, and the residue washed repeatedly. Finally, the leg containing the solution was cooled in liquid ammonia, and the other leg heated to drive out all phosgene; air was introduced by breaking off the tip at A, and the excess of insoluble chloride removed by breaking off the lower half inch of the Faraday tube a t B. The glass and residue were placed in a stoppered weighing bottle, and weighed, after which the chloride was removed and the tare weighed. This furnished all the elements for calculating the ratios A1C13 : NaCl and A1C13 : SrC12. The ratio in the case of the barium salt was unsatisfactory, hence the salt was analyzed after purification as described in the following paragraph. The open end of the tube was then sealed off a t B, the Faraday tube again sealed to the apparatus at A, evacuated, and once more sealed off a t A. The solution of the phosgeno-salt was then crystallized by evaporation of a portion of the solvent, the mother liquor was drained off, fresh solvent introduced, and the salt thus recrystallized several times. When the salt was judged to be pure, the tube was opened a t A, sealed .to ,the evacuation apparatus, and the phosgene allowed t o boil off a t atmospheric pressure. The solid residue was warmed to the melting point, and all phosgene given up was pumped off. Following complete dephosgenation, ,the tube was opened, and the szlt transferred to a bottle and kept in a desiccator. The complete vapor tension diagrams of the three systems with phosgene at 25' were determined, using the volumetric method to determine the compositions as used in previous work by one of us1. It has been mentioned that the data obtained in the synthesis of the barium salt were unsatisfactory; this may be due to the fact that the solution of the barium salt separates into two liquid layers a t room temperature, a heavy oily layer containing the salt, with a layer of liquid phosgene on top. At low temperatures (for example by cooling in liquid ammonia) the two layers coalesce; the system thus exhibits a lower critical solution temperature. Evidently the solution obtained at these lower temperatures is supersaturated, since, once the oily layer has been crystallized, it appears .to be impossible to bring it back into solution by cooling-crystal nuclei appear to persist, and the solution crystallizes instead. The strontium salt also exhibits a lower critical solution temperature, as, on warming its solution to 50' or above, the solution first becomes turbid, due to the formation of an emulsion, then the emulsion breaks, and a heavy oily liquid settles to .the bottom: on cooling, the two layers coalesce. In a previous paper of this series2 it was J. Phys. Chem., 28, 965 (1924);29, 102 (1925). Germann and Gagos: J. Phys. Chem., 28, 965 (1925).
PHOSGENO-ALUMINATES
1471
pointed out that magnesium yields a liquid phosgeno-aluminate insoluble in phasgene : we have attempted to determine the composition of this magnesium salt by synthesis, but the results have been no more satisfactory than those in the case of tbe barium salt. Satisfactory results were, however, obtained jn those cases where the product was soluble: in order to show the applicability of the method, calcium phosgeno-aluminate, whose composition has been thoroughly established, was synthesized quantitatively, and the results incorporated with those for the strontium and sodium salts. Barium phosgeno-aluminate, BaAlzC18.Mol. Wt., 47 j. Melting point, 295.0'. Analysis, found: C1, 59.j6%; AI, 11.37%; Ba, 28.75%. Theory for BaAlzClg:C1, 59.72%; All 11.36%; Ba, 28.92%. Calciumphosgeno-aluminate,CaAlzClg; Melting point, 280' with loss of AlCl3 by distillation; Mol. Wt., 377.7. Synthesis: A1C13 used, 3.5699 gm.; CaC12 used, 4.5555 gm; CaC12excess,3.0877 gm.Ratio CaClz:AIC13= I 2.023. Xtrontium phosgeno- A l u m i n a t e , SrA12C18. Melting point, 325'; Mol. Wt., 425.2, Synthesis: A1C13 used, 5.6023 gm.; SrClz used, 5.9760 gm.; SrClz excess, 2.7671 gm. Ratio, SrCl2:A1Cl3=~ : 2.08.
Sodium phosgeno-aluminate,NaAICL. Melting point, 155.5'. Mol. a t . , 191.8. Synthesis: A1C13 used, 3.9228 gm.; NaCl used, 3.4548 gm. : NaCl excess, 1.7804 gm. Ratio: KaCl : A1C13= I : 1.028. 25' Isotherms. In Table I are assembled the experimental results relating to the vapor tension measurements for the system BaAlzClg- COCl2, in two concordant series. Table I1 contains similar FIG.2 data for the system SrAl2Cl8- COCl2, and Table I11 the vapor tension data for the system NaA1C14- COCl2. character of the 25' isotherms is shown in Figures 2 , 3 and 4.
The
Isotherm of BaAlzClg Solution. The constant vapor tension of this system up t o 49% of BaA1zClg at 1405 mm., the vapor tension of pure phosgene, indicates that the salt is practically insoluble in phosgene at this temperature, and that the salt layer contains j I % of phosgene; these figures are probably The salt solution is capable of a large degree of accurate to less than 1%. supersaturation; in the experimental work cooling was resorted to to induce crystallization. The saturated solution contains 5 2 . 5 % of BaA12C18,as shown by the intersection a t C in Figure 2 . At E there is a second break in the curve, when the dry crystals begin to effloresce; this point is at 64.5% BaAlzC18,
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A. F. 0. GERMANN AND D. M. BIROSEL
Vapor Tension Curve 25' for the System BaAI2Cl8-COClz
TABLE I Vapor Tensions of the System BaAI2Cls.COCl2a t
70 BaA12C18 0
Series A.
1405 mm.
%
9 . o ( 2 layers) 9.6 " 77 10.3 20.3 45. I ( I layer) 47.2 50.4 52.9 53.1 54.8 (crystals) 57.3 59.8 63. I 64.3 64.5 6 8 . 3 (efflorescence) 76.4 82.5 83.4 92.2 94.9 98.0 99.7 )>
100.0
Vapor tension
1405 mm. I405 I405 1405 I 402 1401 I372 1321 I 192 I343 1311 1241 1191 1024 741
557 61 I
5 50 204 282 187 I3 5 42 0
yo BaALC18 0
25'
Series B
36.3 41.7 49.0 54.0
(I
layer)
57.0 j 8 . 4 (crystals) 60.4 64.1 64.5 6 7 . 6 (efflorescence) 78.9 82.0 83.2 87.4 93 ' 1 96.6 100.0
Vapor tension
1405 mm.
%
1401 1401 1401 1316 1232 I338 I305 I 130 731 611 624 498 327 293 258 148 0
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PHOSGENO-ALCMINATES
TABLE I1 Vapor Tensions of the System SrAlzCls.COClzat % SrXlzC18 0
Vapor tension
% SrAI2Cl8
140 j mm.
%
16.2 17.4 18.9
64.7 67.1 69.4 70.4
I398 ’ 5 1395.5 1395.5 1395.5 I393 1391 1385.5 I375 1348.5 I297 1248 1151
22.0
23.4 24.9
27.5 30.6 35.2 39.3 42.2 46.2 48.7 50.9 53.3
55.5
7%
70.8 7 5 . o effforescence 78.6 80.0 80.3 80.5 80.6 81.0 85.5 87.2 89.2 91.6 94.5 97.0 99.5
1079
57.6 59.3 61.0 63.2 crystals
25’
1008 925 849 756 696 63 2 942
100.0
Vapor tension
934 mm. 913 853 608 318 539 541 321 I47 47 I4 0
176 I 66 I74 170 I53 I47 116 0
TABLE I11 Vapor Tensions of the System NahlCl4.COCI2a t 2 5’ % SaAlC14 0 %
8.95 9.44 10.33 11.08 13.06 14.47 17.4 20.7
24.7 28.7 30.6 32.8
Vapor tension
1405 mm. I 400 1399.5 I398 ’ 5 I398 I397 1396.5 1393.5 I389 1380.5 1362 I349 1331
% NaAlClt 35.370 37.9 40.7 crystals 44.2 48.9 58.9 67.5 79 . o 95.1 98.7 98.9 99.6 100.0
Vapor tension
1305 mm. 1270
1287 1286 1285 1282 1276 1268 I221
742 429 I02
9
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A . F. 0. GERMANN AND D. M. BIROSEL
TABLEI V Vapor Tensions a t % Salt' 0%
5 IO
I5 20
25
30 35 40 45
50 55 60
25'
of Solutions of SrALCls, NaAlC14 and BaAlzCls in C0C12 from Curves
SrAbC18
1405 mm. 1403.9 1402.2 1399.6 1396.5 1390.5 1377.5 1350.0 1286.5 1185.0 I 140 867 664
NaAIC14 1405 mm. 1402.2 1399.2 1395.5 1390.5 1378.5 1353.5 1308.0 1240.0
BaA12C18
1405 mm.
1390 mm. 1290 1150
FIG.3 Vapor Tension Curve 25' for the System SrAl~C18-CoCl~
corresponding to 3.03 molecules of the barium salt and 8.00 molecules of phosgene; the compound 3BaA12Cls. 8C0C12 contains 64.30% BaClzCls. At F there is a third break in the curve, at 8 3 . ~ BaA12C18; 7~ this corresponds to 1.032 molecules of the barium salt and 1.000molecule of phosgene; the compound BaA12C18.COC12contains 82.77% BaA12ClR. Isotherm of SrA12ClsSolution. Strontium phosgeno-aluminate has the highest solubility in phosgene at 25' of any salt 30 far investigated. On concentrating the solution, it becomes syrupy, and finally becomes gummy, or on cooling forms a glass. Figure 3 shows the vapor tension curve of this solution up to 6 0 7 ~(curve ABC), when crystallization was brought about by sudden cooling of B thin film of the solution. The intersection at B gives the
PHOSGENO-ALUMINATES
I475
solubility of the salt a t this temperature as 5 2 . 3 % . The horizontal portion of the curve BD represents the constant vapor tension of the saturated solution during evaporation and deposition of crystals, while the vertical portion gives the adsorption isotherm of the crystals. The composition of the crystals is given by the intersection a t D, namely 70.57~of Srhl2Cl8, corresponding to five molecules of the strontium salt and nine molecules of phosgene; the compound 5SrAld21s,gCOClzcontains 70.49% of SrA12C18. These crystals lose only part of their phosgene of crystallization, and yield a second phosgenate a t E which for some reason resists decomposition with remarkable vigor, the interval between the pressure readings a t 80.3% and 81.0q/c (see
Vapor Tension Curve
25'
FIG.4 for the system NaAlC14-COC1~
Table II), representing the portion of the curve below the intersection a t E, being no less than 48 hours. In fact, i t was thought that the end of the curve had been reached, and that the residue was completely dephosgenated ; so that when a pressure of nearly two hundred millimeters was registered the next day, there was a strong suspicion that a leak had developed in the one stop-cock giving access to the vapor tension apparatus; a sample of this gas was therefore pumped off, collected, and analyzed; i t proved to be 100% phosgene; a second proof that no leak was involved is given by the fact that, as the percentages are arrived a t from the weight of salt used and the volume of phosgene pumped off , the volumes being converted to weights by mu1tiplying by the density of the gas, ,the density of the gas pumped off up to the point E was found to be extraordinarily high, whereas after completion to the point F on the curve the density value was perfectly normal. Once the decomposition was started, it appeared to go on readily, apparently catalyzed by the ansolvide, SrhlzCls. The composition of the product at E is given by the point of intersection as 8 0 . 3 7 ~of the strontium salt, which corresponds to one molecule of SrA12C18and 1.055 molecules of phosgene; the compound SrAlzCls. COClz contains 8 I. I 2 % of SrAlzCls.
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A. F. 0. GERMANN AND D. M. BIROSEL
Isotherm of NaA12C14 Solution. The solution of the sodium salt presents the simplest possible isotherm for this type of solution, that is for the solution of a non-volatile crystallizable salt in a volatile solvent. There is but one break in the curve, at the point B (Figure 4), where crystals begin to separate, showing a solubility of 36,jojO NaA1C14. The solution is capable of slight supersaturation. No solvates are stable at 2 5 . MoZecuZar Weights. I t is possible .to calculate the molecular weights of the phosgeno-aluminates of sodium and strontium from the vapor tension data. g Mp' _ , where m is the molecular weight of the solute, Using the formula m = _ P - P' M that of the solvent, p the vapor tension of the solvent, p' that of the solution, and g the weight of solute in I gram of solvent. R e arrive at molecular weights for the strontium salt ranging regularly from 7130 at 2 . j % , to 4530 at IS%, and for the sodium salt from 2545 to 2 5 6 j , the values passing through a maximum in the latter case, indicating that the upper part of the curve is imperfect. These values lead to a value of about 7650 for the strontium salt, and to a value probably in excess of 3000 for the sodium salt; and to molecular aggregates containing from fifteen to twenty molecules of the simple formulas used in this paper. The higher solvate of strontium phosgeno-aluminate contains five of the simple molecules in one of the solvated molecules, and the vapor tension data seem to indicate that three or four of these are banded together to give immense colloid-like aggregates. Whether these solutions give the Tyndall effect has not been determined. In contrast to these solutions, previous papers of this series have shown that the solution of aluminium chloride in phosgene contains molecules with only two atoms of aluminium, while the solution of calcium phosgeno-aluminate contains molecules with four atoms af aluminium. What the significance of these facts may be is not clear. Summary Some new phosgeno-aluminates have been prepared, and their solutions in phosgene studied, The solubility of the salts has been determined at z s 0 , and the isotherms of their solutions a t 2 j o found. The vapor tensions of their solutions have been tabulated in Table IV at round values of the composition. The following solvates have been identified : 3BaA12Cls.8COC12,vapor tension at 2 5 O , 62 j mm.; BaAl2Cl8.COCl2,vapor tension at 2 jo, 290 mm.; 5SrAlzCls.9COCl2,vapor tension a t 2j0, 9 j o mm.; SrA1zCls.COC1z,vapor tension at 2 j 0 , 175 mm. NaA1C14forms no solvate with COClz at 25'. Molecular weight calculations indicate that the phosgeno-aluminates of strotium and sodium contain from fifteen to twenty atoms of strontium or sodium per molecule. In conclusion, we wish to acknowledge the liberal supply of phosgene placed a t our disposal by the officers of the Chemical Warfare Service. Stan.ford University,
California.
