20
ALFBED
w.FRANCIS
VOl. 60
rial deliberately subjected to extensive hydrolyaia. S m for the three strong linee of the reeulting complex pattern wereindeedthesameasth~noticedasimpuritylinesinthe ?ezyT&tione for the K&& uyatsls made by the a - f l o a t method gave as approximate value of the denfflty 4.4 g./cm.’.
Unit Cell Dimensions-Rapid survey of the interplanar spacings d o w s that, unlike the other series, the hexaiodomembers of the K&X( rhenate(IV) is not isometric at room temperature. Use of Werence diagrams and tables for sin* e as described by Henry, Lipson and Wooster‘l led to successful indexing of the pattern on the basis of an orthorhombic unit cell with d@ensions: u = 11.07 f 0.05 A., b = 13.48 0.07 A., c = 10.19 f 0.05 A.; a : b : c = , 1.086:1.323:1. The unit cell volume is 1520 A.’, and the density is 1.121n g./ cm.a where A is the number of molecules in the unit cell. The rough density of 4.4 g./cm.’ indicates n = 4, and the X-ray value of the density is, then. Table I contains interplanar spac4.484 g./cm.’. ings and lrkE values for the observed lines. The existence of general reflectionsestablishes the lattice as primitive. The h02 and McO spectra suggest glide planes e and A perpendicular, respec-
*
(7) N. F. M. Henry, E. Lipson. and W. A. Wooster, “The Inpretation of X-Ray DiErmtion Photogaphs,” Macmill.n and Co.. LM.. London. 1951, p. 182.
TABLE I X-RAY
W J IL T S FOR
InterP*
rn 111
Inter-
bsd. a m a s od .
A.
int:
p
hkl
e
T
Obsd. rel. int:
2.142 (bib 1.980 mw 310 w 244 1.907 W 311 m 404 1.875 W w 113 263 1.771 vw 302 vw 006 1.698 vw 330 vw 372 1.616 vw 400 vw s 226. 1.580 313 m 654 1.307 vw vw 214 536 1.290 vw *va = very strong; s = strong; ma = medium strong; m = medium; mw = medium weak; w = weak; vw = very weak; bl = broad line. 200
6.48 5.56 3.56 3.36 3.11 2.98 2.86 2.77 2.462 2.281
&&&
s
8
440 115
tively. to the axes b and e. The Dossible S D gro&, then, are Pmcn (Dla, P21ci (C:,), h c n (D:b), Pbcn ( D a and Pccn Acknowledgment.-The author is grateful to Dr. Roy Ingram for opportunity to use DebyeScherrer equipment of the Department of Geology and Geography and to the du Pont Company which provided generous financial assistance.
@la.
TERNARY SYSTEMS WITH THREE SEPARATE BINODAL CURVES1 BY ALFREDW.FRANCIS Conifibutwn from Socony Mobil Labomhies ( A LXvkion of Soo~nyMOW Oil Co., Inc.), Research and L h h p m m l Department,P a u l s h , N. J. Racai.sd Mav Si, 1066
Examples have been studied of several novel types of ternary liquid systems. In certain temperature ranges (nearroom temperature and at atmospheric pressure) these ayetema have three separate b i n d curves. With deeressing temperature two of the curves usually merge at their plait points (the ml) to form a band. At a stiU lower temperature the third curve may merge with the band at a “mbml” to form a triangle indicating three liquid phases. In one ayatem the two mtake place in reverse order; while another system has two cols and a m h l between them in temperature. These two ey% tems have unusual relations, which are discussed. The components of the four system studied giving these relatione are ethylene glycol, nitromethane or nitroethane, and decyl or lauryl alcohol.
Several systems with two separate binodal curves have been described recently.*.’ Some systems with threeseparate binodal curves also were shown.’ It was suggested that the phenomenon was favored by the proximity of the critical temperature of one of the components, carbon dioxide, to the temperature of the observations. Such a component has a mixing action with moderate concentrations and a demixing or precipitating action at high concentrations. However, the phenomenon can result from other conditions. It was shown5Jthat two wholly convex binodal curves meeting externally must do so at both plait points. If one b i n d area is a band, and 80 lacks a plait point, ifa border just before contact must be concave. The shapes of these curves at and near (1) Presented before the Di-n of Physical and Inorganic Chemis try at the 128th Meting of the dmerican Chemical Society. Minne apolis. Mnn.. Bept. 1955. In this paper “separate” means isdsted by areas of homogeneous wmpmition. (2) A. W. Francin, J . Am. Chenh &e., T6, 393 (1954). (8) A. W. F r a n k . THls J O ~ A L68, . 1099 (1954).
these contacts have been schematic in physical chemistry text books since no examples of external contact had been ObBerVed. It was impractical to observed these shapes with adequate precision in the carbon dioxide systems’ because of the high pressure, about 65 atmqheres. The systems now described were observed at ordinary pressures and temperatures. About forty ternary systems having compositions separating into three liquid phases have been published.%’ These systems have three b i n d areas,but the latter are not isolated by areas of homogeneous composition. None of these systems changes to one with three separate b i n d curves on raising the temperature, as might be supposed. Instead, one component becomes miscible with at least one of the other two components, giving even(4) Compiled by A. W. Francin in “SoIubil~tiesof Inorganic and Organic Compounds.” A. &idd and W. E W e , eda. D. Van Nob trrnd 0%. New York, N. Y.. Snppl. to the 3rd. ed.. 1952. pp. 847, Bn. 1009. 1015.1028-1031. 1035-1036. 1070.
~
Jan., 1956
TERNARY SYSTEMS WITH THREE SEPARATE BINODAL CTJRVES
21
tually a single binodal area, either a band or a bite.6 On lowering the temperature again, the three phase area results from the eruption of one of the extra binodal curves from within the first one. One binodal area already reaches a side line, and the other two extend toward the other side lines. For three separate binodal curves to result, the components must be selected so that the three binary critical solution temperatures (C.S.T.) are not too greatly different. This requirement is not commonly met. The two least miscible of three liquids normally must be very dissimilar and immiscible in order that the third one be incompletely miscible with either. The C.S.T. of the first pair is then extremely high; or it may not even exist. Thus, in each of the p ~ b l i s h e dthree-liquid ~.~ phase systems one of the binary C.S.T. cannot be observed because it is above the critical temperature of one of the liquid phases. Such a C.S.T. is imaginary. The 44 solvents tested by Drurys were rearranged into an order of mutual miscibility. The first one in the new arrangement, glycerol, is miscible with the first 14 but with no others. The last one, “benzin,” is miscible with 32 of the last 33. Pyridine and ethyl and butyl alcohols are miscible with all 44 solvents. I n descending the series the members have a decreasing number of solvents immiscible with them near the bottom of the list and an increasing number near the top. (Cf. the “octagon figure.’”) A few changes were made in the listed miscibilities as a result of experiments. Some slight inconsistenciesremain which cannot be eliminated by rearrangement. For two of the solvents, adiponitrile and nitromethane, no places can be found in the list which even approach consistency. Their antagonistic solvents are distributed throughout the list. This incongruity helped in the search for reagents in the present investigation, since these two solvents were promising as “intermediate” components. An analogous listing of a much larger number of solvents with respect to hydrocarbon miscibilities showed no inconsistencies. The requirement of three neighboring C.S.T. is satisfied by systems of ethylene glycol, nitromethane or nitroethane, and some aliphatic alcohols of nine to twelve carbon atoms. The C.S.T. of glycol with eightrcarbon alcohols are too low, and those with alcohols containing more than twelve carbons are too high. Four systems were studied in detail. Each shows a novel feature in type of diagram not shared by the others. Acetonitrile and adiponitrile show miscibility relations with glycol and decyl alcohol similar to those found for the nitroalkanes, giving three free binodal curves on the three sides of the triangle, but not in any single temperature range. They mix with ethylene glycol a t -13.5 and +27”, respec- GLYGO ALCOHOL tively (C.S.T.), below the cols or merging temperaFig. 1.-Isotherm of Rystem ethylene glycol-nitrotures of the other two curves, which are a t - 1 and methane-n-decyl alcohol (cf. Table 111): graph la, 26” 41 O , respectively. (curves closer to side lines) and 23.4” (col temperature); It is recognized in several physical chemistry text graph lb, 20” and 10” (curves with prime letters); graph IC, 0”.
(5) A. W. Francis in “Chemistry of Petroleum Hydrocarbons,” B. T. Brooh and others, e&., Reinhold Publ. Corp., New York, N.Y.. 1954, pp. 207, 210-211. (6) J. 8. Drury. Ind. Eng. Chcm.. 44, 2744 (1952). (7) A. W. Francis, ibid.. 56, 1102 (1944). Fig. 4. (8) Ref. 3, Table XI, column 3.
books that as a system with three separate binodal curves is cooled, the curves should expand and eventually overlap, forming an internal triangle, which would indicate compositions separating into
22
ALFREDW. FRANCIS
Vol. 60
NITROMETHANE
Fig. 2.-Isotherms of system ethylene glycol-nitromethane-lauryl alcohol (c., Table IV): graph 2a, 29”; graph 2b, 28” (col temperature); graph 2c,22”; graph 2d, 16” (quadruple point temperature).
three liquid phases. It would be a rare coincidence if the three curves met at the sa.me point. Such a contact would require the curves to be sharply pointed at their plait points, a very unusual though perhaps not impossible shape. Instead, the overlapping takes place in at least two steps. In the simplest, form the steps are presented by Wetmore and LeRoys in schematic agreement with the presetit observations. The points of contact of the curves are here called for convenience the “c01”~ and the “subcol,” since they are distinctly different relations. Col and Subco1.-A col is a point in a ternary system where two separate binodal curves meet at their respective plait points (on lowering the temperature) forming a band (C in Graphs la, Zb, 3b, 4a). In a triangular prism diagram with temperature as the vertical coordinate the col is the low point of a ridge (Figs. 5 and 6) like that in a mountain range (from which the name col is derived). There is an appreciable area on the binodsl surface near the col which is nearly flat and level. A t the col dt/dx = 0 in each direction, but d2t/dx2 is positive in one direction and negative in a direc(9) F. E. W. Wetmore and D. J. LeRoy, “Principles of Phase Equilibria,” McGraw-Hill Book Co.. New York. N. Y., 1951, pp. 126-127.
tion at right angles to it. There is no cusp or angular intersection of surfaces as a result of the meeting, either on the top or sides of the ridge formed. Just above the col in temperature the tie lines in the two curves approach parallelism, and the curves seem to reach toward each other, as by appointment. At the col the isotherm resembles curves intersecting at a finite angle, not curves with a common tangent. Location of a col requires direct observations of the plait points of both curves at progressively lower temperatures and approaching compositions. This is tedious since settling of the layers is slow near the plait points, and changes in composition must be in small increments to avoid uncertainty as to which binodal curve is involved when two layers appear. However, the col temperature can usually be verified easily by observing the cloud point of a mixture of composition between those of neighboring plait points. Observation of the upper col (at 21”) of the system glycol-nitroethane-lauryl alcohol (Graph 4a), presents a peculiar difficulty because the refractive indices of the two phases are identical. A heterogeneous composition in this region is as clear as a homogeneous one. Even the usual structural col-
*
TERNARY SYSTEMS WITH THREE SEPARATE RINODALCURVES
Jan., 1956
23
3a
\v
GLYCOL
GA NITROETHANE
NITROETHANE
3b
NITROETHANE
NITROETHANE
3c I
;
2L
Fig. 4.-Isotherme of system ethylene glycol-nitroFig. 3.-Isotherms of system ethylene glyool-nitroethanm-decyl alcohol (cf. Table V): p p h 3a, loo; etbne-lauryl alcohol (cj. Table VI): gra h 4a, 24O and 20" (curves with prime letters); graph 4b, 'I! (the dashed dot graph 3b, 6' (col temperature); graph 3c, 0 lines on graphs 4a, 4b indicate the vertical section shown in ors1O are almost lacking because the identity of the Fig. 6); graph 4c, 14'.
.
refractive indices extends in this case practically throughout the spectrum. It was necessary to add a trace of an insoluble powder, which after several minutes collected at the interface to make it visible. (10) A.
W.Francis, THISJOURNAL,66, 510 (1952).
A subcol is a point in a ternary system where a third binodal curve meets with its plait point (internally or externally) an isotherm of a ridge such a~ that mentioned above (K in Graphs IC,2a and 4b and Figs. 5, 6). The two curves lie on the same side
ALFRED W. FRANCIS
2p
60
Vol. 60
J I
k
\
.\
J
Nitromethane 20 40 60 80 Glycol % ethylene glycol on lauryl alcohol-free bask. Fig. 5.-hOjWtiOn on plane, ethylene glycol-nitromethane-tem ture of system, ethylene glycol-nitromethane-laury!%mhol (qf. Table VII).
10
20
% lauryl alcohol.
30
40
Fig. 6.-Verticsl section at 54% nitroethane through triangular prism diagram of s stem, ethylene glycolnitroethane-lauryl alcohol (cf. Tahe VI and Fig. 4).
of a common tangent so that if the contact is external (Graphs ICand 2a), the border of one of the ternary system.” This relation is unlikely to ocareas just before contact is concave at that point. cur except in systems which have three separate The tie h e s in the two binodal areas as the curves binodal curves. In a triangular prism diagram meet are at a sharp angle, sometimes almost per- this system shows no essential difference in type pendicular. One of them, the “subcol tie line” from the other three studied, since the side ridge (KZ in Graph 2s) splits to form a triangle (XYZ in still meets at the subcol (Fig. 5 ) the main ridge beGraphs 2b, 2c, 2d, 4b, 4c) whose corners indicate low its crest although at a point higher than the col. The side ridge usually slopes downward when it the compositions of the three liquid phases. The subcol is at the maximum temperature for meets the main ridge. In another system, ethylene glycol-nitroethanecoexistence of three liquid phases in equilibrium. It can also be considered as the critical solution lauryl alcohol, the side ridge contains a second col point of two phases, X and Y, when the system is (C, Graph 4b and Fig. 6) or low point at 15.6”, and saturated with the third phase 2, of substantially meets the main ridge on the up grade. This results different composition. In a solid diagram it is the in a subcol, K, at 16.5” between the two cols in inner end of the plait line or crest of a side ridge as it temperature. The 16 O isotherm (Graph 4b) shows meets the main ridge below its crest. There is a new binodal curve, XOY, which in effect has no flat or level spot on the binodal surface near the erupted from within the binodal band at K, forming subcol; and below the subcol in temperature there a three phase area, XYZ, in the same manner as are cusps X, Y and Z, on each side of each ridge, are those in the classical three phase system^.^,^ three in all (Fig. 5 and Table VII), corresponding Graph 4b resembles in this respect the graph of and to the comers of the triangles on isothermal dia- formic acid-carbon di~xide-n-tetradecane~~; grams. A system with two intersecting or cross- isotherms at lower temperatures resemble that with ing ridges is probably impossible because it would n-hexadecane.16 Advantage was taken of the near seem to involve four liquid phases in equilibrium in equality in percentage of nitroethane for the points GN, NA, P, P‘ on graph 4a and K, 0, C, P a univariant ternary system. In most cases, probably, the col is higher than on graph 4b to show these relations by a vertical the subcol in temperature and near the subcol tie section in Fig. 6. In each of the four systems here described all line in composition. In one system studied, however, that of ethylene glycol-nitromethanelauryl three ridge ends reach the side lines on the up grade. alcohol, the col is about 0.5” lower than the subcol Probably systems can be found with meeting ridges (Graphs 2a and 2b). Thismeans that with descend- (resulting in three liquid phases) in which one ridge ing temperature the first contact of separate curves end is on the down grade. These would have only is a t the side of one of them instead of a t its plait two separate binodal curves. Each of the published point. Such a contact, with its resulting triangu- three-liquid phase systems4has two ridge ends on lar area indicating three liquid phases was unex- the down grade. A system with all three ridge ends on the down grade is less probable. An isornw. In view of Schreinemakers’ rule’l the relation is therm of it might have an island triangle with binonot p ~ s s i b l e ~ . ~unless J ~ J ~ the binodal curve con- dal loops on each side of it. In the carbon dioxide tacted at its side is comave at that point (Graph systems3 some of the ridges are inverted. Materials and Procedure.-The properties of the reagents 2a), an unusual shape for a free binodal curve in a (11) F. A. H. Snhreinemakers: “Die heterogenen Gleiahgewichta,” H. Rooreboom. ed.. Friedr. Viewig u. &hn. Braunschweig. Germany, 1911. Drittea Heft. Zweiter Teil, pp. 6-17. (12) A. W. Francis in “Physical Chemistry of Hydrocarbons,” A. Farkas. ed.. Anadernie Preas. h a . , New York, N. Y.. 1950, pp. 252253. (13) Ref. 4. p. 830.
are listed in Table I. In view of the high freezing point of
(14) The nonspicuoua noncavities in published free binodal curves are due to the presence of a fourth component (impurity or diluent), or to a fourth type of molecule resulting from reversible interaction of two of the components. (Ref. 4, pp. 895, 941, 988-989, 1003-1004. 1065. 1072. 1077. 1080-1081. 1116). (15) Ref. 3, Graphs C10,C24.
.
Jan., 1956
TERNARY SYSTEMS WITH THREE SEPARATE BINODAL Cmms
25
TABLE I PROPERTIES OF REAGENT^ Density (temp., "C.)
Reagent
Ethylene glycol Nitromethane
Obsd. Lit.' Obsd. Lit." Obsd. Lit:
1.1101 (25) 1.1099 (25) 1.1298 (25) 1.1312 (25) l.O469(20) 1.050(20)
nab
1.4315 1.4319 1.3820 1.3820 1.3920 1.392
M.P., OC.
-13.3 -12.6 -30.5 -28.6 < -78
