ROBERT R. hlOD AND EVALD L. S K l U
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catalyze the decomposition of diacetone alcohol into mesityl oxide and water. In mesityl oxide calcium bromide is very sparingly soluble (s being of the order of 0.0001 a t 65") but the salt swells, with liberation of heat and formation of needleshaped crystals of the addition compound, CaBrz, 3(CH&C=CHCOCH3. Strontium bromide be-
Vol. 513
haves similarly and forms the compound SrBrz, 2(CH3)zC=CHCOCH3. The bromides of sodium, potassium and barium are practically insoluble in mesityl oxide. The chlorides of lithium, sodium and potassium are very sparingly soluble in methyl isobutyl ketone, while those of calcium and barium are practically insoluble.
BINARY FREEZING-POINT DIAGRAMS FOR ACETAMIDE WITH OLEIC AYD ELAIDIC ACIDS BY ROBERT R. MODI N D EVALD L. SKAU Southern Regional Research Laboratory,' New Orleans, Louisiana Received dfarch 24, 19.53
Complete binary freezing-point data have been obtained for the stable and unstable forms of acetamide with elaidic acid and with the stable and unstable forms of oleic acid. The freezing-point diagrams show conclusively that acetamide forms a molecular com ound with both elaidic (trans) and oleic (cis) acid. Each of these compounds eshibits two incongruent melting points, t i e one stable and the other metastable. I t can also be concluded from the diagrams that the oleic acid compound tends to dissociate to a lesser degree than the elaidic acid compound.
It has recently been demonstrated by means of binary freezing-point determinations that acetamide forms molecular compounds with various long-chain saturated fatty acids? The present report shows that acetamide forms similar com'
pounds with oleic and elaidic acids, ie., with both the cis and the trans forms of A9~10-octadecenoic acid. Experimental Binary freezing-point data were obtained for acetamide with oleic and with elaidic acid. The oleic acid was purified by vacuum fractional distillation of itts methyl ester followed by fractional low-temperature crystallization of the acid from acetone, f.p. of stable form 16.3', f.p. of unstable form 13.5'. The elaidic acid was obtained by elaidinization of oleic acid followed by fractional crystallization from acetone, f. 43.8'. The acetamide was the best grade of Eastman d d a k product.3 All sample material was dried in vacuum over phosphorus pentoxide. The freezing points were determined by the sealed tube (static) method previously described,* which gives the true equilibrium temperature between the crystals and the liquid mixture of the given composition, with an accuracy of f0.2' after correction for thermometer calibration and emergent stem.
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I"
40 60 80 100 MOLE PERCENT ACETAMIDE. Fig. 1.-Binary freezing-point diagrams for acetamide with: A, oleic acid; B, elaidic acid. Dotted curves represent metastable equilibria.
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(1) One of the laboratories of the Bureau of dgricultural and Industrial Chemistry, Agricultural Research Administration, U. S, Department of Agriculture. Article not copyrighted. (2) F. C. Magne and E. L. Skau, J . Am. Chem. Soc., 74,2628 (1952).
Results and Discussion The data obtained are given in Table I and are plotted in Fig. 1. As can be seen from the diagram it was possible to obtain the freezing-point curves for both the stable (solid curves) and the unstable (dotted curves) forms of acetamide and also of oleic acid. It is apparent that both oleic and elaidic acids form a crystalline molecular compound with acetamide and that each of these molecular compounds exhibits two incongruent melting points, the one stable and the other metastable. For the acetamide side of the diagram the stable or unstable forms could be obtained a t will by proper manipulation of the temperature. The higher freezing point was always obtained on the initial melting of the samples, as would be expected since they contained the stable modification. After the samples had been heated some degrees above this temperature, however, the freezing points invariably fell on the lower (dotted) curves and in order to obtain the higher freezing point again it was necessary to shock-chill the molten sample to -78' in in a Dry Ice-alcohol mixture. Subsequent heating of the solid resulted in momentary local melting (3) The mention of names of firms or trade products does not imply t h a t they are endorsed or recommended by the Department of Bgriculturivover other firms or similar products not mentioned.
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THETHEORY OF h I E M B R . 4 N E
Nov., 1952
POTENTIAL
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near the surface followed by rapid transformation t o the higher melting form.
In contrast, the unstable (low-melting) form of oleic acid tended to transform to the stable form much more readily. On cooling the mixtures rich TABLEI in oleic acid to about 8 to 10' the samples suddenly BINARY FREEZING-POINT DATA" hecame essentially solid; and, on heating in the Acetamide-oleic acid system Acetamide-elaidic acid system Freezing point,, Freezing point, 'C constant temperature bath, melted so that relaMole MetahIofe Y AIetatively few crystals remained a t the temperatures acetarni8e Stable stable acetamic!e Stable stable indicated by the clotted line. At this stage, or 0.00 16.3 13.5 0.00 43.8 sometimes before, the sample again became essen4.42 15.9 10.31 42.5 tially solid because of the formation of the higher9.37 12.2 19.47 41.5 melting crystalline modification of oleic acid, or of 12.60 15.1 29.87 40.2 the molecular compound when the acetamide coii(15 .O)* (14.8)* (34.2jb (39.6)b centration was between 15 and 22 mole %. The 17.20 16.3 11.4 36.01 39.9 sample then showed a melting point corresponding 21.54 18.4 10.7 (37.8)" (4O.O)c to the upper solid curve. Because of this behavior 21.75 18.3 40.08 45.1 40.3 24.65 19.1 44.96 51.G 40.7 the freezing points involving the unstable modifi30.55 20.5 . 46.08 53.6 40.8 cation of oleic acid could not be obtained with the (30.8)" (20.6)' (47.2)d (40.9)d same assured accuracy. 34.14 31.6 20.7 50.59 59.9 47.1 The acetamide branches of the diagrams for these 36.73 37.7 21.3 60.26 69.7 58.4 two cis-trans isomeric acids almost coincide. It (39.2jd (21.G i0.21 75.1 64.G will be noted, however, that the freezing points for 39.34 42.3 23.8 79.75 78.1 67.9 the elaidic acid system tend to fall above the 44.40 35.6)d 90.06 59.4 69.0 curves as d r a m and those for the oleic acid fall be48.54 5G.0 43.0 100.00 79.7 69,5 low. This is in harmony with the idea that the 70.61 75.2 64.3 molecular compound between acetamide and oleic 82.17 78.0 67.8 acid is less dissociated than that between acetamide 100.00 79.7 G9.5 and elaidic acid, which is indicated by the fact that The values in parentheses were obtained by graphical est.rapolation. b Eutectic. Incongruent inplting point the freezing-point curve for the oleic acid compound is steeper. ((stable). Incongruent melting point (metastable). O C
THE THEORY OF MEMBRANE POTENTIAL BY hIITSURU
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