T H E SOLUBILITY RELATIONSHIPS I N MIXTURES OF BRASSIDIC ACID WITH ERUCIC ACID, METHYL BRASSIDATE, AND ETHYL BRASSIDATE' L. J. P. KEFFLER AND A. M. MAIDEN Department of Chemistry, University of Liverpool, Liverpool, England
Received March 36, 1086 INTRODUCTION
Some years ago, Timmermans and Viseur (19) made a thorough study of various binary mixtures of geometrical isomers and found that, in conformity with Bruni's rule, the trans-compounds showed a decidedly greater tendency than the cis-compounds to form mixed crystals with the corresponding saturated compounds. They therefore, along with Bruni, attributed to the saturated compounds a configuration similar to that 'of the trans-forms. Shortly thereafter, Skau and Saxton (17) investigated mixtures of the two b-chlorocrotonic acids and found that the ideal solution law applied very closely. No work of precision has, however, been done on mixtures of cis-trans isomers of high molecular weight, such as erucic and brassidic acids and their esters. Mascarelli and Sanna (12), it is true, have found that erucic and brassidic acids form a simple eutectic system, but, owing to the lack of purity of their preparations, their results need to be confirmed before they can be used for testing the applicability of the ideal solution law. There is another problem upon which an accurate study of such mixtures may throw light, as will appear from the following considerations:Smith (18) finds that ethyl palmitate and ethyl stearate form mixed crystals, as do also hexadecane and octadecane, while hexadecyl iodide and octadecyl iodide form a system containing a compound with a non-congruent melting point. According to Bhatt, Watson, and Patel (2), such compounds are formed also in the following systems : caproic-stearic, lauric-myristic, lauric-stearic, stearic-behenic, and palmitic-cJtearic acids and in the system methyl palmitate-methyl stearate ; but the pairs lauric acid-lignoceric acid, methyl laurate-methyl myristate, and methyl stearatemethyl behenate give simple eutectic diagrams. This article is part of a thesis submitted by A. M. Maiden to the Faculty of Science of the University of Liverpool in partial fulfillment of the requirements for the degree of Doctor of Philosophy. 905
906
L. J. P. KEFFLER AND A. M. MAIDEN
On the other hand, Muller and Shearer (14) have proved by means of x-rays that the saturated fatty acids crystallize in double molecules, while Francis, Piper, and Malkin (4) have shown that compound formation occurs in equimolecular mixtures of such acids differing from each other by one, two, or three carbon atoms, the mixtures melting like a pure compound. Malkin (10) has established further that the methyl esters of the saturated fatty acids crystallize in double molecules, but are also characterized by a metastable form which crystallizes in single molecules. The ethyl esters were found to crystallize always in single molecules. Thus it would appear that mixtures of subst’ances of high molecular weight, which do not differ too much in carbon content and which crystallize in double molecules, yield phase-rule diagrams showing the presence of a compound with a non-congruent melting point. The exceptions to this rule, as exemplified by the systems methyl stearate-methyl behenate and methyl laurate-mcthyl myristate, may be apparent rather than real, for the results of Bhatt and coworkers (2) were obtained by cooling 1net.hods, which are liable in many cases to give erroneous data, as will be i d eated in the course of the discussion of the results reported in this paper. Since Muller and Shearer have shown that both erucic and brassidic acid crystallize also in double molecules, it is of interest to see whether a careful examination of t,heir mixture will, from the point of view of the phase rule, show the presence of a molecular compound. The difference in their configuration would indecd not be expected to interfere with the considerations given above, as compound formation between these molecules appears to be a matter of the terminal groups only of the carbon chain. An investigation of the systems of t’he type acid-est,er might also prove interesting in view of the difference found by Malkin (10) in the states of aggregation of the acids and methyl esters as against that of the corresponding ethyl esters. Two such systems will be examined in the present paper. APPARATUS
Figure 1 shows a cross section of the apparatus, which recalls in many respects that of Andrem, Kohmann, and Johnstone (1) and t h a t of Skau and Saxton (17), except that it was so designed that the specimens might be kept in vacuo during each experiment, in view of their unsaturation and consequent liability to rapid oxidation. The specimens (weighing 1.5 g.) were contained in small test tubes (internal diameter 1 cm.) conncctcd with an exhausting tube by means of a short length of stout rubbcr tubing; this was surrountlrtl by a split brass sleeve, tightened by n “Juldee” circular clip T h mcltj was stirred by means of a miniature glass ring stirrer, attachctl by mcaw of a stout platinum wire to a soft iron armature n.orkirig insid(, a solenoid spool made of brass.
MIXTURES OF GEOMETRICAL ISOMERS
907
Temperatures were measured to within 0.1OC. by means of a tn-o-junction, copper-eureka thermoelement, calibrated a t every 10” from 20°C. to 90°C. against a standard thermometer. The E.M.F. was measured on a Cambridge thermoelectric potentiometer used in conjunction with a 400ohm Cambridge “Ayrton-Mather” galvanometer. Fractions of 100 p volts were obtained by the deflection method, whilst during all readings the potentiometer was frequently balanced against a standard cell. This electrical measuring system, which allowed readings to be taken to within 5 p volts (corresponding to 0.05’C.), was entirely and adequately shielded against leaks from high potential circuits by supporting it throughout on metal, all the metal supports being electrically connected. TO
For the determination of cooling curves the specimen was surrounded by a double-walled metal jacket, through which water a t any convenient temperature was circulated from a thermostat. For the determination of the melting point, the metal jacket was replaced by a double-walled glass jacket (see figure 1). In this manner the specimen was observed through only a thin layer of water and yet, as the thermostat contained 30 liters of water, very fine control over the rate of heating could be obtained. TECHNIQUE
Mixtures of definite composition were made up by direct weighing into the specimen tubes, the total weight of the mixture being always 1.5 g.
908
L. J. P. KEFFLER AXD A. &I. MAIDEN
The contents of the tubes were then just melted and well mixed, the tube placed on the apparatus, and the specimen allowed to set in uucuo. The mixture was now remelted and once more allowed to set in uacuo, so as to avoid completely the dissolution of gases as impuritiesS2 The type of system being dealt with was determined by taking cooling curves of the various mixtures prepared, the E.M.F. of the thermoelement being noted a t regular time intervals. It was found that the convergence temperature for this apparatus was considerably below the temperature of the jacket, so that the method of correction of Andrews, Kohmann, and Johnstone (1) for the supercooling was inapplicable. As the mixtures showed in many cases considerable supercooling, this method could not in any case have been used with any satisfaction; the freezing points of the systems were therefore determined by observing the temperature a t which the last crystal in the melt disappeared (cf. Johnstone and Jones (7), Smith (B), and Skau (16)). This temperature could be easily determined by means of the glass heating apparatus described. The specimen was heated rapidly until only a small portion remained solid, the glass jacket was then raised so as to surround the melt, and water a t a temperature slightly below the expected melting point was circulated from the thermostat. The temperature of this water was now slowly raised, and when the details of the thermoelement wires could be seen clearly, the E.M.F. of the element was noted as the melting point. It was found that the last crystals disintegkating under the action of the stirrer gave a cloudy suspension. Very efficient agitation of the melt during such a determination is obviously necessary. The results thus obtained are considered to be within 0.1OC. of the true freezing point. Repeat determinations always agreed to 0.05OC. Eutectic temperatures were fixed by taking heating curves of mixtures which possessed very nearly the eutectic composition (as seen from the melting point-composition diagram). The procedure followed was similar to that for cooling curves, water slightly above the expected eutectic temperature being circulated through the brass jacket. CONTROL O F PURITY FOR THE SUBSTANCES USED
The preparation and purification of the substances required for this research have already been described elsewhere (9). The melting points and setting points of these substances were found 2 Such gases cause the molten specimen to froth if it is allowed to set under reduced pressure after exposure to the atmosphere. The fact that such substances, when in the molten state, are capable of dissolving appreciable quantities of gas from the atmosphere does not seem to have received very much notice in the past, although it must play an important r81e in the rate of oxidation of the substance (see, however, reference 6).
909
MIXTURES OF GEOMETRICAL ISOMERS
to be within 0.loC., except in the case of ethyl brassidate, where the difference was 0.2"C., probably as a result of the complication due to extensive creeping. This coincidence of melting points and setting points is probably the most sensitive criterion of purity for long-chain coinpounds, particularly for the saturated ones, where there is no other available.3 In the case of unsaturated substances, the control of the purification should always be supplemented by the precise determination of the iodine values (8). The results of such control of purity for the substances examined are shown in table 1. RESULTS
System erucic acid-brassidic acid (see table 2 and figure 2 ) Erucic and brassidic acids were found to have only one form in the region investigated. Mixtures containing up to 81 per cpnt erucic acid gave the TABLE 1 Purity of the substances examined IODINE VALUE SUBSTANCE
BETTINO POINT
Theoretical -1 -
Observed
'C.
Brassidic a c i d . . . . . . . . . . . . . . . . . . . . . . . . . 74.7 Erucic acid.. . . . . . . . . . . . . . . . . . . . . . . . . . . 74.0 Methyl brassidate.. . . . . . . . . . . . . . . . . . . . 71.2 Ethyl brassidate.. . . . . . . . . . . . . . . . . . . . . . 68.7
75.0 75.0 72.1 69.3
59.8 33.25 30.0 24.8
YELTINQ POINT
"C.
59.75 33.35 30.1 25.0
normal cooling curve of a simple eutectic system, while for mixtures richer in erucic acid, the cooling curves were of a different type. Coincident with 3 The determination of the setting point alone does not always provide sufficiently unambiguous guarantee of purity. For instance, after purifying a specimen of brassidic acid by removal of several per cent of impurities, the setting point increased only by O.IoC., but the iodine number went up from 74.2 to 74.7. In another case further purification was accompanied by a rise of iodine number from 73.6 to 74.2 for the same small increase in setting point of 0.1"C. However, the nielting point appears to be, a t least in some cases, more sensitive than the setting point to the presence of impurities; e.g., while two specimens of methyl brassidate had the same iodine number and the same setting point, one of them melted as high as 32.35"C., against 30.1"C. for the other specimen. The melting point may thus be used with advantage as a further control of purification, either with or arithout the simultaneous determination of the setting point. This will especially be the case when the compound examined is very nearly pure, and when the eutectic in the system compound-impurity lies very near 100. per cent pure compound.
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L. J. P. KEFFLER AND A. IM. MAIDEN
this change, the phenonienoii of a double melting point appeared. For example, by allowing a mixture containing 83.5 per cent of erucic acid t o cool for some time after freezing had set in, one observed a melting point of 39.1°C.,vhilst if the melting point was taken immediately after freezing occurred, 30.7"C. was obtained. (Both results were repeatable.) An increase of the erucic acid content to 87.0 per cent caused the cooling curve t o become double-humped if determined with the specimen unseeded; for a specimen which mas not completely melted, a cooling curve similar to that correiponding to 83.5 per cent of erucic acid was obtained. 60'
50'
30'
20'0
20 40 60 80 MOLE PER CENT OF SOLUTE (BRASSIDIC ACID AS SOLVENT)
3';
FIG.2. Cooling curves. X , the system brassidic acid-erucic acid (0 for the results of llascarelli and Sanna); 3, the s l s t e m brassidic acid-methyl brassidate; A, the system brassidic acid-ethyl brassidate.
In this case, the specimen had a melting point of 31.2"C. if cooled until a few cryitals appeared and then remelted; but if cooled until completely solid and then remelted, it was necessary to heat to 36.2"C. before the last crystal disappeared. Thus the change which occurred spontaneously with the 83 5 per cent mixture required nuclei to he present for it to occur with the 85.0 per cent specimen. As the higher melting point undoubtedly lies on the brawidic acid solubility curre, it nould seem that the second hump corresponds to the crystallization of brassidic acid and the first to the crystallization of erucic acid. Supercooling increases as the percentage of erucic acid in the mixture increases, and with 83.5 per cent of erucic acid the crystallization of the latter eyidently occurs before that of the brassidic acid. In this case,
911
MIXTURES OF UEOMETRICAL ISOMERS
therefore, the metastable erucic acid solubility curve can be followed up over a large range. It is this particular phenomenon which renders it imperative to determine the melting points of these mixtures rather than their freezing points by the normal method, if the correct phase-rule diagram is to be constructed. It also caused Mascarelli and Sanna (12) to think that the eutectic mixture was about 80 per cent erucic acid, these workers not cooling to completion any mixture showing this phenomenon. The eutectic temperature determined from the heating curves of the specimens containing 92 per cent and 89.6 per cent of erucic acid was 31.831.9"C., whilst the composition of the eutectic mixture determined from the melting point-composition diagram was 90.5 per cent erucic acid. TABLE 2 The system brassidic acid-erucic acid COYPOBITION I N MOLE PER CENT OF ERUCIC ACID
0 13.8 31.5 42.8 57 .O 67.8 77.5 81 .O 83.5 83.5 87.0 87.0 89.6 89.6 91.2 92.0 95.1 100
MELTINQ POINT
loglo N
0 -0.064 -0.164 -0.243 -0.366 -0.492 -0.648 -0.721 -0.782 -0.078 -0.886 -0.060 -0.983 -0.048 -0.040 -0.036 -0.022 0
10M/T
SOLID P H A S I
Brassidic acid Brassidic acid Brassidic acid Brassidic acid Brassidic acid Brassidic acid Brassidic acid Brassidic acid Brassidic acid Erucic acid Brassidic acid Erucic acid Brassidic acid Erucic acid Erucic acid Erucic acid Erucic acid Erucic acid
"C.
'K.
59.80 57 .,85 55.10 52.80 49.65 46.45 42.75 40.70 39.10 30.70 36.15 31.15 34.20 31.60 31.95 32.10 32.60 33.25
332.8 330.8 328.1 325.8 322.7 319.5 315.8 313.7 312.1 303.7 309.2 304.2 307.2 304.6 305 .O 305.1 305.7 306.3
3005 3023 3048 3069 3099 3130 3167 3187 3204 3294 3234 3287 3255 3283 3279 3278 3272 3265
Mixtures containing more than 90.5 per cent of erucic acid have a melting point independent of the history of the specimen, as here it is normal for the erucic acid to crystallize out first. The cooling curves of these mixtures show primary crystallization of erucic acid, but no eutectic halt, the crystallization of brassidic acid being unduly delayed. The heating curves, however, are those normally shown by mixtures with compositions near that of the eutectic. The melting point-composition diagram, as determined for the present. work, contrasts with that obtained by Mascarelli and Sanna (12) as shown
912
L. 3. P. KEFFLER AND A. M. MAIDEN
in figure 2 (dotted curve). The displacement (towards the left) of the right-hand side of their diagram, caused by supercooling, is very evident. T h e system ethyl brassidate-brassidic acid (see table 3 and figure 2 )
The cooling curves of mixtures of brassidic acid with 22.0, 50.4, 59.1, 77.9, and 88.4 per cent of ethyl brassidate are those of a simple eutectic system. Those of mixtures containing 96.3 per cent and 98.4 per cent of ethyl brassidate are similar to that of the mixture of the previous system containing 83.5 per cent of erucic acid, but have no slight halt corresponding to a low melting point. This type of curve is due to great supercooling, which causes the mixtures to behave as though they were richer in solute than they actually are, mixtures weaker than the eutectic mixture behaving like a eutectic mixture and setting at one temperature. TABLE 3 T h e s y s t e m brassidic acid-ethyl brassidate COMPOSITION I N MOLE PER CENT OF ESTER
0 22.0 40.4 59.1 77.9 88.4 96.3 97.4 98.4 100
log10 x
0 -0.108 -0.225 -0.389 -0.657 -0.934 -1.434 -1.589 -1.803
MBLTIVG POINT
W/T
SOLID PEASE
Brassidic acid Brassidic acid Brassidic acid Brassidic acid Brassidic acid Brassidic acid Brassidic acid Brassidic acid Brassidic acid Ethyl brassidate
"C.
"K.
59.80 57.00 54.15 50.65 46 .00 41 .80 32.50 29.45 24.90 25.05
332.8 330 .O 327,2 323.7 319.0 314.8 305.5 302.5 297.9
3005 3030 3056 3089 3135 3177 3274 3306 3357
All these mixtures have a single melting point. The melting point-composition diagram for the mixture of ethyl brassidate and brassidic acid is notable for its asymme!ry, this being sufficient to render the exact determination of the eutectic a difficult matter. The mixture containing 98.4 per cent of ethyl brassidate was assumed to have the eutectic composition. Ethyl brassidate creeps to a remarkable extent when setting, and only starts to freeze after considerable supercooling. The cooling curve of the pure material always rises very slightly instead of remaining level during setting. For this reason the melting point instead of the setting point was used in the construction of the melting point-composition diagram. No evidence of a second crystalline form of the ester was found. Near the eutectic point, the brassidic acid solubility curve is so steep
913
MIXTURES OF GEOMETRICAL ISOMERS
that the separation in a solid state of a very small amount of brassidic acid greatly influences the melting point of the mixture, it thus being very difficult to determine the exact melting points in this region. It is also clear that a cooling curve investigation in this region must be absolutely useless.
The system methyl brassidate-brassidic acid (see table 4 and figure 2) The cooling curves of mixtures of brassidic acid with 30.9, 49.3, 68.9, and 89.4 per cent of methyl brassidate are those of a simple eutectic system; those of mixtures containing 96.2 and 97.5 per cent of methyl brassidate are similar to those of mixtures containing 96.3 and 98.4 per cent of ethyl brassidate. Again the exact position of the eutectic point is difficult to ascertain. The melting point-composition diagram indicates that it is between 97.5 TABLE 4 T h e s y s t e m brassidic acid-methyl brassidate
I
COMPOSITION
IN MOLE PER CENT OF
logio
N
"C
ESTER
0 30.9 49.3 68.9 89.4 96.2 97.5 98.4 100
MELTINQ POINT
SOLID PHASE
0 -0.161 -0.295 -0.508 -0.975 -1.420 -1.606
Brassidic Brassidic Brassidic Brassidic Brassidic Brassidic Brassidic Ester Ester
acid acid acid acid acid acid acid
.
59.80 55.65 52.65 48.50 40.40 32.60 30.10 30.05 30.10
10olT
'H.
332.8 328.7 325.7 321.5 313.4 305.6 303.1
3006 3042 3070 3110 3191 3273 3299
and 98.4 per cent methyl brassidate, a heating curve of the 89.4 per cent mixture gives 29.85'C. as the temperature, while the two solubility curves cut a t 29.8OC. and 97.7 per cent. Pure methyl brassidate supercools considerably before setting, but it does not creep. Its cooling curve remains level during setting, and does not rise as in the case of ethyl brassidate. No second form of methyl brassidate was found. DISCUSSION
(A) The brassidic acid solubility curves in the systems methyl brassidate-brassidic acid and ethyl brassidate-brassidic acid are so remarkably similar that the two melting point-composition diagrams can be superimposed for the whole of the range (from 0 to 97 per cent) of concentrations (figure 2). One is thus led to the conclusion that methyl and ethyl
914
L. J. P. KEFFLER AND A. M. NAIDEN
brassidates have, when dissolved in brassidic acid, the same state of aggregation (cf. Malkin (10)). This solubility curve of brassidic acid with respect to either ester lies only very slightly above that for the system brassidic acid-erucic acid, which tends to indicate that erucic acid, when in solution in brassidic acid, is in a state of aggregation identical with or a t least very similar to that of the alkyl brassidates. In none of the diagrams investigated is there any trace of compound formation. This, from the evidence given in the introduction, supports the assumption that all these substances exist in solution in the simplest possible molecules.
LOGIo MOLE FRACTION OF SOLVENT
FIG.3. Solubility curves. Curve a, brassidic acid in erucic acid; curve b, erucic acid in brassidic acid; curve e: 0 , ethyl brassidate in brassidic acid; A,methyl brassidate in brassidic acid.
(B) It has been stated by various authors (see, e.g., Johnstone (7)) that, provided the constituents of binary mixtures of certain types of isomers are not too much alike, the plot of log N (where N is the mole fraction of the solute) against 1/T (where T is the absolute freezing point of the mixture) is a straight line. If, however, the constituents are very similar, mixed crystals are formed. In order to form an opinion as to whether the pairs of substances investigated here form, or do not form, ideal solutions, the results have been ptotted in the form logl&' against 106/T (figure 3). For the system brassidic acid-erucic acid points from the erucic acid solttbility curve lie on a straight line (figure 3, curve a), while the,points
MIXTURES OF GEOMETRICAL ISOMERS
915
from the brassidic acid sohtbility curve (figure 3, curve b) lie on a straight line up to 83.5 per cent erucic acid, after which the solubility of brassidic acid increases more rapidly than the ideal solution law would indicate. The fact, however, that a straight line is obtained for such a large proportion of the diagram when the results are computed in the manner described indicates that erucic and brassidic acids have the same molecular complexity in solution in each other and behave to a large extent as ideal solutes; in particular it is evident that there is no change in their state of aggregation with change in concentration. Only the points for the brassidic acid solubility curve can be obtained from the ester diagrams. These, when plotted, lie on one S-shaped curve (figure 3, curve c). According to Mortimer (13) this type of curve is obtained in systems in which one component is polar and the other is nonpolar, and where there is a great difference in the internal pressures. Unfortunately there are no data from which the internal pressures of these esters may be calculated. When the internal pressures of the acids themselves are calculated from the data of Semeria and Ribotti-Limone (B), values in the neighborhood of 400 atmospheres a t 90°C. are found for both acids. These authors determined the parachors of these two acids, and obtained values dependent upon temperature, a fact which would tend to show the presence of some association in these pure liquids. The results here reported show that no such association occurs. Waentig and Pescheck (20) have inferred from freezing-point measurements that lauric and palmitic acids exist, to some extent, as double molecules when dissolved in carbon tetrachloride. Our results for the ester systems show the danger of basing conclusions upon freezing-point depressions alone (see, for example, Bruni and Gorni (3)). The freezing-point depressions for the esters dissolved in brassidic acid are smaller than the ideal solution law would indicate. This might have been interpreted as evidence of solid solution formation; the determination of the cooling curves of the system showed, however, that this did not occur. Thus while the true freezing point cannot be obtained with these systems from cooling-curve determinations, such measurements must be carried out for fixing the type of system being investigated. The heat of fusion of brassidic acid, calculated from the slope of the loglo Nbraaaidio versus 106/T curve for the system brassidic acid-erucic acid is 18.0 kg-cal. per mole, while that of erucic acid, calculated similarly from the loglo Nerucic versus 106/Tcurve, is 12.3kg-cal. per mole. Mascarelli (ll), by similar means (using the normal freezing-point method and formula), found 17.8 and 12.1 kg-cal. per mole, respectively. As these methods do not permit of any great accuracy, the divergence between these results is within the experimental error.
916
L. J . P. KEFFLER AND A. M. MAIDEN
These values, when compared with that determined calorimetrically by Garner and King (5) for behenic acid, namely 18.6 kg-cal. per mole, add further support to Bruni’s contention that the structures of brassidic and behenic acids must be very similar. On the other hand, Muller and Shearer have shown (14) that the long spacings of erucic and behenic acids are practically the same, while that of brassidic acid is much greater. From this it might have been expected that the heats of crystallization of erucic and behenic acids would have been closer to each other than those of the latter and of brassidic acid, instead of what has been found from the phase-rule diagrams. This remark shows that there must be, as has often been emphasized for other compounds, a very close relation between the heat of crystallization and the melting point, and that the length of the crystal cell plays only a secondary r81e in determining the magnitude of the heat of crystallization. SUMMARY
L An apparatus for the accurate determination of phase-rule diagrams for mixtures of long-chain compounds has been described. It has been found that melting points rather than cooling curves must be determined with these systems. 2. The systems brassidic acid-erucic acid, brassidic acid-methyl brassidate, and brassidic acidckhyl brassidate have been investigated. All are simple eutectic systems. The brassidic acid solubility curves in the ester systems are superimposable. 3. The ideal solution law holds in the case of brassidic acid and erucic acid, but not for the ester systems; these latter give an S-shaped curve for the log,, N versus 1/T plot, the solubility of brassidic acid in this system being always less than the ideal solubility. 4. Evidence has been obtained that all these compounds exist in the simplest possible molecules in the liquid state. 5. No evidence for the existence of a second crystalline form of any of these compounds could be obtained. 6. The solubility of gases from the atmosphere in these compounds has been emphasized. In conclusion the authors wish to thank Prof. E. C. C. Baly, F.R.S., for facilities granted, and the Imperial Chemical Industries, Ltd., whose United Alkali Scholarship was held by one of them (a. M. XI.). REFERENCES (1) (2) (3) (4)
ANDREVS, KOHMANN, AND JOHNSTONE: J. Phys. Chem. 29,915 (1926). AND PATEL:J. Indian Inst. Sci. 13A, 141 (1930). BHATT,WATSON, BRUNIAND GORNI:Atti accad. Lincei [51 8,454. FRANCIS, PIPER,AND MALKIN:Proc. Roy. SOC. London 133A,214 (1930).
MIXTURES OF GEOMETRICAL ISOMERS
GARNER AND KING: J. Chem. Soo. 1929,1849. GARNER AND RYDER:J. Chem. SOC. 127,727 (1928). JOEINSTONE AND JONES: J. Phys. Chem. 32,592 (1928). KEFFLERAND MAIDEN:J. Soc. Chem. Ind. 62, 2421' (1933). KEFFLERAND MAIDEN:Bull. SOC. chim. Belg. 44,467 (1935). MALKIN:J. Chem. Soo. 1931, 2796. MASCARELLI: Gazz. chim. ital. [2] 46,209 (1915). MASCARELLI AND SANNA: Gaze. chim. ital. [2] 46,335 (1915). MORTIMER: J. Am. Chem. Soo. 46, 633 (1923). MULLERAND SHEARER: J. Chem. Soo. 123,2043 (1923). SEMERIA AND RIBOTTI-LIMONE: Gaez. chim. ital. 60,862 (1930). SKAU:J. Am. Chem. Soc.62,945 (1930). SKAUAND SAXTON:J. Am. Chem. Soo. 60,2693 (1928). SMITH:J. Chem. Soo. 1931,802; 1933,737. TIMMERUANS: Bull. SOC. chim. Belg. 36, 179 (1927). TIMMERMANS AND VISEUR:Bull. soo. chim. Belg. 36,426 (1926). (20) WAENTIGAND FESCHECK: 2.physik. Chem. 93,529 (1919).
(5) (6) (7) (8) (9) (10) (11) (12) (13) (14) (15) (16) (17) (18) (19)
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