T H E J O U R h T A L OF I N D U S T R I A L A N D ENGINEERING C N E M I S T R Y
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I n many of our cooling curves we find t h a t t h e temperature of point B , Fig. J , a t which crystals first appear, agrees with t h e values recorded by Giua. We have plotted his results on Fig. 3 for DNT-TNT. These freezing-point curves do not intersect a t t h e eutectic point, a condition which is interpreted as indicating the existence of a compound of t h e components. Of course, if Giua’s d a t a are taken as correct, this must be t h e proper interpretation of the curves.
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and it is concluded t h a t the mixtures obey t h e ideal solution law. The curves for D N T do not lie so close together. The effect of p-toluidine on the freezing point of D N T is from t h e results of Mremann a n d Petritschek-* T h e cause or causes of t h e deviation may be found when a n o Q e r investigation now in progress has been completed. The formula based on “ideal solutions” involves t h e latent heat of fusion, regarding which no d a t a could be found in t h e literature. T h e direct determination of t h e latent heat of fusion of all of these nitrotoluenes will form another paper of this series. SUMMARY
I n this paper we have given a discussion of t h e melting points of M N T , D N T a n d T N T , a discusqion of t h e interpretation of cooling curves, and t h e d a t a for t h e three binary systems of these nitrotoluenes.
70’-
UNIVERSITY O F NORTH CAROLINA CHAPEL HILL, N. C.
60’-
tb
STUDIES ON THE NITROTOLUENES. IV-THE THREECOMPONENT SYSTEM: P-NITROTOLUENE, 1,2,4DINITROTOLUENE, I ,2,4,6-TRINITROTOLUENE2
u, h
By JAMESM. BELLAND CHARLES H. HERTY,JR. Received July 17, 1919
$ 50?
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40%
30“
20’ 100
Molecu/ar Per cent FIG.5
Thus in all three of these binary systems Giua claims t h e existence of compounds over a narrow range of concentration. I n none of t h e cases did we obtain a result other t h a n t h e intersection of t h e freezing-point curves a t t h e temperature found for t h e eutectic point. Giua’s conclusions therefore regarding t h e existence of molecular compounds in these three cases seem t o be erroneous. In t h e first paper of this series,’ t h e effect of various nitrotoluenes on t h e freezing point of trinitroxylene was studied and t h e results were found t o accord fairly well with a formula based on t h e assumption t h a t these mixtures were “ideal solutions.” It is possible t o test t h e validity of t h e assumption of “ideal solutions” in another way. T h u s t h e freezing point of such a mixture should depend on t h e molecular fraction of t h e freezing component and not on t h e nature of t h e other component or components, provided t h e components are of like chemical character. When, therefore, t h e freezing-point curves are drawn using molecular percentages, the curves should coincide. I n Pig. 5 are shown t h e freezing points of t h e nitrotoluenes as influenced by other substances. The curves for M N T and t h e curves for T N T fall quite close together, 1
THISJOURNAL, 11 (1919), 1025.
I n t h e third paper of this series we have given t h e results of a study of t h e three binary systems of t h e nitrotoluenes: $-Nitrotoluene ( M N T ) , I , 2,4-dinitrotoluene ( D K T ) , and I , 2,4,6-trinitrotoluene ( T N T ) . T h e present paper contains t h e resuIts of a s t u d y of t h e ternary system of these components. We have again employed t h e cooling-curve method of finding t h e temperatures a t which t h e various solid phases appear, using t h e extrapolation method of overcoming t h e difficulty introduced b y t h e phenomenon of supercooling. This method was described in detail in t h e paper above referred to.3
L
Time
Y
U
Z
FIG.1
For a binary mixture there are two freezing points: The primary freezing point a t which t h e first solid appears, and t h e binary eutectic point where t h e two solids are in equilibrium with t h e melt. For a ternary mixture there are three freezing points: The primary freezing point a t which t h e first solid appears, t h e secondary freezing point a t which t h e second solid appears, and t h e ternary eutectic point where all three solids are in equilibrium with t h e melt or eutectic mixture. The last temperature was not difficult t o determine Monatsh., 88 (1917). 385. paper is the fourth of a series dealing with the freezing points and thermal properties of the nitrotoluenes, the investigation having been undertaken at the request of the Division of Chemistry and Chemical Technology of the National Research Council. 8 THIS JOURNAL, 11 (1919). 1025. 1
* This
Dec.,
T H E J O U R N A L OF I N D U S T R I A L A N D ENGINEERING C H E M I S T R F
IQIQ
4
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34,057 0.1 (r~ermomeferCorrecf/bn/= 34.15"
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of t h e triangular figure. A preliminary trial showed t h a t t h e primary freezing point was near 34' and t h a t t h e secondary freezing point was near 29'. I n order t o determine more accurately the first freezing point, t h e b a t h was held a t 30' and t h e time-temperature curve plotted. This is t h e portion A B C of Fig. I and is given on larger scale in t h e first section of Fig. a. It is seen t h a t 34.15' is t h e primary temperature of freezing. At C t h e temperature of t h e bath was lowered t o 24" and t h e cooling of course became more rapid. Section z of Fig. 2 shows t h a t t h e secondary temperature of freezing is 28.6". At E t h e bath was again cooled t o 12' and Section 3 of Fig. 2 shows t h e eutectic temperature t o be 16.7". During these changes of temperature t h e composition Qf t h e melt has undergone changes which m a y be followed on t h e triangular diagram, Fig. I . The melt passes first from composition B t o D , a point on t h e boundary curve, and then follows the boundary curve t o F, t h e eutectic mixture. Many such ternary mixtures have been studied in this way and t h e freezing points found are given in Table I. The results in Table I also furnish t h e necessary d a t a for finding points on t h e boundary curves. Fig. 3 shows t h e d a t a for different mixtures, each containing I O per cent D N T , t h e percentages of T N T being t h e abscissae. It is obvious t h a t on t h e line for I O per cent of D N T in t h e triangular diagram, t h e lowest primary freezing point and also t h e highest secondary freezing point are both where t h e I O per cent line cuts t h e boundary curve. Moreover,these points are co-
Coofhnq curve for Mixture 30% TNT 10%DN7; 60% MNT
A
PIG.2
in most cases, for t h e temperature remains constant for a considerable time. I n t h e case of t h e primary and secondary freezing points, great supercooling frequently occurred where D N T was t h e solid which should separate out. I n such cases i t became necessary t o "seed" t h e mixture with a few small crystals of D N T in order t o s t a r t crystallization. Where successive freezing points are close together, i t was necessary t o maintain t h e bath a t an intermediate temperature, so t h a t no confusion would arise, due t o t h e possible appearance of crystals out of turn. Suppose, for instance, t h a t t h e liquid is supercooled with respect t o two solids. There is no assurance t h a t t h e one which normally appears a t t h e higher temperature wil1 appear first in the supercooled mixture. T h e results for this ternary system have been plotted on t h e conventional triangular diagram. We have found t h a t there are only three solid phases which separate, v i z . , t h e three components. N o evidence whatever was discovered pointing t o binary molecmlar compounds, as claimed by Giua,l or of ternary molecular compounds. The diagram therefore consists of three fields separated b y three boundary curves which intersect in t h e ternary eutectic point. I n Fig. I we have shown t h e behavior of a typical mixture upon cooling. This mixture had t h e composition: 6 0 per cent M N T , I O per cent D N T , and 30 per cent T N T , and is represented b y t h e point B 1
B w . , 47 (1914), 1718; Gaze. chim. itd., (11 46 (1915), 339.
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36'.
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1 30
35 40 Per cent TNT FIG.3
45
T H E JOURNAL OF I N D U S T R I A L A N D ENGINEERING CHEMISTRY
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No. 1 2
MNT 5/.25*
FIG.4
FIG.5
ihcident. T h u s by t h e interpolation method of Fig. 3 both t h e temperature and composition of points on the boundary curves may be found. By this method the points given in Table I1 have been located.
With the above tabulated d a t a i t is possible t o identify a n y unknown mixture of these three components. First, t h e primary and t h e secondary freezing points should be determined, a n d then the identity of t h e solid phases should be established. The methods TI-LE I-FREEZINGPOINTS OF TERNARY MIXTURES COMPOSITION IN WEIGHT, PERCENTS FREEZING POINTS,DEGREES of finding freezing points have already been given. MNT DNT TNT Primary Secondary For t h e identification of t h e solid phases an indirect 60 30 10 22.55 60 10 30 28.6 method is proposed rather t h a n the doubtful method 10 55 35 22.9 20 55 25 16.85 of trying t o isolate t h e freezing component free from 35 55 10 29.3 20 50 30 17.9 the melt. T h e following consideration demonstrated 25 50 25 18.7 40 50 10 29.2 how this indirect identification may be made. Take 10 45 45 23.2 45 45 10 28.95 any mixture, say B of Fig. I . The addition of com10 23.0 40 50 20 40 40 ponent X t o t h e mixture raises t h e primary freezing 18.6 30 17.6 40 30 point, and t h e addition of either Y or Z t o t h e mixture 20.6 40 25 35 35 50 15 . . . . lowers t h e primary freezing point. T h e first phase t o 20 35 45 17.75 35 40 25 .... separate is therefore t h a t one which, when added t o 35 35 30 16.85 40 35 25 19.1 t h e unknown mixture, raises t h e primary freezing 25 25 50 22.25 30 25 45 24.6 point. Similarly i t may also be shown t h a t t h e second 40 '25 35 24.1 45 phase t o separate is t h a t one of Y or Z whose addition 25 30 22.85 30 10 60 36.9 t o the unknown mixture raises the secondary freezing 35 37.95 10 55 45 39.15 10 45 point. We are t h u s able t o locate t h e unknown in 50 38.35 10 40 one of the six triangles of Fig. I : X M F , XNF, Y M F , TABLE 11-DATA FOR POINTS ON BOUNDARY CURVES Reference t o Figs. 4 and 5 COMPOSITION IN WEIGHT, PER CENTS FRFEZING TEMPERATURE YOF, Z O F , or ZNF. MNT DNT TNT DEGREES locates t h e point from t h e temperatures of primary , 48.5 10 41.5 23.4 and of secondary freezing. 18.95 43.5 20 36.5 52.5 44
4 1. . 10
25 35
10
25 30 46.7 39.8 35.2
37.5 31 29 43.3 35.2 29.8
29.35 20.8 17.8 39.2 25.1 17.5
These points fall exactly on smooth curves which approximate t o straight lines, the boundary curves beifig drawn t o scale in Figs. 4 and 5 . From t h e d a t a of Tables I a n d 11, and from the d a t a for t h e binary systems in the third paper of this series, Figs. 4 and 5 have been constructed. Fig. 4 shows t h e isothermals for t h e primary freezing points, and Fig. 5 shows the isothermals for t h e secondary freezing points, the latter isothermals being of course straight lines from the vertices of the triangle. The composition of t h e eutectic mixture is 39 per cent M N T , 3 3 . 5 per cent D N T , and 2 7 . 5 per cent T N T and t h e eutectic temperature is 16.7
'.
SUMMARY
In this paper we have shown how t o identify any unknown mixture of the three nitrotoluenes, M N T , D N T , and T N T , from a s t u d y of t h e ternary system of these components. NORTH CAROLINA CHAPELHILL, N. C.
UNIVERSITY OF
PARACYMENE. 111-PREPARATION OF 2-CHLORO-5,6DINlTROCYMENE By H. A. LUES AND R. C . YOUNG Received July 31, 1919
This compound was first prepared b y von Gerichtenl in 1878, who, however, simply described it as a dinitrochlorocymene melting from 108' t o ~og', a n d 1
Ba., 11 (1878),
1091.
I
