H. H. SISLER,C. A. VANDERWERF AND STBPIIEN STEPI-IANOU
253s
TABLE I ~ ~ S P E R I M B N T A IHEAT , CAP.4CITIES
OF
GASEOUSCYCLO-
Methylcyclohr\aiie
1
P E S T A S E , CBC1,OHEXANE AXD hfETHYLCYCLOHEXANE
Calories per degree per mole Press., attn. T ," W .
Substance
Cyclopcntaiie
1
0 6
Cyclohrsaiie
1
353 372 395 424 463 5113 589 363 384 428 4(iO 495 521 544 384
0.46 0 . 3 0 384
CP
21.74 * 26.16 * 28.29 * 30.40 * 33.32 + 36.14 =t 38.36 * 24.67 * 34.59 * 38.94 =t 41.9 * 45.5 =t 47.2 =t 49.4 * 34.31 * 34.35 *
c p -
c,o
0.36 .31 ,526 .21 .16 .4 .12 .4 .10 .3 .22 .3 .38 .4 .27 .4 .22 .5 .18 .5 .15 .5 .13 .3 .17 .3 .11
0.2 .2 .3 .3 .3
cno
34.38 25.85 28.03 30.19 33.16 36.02 38.26 24.45 34.21 38.67 41.7 45.3 47.0 49.3 34.14 34.24
11.'
44 49 ,j3 38
4 6
43
18 *
.5
24
06
ii
18
58 00
=t
*
41 48 53 ,57
3s
CORVALLIS, ORECOY
RECEIVED AUGUST29, 1946
LABORATORY, cNIVERSITP
O F KaNSAS]
The System Formamide-Ammonia
BY HARRY H . S I S L E RCALVIN , ~ ~ A. VXNDERIYERFXKD STEPHEN STEPHANOU The fact that amides of the carboxylic acids stand a t a point intermediate between ammonia and carboxylic acids in the Brbnsted scale of acidities has already been discussed. Likewise, experimental evidience for the basic properties of these amides in anhydrous acetic acid and for their acidic properties in liquid ammonia has been cited. Compound formation was shown to take place in the systems acetamide-ammonia and acetamide-acetic acid. The systems formamideacetic acid, formamide-formic acid, formamidew-butyric acid, and forinamide-water also have been studied. The system formamide-ammonia remained, however, to be investigated. The investigation of this system was therefore undertaken as the second step in the present series of experiments. Experimental Materials.--The formamide was obtained from the Eastrnan Kodak Co. I t was dried by allowing it to stand over drierite f l x one week, and was purified by distillation under vacuurr , a middle fraction boiling from 107 to 109" uiitler 15 mm . pressure being retaiL1ed. The substance thus obtained melted a t 2.2 + 0.2 , in good agreement n i t h the values of 2.0 to 2.55" given in the l i t e r a t ~ r e . ~ The ammonia used was synthetic anhydrous ammonia ( 1 ) The first paper i n this series: Sisler, Davidson, Stoenner a n d Lyon, THISJ O U R N A L , 66, 1888 (1944). ( l a ) Present addres4: T h e Ohio S t a t e University, Columbus, Ohio. (2) English a n d T u r n e r , J . Chem. Soc., 107,774 (1'315). (3) E . g English and T u r n e r , ref. 2 ; Lowry a n d C u t t e r , J . Chem. S u c . . 136, 1.46'3 (1033); Taylor a n d Davis. J . P h y s . Chem.. 39, 1469 I, 192R 1.
13 62 24 82
Acknowledgments.-\Ye are grateful t o Dr. F. D. Rossini of the Bureau of Standards and Dr. H. U. Hyde of the Tidewater Associated Oil Company for providing the samples. Professor IT.D. Gwinn assisted in the design and construction of the new vaporizing unit with floating heater. Summary The heat capacities of gaseous cyclopentane, cyclohexane and methylcyclohexane have been measured from slightly above the boiling point to about 250'. h few measurements made a t reduced pressures indicated that the heat capacities of the ideal gas are given to good approximation by the Berthelot correction.
lCONTRIBUTION FROM T H E BAILEY CHEMICAL
Amphiprotic Substances.
398 439 480 . 1 -75.5 67.3 -76.0 -77.6 68.5 -77.6 fi8.0
-36.3 -44.0 -50.9 -55.2 -62.5 -7,5.1* -67.7 -75.4* -72.7 -74.0 -83.0 -990.5* -85.4 -86.6 -88.5
(c) Solid phasc, 2NH3.1-ICOSH2?
71.1 71.0
73.5 75.4 80.2 82.2 83.4 86.9
-91.9 -91.5 -94. o* -92.3 -93.0
-.. ii.T, rr
I I .9 79.2
(d) Solid phase, SHs -91.0 91.9 -91.4 94.3 100.0 -90.6 -85.8
-97.5* -95.0 -94.8 -96.0
-83.2 -80.9 -77.5
Dee., lMG
THESYSTEM FORMAMIDE-AMMONIA
obtained from E . I. d u Pont de Seinours and Co. and having a stated purity of 99.95%. Its freezing point was found to be - 7 7 . 5 * 0.4", it1 accord with values between - i . i arid -77.8" found in the literature.* Method.-The system was studied by means of the freezing .point method, the freezing points being determined by mean. of cooling curves recorded by a Leeds and Northrup Micrornax recorder ,5 The cell used was identical lyith thc one ttescribed in previous papers from this L a b o r a t ~ r y . ~I k t a obtained by thii methoti are believed t o be correct to =!=l.FjO. All points recorded were dctermined a t least twice. Data obtained for the system are listed in Table I and recorded graphically in Fig. 1. S denotes the mole per cciit. of ammonia and T the equilibrium temperature. Bccause of the high vapor pressure of ammonia, direct analysis of the various solid phases was not considered practicable. Ilnta marked with an asterisk indicate irict ast able equilibria.
20
-- .
'Discussion of Results It is evident from the course of the curve in Fig. 1 that formamide and ammonia form a solid addition compound in which the mole ratio is 1: 1 and a second compound in which the mole ratio is probably 1: 2. Neither compound melts congruently, but the 1: 1 compound was obtained in metastable equilibrium with a solution of the same composition a t a temperature of - 7.5'. The composition and melting point of the second compound cannot be determined precisely from the curve ; ;I short extrapolation indicates, however, that the mole ratio is 1 : 2 and that the melting point is around - 90 to - 91'. The 1 : 1 compound undergoes dissociation to formamide and solution a t a temperature just below its melting point. The second compound undergoes dissociation into the 1: 1 compound and solution a t a temperature between -91 and -92'. A eutectic point with ammonia occurs a t a composition of 79 mole per cent. of ammonia and a temperature of - 136'. By an,zlogy with the sodium salts of formamide formed in liquid ammonia solution6 we may con(4) Elliott, J. P h y s . Chem., 28, 611 (1924). ( 5 ) Davidson, S k i e r and Stoenner, THISJOURNAL, 66, 779 (1944). ( 0 ) Franklin. " T h e S i t r o g e n System of Compounds," Reinhold Publishing Corp., K e w Y o r k , N. Y . ,1031, C h a p t e r XXIX.
2539
0
tj 0
-20
" i i
5
2 2
u
? i
-40 --GO
-80 - 100 0
20 40 GO Mole % ammonia. Fig. 1.
80
100
sider the 1:1compound to be an ammonium aquoammono formate of the formula, HCONH[h"r]. One is tempted to interpret the formation of a 1: 2 compound as taking place through the interaction of the second proton on the amide group with an ammonia molecule. There is no 'direct experimental basis for this interpretation, however; in fact, it is not a t all impossible that the second ammonia be joined by the sharing of its electron pair with the carbon atom on the formamide. This carbon atom is electron deficient as a result of the electron withdrawal by the oxygen atom.
Summary 1. The temperature-concentration curve for the system formamide-ammonia has been determined throughout the entire concentration range. 2. The existence of two new compounds, HCONH2.NH3 and HCONH2.2NH3 (?I, has been demonstrated. The name ammonium aquo-arnmono formate has been suggested for the former. COLUMBUS, OHIO
RECEIVED JULY 18, 1946
