April, 1963
SOLUBILITY O F
NAPHTHALENE IL?;SUPERCRITICAL lE]TH.iNE
755
CFBr3,and CFC13 show large deviations (between 0.018 ane is 79.23 f 0.10 C.P.S.and this is 0.49 f 0.17 C.P.S. and 0.040 p.p.m.). Thus equation 2 holds approxiless than in pure liquid CHF3. mately for molecules that contain only 1st row eleTABLE IV ments and hydrogen, or less than three 2nd row eleJ C F A S D h~b("c-'~C)FOR F BOVND TO Sp2HYBRIDIZED ments directly bound1 to the 13Catom. Molecule JCF A$( '3C-'aC)oos A 4 (I3C-lZC) ioa A linear relationship between AI$( 13C-12C)and JCF CF?: c c 1 , 1 4 288 9 0 103 =t 0 002 0 107 has also been found for fluorine bound to an unsaturated 303 I CFC1: CC1214 ,112 =I= 002 ,114 (spz) 13C atom. The equation of this line,lZ which is COFP 308 35 .121 =k ,003 ,116 significaiitly displaced from that given by equation 2 CSFp'j 366 0 ,143 =I=,004 ,145 towards larger J c F is 395 CF,S:WFS16 0 16 f 05 .160 011
A$(13C-12C)
=
-0.039
+ ~ . O L I . ~ O - ~ J C F(3)
The maximum deviation of Ad(13C-12C)ob,from this line is 0.005 p.p.m., which is close to the quoted errors (Table IV). Finally we report that JHF in CHF3 is concentration in a 5% solution of CHFI in cyclohexdependent. JHF
a Calculated from
JCFusing equation 3.
Acknowledgment.-The author is very grateful to Dr. E. A. V. Ebsworth for helpful discussions; to the Department of Scientific and Industrial Research, for a maintenance grant; and to the Wellcome Trustees, who lent the T'arian Spectrometer to the Department.
THE SOLUBILITY OF NAPHTHALENE I N SUPERCRITICAL ETHAKE BY G. S. A.
VAN
WELIEAND G. A. hl. DIEPEN
Laboratory of General and Inorganic Chemistry, Julianalaan 1S6, Delft, Holland Received July 17, 1963 Unlike Prins, we found, in measuring the P-T projection of the system ethane-naphthalene, no temperature minimum on the three phase curve solid naphthalene-liquid-gas. It follows that there is no essential difference in phase-behavior between the eystems ethane-naphthalene and ethylene-naphthalene. Together with the P-T projection we have measured some P-T cross-sections a t constant composition of the binary mixture. The first critical end-point is situated a t 51.5 atm. and 36.8', the second critical end-point, with a composition of approximately 19.5 mole yo,was found a t 122.5 atm. and 56.6'.
Introduction For binary systems, characterized by metastable immiscibility of the liquid phase and intersection of the three phase line solid-liquid-gas and the critical curve it is usual to draw the P-T projection of the three phase curve S B L ~ G with a negative slope dP/dT. According to measurements taken by Prins, the system ethane-naphthalene should belong to this type, with the difference that whereas a t lower pressures the SBL2G-curve has a negative slope, the curve passes a temperature minimum, to end finally into the second critical end-point with a positive slope dP/dT. This would lead, as a consequence, to a T-x projection as given in Fig. 1. From 0, the triple point of naphthalene, the gas- and liquid branch of the SBL~Gequilibrium move to lower naphthalene-compositions and lower temperatures. The gas phase in equilibrium with the liquid phase will always be richer in the most volatile component. As a result the gas branch will move a t smaller x-values than the corresponding liquid branch. It follows from the P-T projection of the SB-L~-G equilibrium that both branches passaminimum temperature and move to higher temperatures, their x-values steadily coming closer. Finally, a t the temperature of the second critical end-point, the gas- and liquid branch will merge smoothly into each other. The composition of the two phases will then be equal and the slope of the T-x projection, dT/dx, becomes zero. Figures 2 and 3 are P-x cross-sections, through Fig. 1, respectively, for a temperature below the critical endpoint and the temperature of this point. (1) A. Prins, Verelag Akad. Wetenschappen Amsterdam, 28, 1037 (1915).
From Fig. 3 the conclusion must be drawn that in the vicinity of the second critical end-point the solubility of solid naphthalene in the fluid phase falls sharply if the pressure is increased a t constant temperature. In other words: at the temperature of the second critical end-point the system ethane-naphthalene should demonstrate a behavior just opposite to that of the system eth ylene-naph thalene ,z We have measured some P-T cross-sections a t constant composition to investigate this phenomenon quantitatively. Since our results did not shorn any substantial difference with those of the system ethylene-naphthalene, we were compelled to reinvestigate the P-T projection of the system ethane-naphthalene according to Prins. Experimental Procedure For all data given in this communication use was made of the Cailletet-apparatus. The technique of measuring P-T crosssections and determining the equilibrium conditions for three phase coexistence has been described earlier.2 The ethane is a research grade-product of Phillips Petroleum Co. with a purity of 99.99 mole %. Our naphthalene had a melting point of 80.25".
Determination of P-T Cross-sections at Constant Composition.-After some orientation we succeeded in establishing the composition of the second critical end' CloHs. The point point: approximately 19.5 mole % was found a t 122.5 atm. and 56.6'. I n its vicinity we have measured some P-T cross(2) G. S. A. van Welie and G. A. X. Diepen, Rec. trav. zhzm., 80, 659 (1961).
TABLE 1
P-2 SECTIoN
T H E SYSTEM E T H A N E - ~ ~ ~ P H T H b L E N E
-4T \'ARIULJS
CONSTAKT COYPOSITIOKS x < 10.57 mole CmHs 10.57 mole P, atm. t , OC. P,atm.
TiTn o T Fig. l.-P-T and T-x projection of a binary system in vhich the three phase curve SB, L?, G passes a temperature miriiniuin and ends into a second critical end point.
>'
Sat
SB-FI 153 5 53 30 136 0 54 35 124 0 55 20 114 2 56 10 L-G Liquid vanishing points 119 3 66 40 114 2 61 40 110 0 57 60
fR 19.78 mole % CloHs P,atm. 1, O C .
SB-FI 155 0 55 154 3 56 136 0 56 126.7 56
Ln A
X
B
Fig. ~.-P-x section through Fig. 1 for T Ti.
B
X
Fig. 3. -P-x section through Fig. 1 for
T
=
T,.
=
139.8 135.5 134,O 129.4 124.1
90 05 25 45
G 77.25 72.00 70.50 65.25 58.35
160
t
155
140
Cd3s t,
oc.
SB-F1 154.1 54.40 136.6 55.35 125.9 56.05 116.7 56.60 L-G Liquid vanishing points 134.4 79,30 70,70 126.3 120,9 64.60 116.4 60.15 114.1 58,OO 25.26 mole o/o C:aHs t , "C.
P , atm.
SB-F1 16C3.6 56.80 153,3 56.75 131.2 56.75 121.4 56.85 Gas vanishing points L-G 131.0 70.30 126.3 64.55 122,3 60.05 120.3 56.75 119.6 56.40
16.23 mole
% ' CioHs
P, atm.
t, O C .
SrF1 193.8 5d.50 153.4 55.90 136.0 56.20 124.8 56.55 L-G Liquid vanishing points 134.9 83.20 136.9 75.55 132.0 69.60 126.4 63.10 123.5 59.75 121.5 57.35 35.97 mole c/o C I O H ~ P,atm. t, OC.
SB-FI 153.4 57.95 134.9 57.70 106.7 57.15 Gas vanishing points L-G 118.6 73.50 113.2 68.10 109.2 63.75 104.2 58.60
150 120
145 140
100
E 135
4
8
&- 130
122
80
&-
120
60
115 110
40
105 100 54
58
62 66 70 74 78 Temp., "C. Fig. 4.-The system et,hane-naphthalene. P-T measurements for various constant compositions (in mole 70).
sections. The data are listed in Table I and set out in Fig. 4. It appeared from visual observations that a composi' is very close to the critical comtion of 19.78 mole % position. Consequently the LzG-boundary curve for this composition may be supposed to coincide with the curve Lz= G. It should be clear that in the P-T projection (Fig. 3 ) the second critical end-point may be considered as a
20 0
20
30
40 50 60 70 T e m p , "C Fig. 5.-The system ethane-naphthalene, P-T projection of the three phase curve SB,L, G: 0,first critical end-point according to Prins; f, second critical end-point according to Prins; A , thrce-phase curve, solid naphthalene--liquid-gas according to Prins; 0, own measuremsnt.
limit case in which the SB-F1-equilibrium becomes identical with the SBLaG-equilibrium. Hence the corresponding equilibrium curves should have equal slopes at critical end-point conditions.
April, 1963
STOICHIOMETRY OF J'OKMIC ACIDVAPORPHOTOLYSIS
It follows from Fig. 4 that the slope of the SB-Flequilibrium for the critical composition (19.78 mole %) is negative. This experimental result excludes the occurrence of a temperature minimum on the S B L I G curve and so we are justified in concluding that there is no essential difference in phase behavior between the system ethane-naphthalene and the system ethylenenaphthalene. Determination of the Three Phase Curve SB-L-G.. From direct measurements of the three phase equilibrium and the P-T measurements deecribed above, we have constructed the three phase curve, as represented in Fig. 5 . The data are listed in Table II.3 The liquidgas equilibrium of ethane is given in Fig. 5 from literature data.4 Figure 5 shows that the first critical end-point is situated a t 51.5 atm. and 36.8'. The rise in critical temperature is 4.6') and not 7.2" as found ,4da Prins. This increase is eoiisiderably lon7er in the system ethylene-naphthalene (l.5')6 which points to a greater solubility of naphthalene in ethane, a t least for conditions close to tlhe first critical end-point . Figure 5 demonstrates a t the same time the remarkable fact that contrary to Prim' findings, there is no temperature minimum. %) are given i n Table I* (4) J. A. Beattie, G. J. Sn and G. L. Simard, J . Am Chem. Soc., 61, 924 (lY39). ( 5 ) J. A. Beattie, C. Hadlook a n d W. Poffenberger, J . Chem. Phys., 3, 93 (193.5). (6) G. -4.hI. Diepen and F. E. C. Scheffer, J . Am. Chem. SOC.,70, 4085 (1948). (7) G A. M. Diepen and F. E. C. Soheffer, J . P ~ Y QChem., . 67, 575 (1963). ( 3 ) L ? = G d a t a (for a composition of 19 78 mole
754
TABLE I1 THE SYSTEM
&HAXE--NAPHTHALENE P-2' P R O J E C T I O S OF THE THREE PHASE CURVE 1 2 , G.
SB,
P , atm.
t , OC.
P , atm. t ,
'c.
Second critical end-point 122.5 56.6 SR,
h,G
38 3 22 25 41 7 26 25 44 5 29 65 45 4 30 65 46 9 32 25 47 8 33 30 48 3 33 80 49 3 34 80 50 2 35 60 50 3 35 80 36 00 50 6 50 9 36 30 36 50 51 1 First critical end-point 51.5 36 8
SB,Lz,G 122.6 121.1 120.0 113.2 109.2 102.8 95.5 85.8 74.5 66.6 64 1 58.0 45.8 44.0 39.7 23.8
56.60 56.70 56.80 56.90 56.90 57.15 57.20 57.60 58.20 59.55 60. 30 61.70 65 50 66.10 67.60 72.40
As a result we may conclude that the systems ethane-naphthalene and ethylene-naphthalene are similar in their phase behavior. Meanwhile we discovered a system, that does show a temperature minimum, vix., the system methanenaphthalene,8 about which another communication has appeared. (8) Y van Ilest, T h e m , Delft, 1962
RATE DEPENDESCE OF THE STOICHIOMETRY OF FORRTIC ACID VAPOR PHOTOLYSIS BY PETER E. YAXKWICH ASD EDWARD F. STEIGELMANS 9 o y e s Laboratory of Chemistry, University of Illinois, Urbana, Illinozs Received July 63,1962
Formic acid vapor was phot,olysed at 3043°K. and a total pressure of 26.3 mm. in an end-illuminated tubular vessel; a high pressure mercury arc lamp was used. The photolysis rate was varied from 0.187-59.0 x 10-9 mole per 6ec , and the degree of decomposition was limited to 1yo. Over the rate range studied, the mole fraction of carbon dioxide in the product fell from 0.53 to 0.38. Analysis of the data in terms of a model suggested by the work of R. M. Noyes showed that this mole fraction should be a linear function of the inverse one-fourth power of the intensity of illumination (as measured by the rate of appearance of products). Within modest experimental errors, the results obtained are in fair agreement with the predictions of this simple treatment.
Introduction One of the first investigations of the photochemical decomposition of formic acid was that of Berthelot and Gaudechon,' who reported the products of the decomposition of the liquid to be carbon dioxide, carbon monoxide, hydrogen, and a small amount of methane. Later, Ramsperger and Porter2 found that formic acid vapor decomposed photochemically into two different product sets: carbon dioxide and hydrogen, and carbon monoxide and water, the yields of each set being 36 and 647,) respectively. Herr and Koyes3 found that the quantum yield for the vapor photolysis was (1) D. Berthelot a n d 13. Gaudechon, Compt. lend., 151, 478 (1910). (2) H. C. Ramsperger a n d C. W. Porter, J . Am. Chem. SOC.,48, 1268 (1926). (3) W . N. Herr a n d W. A. Noyes, Jr., %bad.,SO, 2345 (1928).
slightly less than unity and that the amount of hydrogen formed was somewhat smaller than the amount of carbon dioxide. The studies of Gorin and Taylor4 revealed the quantum yield to be unity at, three different wave lengths (2540, 2100, and 1900 A.) and independent of temperature and pressure. They found the dimer to decompose exclusively to carbon dioxide and hydrogen, while the monomer formed both product sets; tests with parahydrogen for the presence of hydrogen atoms in the decomposition mere negative. Using the antimony mirror technique, Burton5 also was unable to detect the presence of free radicals in the decomposition. (4) E. Gorin and H. S.Taylor, J . Am. Chem. S o c . , 56, 2042 (1934). ( 5 ) M. Burton, cbid., 58, 1665 (1936).
