FUSION OF PENTAERYTHRITYL FLUORIDE
state is not affected by high concentrations of the salts now employed. After the completion of this manuscript Hart and Boag's workz7 appeared, showing the absorption spectrum of the hydrated electron in water and in aqueous solutions irradiated with pulses of ionizing radiation. Subsequently, R'Iatheson and RabaniZ8 found SpeCtrOSCOpiC evidence for the fOmatiOn Of Sol-
255
vated electrons in the flash photolysis of aqueous solutions, including those of halide ions. These results give strong support for the views expressed in the present and previous1-5J papers.
(27) (28)
E. J. Hart and J. W. Boag, J . A m . Chem. Soc., 84,4090 (1962). M. s. Matheson and J . Rabani, to be published.
Heat Capacities and Thermodynamic Properties of Globular
Molecules.
X.
Fusion of Pentaerythrityl Fluoride1
by John C. Trowbridge and Edgar F. Westrum, Jr. Department of Chemistry, Uniaersdy of Michigan, Ann Arbor, Michigan
(Received June 3,1963)
The heat capacity of crystalline and liquid C(CH2I;)I has been determined by adiabatic calorimetry from 295 to 385'K. The small entropy of fusion, 3.35 cal./(mole O K . ) , a t the 367.43OK. triple point temperature confirms the plastically crystallhe nature of this substance.
Introduction Low temperature heat capacity studies on pentaerythritol2 and the pentaerythrityl halides3 revealed the presence of a transition a t 249.4O0K. to the plastically crystalline state in pentaerythrityl fluoride, C(CH2V),, with 12.66 cal./(mole OK.) entropy of transit i ~ n . Study ~ of the thermodynamics of the fusion process was undertaken to provide a basis for further correlation of the crystal I1 + crystal I transition in the fluoride with that in pentaerythritol and to give an added test of the proposed mechanism of transition in the former. Experimental Calorimetric Sample. The identical sample used previously4 was loaded in the nitrogen atmosphere of the drybox. E'or these measurements 58.6279 g. (in vacuo) of pentaerythrityl fluoride were used.
Further indication of purity is provided by the fractional fusion studies. Calorimeter and Thermostat. The Mark IV intermediate temperature thermostat and silver calorimeter W - Z 5 were used in these measurements with the quasiadiabatic techniq1Je previously employed.6 The calorimetric system had previously been calibrated? with the Calorimetry Conference Sample of synthetic sapphire.8 (1)
(2) (3) (4) (5)
(6) (7) (8)
This work was supported in part hy t h e United States Atomic Energy Commission. E. F. Westrum, Jr., arid D. H. I'ayne, J . Phys. Chem., in press. D. H . Payne and 15. E'. Westrum, Jr., ibid., 66, 748 (1962). E. F. Westrum. Jr., and D. H. I'ayne, ibid., in press. J . C. Trowbridge and E. F. Westrum, Jr., ibid., 67, 2381 (1963). E. F. Westrum, Jr.. J. B. Hatcher, and I>. W. Osborne, J . Chem. P h y s . , 21, 419 (1953).
E. .'1 Westrum, Jr., and J. C. Trowbridge, t o be published. G. T. Furukawa. T. B. Douglas, It. E. McCoskey, and D. C . Ginnings, J . Res. Nall. Bur. Std., 57, 67 (1956)
Volume 68, Number 2
February, 1,964
JOHN C. TROWBRIDGE A N D EDGAR F. WESTRUM, JR.
256
For thermal conduction 12.5 cm. pressure of helium gas a t 300OK. was put into the sample space before sealing off the calorimeter.
curve. Smoothed heat capacities from a least-squaresfit curve through the experimental data are presented at selected temperatures in Table 111.
Results Heat Capacity. The experimental heat capacities are presented in Table I in chronological order in terms of the ice point as 273.15'K., the defined thermochemical calorie as 4.184 j., and a molecular weight of 144.119 g. Adjustments (which amounted to less than O . O l ~ oover the entire temperature range investigated) were applied to the data for the finite temperature increments used. No correction was made for sublimation or vaporization since no adequate representation of the vapor pressure as a function of temperature was available. However, this emendation is estimated from rough vapor pressure values to be less than 0.05%. Figure 1 shows the experimentally determined heat
-
60
-
Table I : Heat Capacity of Pentaerythrityl Fluoride. (Units: cal., mole, OK.) -
T
301 31 50 67 309 07 51 37 319 34 52 12 329 28 52 91 339 28 53 i o 349 19 54 63 Fusion Runs A 371 04 60 80 374 97 61 09
362 88 363 75 364 35
300.98 308.62 317.15 326.40 335.74 345.08 354.38 360.82
Fusion Run 1) Series V
Enthalpy Run B Fusion Runs C 371 13 60.74 374 93 61.07
Series VI
60 99 61 15 61 36
Series \'I1
Series IV
Fusion Runs E
C8
373 30 377 85 381.04
56 64 62 83 73 13
Series I1
50,71 51.27 51.90 52.65 53.44 54.30 55.15 56.05
Series VI11 369.18 369.99
59.83 60.30
Fusion Run F
Fusion runs -
0
E
-
T
CeO
AT
I
T
AT
Runs A
50 359 365 366 366 366 368
h
0
T
C.
Series 111
Series I
I 0)
CT,
-
r
C3
40
43 39 46 80 99 08
10 1 0 0 0 1
293 682 523 213 164 954
C.
Runs E (56 17) (165 1) 576 1440 1970 (139 4)
367 367 367 367 367
02 04 05 07 O!)
0 0 0 0 0
030 023 024 026 026
1450 1900 1790 1690 1660
Runs C
30
(Cf. Table IV) 200
250 300 TEMPERATURE, 'K
350
Figure 1. Heat capacity of pentaerythrityl fluoride: 0, cryogenic data of Westrum and Payne'; 0,data from this research.
capacities together with some of the low temperature value^.^ The nearly O.lSyO discrepancy in the heat capacities measured by the two instruments a t the point of overlap has a negligible effect on the thermodynamic functions. These data are considered to be characterized by a probable error of 0.1%. A further test of the measurement and computation procedure is affor.'ed by the enthalpy-type run B indicated in Table I1 and its comparison with the enthalpy of the regular runs and the integral of the smoothed heat capacity The Journal of Physical Chemistry
l'alues in parentheses involve finite temperature increments in regions of high curvature.
Melting. The triple point of this sample occurs a t 367.06"K. with an enthalpy increment of 1230 cal./ mole and a corresponding entropy of melting of 3.35 cal./(mole OK.). Molal heat capacities as high as 1900 cal./(mole OK.) were observed and thermal equilibrium was attained typically only after a 3.5-hr. period in this region. It was consequently desirable to obtain several enthalpy increment runs through the entire melting regions. Such runs (D and E') are compared with the sum of the enthalpy increments of the series of heat capacity runs through the transition region as shown in Table 11.
FUSION OF PENTAERYTHRITYL FLUORIDD
257
Table I V : Fractional Melting of Pentaerythrityl Fluoride. (Unita: cal., mole, OK.)
Table I1 : Enthalpy and Entropy Incrementa of Pentaerythrityl Fluoride. (Unita: cal., mole, OK.)
Designation
Number of runs
Trlnsi
Tln8txaiH a n s
Fusion Series I(A) Runs C Run D Run F
8 9 1 1
354.28 364.25 362.68 353.21
376.89 376.82 369.17 374.80
2387.7 (2367.1)n 2381.7 2385.2
-
2384.9
Average: Crystal I
How
Series I Series V I Runs B
3 4 1
6.518 (6.462)" 6.502 6.511 6.510
1629.0 1629.2 1629.2
Average:
1629.1
Rejected from average by Chauvenet's criterion. ~ _ _ _ _ _ _ __ _ _ _ _ _ _ ~
~
Table I11 : Thermodynamic Functions of Pentaerythrityl Fluoride. (C,H,F,; 1 mole = 144.119 g. Units: cal., mole, OK.) T
CS
50
H0
- Hoo
-(Go
- Hoo)/T
Crystal I 298.15" 300 310 320 330 340 350 360 367.06
50.71 50.82 51.47 52.15 52.91 53.76 54.76 55.94 (56.84)
69.31 69.63 71.30 72.95 74.56 76.16 77.73 79.27 80.45
11333 11427 11939 12457 12982 13515 14058 14611 15030
31.30 31.53 32.79 34.02 35.22 36.40 37.56 38.69 39.50
16259 16413 17024
39.50 39.81 41.03
Liquid 367,06 370 380
(60.61 ) 60.69 61.31
83.80 84.21 85.83
A H ~ X O ~ U B 1/F
364.54 364.93 365.52 366.32 366.76 368.06
0.588 0,248 0.985 0.620 0.259 2.339
74.21 92.06 176.5 477.9 1170 257.4
21.53 32.69 153.11 411.71 6'39 ,42 1227.05
Triple point; this sample Triple point; pure compound
Numerical quadrature of smoothed curve: 1629.0 a
c.
' From Westrum and Payne.'
Fractional melting data from Table IV for this sample of pentaerythrityl fluoride show that the reciprocal fraction melted (l/F) is not a linear function of temperature and suggests that the impurity forms a solid solution with the sample. By applying the method of Mastrangelo and DornteYto correct for the presence of solid solution, the sample was found t o contain 0.0018 mole fraction of impurity. Furthermore, the triple point of this sample is 367.06'K. and that of the pure substance extrapolated is 367.43'K.
?'final
Fusion Runs C
- Horn
364.57 334.46 362.64 331 07 364.26 328.38
AT
T
- H'MLSom - Souc
56.062 36.920 7.884 2.932 1,726
364.834 365.052 366.012 366.612 366.888 369.226
(1.OOO) 367.06 ( 0 .OOO) 367,43
Thermodynamic Properties. The thermodynamic properties calculated by quadrature of the experimental heat capacity data on a digital computer are also provided a t selected temperatures in Table 111. Nuclear spin and isotopic mixing contributions have not been included in the entropy or in the free energy function. The tabulated functions are based on the low temperature values for the enthalpy and entropy obtained by Westrum and Payne4 below 300OK.
Discussion Upon taking into account only the changes in the symmetry features on traversing the solid I1 + I transition in pentaerythrityl fluoride, Westrum and Payne* could account for the magnitude and mechanism of the transition. This mechanism then was applied t o the solid phase anomaly in pentaerythritol, C(CH20H)4,studied by Xitta, et oZ.,l0 and found to predict exactly the experimental results after correction terms were added for the additional symmetry modes available t o the hydrogen atoms. Having experimentally determined the fusion properties of pentaerythrityl fluoride, a further check is now possible on the effects of the hydrogen atoms in pentaerythritol. Because of the proximity in size of oxygen and fluorine atoms, the basic lattice heat capacity should be the same in both cases with differences in entropies due only t o symmetry factors. Westrum and Payne4 showed that this difference in configurational entropy would be R In 2 4R In 3 = 10.11 cal./ (mole O K . ) . The entropies of transition and fusion in pentaerythritol are, respectively, 22.8 and 3.2 cal./ (mole O K . ) , while the corresponding increments are
+
S. V. R. Mastrangelo and R. W. Dornte, J. Am. Chem. Soc., 7 7 , 6200 (1955). (10) 1. Nitta. T. Watsnabe, 9. Seki, and M. Momotani, Proc. Japan Acad., 26, 1019 (1950). (9)
Volume 68, Number d
February, 1964
258
STANLEY BUKATA A N D JACOB A. MARINSKY
12.66 and 3.35 cal./(mole OK.), respectively, for pentaerythrityl fluoride. A sum of the two transitions in each of these substances gives the disorder present above their common lattice energy. Subtracting this sum for the fluoride from that of the alcohol gives 26.0 - 16.0 = 10.0 cal./(mole OK.). This is well within experimental error of the 10.1 cal./(mole O K . ) calcu-
lated by Westrum and Payne and, as such, is further evidence for the proper choice of mechanism for the observed transitions. Acknowledgment. This work was performed under the auspices of the United States Atomic Energy Commission. The authors are indebted to Dr. Elfreda Chang for assistance in the evaluation of the data.
Job’s Method of Continuous Variations with Ion Exchange
for the Study of Complexes in Solution
by Stanley Bukata1f2and Jacob A. Marinsky3 Department o j Chemistry, State University o j A’ew York at Buffalo, Buffalo, New York (Received J u n e 18, 1963)
The use of ion-exchange properties for determining the nature of complex species in solution by Job’s continuous variations method has been developed. The CU+~-EDTA,Caf2EDTA, and Ca+2-citrate systems were studied to demonstrate the method. The results obtained were in agreement with the results of earlier investigations of these systems.
Introduction Job’s method of continuous variations4 of isomolar solutions has been used frequently for the study of complexes in solution. Solution properties, which are linear functions of the concentrations of the species involved, are analyzed in applying the method. Some properties which have been employed are refractive index15heat of mixing6 densityI7 dielectric constantI8 and light a b s o r p t i ~ n . ~ A ~ ’solution ~ property adaptable to ,Job’s method and not previously discussed in the literature is ion exchange. The discussion below is given for cation exchange but would be similar for anion exchange. 1st mixtures be made by the addition of z ml. of B to (VT - t) ml. of A when both solutions are a t a concentration of 114 moles/l. The symbol VT corresponds to the total volume of the mixtures which is presumed to be essentially constant in the absence of appreciable volume change on mixing. Allow these isomolar solutions to undergo cation exchange with a suitable The Journal of Physical Chemistry
resin. Assume that A and B react to form a single complex according t o A
+ nB
AB,
(1)
Further, assume A undergoes cation exchange according to the equation
(1) (2)
(3) (4)
(5) (6)
Union Carbide Predoctoral Fellow, 1961-1962. This paper is based on a portion of a dissertation submitted by S. Bukata in partial fulfillment of the requirements for the degree of Doctor of Philosophy. Correspondence t,o be addressed to this author. P. Job, Ann. Chem., 9 , 113 (1928). G. Spacu and E. Popper. Bul. soc. stiints Cluj.. 7,400 (1934) M. M. Chauvenet, P. Job, and G . Urbain, Compt. rend., 171,855 (1920).
(7)
(8) (9)
Y. Wormser, Bull. aoc. chim. France, 15, 395 (1948). N. Q. Trinh, Compt. rend.. 226, 403 (1948). W .C. Vosburgh and G . R. Cooper. J . Am. Chem. SOC..63, 437 (1941).
(10)
R. K. Gould and W. C . Vosburgh, ibid., 64, 1630 (1942).
