T H E
J O U R N A L
OF
PHYSICAL CHEMISTRY Registered in
U . S. Patent Ojice
@ Copyright, 1965, by the American Chemical Society
VOLUME 69, NUMBER 2 FEBRUARY 15,1965
Low-Temperature Thermodynamic Properties of n-Propyl-, n-Butyl-, and n-Decyl-Substituted Cyclopentanes
by John F. Messerly, Samuel S. Todd, and Herman L. Finke Contribution N o . 136 from the Thermodynamics Laboratory of the Bartlesville Petroleum Research Center, Bureau of Mines, U . 5.Department of the Interior, Bartlesville, Oklahoma (Received October 1 , 1964)
The heat capacities in the range 12-37OoK., heats of fusion, triple points, and purity of n-propylcyclopentane, n-butylcyclopentane, and n-decylcyclopentane were measured in an adiabatic calorimeter. From these data the thermodynamic functions, (G, - Ho,)/ TI ( H , - H o o ) / T ,H , - HoglS,, and C,, were calculated for the solid and liquid states a t selected temperatures in the range 10-37OOK. The entropies of these compounds in the ideal gas state a t 298.15OK. were calculated using a Cox equation fitted to vapor pressure data from the literature. The average entropy increments per methylene group from nbutyl- through n-decylcyclopentane in the liquid and ideal gas states were found to be 7.76 and 9.33 cal. deg.-' mole-', respectively, in close agreement with the constant value for higher members of the normal alkane series of hydrocarbons.
Introduction In the continuing program of therniodynaniics research on hydrocarbons and related substances conducted in this laboratory, the low-temperature thermal properties of a number of homologous series of conipounds have been determined. Because the effects of systematic errors can be niininiized by utilizing the same apparatus and methods in all the measurements, the low-temperature studies yield incremental results of greater precision than those derivable from the determinations of a nuniber of different investigators. Aleasurenients on nine n-paraffins by Finlte, et uLll and on seven selected 1-olefins froin ce to c16 by AlcCullough, et aLI2have shown that the entropy increment per methylene group in the liquid state a t 298.15'K. is a constant within the limits of precision of the meas-
urements. Person and Piniente13 have shown the same relation to hold for the ideal gas state for t,he n-paraffins c 8 through C16. From the entropy of n-heptane,* the entropies of the n-alkanes from c8 to C16,l and unpublished data on n-pentane, n-hexane, n-heptadecane, and n-octadecane, the entropy increment per methylene group in n-alkanes from C5 to cl8 has been found to be essentially constant. With the view of verifying the (1) H. L. Finke, M. E. Gross, G. Waddington, and H.
M.Huffman,
J. A m . Chem Soc., 7 6 , 333 (1954). (2) J. 1'. hlcCullough, H. L. Finke, M . E. Gross, J. F. Messerly. and G. Waddington, J. Phys. Chem., 61, 289 (1957). (3) W. B. Person and G. C. Pirnentel, J . A m . Chem. Soc., 7 5 , 532 (1953). (4) J. P. McCullough and J. F. Messerly. U. S. Bureau of Mines Bulletin 596, U. S. Government Printing Office, Washington, D. C ,
1961.
353
JOHN F. MESSERLY, SAMUEL S. TODD, AND HERMAN L. FINKE
354
constancy of the value of the entropy iricrenient for higher ineiiibers of other n-alkyl series, studies were undertaken on several series of n-alkyl-substituted ring compounds. The results of the first of these investigations on the substituted cyclopentanes are presented in this paper. As the first inembers of the series show irregular increments in both the liquid and ideal gas states, the n-propyl, n-butyl, and n-decyl substituents were chosen for these studies. Discussion From the heat capacities and heats of fusion of the three conipounds studied, the entropies in the liquid phase a t 298.13°1i. were calculated. From these values, together with the vapor pressure and the entropy of vaporization, the entropies of the conipourids in the ideal gas state a t 1 atm. were calculated. These entropy values are presented in Table I with the average entropy increment per inethylene group, AS/CH,.
Table I : Molal Entropies at 298.15”K. (cal. deg.-l mole-’) Compound
n-Propylcyclopentane n-Butylcyclopentane n-Decylcyclopentane
--Liquid----So
74.29 82’18 128.71
AS/CK2
,
,
89
7.76
--Ideal So
99’06 108.46 164,45
gas-AS/CHz
9.40 9,33
It will be noted in Table I that the increnient from n-propyl to n-butyl, 7.89 cal. deg.-l niole-l, is somewhat larger than the average increnient from n-butyl to n-decyl, 7.76 cal. deg.-’ i~iole-~.This latter value agrees quite well with the average increment of 7.74 cal. deg.-’ ni01e-l found for the liquid n-paraffins from C5 to C, in this laboratory. For the ideal gas, the average inethylene increnient from n-butyl- through ndecylcyclopentane is 9.33 cal. deg.-l in close agreement with the average value of the methylene increment of 9.31 cal. deg.-l mole-’ calculated for the C8 t o C16 normal paraffins in the ideal gas state by Person and P i n ~ e n t e l . ~For alkyl cyclopentanes lower than n-butylcyclopentane in both the liquid and ideal gas states, the entropy differences per CH, group a t 298.15OK. are irregular. Experimental Apparatus and Physical Constants. The low-temperature calorimetric measurements were made with apparatus described by Huffman arid c o - ~ o r k e r s . ~The “1951 International Atoiiiic Weights”6 arid values of the fundanwntal physical constants’ were used. Measurements of teiiiperature were made with platinuiii reThe Journal of Physical Chemistry
sistance therinoiiieters calibrated in terms of the International Temperature Scale of 19488from 90 to 400°1as noted in Table 11. The precision uncertainty of the results was, in general, less than 0.lyO, and above 3OoK the accuracy uncertainty should
Table I1 : Heat Capacity (cal. deg. -1 mole-') T"
C.
T"
Cab
Ta
CS6
n-Propylcyclopen tane 12 12 13 13 14 14 15 16 17 17 18 19 20 21 23 23 25 26
12 37 16 52 32 82 62 26 08 88 76 57 68 55 41 96 81 70
162 166 168 173 175 181 189 199 210
15 52 15 51 10 44 76 82 21
0 873 0 936 1 124 1 203 1 415 1 552 1 763 1 941 2 189 2 412 2 679 2 935 3 282 3 563 4 159 4 334 4 934 5 210 41 41 41 41 41 42 42 43 43
560 702 768 934 997 251 628 166 780
Crystal 39 5 56 6 7 58 00 8 64 9 86 10 56 11 35 12 78 13 43 13 90 14 20 15 55 16 01 17 61 18 36 19 38 19
748 114 078 129 180 335 551 687 244 828 369 444 419 380 363 284 303
93.84 94.37 99.59 105.61 111.40 117.43 119.73 123.71 124.85 125.05 129.78 130.04 135.08 135.67 141 79 144.46 149.13
20.084 20.168 20.900 21.719 22.498 23.287 23.568 24.087 24.193 24.226 24.841 24.843 25.490 25.564 26.389" 26.730" 27.831"
Liquid 220.45 44.474 230.96 45,257 241. 73 46,137 252.32 47.057 262.70 48.018 272.89 49,031 282.90 50.050 292.72 51.109
300.27 302.37 310.88 321.68 332.26 343.00 353.89 364.57
51.912 52.147 53.103 54.337 55.544 56,792 58,061 59.367
102 108 114 119 125 125 132 132 132 139 140 140 140 145 147 150 154
23.936 24.851 25.724 26.555 27.311 27,419 28,361 28.445 28.442 29.366 29.561 29.630 29.636 30.359 30.800 31 286d 32 152d
28 29 32 36 39 43 48 53 55 58 60 66 71 77 82 88 88
n-Britylcyclopentane 11 11 12 13 13 14 15 15 17 18 19 20 20 23 23 25 25
34 80 47 14 83 41 43 74 26 11 00 90
93 10 10 61 62
0 884 1 1 1 1
1 1 2 2 2 3 3 3 4 4 5 5
020 170 353 ,532 704 978 065 519 775 065 696 693 431 440 307 298
Crystal 31 6 73 6 48 7 44 9 93 11 70 13 83 14 46 14 55 15 85 16 45 17 11 19 81 20 03 21 59 21 91 68 22 23
28 28 32 36 42 49 53 54 58 63 69 75 80 86 86
'' ''
216 363 669 001 059 039 146 308 349 651 875 033 188 205 298 163
oZ7
73 67 39 91 17 70 25 70 79 07 14 62 77 14 92 48 28
355
Table I1 Continued T'
167.87 173.24 181.25 190.45 190.91 199.88 209.65 219.76
Csb
48.315 48.471 48.795 49.158 49.197 49.653 50.248 50.928
CsFj
TO
C."
298.75 307.68 317 35 327.43 337.31 347.58 357.66 367.57
58.699 59 788 60.967 62.200 63.454 64.763 66.026 67.262
Crystal 78.55 30.720 85.11 32.852 86.26 33.180 88.72 33.911 91.90 34.789 92.79 34.993 94.68 35.446 99.05 36.646 99.47 36.726 106.26 38.483 114.00 40.354 122.20 42.291 128.82 43.654 130.42 44.157 137.18 45.577 139.04 46.061 144.72 47.262 147.33 47.903 147.42 47.818 152.47 49.029 154.99 49.608 155.05 49.470 158.64 50.192 159.97 50,719 162,85 51.369 163.15 51,488 166.18 51.972 169,lO 52.566
171 21 171 37 171 53 172 72 175 07 179 97 180 24 183 65 186 36 188 43 188 67 193 97 197 02 200 55 201 46 203 42 208 74 209 49 215 79 223 11 223 76 227 41 229 40 229 73 233 07 239 04 241 07 246 41
53 102 53 202 53 188 53 463 54 043 55 201 55 306 56 127 56 644 57 266 57 376 58 629 59 484 60 414 60 676 61 374 62 869 63 149 65 120 67 779 68 007 69 350 69 227 70 518 71 95Y 74 934* 76 553" 82 426'
Liquid 271.95 98.228 273.87 98.446 282.67 99.591 292.04 100.$168
299.44 301.64 311.43 321.40
102.107 102.534 104.163 105,967
T U
Liquid 229.71 51.688 239.51 52.516 249.16 53.392 259.09 54.340 269.26 55.384 279.26 56.464 289.09 57.568 298.24 58.654 n-Decylcy clopentane
11.30 12.68 12.79 14.38 14.75 16.15 16.75 18.08 19.01 20.44 21.44 23.17 23.77 25.90 26.19 28.54 28.78 32.05 35.99 39.99 44.51 49.54 54.71 54.77 55.04 59.79 60.71 65.43 71.83
1.148 1.616 1.641 2,214 2.359 2.919 3.160 3.741 4.168 4.853 5.356 6 206 6.510 7.602 7,744 8.953 9.088 10.830 12.943 15.037 17,454 19.856 22.140 22.112 22.258 24.063 24.419 26.238 28.450
258.18 258.37 264.82 265.34
97.041 97.070 97.506 97.554
a T is the mean temperature ( i n OK.) of each heat capacity measurement. C, is the heat, capacity of the condensed phase a t satriration presstire. Yalries of C, for crystals are not corrected for effects of prernelting raused by irnpiirities. c , d , c The temperature incrernents of these measureriients are i n the order of increasing T , OK.: ( c ) 6.446, 4.765, 4.611; ( d ) 5.2175. 6.246; (e) 9.090, 9.790, 6.912, 4.941.
not exceed 0.2%, except in regions near phase transformations. Xear phase changes, data for the solid Vohime 69. Number 2
February 1965
JOHN F. MESSERLY, SAMUEL S. TODD, AND HERMAN L. FINKE
356
Table 111: Equations for Heat Capacity of Liquid Using C, = A
cx
Compound
A
B
n-Propylcy clopentane n-B utyk yclopentane n-Decylayclopentane
54 288 67 971 398 61
-0 20145 -0 28063 -3 1295
Table IV: Triple Point Temperatures, Heats of Fusion, and Cryoscopic Constants AHm, csl. mole-1
Ttp,
OK.
B,
A.
deg.
deg.
-1
-1
n-Propylcyclopentane 155.79 2398 f ja 0.04971 0.00360 n-Butylcyclopentane 165.18 2704 f 2" 0,04987 0 00340 n-Decylcyclopentane 251.02 7917 f 10" 0,06323 0.00330 The uncertainty indicated is the maximum deviation from the mean.
The triple point temperature and sample purity for each compound were determined from studies of the equilibrium melting temperature as a function of the fraction of sample nielted.I2 The resulting melting point summaries are given for the three compounds in Table V. In all cases the equilibrium teniperatures, T F ,were plotted as functions of 1 / ~ the , reciprocal of the fraction of the total sample in the liquid state. The triple point temperatures, Tt,, were determined by linear extrapolations to zero value of 1 / ~ . If the iinpurities forin ideal solutions in the liquid phase and are insoluble in the solid phase, the relation between mole fraction of total impurity, Nz*, and melting point depression, A 7 = T t p- T F ,is13 -In (1 - N z )
=
+
~ h T ( 1 BAT
The Journal of Physical Chemistry
+
)
D
104
(1)
X 10'
-8 4105 -11 2270 -109 63
8 9720 11 710 104 27
state may be less precise and less accurate owing to rapid changes in C, with T, slow equilibration, or uncertainties caused by the presence of impurities. Eiiipirical equations were obtained to represent the heat capacity of each conipound in the liquid state. The constants for these equations are listed in Table 111, together with values of the deviations from observed data as an estimate of reliability. Heats o j Fusion, Triple Point Temperatures, and Purity of Samples. The heats of fusion, AHm, were determined from the heat capacity data and enthalpy measurements made over finite teniperature intervals that included the triple point temperature. The average of two or more measurements for each compound is listed in Table IV.
Compound
+ BT + C T 2 + DT3 (cal. deg.-l
mole-')
Range. OK.
AY. dev., cal.
Max. dev.. cal.
175-365 210-370 260-320
0 01 0 01 0 02
0 03 0 02 0 04
where N2 = N 2 * / ~ .The cryoscopic constants, A = A H m / R T t p 2and B = l/Tt, - ACm/2AHm, were calculated from the values of A H m and T, in Table IV and from the values of ACm, the difference between the heat capacities of the compound in the solid and liquid states a t the triple point, obtained from data in Table VI (discussed in the following section). Values of A and B are included in Table IV. Iiiipurity values given in Table V were calculated using eq. 1 in its simplified form (for Nz* Rb > Mg > Sr > S a > Ca > I< > Li > Ba.
Previous studies on the radiation-induced decomposition of the solid inorganic perchlorates have indicated that chlorine in almost all of its oxidat on states appears in the products of the decomposition. Heal2 identified chloride, chlorate, and oxygen, and indicated the possible presence of hypochlorite and chlorite as products in the radiolysis of solid I
