August, 1961
CHEMICAL THERMODYNAMIC PROPERTIES OF CYCLOPENTANETIIIOL
1425
TI tl3 CHEMICAL THERMODYNAMIC PltOPERTEES OF CYCLOPENTANETHIOL' Hi7 W. T. BERG,D. W. SCOTT,W. N. HUBBARD, S. S. TODD, J. F. MESSEHLY, I. A. HOSSENLOPP, ANN OSBORN,D. R. DOUSLIN AND J. P. MCCULLOUGH L'ontribution -Yo. 104 jrom the Thermodynamics Laboratory of the Bartlesville Petroleum Research Center, Bureau of M i n e s , U.S. Department of the Interior, Bartlesville, Okla. Received A p n l 3,1961
The cheniical thermodj narnic properties of cyclopentanethiol (cyclopentyl mercaptan) in the ideal gas state (0 to 1000°K.) m r e calculated hy using calorimetric, spectroscopic and molecular structure information. Pseudorotation of the fivemembered ring was demonstrated. Experimental studies provided: values of heat capacity for t\vo crystalline forms of t!ie solid (12°K. to the triple point), for the liquid (triple point to 367'K.) and for the vapor (390 to 500'K.); the triple point temperatures; the heats of fusion; thermodynamic functions for the solid and liquid (0 to 370'K.); heat of vaporization (360 to 405°K.); parameters of the equation of state; vapor pressure (353 to 446OK.); and the standard heat of formation a t 298.15%
Thermodynamic studies of cyclopentanethiol jcyclopentyl mercaptan) were made as part of continuing research on organic sulfur compounds of interest in petroleum technology. Experimental results were obtained by low temperature calorimetry, vapor flow calorimetry, combustion calorimetry and comparative ebulliometry. These results were used with spectral and molecular structure information to calculate a table of chemical thermodynamic properties for the ideal gas state. Pseudorotation of ring puckeringZ was demonstrated; that is, the calorimetric results could be interpreted only if an internal degree of freedom were taken as a pseudorotation instead of a vibration. The result for cyclopentanethiol is additional evidence for the already well-substantiated conw p t of pseudorotation in cyclopentane, related hPterocyclic compounds, and many of their derivatives. The first section of this paper is on the thermodynamic properties for the ideal gas state, and the second section is on the experimental measurements. Some obscrmtions on polymorphism of solid cyclopentanethiol are reported with the results of low temperature calorimetry. Thermodynamic Properties Thermodynamic Functions.-Calculating theriiiodynamic functions of cyclopentanethiol required considering all 48 degrees of freedom of the molecule. These degrees of freedom may be classified as three translations, three over-all rotations, one internal rotation of the thiol group, 40 vibrations and one pseudorotation of ring puckering. The contributions of translation and over-all rotation were calculated by standard formulas. In the simplified model used for calculating moments of inertia, the ring was planar, and the bond distaGces and anglesowere: C-C, 1.34 A. ; C-H, 1.09 A.; C-S,1.819 A.; S-H, 1.336 A.; CC-C, 108". H-C-H and H-CS, 109" 28'; CS-H, 96" $0'. The bisectors of the H-C-H and H - C S angles intersected in the center of the ring, snd the hydrogen atoms of the SH and CH groups were trans to each other. For this model, the (1) This investigation was part of American Petroleum Institute Rtwearch Project 48A on the "Production, Isolation and Purification of Sulfur Compounds and Measurement of their Properties," whlch the Bureau of Mines conducts a t Bartlesville, Okia., and Laramie, Wyo. ( 2 ) K. S. Pitzer and W. E. Donath, J. Am. Chem. Soc., 81, 3213 (1959). Earlier work is cited.
product of principal moments of inertia is 3.250 X 10-113 g.3 cm.6, and the reduced moment of inertia for internal rotation is 2.834 X g. cm.2. Corresponding values for the actual molecule with a puckered ring cannot differ much from the foregoing values. The symmetry number is unity for over-all rotation, the thiol rotation and the pseudorotation. Because of the low symmetry of the molecule and the diffuse spectra characteristic of molecules with pseudorotation, a complete and unambiguous vibrational assignment for cycloperitanethiol was not possible. Instead, a somewhat schematic set of vibrational frequencies, listed in Table I, was selected for thermodynamic calculations. All available Raman and infrared spectral data3 were considered, analogies to other molecules were used, and agreement with the calorimetric data, for reasonable values of all molecular-structure parameters, was required. The skeletal bending frequency of 322 cm.-1 (in brackets in Table I) was not observed in the spectra of cyclopentanethiol, but it is from the Raman spectrum of cyclopentyl chloride, which has very nearly the same frequencies because of the similar mass and electronic stmcture of the thiol group and chlorine atom. In Table I, the descriptive names for the modes of vibration TABLE I lrIBRATIONAL FREQUEXCICS O F C Y C L O l ' I ~ ~ ~ T A ~ h T H I O l i ,
CM. -1 a 254, [322],bX 4 , 6 6 , 604 Skeletal bending C-S stretching ( 604) 889, !no,nc;:c(:!), 11 1.; C-C stretching C-S-II bending 863 764, 837, 1029, lalo CH2 rocking CH2 wagging (1029)(2), 1244, 1292 CH2 twisting 1077, (1145), 1271, 1318 CH wagging (1292), 1360 CHI bending 1450(2), 1475(2) S-H stretching 2568 C-H stretching 2920(9) Frequencies used a second time are in parentheses. Multiple weights are indicated by numhers in parentheses immediately following the frequencies. b Transferred from cyclopentyl chloride. (3) Raman: K. W. F. Kohlrausch, A. W. Reitr and W. Stockmair, 2. physak. Chem., B32, 229 (1936); A P I R P 44 at the Carnegie Inst. of Tech., Catalog of Raman Spectral Data, Serial No. 302. Infrared: tbad., Catalog of Infrared Spectral Data, Serial Nos. 1520, 1521, 1622, 1667, 1668, 1873 and 1874.
I~ERG,SCOTT,HUBBARD, TODD, MESSERLY AND MCCULLOUGH
1426
are intended only to shm- that the expected number of frequencies is assigned in each region of the spectrum Values of five other molecular-structure parameters were selected to fit the experimental values of heat capacity and entropy: The height of the potential barrier restricting internal rotation of the thiol group, 1200 cal. mole-'; the height of the potential barriw restricting pseudorotation of the &membered ring, zero (free pseudorotation) ; the effective moment of inertia for the pseudorotation, 18.9 < ; g. em.*; and parameters of an empirical anharrnonicity function,* v = 1130 cm.-l and 2 = 0.684 pal. deg. -' mole-'. All of these values are reasonable. The thiol barrier height of 1200 cal. mole-' is close to that in methanethial, 1270 cal. m0le-1.~ The barrier height for pseiidorotation can be predicted by the formula proposed by Pitzer and Donath,2 1.45(V12 - 2.8) kcal. mole-', in which Vlz is the barrier height for rotation about the bond between ring
Vol. 65
0.27 and 0.66 cal. deg.-l mole-l in ,Soand CPo, respectively. The calculated values of the thermodynamic functions of cyclopentanethiol are listed in columns 2-6 of' Table II.8 A comparison with the experimental results is shown in Table 111. Such a simultaneous fit to all of the calorimetric data could not be obtained with any reasonable treatment that did not include pseudorotation. Heat, Free Energy and Equilibrium Constant of Formation.-The calculated values of the thermodynamic functions, the experimental value of AHfoz98 16 (-26.84 0.19 kcal. mole-I) and values of the thermodynamic functions of C(c, g r a ~ h i t e ) , ~ H2(g)9 and SZ(g)'O were used in computing values of AHj", AFf O and log Kf a t selected temperatures between 0 and 1000°K. The results are listed in columns 7-9, Table 11. Experimental The basic experimental techniques used for cyclopentanethiol are described in published accounts of apparatus and methods for lowtemperature calorimetry," vapor flow
TABLE I1 T ,OK.
'rHE 31OLAL THERMODYX.4XlC PROPERTIES O F CYCT.OPENTANETHIOL IN THE IDEAL (i"" HOO)_/~T, (H' - H o o ) / T , H o H'a, So, CPO, AHfo,b cal. deg. cal. deg.-1 kcal. cal. deg. -1 cal. deg. -1 kcal.,
-
-
GASSTATEa log
AFjO, b kcal.
Kfb
-
0 0 0 0 0 0 - 19.00 19.00 Infinite 273.15 -69.60 14.62 3.993 84.22 23.66 -26.26 1.52 - 1.22 298.15 -70.92 15.46 4.611 86.38 25.79 -26.84 4.09 - 3.00 15.53 4.659 86.54 25.94 -26.88 4.28 3.12 300 -71.01 14.99 - 8.19 7.685 34.53 -28.96 400 -75.97 19.21 95.19 42.20 -30.61 26.18 -11.44 500 -80.68 23.06 11.53 103.74 48.65 -31.87 37.66 -13.72 112.02 26.81 16.08 600 -85.21 54.05 -32.79 49.33 -15.40 30.32 21.23 119.94 700 -89.62 58.61 -33.41 91.10 -16.69 26.87 127.46 so0 -93.88 33.58 62.51 -33.78 72.94 -17.71 32.93 900 -98.01 36.59 134.60 65.84 -33.91 84.82 -18.54 39.35 39.35 141.36 1000 -102.01 To retain internal consistency, some values are given to one more decimal place than is justified by the absolute accuracy. b The standard heat, standard free energy and common logarithm of the equilibrium constant for the formation of cyclopentanethiol by the reaction 5 C(c, graphite) 5 H2(g) 1/2 &(g) = C5HloS(g).
+
-
Q
+
+
positions one and two. If V12 is given the value 3.3 calorimetry,12 comparative ebulliometry'* and combustion The reported values are based on a molecual~rimet~ry .14 kcal. mole-l, as in the model compound ethane- clar weight of I-02.196 g. mole-' (1951 International Atomic thioljB the barrier height for pseudorotation is TABLE I11 predicted to be only 0.7 kcal. mole-'. As Pitzer and Donath's formula tends to predict too great OBSERVED AND C.ZLCGLATED MOLAL 'rHbRNODYNAMIC a barrier height, the value of zero selected to ROPERTI TIES OF CYCL(IPENTANETHIVL IP; T H E IDEAL GAS fit the calorimet>ricdat'a is in qualitative agreement, STATE with expectations. The value for the effect'ive Entropy. S o , Heat capacity, Cp', deg. -I----Y c a l . deg. moment of inertia for pseudorotation in cyclo- ----tal. Ohsd. Calcd. T , OK. Calcd. T ,OK. Obsd. pentanethiol, 18.9 X g. differs from the 390.20 33.74 33.71 360.62 91.78 91.7!) value in cyclo~nentane,~ 10.6 X g. cm.2, 381.41 93.58 93.58 415.20 35.76 35.78 in the direction expected because of the added mass 436.20 37.46 37 45 405.31 95.65 95.65 of the sulfur atom. The values of the tmo anhar458.20 39.11 39.15 monicit'y parameters correspond t'o very small 500 20 42.26 42 21 rontributions of' anharmonicity over the t'emperature range of caloriInetric measurements; even at (8) The vihratiorial and anharnionicity contributions were cornliuterl I OOOOK., t'he c.alculated cont'ributions are only by the Bureau of Mines Electronic Computer Service. Pittsburgh.
-
(4) .T. P. blcCiilliJiigli, H. 1,. fink?, W. N. Hiibhard, W. L). C ; < J O ~ , R . E. Pennington. .I. 14'. Mrsnerl?. and 0.Waddington, .I. Am. r b e m . Soc., 7 6 , 2661 (IU.541 ( 5 ) T. Kojrtna and .'l Ni.hik:i\w, J . P i i y s . Soc. Jnpa?i, l a , ti60
(1957). (6) J. P. McCiillough, D.
W. Scott, 1%. L. Finke, M. E:. Gross, K. D. Williamson, R . E. Penninabon, G. Waddington and H. SI.Hiiffman, J . Am. Chem. Soc., 74, 2601 (1952). (7) J. P. IllcCullough, R. E. Pennington, J. C . Smith. I. .4. Hossenloyp and G. Waddington, i b i d . , 81, 5880 (1959).
--I------
Pa.; the contributions of internal rotation were computed by Denver Electronic Computing Service, Inc., hy tv;o-way curvilinear interuolation in tables of K. S. Pitzer and W. D. Gwinn, J. C h e m . Phva.. 10, 428 (1942). (9) D. D. Wagman, T . E. Elpatrick, W. .T. Taylor, K. F. T'itaetand F. D. Rossini, J . Reseawh Wall. Bur. Standards, 34, 143 (194*i). (10) W. H. Evans and D. D. Wngman, zhid., 49, 141 (1952). (11) H. M.Huffman, Chem. Rers., 40, 1 (1947): H. &I. Huffman. S. S. Todd and G. D. Oliver, J. dm. Chem. Soc.. 71, 584 (1949): D. W. Scott, D. R. Douslin, hl. E. Gross, G. D. Oliyer and H. M. Huffman, ibid., 74, 883 (1952).
August, 1961
1427
CHEMICAL THERMODYNAMIC PI~OPERTIES OF CYCLOITSTANET 11 I O L
Weights's), the 1951 values of fundamental physical constants16 and the relations: 0" = 273.15"K." and 1 cal. = 4.184 j. (exactly). Measurements of temperature were made with platlnum resistance thermometers calibrated in terms of the International Temperature Scalela between 90 and 500°K. and the provisional scale'g of the National Bureau of Standards between 11 and 90°K. All electrical and mass measurements were referred to standard devices calibrated at the National Bureau of Standards. The energy equivalent of the combustion calorimetric system, &(Calor.), was determined by combustion of benzoic acid (SBS Sample 39 g. certified to evolve 26.4338 i 0.0026 kj. (6317.83 i 0.62 cal.)/g. mass under certificate conditions). Material.-The sample of cyclopentanethiol used for low temperature calorimetry, comparative ebulliometry and combustion calorimetry was part of the Standard Sample of Organic Sulfur Compound API-USBM 32, prepared a t the Laramie (Wyo.) Petroleum Research Center of the Bureau of Mines. The purity, determined by calorimetric studies of melting point as a function of fraction melted, was 99.99 i 0.01 mole Yo. A sample of slightly lower purity was used for vapor flow calorimetry. Heat Capacity in the Solid and Liquid States.-Low temperature calorimetric measurements were made with 53.243 g. of sample sealed in a platinum calorimeter with helium (35 mm. a t room temperature) as exchange gas to promote thermal equilibration. The observed values of heat capacity, Csatd,are listed in Table IV. Above 30"K., the accuracy uncertainty is estimated to be no greater than 0.270. Two distinct polymorphic forms of crystalline cyclopentanethiol were obtained and studied calorimetrically. Crystallization after cooling from room temperature gave a metastable form; it could be studied only below about 140°K. because it transformed rapidly to a stable form above that temperature. If the stable crystals were melted and the liquid heated no more than 20" above the melting point, stable crystals were obtained upon recrystallization. However, if the liquid was heated to 80" or more above the melting point, metastable crystals were obtained upon recrystallization. The heat capacity of the metastable crystals is greater than that of the stable crystals a t low temperatures, but above about 115'K. the heat capacity of the stable crystals is greater. A metastable form with lower heat capacity than a stable form is unusual. If the differences between the two crystalline forms are primarily in the orientation of the thiol groups in the crystal lattice, the observed differences in heat capacity can be explained qualitatively as effects of differences in crystal binding and in barriers to rotation of the thiol groups. The stable crystals are likely to be more compact and have an appreciably higher effective barrier for internal rotation, or oscillation, of the thiol group than the metastable crystals. Approximate calculations show that a reasonable difference in thiol barrier height would cause a significantly more rapid rise in heat capacity for the stable crystals in the region where the curves cross. The heat capacity of the liquid goes through a minimum about 30" above the melting point. From 162 to 366°K. the observed heat capacity of the liquid is represented with (12) G. Waddington. S. P. Todd and H. 31. Huffmsn, ibid., 69, 22 (1947); J. P. McCullough. I). W. Scott, R. E. Penninyton, I. A. Hossenlopp and G. Waddington, ibid., '76, 4791 (1954). (13) G. Waddington, .J. W. Knowlton, D. W. Scott, G. D. Olivrr, 8. P. Todd, W. S . Hiihhard, .J. C. Smith and H. M. FIiiffinan. h i d . , 71, 797 (1949). (14) W. N. Huhhard, C. Katz and G. Waddinaton, .I. I'hus. Chem., 68, 142 (1954). (1.5) E. Wichem, .J. d m . ('hem. Sor.. 74, 2447 (1952). (16) F. D. Rnssini, F. T. Gucker, Jr., H. L. .Johnstorr, I,. Paiiliiiy and G. W. Vinal, (bad., 74, 2699 (1952). (17) Borne of the results originally were computed with constants and temperal,ures in terms of the relation 0' = 273.16'K. Only results affected significantly b y the new definition of the absolute temperature scale [H. F. Ptimson. A m . J . Phys., 28, 614 (1955)l were recslculsted. Therefore, numerical inconsistencies, niuch smaller than the accuracy uncertainty, may he noted in some of the reported data. (18) 11. F. Stinison, J . Revearch Natl. BUT.,Standards. 42, 209 (1949). (19) H. J. Hose and F.G. Brickwedde, ibid., 22, 351 (1939).
TABLE
THE MOLAL
Iv
HE.4T CAPACITY OF
CYCLOPEXTANETHIOL
iN
C ~ DEG.-' L T,
CBrtdb
T , OK
a
Caatd
T , OK."
Csntdb
58.26 11.900 106 17 17 962 Stable Crystals 63.66 12.741 112 11 18 810 11.84 0.845 69.65 13.572 113 13 18 945 11.98 0.871 75.94 14.396 118 28 19 761 13.14 1.115 82.33 15.211 118 82 19 818 13.43 1.174 84.65 15.526 124 45 20 716 14.49 1.440 88.39 16.012 124 53 20 734 14.96 1,551 80.79 16.173 127 54 21 267 15.87 1.793 93.81 16 636 130 13 21 713 16.67 2,010 95.06 16.778 130 26 21 722 17.40 2 204 99.21 17 269 130 71 21 801 18,54 2.524 100 99 17.474 131 23 21 906 19.13 2.693 107.22 18.288 132 41 22 123 20.40 3.063 107.70 18.281 132 71 22 177 20.94 3.217 113.54 19.033 135 77 22 738 22.31 3.637 119.63 19 872 135 97 22 753 22,82 3.774 121.98 20.173 136 03 22 789 24.49 4.278 125 74 20.784 136 25 22 841 25.13 4.468 126.83 20,935 137 71 23 108 27.04 5.021 132.31 21.751 138 02 23 202 27.96 5.278 137.23 22.705' 141 09 23 770 29.92 5.816 Liquid 141 96 23 972 33.12 6.660 162.49 35.625 143 42 24 265" 36.60 7.516 40.32 8.344 Metastable Crystals 166 19 35.529 166.72 35.517 12 5.5 1.031 44.46 9.177 170.62 35.479 12 76 1 081 49.10 10.021 172 87 35.437 13 74 1.322 53.78 10.826 180.49 35.387 13.92 1.359 54.12 10.883 186.06 35.365 15 19 1.695 54.72 10.989 188.56 35.3811 15.33 1.731 38.55 11.590 196.09 35.421 16.76 2.138 59.23 11.693 206.24 35.530 16 87 2.169 63.84 12.376 216.85 35.755 18 50 2.653 64.26 12.446 227.38 36.041 18.60 2.676 69.23 13.115 237.80 36.390 20 26 3.184 69.41 13.142 248.12 36.815 20 34 3.202 74.74 13.835 258.31 37.271 22 19 3.770 74.81 13,841 268.86 37.805 22 27 3.793 80.27 14.557 279.77 38.415 24 46 4,470 80.58 14.599 290.51 39.020 24 58 4.513 84,54 15,125 301.10 39.682 27 07 5.246 85.87 15.290 302.62 39. 780 27.36 5.328 86.31 15.365 312.95 40.443 30.37 6.173 89 57 15.828 323.59 41.168 33 80 7,073 91.55 16.069 334.5% 41 ,901 37.71 8.033 92.32 16.154 345 38 42 682 41 71 8.906 95.15 16 513 356 07 43,444 46 18 I1.787 96.08 16.739 :366.19 44.1% 51 40 LO. 770 100.51 17.20'2 53.67 11.150 102.71 17.409 n T is the mean temperature of each heat capacity measrlrement. b C&d. is the heat capacity of the condensed phase a t saturstlon pressure. c\'a,'alues of Castd for both stable and mctmtable crystals are not corrected for the effect of premelting. a maximum deviation of 0.08% by the empirical equation CsSt8i(liq)= 55.24I) - 0.24225T 8.8181 X 10-4T2 - 8.2702 X 10-"T3, cal. deg.-' mole-' (1) Heats and Temperatures of Fusion and Transition.Five determinations of the heat of fusion, AHm, of the stable crystals gave the average value 1871.6 z!= 0.6 cal. mole-' a t the triple point, 155.39"K.; the indicated uncertainty is the maximum deviation from the mean. Measured heat effects for the other two transformations amonr: the three condensed phases also were referred to 155.39"K
+
BERG,HOSSENLOPP, OSBORN,DOUSLIN AND MCCULLOUQH
1428
by use of appropriate heat capacity data. From one enthalpy measurement over the region 102-162"K., AHl65.89 for the transformation, metastable crystals 4 liquid, was found to be 1764 cal. mole-'. From an experiment in which the change from metastable to stable form was allowed to go to completion under adiabatic conditions, A H M . , for ~ the transformation, metastable crystals 4 stable crystals, was found to be -108 cal. mole-'. The sum, 1764 $- 108 := 1872 cal. mole-', agrees exactly with the directly measured heat of fusion of the stable crystals. The results of duplicate studies of melting temperature, Tob&., as a function of fraction of total sample melted, F, for the stable crystals, are combined in Table V. Also listed in Table V are values obtained for the triple point temperature, TT.P., the mole fraction impurity in the sample, N2*, and the cryoscopic constants,% A = AHm/ R T T . ~and . ~ B = l / T ~ . p . ACrn/aAHm, calculated from the observed values of TT.P., AHm, and ACm (9.18 cal. deg.-l mole-').
-
TABLE V CYCLOPEEJTANETHIOL: MELTINQPOINT SUMMARY TT.P.= 155.39 2z 0.05'K.; Nz* = AP(TT.P.- Tobsd.) = 0.OOO:l f 0.0001; A = 0.03900 deg. -1; B = 0.00398 deg. Series
-l
Melted,
%
Tobed.
1/F
I 11 I I1 I I1 I I1 I
OK.
155.3793 .3775 .3819 .3810 .3825 .3827 .3836 ,3832 .3847 .3843 .384" 155.387"
9.81 10.19 9.89 10.11 23.64 4.230 3.871 25.83 2.143 46.67 1.966 50.87 65.09 1.536 71.34 1.402 83.51 1.197 1.089 I1 91.82 100.00 1 .000 0 Pure Visual curvilinear extrapolation.
The melting point of the metastable crystals could not be determined directly, but it was calculated to be 151.6"K. by finding the temperature a t which the free energy difference between metastable crystals and liquid is zero. The calculation amimes no residual entropy is retained by either crystalline form a t very low temperatures. The heat of fusion of metastable crystals a t 151.6"K. is 1724 cal. mole-'. The calculated melting point is only 3.8" below the melting point of the stable crystals, a reasonable difference for two polymorphic forms. Similar free energy calculations show that equilibrium between the two polymorphic forms is not experimentally realizable because the extrapolated transition temperature is well above the melting points. Thermodynamic Properties in the Solid and Liquid States.-Values of the thermodynamic properties of the stable crystals and liquid a t selected temperahres between 10 and 370'K. are given in Table VI. The values at 10°K. were computed. from a Debye function for 5.5 degrees of freedom with 0 = 118.7'; these parameters were evaluated from the heat capacity data between 12 and 21'K. (For the entropy caiculations for the metastable form, a Debye function for 5.5 degrees of freedom and 0 = 116.1' was used.) Corrections for the effect of premelting have been applied to the "smoothed" data in Table VI. Vapor Pressure.-Observed values of vapor pressure, determined by comparative ebulliometry with water as the reference substance, are listed in Table VII. At one atmosphere of pressure the ebullition temperature waa 0.002' higher than the condensation temperature. The Antoine and Cox equations selected to represent the results are log p =: 6.91375 - 1387.803/(t 211.952) (2) 106: ( p / 7 6 0 ) A ( l - 405.315/2') ( 3) log A = 0.850222 - 6.6386 x 1O-'T 5.8136 X 10-'T2 i=.
+ +
(20) A. R. G l a ~ g o w ,A. J. Streiff and F. D . Rossini, J . Research NaU. Bur, Standards, 56, 355 (1045).
Vol. 65
TABLE VI THE MOLALTHERMODYNAMIC PROPERTIES OF CYCLOPENTANETEIOL IN THE SOLID AND LIQUIDSTATES^ -(hatd
- H cal. Oo)/T, deg. -1
10 15 20 25 30 35 40 45 50
60 70 80 90 100 110 120 130 140 150 155.39
0.042 .142 .321 .574 .889 1.253 1.653 2.079 2.522 3.440 4.377 5.317 6.248 7.171 8.081 8.980 9.868 10,749 11.625 12.096
(Hmtd
-
H o d T, c 1 deg. -1
- Hoe, eal.
H.atd
Crystals 0.127 1.269 .416 6.236 .871 17.419 1.433 35.83 2.051 61.52 2.685 93.96 3.314 132.56 3.922 176.50 4.503 225.14 5.588 335.2 6.580 460.5 7.491 599.3 8.346 751.1 916.0 9.160 9.946 1094.1 10,721 1286.5 11.499 1494.8 12,293 1720.9 13.110 1966.5 13.561 2107.3
Sutd.
Caatd,
cal. deg. -1
cal. deg. -3
0.169 .558 1.192 2.007 2.940 3.938 4.967 6.001 7.025 9.028 10.957 12.808 14.594 16.331 18.027 19.701 21.367 23.042 24.735 25.657
0.505 1.560 2.943 4.428 5.831 7.127 8.283 9.274 10.172 11.807 13.214 14.524 15.844 17.133 18.504 20.009 21.680 23.569 25.542 26.616
Liquid 155.39 12.096 25.605 3978.9 37.701 35.798 160 12.848 25.896 4143 38.74 35.68 170 14.435 26.465 4499 40.90 35.47 I80 15.962 26.963 4853 42.92 35.38 190 17.432 27.406 5207 44.83 35.38 200 18.849 27.806 5561 46.65 35.45 210 20.214 28.174 5916 48.38 35.60 220 21.533 28.516 6273 50.04 35.83 230 22.807 28.841 6633 51.64 36.12 240 24.042 29.151 6996 53.19 36.47 250 25.238 29.452 7363 54.69 36.89 260 26.399 29.747 7734 56.14 37.35 270 27.52 30.03 8110 57.56 37.86 273.15 27.87 30.13 8230 58.00 38.03 58.95 38.42 8491 280 28.62 30.32 8878 60.31 38.99 29.69 30.61 290 9198 61.39 39.41) 298.15 30.54 30.85 9271 81.64 39.61 300 30.73 30.90 9671 62.95 40.25 310 31.75 31.19 64.24 40.92 10076 320 32.75 31.49 65.50 41.59 330 33.72 31.78 10489 66.76 42.30 340 34.67 32.08 10908 67.99 43.00 350 35.61 32.38 11335 69.21 43.72 360 36.52 32.69 11769 70.42 44.45 370 37.42 33.00 12200 0 The values tabulated are the free energy function, h m t content function, heat content, entropy and heat capwity of the condensed phases a t saturation pressure. In these equations, p is in mm., t is in "C. and T is in "K. Observed and calculated vapor pressure for both equations are compared in Table VII. The normal boiling point calculated from either equation is 132.17' (405.32 K.). Heat of Vaporization, Vapor Heat Capacity and Effects of Gas Imperfection.-The experimental values of the heat of vaporization and vapor heat capacity are given in Tables VI11 and IX. The estimated accuracy uncertainty of the values of AHv and C,' are 0.1 and 0.2'%, respectively. The heat of vaporization may be represented by the empirical equation
August, 1961
CHEMICAL THERMODYNAMIC PROPERTIES OF CYCLOPENTANETHIOL
TABLE VI1 VAPORPRESSURE OF CYCLOPENTANETHIOL Boiling point, OC. CyeloWater pentanethiol
-
p(obsd.)a mm.
p(obsd.1 p(calc.), mm. Antoine cox eq. 2 eq. 3
80.874 149.41 -0.01 -0.01 87.107 187.57 .01 -00 93.390 233.72 .01 .03 99.729 289.13 .01 .00 106.113 355.22 .01 .Ol 112.548 433.56 -04 .04 119.037 525.86 .02 .oo 125.577 633.99 .01 .03 132.165 100 760.00 00 .00 105 138.806 906.06 $02 * 00 110 145.501 1074.6 .I .o 115 152.245 1268.0 .1 .1 120 159.040 1489.1 .1 .o 125 165.887 1740.8 .o .o 130 172.783 2026.0 .2 .o From the vapor pressure data for water given by N. S. Oshorne, H. F. Stimson and D. C. Ginnings, J . Research Natl. Bur. Standards, 23,261 (1939). 60.000 65 70 75 80 85 90 95
+ -
+
+
. -
-
+
1429
heat of vaporization was calculated, A H Z I ' ~=~ 9.93 , ~ ~ kcal. mole-'. Entropy in the Ideal Gas State.-The entropy in the ideal gas state a t 1 atm. pressure was calculated as shown in Table X
.
TABLE X THE MOLALENTROPY OF CYCLOPENTANETHIOL IN THE IDEAL GASEOUS STATEIN CAL.DEG.-' T, "K 360.62 381.41 405.31 Seatd(lis.) 69,296" 71. 790b 74. 58ga AHv/T 26.151 23.024 20.831 s* Sa 0.090 0.144 0.229 R In Pd -2.755 -1.377 0.000
-
- -
So(obsd.)
__
f 0. 206
91.78 93.58 95.65 " B y interpolation in Table VI. b Extrapolated by use of ey. 1. The entropy in the ideal gas state less t h a t in the real gas state, calculated from eq. 5. d Entropy of compression, calculated from eq. 3. e Estimated accuracy uncertainty.
Heat of Combustion and Formation.-A typical determination of the heat of combustion of cyclopentanethiol is summarized in Table XI. Except m noted, the symbols and abbreviations are those of Hubbard, Scott and Waddington.22 S i determinations gave the following values of AEc"/M: -9117.82, -9117.15, -9119.75, -9118.52, TABLE VI11 -9119.67 and -9117.52 cal. g.-'. The average value THE MOLALHEATOF VAPORIZATION AND SECOND VIRIAL with the standard deviation of the mean is -9118.41 f 0.45 cal. g.-l. The values of AEc"/M apply to the followOF CYCLOPENTANETHIOL COEFFICIENT ing idealiied combustion reaction a t 298.15'K. For this B, CC. T,OK. P,atm. AHv, cal. Obsd. Ca1cd.a C d L S (lis) 90dd 71Hz0 ( l i d 360.62 0.2500 9070 f 2b -1674 -1594 = 5c02(g) HzS04.75H20(liq) 381.41 0.5000 8782 f 4b -1442 -1399 reaction, the ex erimental value of A E c o z g s .is~ ~-931.87 -1212 -1234 405.31 1.0000 8443 f 4* f 0.15 kcal. mofe-l and AHc0298.15 is -934.24 f 0.15 kcal. 0 Calculated from eq. 5 . b Maximum deviation from mole-'. The uncertainties are "uncertainty intervals" the mean of three or more determinations. equal to twice the final "over-all" standard deviation.28 AHv = 13046 - 8.352 T 7.413 TABLE XI x 10-8T* cal. mole-' (360405°K.) (4) SUMMARYOF A TYPICAL COMBUSTIONCALORIMETRIC The effects of gas imperfection were correlated by the proEXPERIMENT WITH CYCLOPEKTANETHIOL~ cedure described in an earlier paper." The empirical equam' (cyclopentanethiol), g. 0.76935 tion for B , the second viria! coefficient in the equation of state, P V = RT(1 + B / V ) , is Atc = t t ti Atcorr., deg. 2.00103 B = -420 - 42.12 exp(1200/T)cc. mole-' - 7821 .63 &(Calor.)( Atc), ca,l. &(Cont.)(cal. -27.62 (360-500°K.) (5) AEipn.,cal. 1.35 "Observed" values of B and -T(dzB/dT2) = lim P40 m ' d e c o m p . ("01 f HNO*J, Gal. 10.64 (BCp/dP)T and those calculated from eq. 5 are compared 3.23 AB, con. to s t . states," cal. in Tables VI11 and IX. -m"AEc'/ilf (auxiliary oil), cal. 802.89 -m"'AEc'/M (fuse), cal. 15.81 TABLE IX
+
+
+
-
- -
THEMOLAL VAPOR HEATCAPACITY OF CYCLOPENTANETHIOL m'AEc"/M (cyclopentanethiol), cal. IN CAL.DEG.-' AEc"/M (cyclopentanethiol), cal. g.-l T,O K . C , (1.000atrn.) C , (0.500atrn.) C, (0.250atrn.) CPo(obsd.) -2'TB" fobsdJ5 -TB' (calcd.)*
415.20 436.20 458.20 500.20 36.459 37.955 39.518 42.487 34.176 36.084 33.952 35.927 37.578 39.208 42.313 33.74 35.76 37.46 39.11 42.26 0.84 0.65 0.46 0.38 0.22 0.88 0.63 0.48 0.37 0.24
= -'T'(deB/dTZ), Calculated from eq. 5. a
b
-TB"
390.20
cal. deg.-l mole-' atm.-'.
The heat of vaporization a t 298.15"K. was calculated
by extrapolation with eq. 4 (9.90 kcal. mole-'), by using the Clapeyron equation with eqs. 3 and 5 (9.90 kcal. mole-')
and by using a thermodynamic network with the thermodynamic functions of Table I1 (9.92 kcal. mole-'). The value from the thermodynamic network was selected as the most reliable. From this value and eq. 5, the standard (21) .I. P. MrColloiinh, H. I,. Finkr. J. F. Messerly, R . E. Penningt i n . I . A . I l ~ ~ v 1 1 1 u:id p ~ ~i;. Wsddinyton, J . Am. Cheni. Soc.. 17,
G 1 1 9 (12.55).
- 7015.33
-9118.52 Auxiliary data: &(Calor.) = 3908.8 c,al. deg.-*; TI(Bomb) = 0.347 1.; AEc"/M (auxiliary oil) = -1OBS3.7 cal. g.-l; AEc"/M(fuse) = -3923 cal. g.-I; physical roperties a t 25" of cyclopentancthiol, p = 0.95048 e . ml.-I, fhE/bP)T = -0.0075 cal. g.-1 atm.-1, C, = 0.386 cal. deg.-l g.-l. Ei(Cont.)(ti - 25") +Gf(Cont.)(25" - Lr AkOrr.). CItems 81-85, incl., 87-91, incl., 93 and 94 of the computation form of ref. 22. The derived results in Table XI1 were computed by use of the values of A H c O , AHv", Saatd,and Sofor cyclopentanethiol and literature values of the standard heat of formation of CO2(g),2&H20 (lis),' H2S04.75Hz0 [ -212.06 kcal. mole-'],% and S2(g)10 and of the standard entropy of grapha
+
(22) W. N . Hubbard, D. W. Scott and G. Waddington, "Experimental Thermochemistry," 2'. D. Roesini, Editor, Interscicnce Publishers, Inc., New York, N. Y.,1956,Chapter 5,PP. 75-128. (23) F. D. Rossini, ref. 22,Chapter 14,pp. 297-320. (24) E. J. Prosen, R . 6. Jessup and F. D. Rossini, J . Research Natl. RUT.Standards, 33, 447 (1944). ( 2 5 ) W , 1). C : ~ m l , .T. 1,. I.,zcina ani1 J. P. SlcCul!uug!i, J . .im. Chem. SOC.,82, 5 5 S 3 (1953j.
Vol. 65
JOHXP. ~ICCULLOUGH AND WILLIAM D. GOOD
1430
TARLE XI1 b301..41> THERMODYXAMIC PROPERTIES O F FORMATION O F CYC1,OPENTANETHIOL IT
Reference state
AHf",
Ref. state of sulfur
kcaf.
298.15"K.
LFP, kcal.
ASfO cal. de& -1
- 109.08 11.17 -21.35zk0.18 S (c, rhombic) - 84.10 13.65 -11.42 3 ~ 0 . 1 8 Gas S (c, rhombic:) - 103.73 4.00 -26.84h0.19 Gas Sdg) For the reaction: 5C(c, graphite) 5H*(g) S (c, rhombic) or l/&z(g) = CsHl~S(liq. or g). Liquid
a
+
+
ite,g hydrogen gas,Qrhombic sulfur,'O and diatomic sulfur gas,'O all a t 298.15"K.
KI 8.19 -10.01 - 3.00 log
-
Acknowledgment.-The help of Derek 21. Fairbrother and Thelma C. Kincheloe in some of the experimental work is gratefully acknowledged.
CORRELATION OF HEAT OF FORMATIOX DATA FOR ORGAKIC SULFUR COMPOUNDS' B Y JOHN P. MCCULLOUGH AND
~%71LLIAR.l D.
GOOD
Contribution nTo. 105 from the Thermodynamics Laboratory, Petroleum Research Center, Bureau of 3firzes, I'. S . Department of the Interior, Bartlesville, Oklahoma Reeeiaed April 3, 1961
The method of Allen2 was used to correlate unpublished and recently published Bureau of Mines results for the heats of formation of organic sulfur compounds. Six parameters were evaluated from data for 25 acyclic alkane thiols, sulfides and disulfides. With the inclusion of appropriate strain energies, the results for seven cyclic sulfur compounds also were correlated. For all 32 compounds, the average deviation between calculated and experimental values, 0.17 kcal. mole-', was a little lesri than the average experimental uncertainty interval, 0.22 kcal. mole-'. The correlation can be used to predict reliable vzlues of heat of formation for many other organic sulfur compounds.
Allen? recently described one of the most accurate methods of correlating and predicting heats of formation of organic compounds. Selecting appropriate values for thermochemical bond energies and using them as constant in all compounds, he evaluated a small number of interaction energy parameters for use in equation (1) for the heat of atomization of paraffin hydrocarbons AHa"zss16 =
J'CHECH 4-NccEcc
+ X%cc
- TPccc - S A ( 1)
where NCE and Nc,: are the number of C-H and C-C bonds in the molecule ECH and ECC are the C-H and C-C thermochemical bond energies (YCCC is the interaction energy for a pair of next-nearestr neighbor carbon atoms joined to a common carbon atom X is the number of such pairs pccc 1s a trigonal interaction energy involving three carbon atoms, each of which is a next-nearest neighbor of the other two T is the number of trigonal interactions A is the gauche-n-butane interaction energy3 S is the number of such interactions
This relationship is equivalent to assuming that the heat of formation of a paraffin hydrocarbon can be calculated by adding to the heat of formation of methane the appropriate number of methylene increments4 (assumed constant for all com(1) This investi.gation was part of American Petroleum Institute Research 'Project 48A on "The Production, Isolation and Purification of Sulfur Compounds and Measurement of their Properties," which the Bureau of hl.ines conducts a t Bartlesville, Okla., and Laramie. WcVyO.
( 2 ) T. I,. Allen, J . Chem. Phys., 11, 1039 (1959). (3) K. R. Pitzer, ibid., 8, 711 (1940). (4) W . B. Person and G . C . Pimentel, 3. Am. Chem. S o c . , 7 6 , 532 (1S531.
pounds) and appropriate interaction energy terms; that is, for C,HP,+~hydrocarbons A H ~ O Z S15S = AHf(CH*,g)
+ ( n - 1)[AHf0(CzH6,g)
- AHf"(CHa,g)] - X a c c c - TPccc + SA ( 2 ) For cyclic hydrocarbons, C,H2,, similar reasoning leads to the equation afozes
16
- n[AHfo(CtH6,g) - AHf"(CH4,g)I - Xaccc + TBCCC + 8-4+ E.
(3)
where E, is the strain energy of the cyclic molecule. Correlation for Organic Sulfur Compounds.Allen also determined some interaction energy terms for organic sulfur compounds, but not enough data were available to him for a thorough correlation. Nevertheless, the value he predicted for the heat of formation of methanethiol, -20.8 kcal. mole-l, is in excellent agreement with that recently determined experimentally in this Laboratory, -20.88 kcal. mole-' (both values for formatioil a t 298.1EioE
