479G
bfCCULLOUG€I,
FINKE, SCOTT,
GROSS, MESSERLY, PEXNINGTON .IND ~~.lDDISCTON
Acknowledgments.-The cooperation of Comrnercial Solvents Corporation, Terre Haute, Indiana, donor of the sample of nitromethane, is gratefully acknowledged. The authors also wish to thank Messrs. C. J. Thompson and H. J. Coleman of this Station for their careful purification of the
1701.
76
sample of nitromethane used in this investigation. We are indebted to Prof. W. D. Gwinn, University of California, and Mr. E. J. Prosen, National Bureau of Standards, for making data available to US in advance of Publication. BARLTESVILLE, OKLA. _^__-_
[CONTRIBUTION NO.46
FROM THE
THERMODYXAMICS LABORATORY, PETROLEUM EXPERIMENT STATION, BUREAU O F MINES]
Experimental Thermodynamic Studies from 12 to 500 OK. The Chemical Thermodynamic Properties from 0 to 1000OK. BY J. P. MCCULLOUGH, H. L. FINKE, D. W. SCOTT, M. E. GROSS,J. F.MESSERLY, R. E. PENNINCTON AND 2-Propanethiol :
GUYWADDINGTON RECEIVED MAY24, 1954 Experimental studies were made of the thermodynamic properties of 2-propanethiol. The entropy of the liquid a t saturation pressure a t 298.16 OK., 55.82 cal. deg.-l mole-', was computed from calorimetric values of the heat capacity in the solid and liquid states (13 to 322'K.) and of the heats of transition and fusion (12.63 cal. mole-' a t 112.5OK. and 1371 cal. mole-' a t the triple point, 142.64"K., respectively). Results obtained for the heat capacity in the liquid state [ C B a t d ] . vapor pressure [ p ] ,heat of vaporization [ A H , ] , heat capacity in the ideal gaseous state [ C z ] , and second virial coefficient [ B = ( P V R T ) / P ]are represented by the following empirical equations: (1) C.,d(liq.) = 37.14 4.956 X 10-2T 1.481 X 10-4T2 - 238.3/T, cal. deg.-' mole-' (150 to 330'K.); (2) loglo p (mm.) = 6.87734-1113.895/(t 226.157), (10 to 86"); (3) 0.07564T - 3.167 X 1OwbTZ, A H , = 10,066 7.214 T - 9.864 X 10-aT*, cal. mole-' (290 to 326OK.); (4) Cz = 3.17 cal. deg.-' mole-' (317 to 487°K.); and (5) B = -318 - 32.8 exp (lOOO/T), cc. mole-' (290 to 487OK.). The entropy in the ideal gaseous state a t 298.16"K., 77.51 cal. deg.-' mole-', and the standard heat of formation from graphite, hydrogen and gaseous diatomic sulfur, -33.46 kcal. mole-' a t 298.1G°K., were computed from these data and heat of combustion data So and C,O a t selected temperatures reported elsewhere. Values of the functions (F" - H;)/T, ( H " - H ; ) / T , H" - Ho, to 1000OK. were calculated from spectroscopic and molecular structure information. The heights of the potential barriers hindering internal rotation required for these calculations were evaluated from the calorimetric entropy and vapor heat capacity data. Values of the heat, free energy and equilibrium constant of formation of 2-propanethiol were computed from the calculated thermodynamic functions and the experimental value of the heat of formation a t 298.16 O K .
-
-
As part of American Petroleum Institute Research Project 48A, this Laboratory is conducting studies of the thermodynamic properties of organic sulfur compounds that occur in crude petroleum or are encountered in refining processes. One of the most important types of sulfur compounds under investigation is the family of alkanethiols (mercaptans), and it is planned to determine the thermodynamic properties of key members of this family. The data obtained will provide a sound basis for the construction, by approximate statistical mechanical of relatively complete tables of the chemical thermodynamic properties of the entire family of alkanethiol~.~Toward this end, the properties of ethanethi01,~1-pentanethio15 and 2methyl-2-propanethioI6 have already been determined. This paper presents the results of detailed studies of the thermodynamic properties of 2-propanethiol, the first of the series of secondary alkanethiols. The closely integrated experimental and (1) This investigation 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 Mines conducts a t Bartlesville, Okla., and Latamie, Wyo. (2) E I . , (a) K. S. Pitzer and J. E. Kilpatrick, Chem. Reus., 39,435 (1946); J. E. Kilpatrick, E. J . Prosen, K. S. Pitzer and F. D. Rossini, J . Research Nal2. Bur. Standards, 36, 559 (1946). (3) The compilation and tabulation of selected values of the properties of organic sulfur compounds will be part of the program of American Petroleum Institute Research Project 44. (4) J. P. McCullough, D. W,Scott, H. L. Finke, M . E. Gross, K. D. Williamson, R . E . Pennington, Guy Waddington and H. M. Huffman, THIS JOURNAL, 74, 2801 (1952). (5) H. L. Finke, D. W. Scott, M. E. Gross, Guy Waddington and H. M. Huffman, ibid., 74, 2804 (1952). ( 6 ) J. P. McCullough, D. W. Scott, H. L. Finke, W. N. Hubbard. M. E. Gross, C. Katz, R. E. Pennington, J. F. Messerly and Guy Waddington. ibid., 76, 1818 (1953).
++
+
computational investigations will be discussed in the following order: (1) low-temperature calorimetric studies; (2) vapor pressure studies; (3) measurements of the heat of vaporization and vapor heat capacity; (4) determination of the heat of formation ; (5) calculation of thermodynamic functions from spectroscopic, molecular structure and calorimetric data. Experimental Physical Constants.-The 1961 International Atomic Weights' and the 1961 values of the fundamental physical constantss were used for all computations. The calorimetric data are based on a molecular weight of 76.160 for 2-propanethiol and the following definitions: 0' = 2i3.16'K.; 1 cal. = 4.1840 abs. j . = 4.1833 int. j . The Material.-The 2-propanethiol used was part of the Standard Sample of Sulfur Compound, API-USBM serial hTo. 11, prepared and purified a t the Laramie (Wyo.) Station of the Bureau of Mines. In calorimetric melting point studies to be described below, the material was found to contain 0.011 =t 0.003 mole yo liquid-soluble, solidinsoluble impurity. Before use in the experimental studies, the sample was dried, in the vapor phase, with anhydrous magnesium perchlorate and transfers to appropriate receivers were made by vacuum distillations. At no time in the handling of the material or in the experiments were the samples in contact with gases other than helium. The Heat Capacity in the Solid and Liquid States.-The low temperature themial properties of 2-propanethiol were measured in an adiabatic cryostat similar to that described by Ruehrwein and Huffman.9 About 0.6 mole of the compound was sealed in a cylindrical platinum calorimeter equipped with horizontal, perforated, heat-distributing disks of gold. A small amount of helium (about 30 mm. pressure a t room temperature) was put in the calorimeter to (7) Edward Wichers, ibid., 74, 2447 (1952). (8) F. D. Rossini, F. T. Gucker, Jr., H. L. Johnston, L. Pauling and G. W. Vinal, ibid., 74, 2699 (1952). (9) R. A. Ruehrwein and H. M. Huffman. i b i d . , 66, 1620 (1943).
Oct. 5, 1934
CHEMICAL
promote thermal equilibration a t low temperatures. The observed heat capacities a t saturation pressure, &td, of solid and liquid 2-propanethiol are recorded in Table I. The temperature increments used in the experiments were small enough that corrections for non-linear variation of C&d with T were unnecessary (the increments were approximately 10% of the absolute temperature below 50"K., 5 to 6' from 50°K. to the melting point, and 10' in the liquid region), The precision of the heat capacity measurements was usually within 0.1%; above 3O'K., the accuracy uncertainty of the values of Casushould not exceed 0.2%. The following empirical equation represents the heat capacity data for liquid 2-propanethiol in the temperature range, 150-330°K., with an average deviation of 0.01 and a maximum deviation of 0.04 cal. deg.-l mole-': Cs8td(liq.) = 37.14
+
- 4.956 X
10-zT 1.481 X 10-4T2 238.3/T, cal. deg.-1 mole-' (1)
TABLE I
Caatdb
Crystals I
T.
OK.
66.60 70.10 73.07 74.38 79.74 79.84 85.54 86.54 91.47 93.28 96.71 100.07 100.90 104.95 108 14 108.54 108.83 110.27 110.74
Caatd
11.333 11.740 12.104 12.266 12.942 12.959 13.728 13.860 14.513 14.751 15.222 15.709 15.831 16.471 16.994 17.083 17.138 17.539 17.618
of the equilibrium melting temperature as a function of the fraction of sample melted.'" The results of this study are presented in Table 11. The equilibrium melting temperatures, T,,b.d, were plotted against the reciprocal of the fraction melted, 1 / F . The triple point temperature, TT.P., was determined by linear extrapolation of these data to 1/F = 0. The mole fraction of total impurity in the sample, NZ, was calculated by the relationship N$/F = A(TT.P. Tobod),where A is the cryoscopic constant, AHfuaion/ RT$.p.. This procedure is based on the assumptions that ideal solutions are formed in the liquid phase and that the impurity is insoluble in the solid phase.
-
TABLE I1 2-PROPANETHIOL MELTINGP O I N T SUMMARY Heat of fusion, AHfuaion = 1371 cal. mole-'; triple point, T T . ~= . 142.64 i 0.05"K.; cryoscopic constant, A = (0.0339) deg.-'; impurity = 0.011 =t0.003 mole % Me1t ed ,
THE MOLALHEAT CAPACITY OF 2-PROPANETHIOL, CAL. DEG.-' T , OK.'
4797
THERMODYNAMIC PROPERTIES OF 2-PROPANETHIOL
T,OK. 125.43 127.67 132.09 133.15 138.40
Caatd
21.336 21.869 23.138 23.434 25.777"
0.986 12.89 1.034 13.07 1.309 14.25 1.409 14.62 Liquid 1.689 15.73 1.834 16.26 149.26 31.401 2.240 17.72 156.82 31.476 2.329 18.04 165.17 31.554 2.929 20.11 173.39 31.635 2.986 20.31 177.26 31.672 3.618 22.50 181.57 31.725 3.742 22.92 187.03 31.790 25.03 4.338 197.13 31.924 4 469 25.50 207.43 32.076 5.097 27.83 217.51 32.263 5.191 28.23 227.51 32.461 5.902 31.06 237.43 32.705 34.14 6.589 247.75 32.986 Crystals I1 7.263 37.57 248.98 33.014 7.916 41.23 8.560 114.06 19.196 257.97 33.282 45.37 115.85 19.497 258.45 33.293 9.237 50.07 9.841 116.79 19.656 268.79 33.634 54.65 55.31 9 931 118.47 19.933 279.95 34.052 55 48 118.69 19.965 290.98 34.469 9.946 301.86 34.895 60.44 10,571 119.26 20.027 61.23 10.678 122.19 20.631 312.27 35.333 66.20 11.292 125.26 21.293 321.63 35.764 T is the mean temperature of each heat capacity measurement. * Csstd is the heat capacity of the condensed phase under its own vapor pressure. The heat capacity data immediately below the melting point have not been corrected for the effects of hetero-phase premelting. I
The Isothermal Transition.-An isothermal transition involving an extremely small absorption of energy was observed to occur in crystalline 2-propanethiol a t about 112.5'K. Two measurements were made of the enthalpy change over a finite temperature interval that included the transition temperature. The heat of transition was determined from these results by subtraction of the energy absorbed non-isothermally, as computed from the heat capacity data. The mean of the two values obtained for the heat of transition was 12.63 f 0.03 cal. mole-'; the precision uncertainty given denotes the deviation of the experimental results from the mean. The Triple Point and Sample Purity.-The triple point and sample purity were determined in a calorimetric study
%
1/F
Obsd.
T,
OK.
Graph. b
13.09 7.64 142.6226 142.6 177 25.17 3.97 142.6319 142.6299 49.35 2.03" 142.6364" 142.6364 70.48 1.42" 142,6384" 142.6384 91.63 1.09" 142.6395" 142.6395 100.00 1.00 142.6398 0.00 142. 643lC Pure A straight line through these points was extrapolated to 1 / F = 0 to obtain the triple point temperature, T T . ~ . . Temperatures read from the straight line of footnote a; deviations from Tabsd indicate departure from assumed conditions. Triple point temperature. The Heat of Fusion.-The heat of fusion of 2-propanethiol was measured in the manner described for the heat of transition. For use in computation of the energy absorbed nonisothermally, the heat capacity data just below the melting point were corrected for the effect of hetero-phase premelting. The result of each of two direct measurements was 1371 cal. mole-', and the same value was computed from data obtained in the melting point study. The spread of the 3 values was 0.4 cal. molez1. The Thermodvnamic Properties of 2-Prouanethiol in the Solid and Liquid States.-values of the entropy, heat content and free energy function of 2-propanethiol in the solid and liquid states a t saturation pressure were computed from the thermal data presented in the foregoing sections. The results a t selected temperatures from 10 to 330°K. are presented in Table 111. These values were calculated by appropriate numerical integration of values of c&d read a t integral temperatures from a large scale plot of the data of Table I. Corrections for the effects of hetero-phase premelting have been applied to the data in Table 111. The Vapor Pressure.-The vapor pressure of 2-propanethiol from 11 to 86' was measured with the twine bulliometer system described in an earlier publication from this Laboratory.ll The ebulliometer described in ref. 11 has been modified by enclosing the heating element in a glass reentrant well so that samples of corrosive compounds come into contact with glass only. The boiling and condensation temperatures of water and 2-propanethiol were measured as both compounds boiled simultaneously a t the same pressure. The "observed" vapor pressures, presented in Table IV, were obtained from the vapor pressure data for water given by Osborne, Stimson and Ginnings.12 At both the beginning and end of the measurements, the difference in the boiling and condensation temperatures of 2-propanethiol was only 0.003' a t 760 mm. pressure. This small, constant difference is evidence that the sample was essentially free of impurity of different volatility and that no change in purity occurred during the experiments. An (10) S. S. Todd, G. D. Oliver and H . M. Huffman, THISJOURNAL, 69, 1519 (1947). (11) G. Waddington, J. W. Knowlton, D. W. Scott, G. D. Oliver, S. S. Todd, W. N. Hubbard, J. C. Smith and H. M. Huffman, ibid., 71, 797 (1949). (12) N. S. Osborne, H. F. Stimson and D. C. Ginnings, J . Rescurch N a L Bur. Standards. 13, 261 (1939).
4798
MCCULLOUGH, FINKE, SCOTT,GROSS,MESSERLY,PENNINGTON AND WADDINGTON Vol. 76
TABLE 111 THE MOLALTHERMODYXAMIC PROPERTIES O F 2-PROPAXETHIOL IN THE SOLID AXD LIQUID STATES" Caatd.
r , OK 10 12 211 25 30 35
40 45 50 60 70 80 90 100 110 112 5 112 5 120 130 140 142 64
deg. - 1
0.04 .14 .3 1 .52 . 86 1.22 1.60 2.01 2.42 3.28 4.14 5.01 5 85
6.70 7,52 7.73
7.73 8.35 9.18 10.03 10.24
Crystals I 0.12 1.22 ,40 5.92 .84 16.88 1.40 :35, 0 2 . orj (XI. 0 2.60 '31.1 3.18 127.3 3.73 l68,O 4.25 212.3 5.19 311.2 6.04 422.5 6.82 545.9 7.58 682.3 8.32 832.4 9.07 997.4 9.26 1042.0 Crystals I1 9.37 1054 10.01 1201 10.88 1414 11.81 1654 12.09 1724
cal. rieg. -1
ii. 1 ti
0.48
. 53
1 ,511 2.90 4,3s 5 . ti5
1 , lt5 1.93 2 . 8ti 3.82 4 78 ;i 74 .
ii.i ( i
7.71 8.51 6,67 9 . 2 3 8 . 4 7 10.52 10.18 11.73 11.83 12 98 13.43 14.32 15.02 15.70 16.59 17.41 16.99 18.25
17.10 18.36 20 06 21.84 22.33
18.93 20.21 22.45 25.86 26.87
Liquid 31.94 3 1 . 3 1 21 70 3095 10.24 33.52 31.42 22 17 3326 11.35 35,55 31.51 22 7 5 3610 12.80 3 7 .46 31.60 23 27 33956 14.19 39.27 31.71 1273 23 74 15.53 40.99 31.83 21 l h G90 16.83 42.62 31.96 24 54 1909 18.08 44.19 32.12 c5230 24 90 19.29 45. 69 32.31 25 24 5552 20.45 47.13 32. 52 5876 25 55 21.58 48.52 32.77 6202 25 84 22.68 49.86 38 04 6532 26 13 23.73 51.10 3-3.34 26 40 6863 24.76 52.48 33.68 26 66 7198 25.77 52,82 33.79 26 74 730j 26.08 53,66 34.05 7537 20 92 26.74 54.86 34.43 7880 27 17 27.69 55.82 34.74 8162 27 37 28.45 34,82 27 42 56. OR 8226 28.61 ?, 8,57fi 57.1s ?I!-33 27 66 29,52 X!x 1 58.31 : 3 5 . 69 27 $1 30.40 35.96 28 or, 9133 38.04 30.89 9290 59.41 36.15 28 13 3 1 , 2ii ,LiO Thc \ralues tabulated are the free ciiergh- fuiictioii, heat content function, heat content, entropy and heat cap:icit!of the condensed phases at saturation pressure. ', The normal boiling point.
142 64 150 160 170 180 190 200 210 220 230 240 250 260 270 273 16 280 290 298 16 ROO 310 :Eo .$.27 72" '1
Xntoine equation, eq. 2, was obtaiiied from the data of Table IV by- a least squares a d j u ~ t r n e n t . ' ~ log,, p(mm.) = 6.877:34- 1113,83O/(t + 226.1371 ( 2 j where t is in ' C . '\.slues of the vapor pressure computed from eq. 2 are given in the last colurnri of Table 111. Thr normal boiling poiiit from eq. 2 is 52.5fi". ( 1 3 ) C. B. Willinghani, W. J. Taylor, J . RI. Pignoccir Russini, J . Rescuich Nail. Bur. Siu,tdu7,ds, 36, 219 (1942).
iiii(I
1;. 1).
TABLE IV T H E1.APOR
PRESSURE O F 2 - P R O P A S E T H I O L Boiling poiiit, ' C . Pressures, mrn. Obsd. Ca1cd.G Water 2-Propanethiol
10.697 15.770 20.899 C r 26.071 10 80 31.282 85 36,536 90 41,833 I,r, 47.173 IIK) 52.558 105 57,985 110 63.41il 115 68,979 120 74.540 125 80 143 130 85. 795 Calculated from eq. 2. 60.000 65 70
149.41 187,57 233.72 289.13 355.22 433.56
149.44 187.53 233.71 289.15 355.23 433,5ij j25.85 684, 00 759.9s 9oii 00 1074.(i 12138. I 1489.2 1740.7
525,8fi
633 . 99
760. 01I 906. O f i 1074.6 1268.0 1489.1 1540.8 2026.0
2025,Y
The Heat of Vaporization.-The heat of vaporization and vapor heat capacity of 2-propanethiol were determined in the flow calorimeter system previously described.14 The glass vaporizer used differed from that described in ref. 14 in that the heating element and leads were enclosed in glass to prevent contact with the corrosive thiol. The tube shielding the heating element was wrapped with glass thread to promote steady ebullition. The results of triplicate determinations of the heat of vaporization a t each of three temperatures from 290 to 326°K. are recorded in Table 1;. The accuracy uncertainty of these data should not exceed 0.1%. The following empirical equation may be used for interpolation in the temperature range of the measurements AHv = 10,066 - 7.214T - 9.864 X 10-3T2, cal. mole-' (290-326°K.) (3) TABLE L' Tm ~ I O L X~ II ,E AOF T YAPORIZATIONASD GASIMPERFECTION OF 2-PROPASETHIOL 7', %.
p,n mm.
A H v , cal.
6oi,sd,
cc.
&ded,bCc.
-1356 -1343 7139 f 3c 290.41 200.0 -1180 -1176 6932 i 3 306.20 380.0 -1015 -1024 6670 f 3 325.72 760.0 Calculated from eq. 2. Calculated from cq. .i. c Maximum deviation of the experimental results from the mean. The Vapor Heat Capacity.-Lleasurements of the vapor heat capacity were made a t 2 or more pressures a t each of 5 temperatures between 317 and 449'K. and at one pressure a t 4 8 7 O E T . The results are listed in Table 1.1. From 317 to 449°K. values of the heat capacity in the ideal gaseous state, C: mere determined from the data a t finite pressures by linear extrapolations to zero pressure.14 T o determine C: at 487"K., the variation of C, with I' was estimated from the data a t lower temperatures. It i h believed that the accuracy uncertaiiity of the tabulatctl \-alucs of C z (ohsd.) i.; less t h x n 0.2570',. The folloning empirical equatioii represents the experimental values of C: within 0.02 cal. deg:-' mole-' Ctp = 3.17 0.07564T - 3.167r2, cal. deg.-' inole-' (317-487'K.) (4) ,4t 449 and 487'K., tests for thermal decomposition of the sample were made as described in an earlier paper.I5 KO effect of decomposition was detected Gas Imperfection and the Second Virial Coeficient.The second virial coeflicient B , in the equation of state P 'I/ = R 7' HP,mas evaluated a t 3 temperatures from the experi-
+
+ _____-_
(14) G. \Taddington,
S.5'. Todd a n d H . A I Iiuflman, THISJ O U R N A L ,
6 9 , 2 2 7 5 (1947).
(15) D . \V, Scott, H. L. Finke, J. P. >TcCullough, M. E.Gross, R.E . P a i n i n s t o n and Guy WaddingL
