PYRROLE : CHEMICAL THERMODYNAMIC PROPERTIES
2263
Pyrrole: Chemical Thermodynamic Properties'
by D. W. Scott, W. T. Berg, I. A. Hossenlopp, W. N. Hubbard, J. F. Messerly, S. S. Todd, D. R. Douslin, J. P. McCullough, and G. Waddington Contribution No. l.@ from the Thermodymmks Laboratory of the Bartlemille Petroleum Research Center, Bureau of Mines, U.S. Department of the Interior, Bartlemille, Oklahoma Y4003 (Received December 67, 1966)
Experimental studies of pyrrole provided the following information : values of heat capacity for the solid (11-249.74"K, the triple point), for the liquid (249.74-365"K), and for the vapor (338-500°K); the temperature of a X-type transition of the solid; the enthalpy of fusion; thermodynamic properties for the solid and liquid ( M 0 0 " K ) ; the enthalpy of vaporization (362403°K) ; equation-of-state constants; vapor pressure (339439°K) ; and standard enthalpies of combustion and formation at 298.15"K. Association of pyrrole was revealed by an unusual linear variation of the heat capacity of the liquid with temperature and by other properties. The chemical thermodynamic properties in the ideal gas state (0-1500'K) were calculated by methods of statistical mechanics.
Introduction A comprehensive thermodynamic investigation of pyrrole HC-CH
I1 It
HC CH \/
N
I
U
was made as part of a continuing program of studies of organic nitrogen compounds. The experimental part of this investigation included measurements of thennodynamic properties by methods of low-temperature calorimetry, comparative ebulliometry, vapor flow calorimetry, and combustion calorimetry. One of the significant features of the experimental part of this research was the elaborate precautions necessary to protect pyrrole samples from even minute traces of atmospheric oxygen. The accurate experimental va.lues of vapor heat capacity and entropy were used to aid in interpreting the molecular spectra and to arrive at a vibrational assignment, which, in turn, was used in statistical thermodynamic calculations of the vaporstate chemical thermodynamic properties for the entire temperature range of likely interest.
Experimental Section and Results Physical Constants and Techniques. The reported
values are based on a molecular weight of 67.091 (1961 atomic weights2) and the relations: 0°C = 273.15"K and 1 cal = 4.184 joules (exactly). The 1963 values of the fundamental physical constantsS were used.4 Measurements of temperature were made with platinum resistance thermometers calibrated in terms of the international temperature scale6 between 90 and 500°K and the provisional scale6 of the National Bureau of standards below 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 (NBS sample 39 g). The basic experimental techniques used for pyrrole are as described in published descriptions of apparatus (1) This investigation was performed as part of American Petroleum Institute Research Project 52,"Nitrogen Constituents of Petroleum," which was conducted at the University of Kansas, Lawrence, Kan., and at the Bureau of Mines Research Centers in Laramie, Wyo., and Bartlesville, Okla. (2) A. E. Cameron and E. Wichers, J. Am. Chem. SOC.,84, 4175
(1962). (3) F.D.Rossini, J. Pure A p p l . Chem., 9, 453 (1964). (4) Some of the results originally were computed with previously
accepted atomic weights and physical constants and the relation: O°C = 273.16'K. Only results affected significantly were recalculated. Any remaining inconsistencies are much smaller than the accuracy uncertainty of the reported data. (5) H.F.Stimson, J. Res. Natl. Bur. Std., 42,209 (1949). (6) H.J. Hoge and F. G. Brickwedde, t%id., 22,351 (1939).
Volume 71, Number 7 Juna 1967
D. W. SCOTT, et al.
2264
and methods for low-temperature calorimetry,' vaporflow calorimetry,8 comparative ebulli~metry,~ and combustion calorimetry. lo The Material. The sample of pyrrole used for lowtemperature calorimetry, comparative ebulliometry, and combustion calorimetry was part of the Standard Sample of Organic Nitrogen Compound, API-USBM 52-2, prepared at the Bureau of Mines Research Center in Laramie, Wyo. The purity, as determined by a calorimetric study of melting point as a function of fraction melted, was 99.994 mole yo. For vapor flow calorimetry, which required a larger volume of material, a sample of slightly lower purity was used. Scrupulous care was taken to avoid exposure of the samples to atmospheric oxygen. The material was always transferred in a vacuum system and stored in vacuo in ampoules with break-off tips. In the vaporflow calorimetry and comparative ebulliometry, the material was blanketed with dry helium in which the concentration of oxygen had been reduced to the partsper-million range by passage over activated charcoal at liquid air temperature. The sample used for vapor-flow calorimetry eventually did darken slightly in spite of the precautions to exclude oxygen, but heatof-vaporization determinations with the darkened sample checked ones made earlier when the material was still "water white." The pyrrole was dried when necessary with calcium hydride. Heat Capacity in the Solid and Liquid States. The observed values of heat capacity, C,, are listed in Table I. Above 30"K, the accuracy uncertainty is estimated to be no greater than 0.2%. The heat capacity curve for the solid (C, vs. T ) shows a small A-type transition with peak near 65.5"K; the excess enthalpy relative to the "normal" curve is only about 3 cal mole-'. No hysteresis was observed in two series of measurements through this region. The heat capacity curve foi the liquid is unusual in being linear over the experimental range of more than 100" with no trace of the positive curvature observed for nearly all liquids. The following equation represents the observed values with a maximum deviation of 0.03 cal deg-' mole-'.
C, (liq) = 12.699
+ 0.059825T cal deg-l mole-'
T," OK
T." C,b
T,"
OK
CBb
O K
CSb
Crystals
11.48 12.10 12.41 13.33 13.46 14.60 14.62 16.16 16.23 17.77 18.30 19.68 20.56 21.90 22.72 24.26 25.03 26.82 27.62 29.47 30.45 33.48 35.12 37.00 38.64 41.09 42.54 45.60
0.587 0.670 0.708 0.859 0.875 1.076 1.083 1.365 1.377 1.679 1.786 2.067 2.242 2,525 2.699 3.033 3.199 3.567 3.736 4.107 4.301 4.896 5.205 5.551 5.826 6.238 6.456 6.929
46.89 49.82 51.68 52.88 53.81 55.93 56.48 58.36 60.21 61.88 62.74 63.27 64.38 65.33 66.28 67.25 67.56 68.44 69.87 71.83 72.73 74.99 78.19 83.88 84.81 89.53 89.80 95.70
256.15 28.05 256.79 28.08 264.17 28.504 264.88 28.549 271.96 28.961 273.56 29.050 274.03 29.080
281.35 284.49 290.95 295.13 300.77 301.19 305.20
7.109 7.522 7.766 7.924 8.039 8.306 8.364 8.599" 8.80lC 9.027" 9.158" 9.209" 9.377c 10.O3lc 9.378.: 9.472" 9.546c 9.470" 9.5Olc 9.57OC 9.616 9.728 9.902 10.207 10.254 10.476 10.507 10.733
102.16 108.53 114.74 120.80 126.73 132.54 138.69 145.18 149.28 155.12 161.40 168.12 174.68 181.09 187.35 193.47 199.47 205.34 208.10 213.16 215.32 219.25 222.33 225.67 229.16 231.93 235.80 238.03
10.995 11.250 11.501 11.752 11.996 12.248 12.519 12.820 13.014 13.319 13.651 14.032 14.419 14.821 15.231 15.674 16.104 16.541d 16.756d 17.168d 17.348d 17.685d 17.963d 18.263d 18.582d 18.860d 19.223d 19.439d
310.32 320.12 329.78 339.67 349.79 359.74
31.280 31.865 32.434 33.032 33.623 34.210
Liquid
29.518 29.710 30.086 30.351 30.679 30.729 30.957
T is the mean temperature of each heat capacity measurement. C. is the heat capacity of the condensed phase a t saturation pressure. The temperature increments and series number of measurements in the A region are given in order of increasing temperature (OK): 1.877,11; 1.826,11; 1.526,11; 4.879,I; 1.244,11; 0.977,11; 0.930,11; 0.971,11; 0.960,11; 4.762,I; 1.435,11; 1.420,11; 2.501,11. The temperature increment of each measurement for which premelting corrections were made is given in order of increasing temperature ("K): 5.801, 7.318, 5.683, 7.116, 6.498,6.920, 6.338, 6.735, 6.186, 6.551, 6.017.
(250-365'K)
(1)
The unusual heat capacity of the liquid is probably a manifestation of association. Enthalpy of Fusion, Triple Point Temperature, Cryoscopic Constants, and Purity of Sample. Values of the enthalpy of fusion, AHm, from three determinations were 1889.7, 1890.1, and 1890.1 cal mole-'. The Journal of Physical Chemistry
Table I: Molal Heat Capacity (cal deg-1)
(7) H. M. Huffman, Chem. Rev., 40, 1 (1947); H. M. Huffman, 8. S. Todd, and G. D. Oliver, J. Am. Chem. Soc., 71, 584 (1949); D. W. Scott, D. R. Douslin, M. E. Gross, G. D. Oliver, and H. M. Huffman, ibid., 74, 883 (1952). (8) G. Waddington, S. S. Todd, and H. M. Huffman, ibid., 69, 22 (1947); J. P. McCullough, D. W. Scott, R. E. Pennington, I. A. Hossenlopp, and G. Waddington, ibid., 76,4791 (1954).
PYRROLE : CHEMICAL THERMODYNAMIC PROPERTIES
2265
In these equations, p is in millimeters, t is in degrees Celsius, and T is in degrees Kelvin. The observed and calculated vapor pressures for both the Antoine and Cox equations are compared in Table IV. The comparison demonstrates clearly the superiority of the Cox equation in representing accurate vapor pressure data over a wide temperature r a n g e a suTable 11: Melting PoinL Summaryo periority that derives from the functional form as well F 1/F TF,OK Toalod** as the extra constant. The normal boiling point, evaluated from the experimental measurements, is 0.1084 9.225 249.6975 249.6992 0.2559 3.908 249.7201 249.7201 129.76"C (402.91"K). 0.4921 2 032 249.7277 249.7274 Enthalpy of Vaporization, Vapor Heat Capacity, 0.6989 1.431 249.7298 249.7298 Efects of Gas Imperfection. The experimental and 0.9057 1.104 249.7297 249.731 1 values of enthalpy of vaporization and vapor heat 1.0000 1,000 249.7315 capacity are given in Tables V and VI. The estimated (Pure) 249.7354 accuracy uncertainty of the values of AHv and C," a T t , = 249.74 i 0.05'K; NZ* = A F ( T~ TF) ~ = 0.00006 i are 0.1 and 0.2%, respectively. The enthalpy of 0,00005; A = 0.01525 deg-1; B = 0.00208 deg-1. Temperatures read from a straight line through a plot of TFus. 1 / ~ . vaporization may be represented by the empirical equation
The accepted value is 1890.0 i 0.3 cal mole-'. The results of a study of the melting temperature, TF, as a funct,ion of the fraction of total sample melted, F, are listed in Table 11. Also listed in Table I1 are
the values obtained for the triple point temperature, Tt,, the mole fraction of impurity in the sample, N2*, and the cryoscopic constants,'l A = AHm/RTtP2 and B = (l/Ttp) - (ACm/2AHm), calculated from the observed values of T,, AHm, and ACm (the heat capacity of the liquid minus that of the solid, 7.26 cal deg-l mole-'). Thermodynamic Properties in the Solid and Liquid States. Values of the thermodynamic properties for the condensed phases were computed from the calorimetric data for selected temperatures between 10 and 400°K. The results are given in Table 111. The values at 10°K were computed from a Debye function for 3.5 degrees of freedom with 0 = 111.6"; these constants were evaluated from the heat capacity data between 12 and 21'K. Extrapolation above the temperature range of the experimental measurements was done with eq 1. Corrections for the premelting effects of 0.00005 mole fraction of impurity have been applied to the "smoothed" data recorded in Table 111. Vapor Pressure. Observed values of vapor pressure are listed in Table IV. The condensation temperature of the sample was 0.002" lower than the ebullition temperature at 1 atm. The Antoine and Cox equations selected to represent the results are log p = 7.30296 - [1507.015/(t
+ 211.010)]
(2)
and log (p/760) = A [ l logA
=
- (402.914/T)]
0.870073 (5.43768 X 10-4)T
(3)
+ (4.16086 X 10-')T2
AHv = 12,734 - 0.97662T
-
(1.8971 X 10-2)T2cal mole-'
(362-403'K)
(4)
The effects of gas imperfection were correlated by the procedure described in an earlier paper.12 The empirical equation obtained for B, the second virial coefficient in the equation of state, P V = RT[1 (B/V) I, is
+
B = -536 - 2.160 exp(2300/T) cc mole-'
(334-500OK)
(5)
"Observed" values of B and -T(d2B/dT2) = lim PdO
( ~ C , / ~ P ) and T those calculated from eq 5 are compared in Tables V and VI. The enthalpy of vaporization and gas imperfection are both somewhat greater than for a normal unassociated substance of the same molecular weight and therefore indicate some association of pyrrole by hydrogen bonding in both liquid and vapor states.
(9) (a) A. G. Osborn and D. R. Douslin, J . Chem. Eng. Data, 11, 502 (1966); (b) G. Waddington, J. W. Knowlton, D. W. Scott, G. D. Oliver, 5. S. Todd, W. N. Hubbard, J. C. Smith, and H. M. Huffman, J. Am. Chem. SOC.,71, 797 (1949). (10) W. N. Hubbard, F. R. Frow, and G. Waddington, J . Phys. C h m . , 65, 1326 (1961). (11) A. R. Glasgow, A. J. Streiff, and F. D. Rossini, J . Rea. Natl. BUT.Std., 35, 355 (1945). (12) J. P.McCullough, H. L. Finke, J. F. Messerly, R. E. Pennington, I. A. Hossenlopp, and G. Waddington, J . A m . Chem. SOC.,77, 6119 (1955).
Volume 71, Number 7 June 1967
D. W. SCOTT, et aE.
2266
Table IV : Vapor Pressure
Table 111 : Molal Thermodynamic Properties for Condensed Phases" -(Uu
-
T, OK
Hoo)/T, cnl deg-1
10 15 20 25 30 35 40 45 50 60 64 65.5 66 70 80 90 100 110 120 130 140 150 160 170 180 190 200 210 220 230 240 249.74
0.033 0.109 0.241 0.425 0.654 0.917 1.207 1.517 1.840 2.513 2.787 2.891 2.925 3.203 3.891 4.566 5.223 5.859 6.475 7.071 7.650 8,210 8.755 9.286 9.805 10.311 :10.808 11.295 I1 ,776 12.248 12,717 13.168
-
(HB
H'Q)/T, cal deg-1
Hs
- H'o, oal
Crystals 0.097 0.970 0.310 4.655 0.639 12 785 1.042 26.047 1.486 44.56 1.945 68.06 2.405 96.19 2.854 128.44 3.288 164 41 4.103 246,19 4.412 282.36 4.532 296 86 4.572 301.7 4.851 339.5 5.462 436.9 5.995 539.5 6.465 646.5 6.887 757.5 7,272 872,6 7.630 991.8 7.967 1115.4 8.290 1243.5 8.604 1376.5 8.912 1515.0 1659,4 9.219 9.528 1810.2 9.840 1968.0 10.158 2133.1 10.483 2306.3 10.819 2488.3 11,164 2679.4 11,509 2874.4 Liquid 19.077 4764.4 19.086 4771 19.428 5051 19.766 5336 19.872 5428 20.101 5628 20.434 5925 20.704 6173 20.765 6229 21.093 6538 21.420 6854 21.745 7175 22.068 7503 22.390 7836 22.711 8175 23.030 8521 23.349 8872 23.666 9229 23.983 9593 I
I
~
SI,
C.,
oal deg-1
cal deg-1
0.130 0.419 0,880 1.467 2.140 2.862 3.612 4.371 5.128 6.616 7.199 7.423 7.497 8.054 9.353 10 561 11.688 12.746 13.747 14.701 15.617 16.500 17.359 18.198 19.024 19.839 20,648 21.453 22,259 23.067 23.881 24.677
0.385 1.145 2.124 3.189 4.208 5.178 6.057 6.832 7.543 8.787 9.314 10.023 9.426 9.508 9.999 10.496 10.906 11.308 11.713 12.134 12.577 13.048 13.572 14.136 14.748 15.418 16.140 16.902 17.745 18.653 19.562 20.447
32,245 27.707 13.168 249.74 32.27 13.18 27.720 250 33.37 13.94 28.265 260 34.44 14.68 28 853 270 14.91 34.78 273.15 29.042 35.50 15.40 29,451 280 36.55 16.11 30.04 290 37.39 16.68 298.15 30.53 37.58 16.81 30.64 300 38.59 '17.50 31.24 310 39.59 18.17 31.84 320 40.58 .L8.84 32.44 330 41.56 19.49 33.04 340 42.53 20.14 33.63 350 43.48 20.77 34.23 360 44.43 21.40 370 34.83 45.36 22.02 380 35.43 46.29 22.63 390 36.03 47.21 23.23 36.63 400 a The properties tabulated are the Gibbs energy function, enthalpy function, enthalpy content, entropy, and heat capacity of the condensed phases at saturation pressure.
The Journal of Phyaicol Chemistry
_ . "O-----
-BD. Ref compd"
19.061 21.720 24.388 27.068 29.757 32.460 60.000 65 70 75 80 85 90 95 100 105 110 115 120 125 130
Pyrrole
p(obsd),b mm
Antoine eq 2
cox eq 3
65.671 68.522 71.374 74.233 77.098 79.970 82.847 88.622 94.422 100,244 106.096 111,972 117,875 123,806 129,764 135.753 141.768 147.812 153,884 159.984 166 109
71.87 81.64 92.52 104.63 118.06 132.95 149.41 187.57 233.72 289.13 355.22 433.56 525.86 633.99 760.00 906.06 1074.6 1268.0 1489.1 1740.8 2026.0
$0.06 +0.03 f 0.01 -0.01 -0.03 -0.05 -0.06 -0.11 -0.12 -0.08 -0.05 $0.03 f O . 13 $0. 22 $0.32 $0.31 $0.3 $0. 1 -0.1 -0.4 -0.9
$0.01 0.00
I
0.00 $0.01 0.00 $0.01 $0.02 -0.01 -0.01 +O.Ol 0.00 $0.01 +O.Ol 0.00 0.00 -0.09 -0.1 -0.2 -0.2 -0.1 0.0
a The reference compound from 71.87 to 132.95 mm was pure benzene and that from 149.41 to 2026.0 mm was pure water. b From vapor pressure data for benzene IF. D. Rossini, K. S. Pitzer, R. L. Arnett, R. M. Braun, and G. C. Pimentel, "Selected Values of Physical and Thermodynamic Properties of Hydrccarbons and Related Compounds," Carnegie Press, Pittsburgh, Pa., 1953, Table 21k] and for water [N. S. Osborne, H. F. Stimson, and D. C. Ginnings, J . Res. Natl. Bur. Std., 23,261 (1939)l.
Table V : Molal Enthalpy of Vaporization and Second Virial Coefficient T, OK
p, atm
362.11 381.21 402.91
0.250 0.500 1,000
I
AHv,
cal
Obsd
9893 f 9" -1759 9605 f 5" -1456 9261 4 ~ 3 -1185 ~
B, c c - Calcdb
-1775 -1437 -1187
0 Maximum deviation from the mean of five or more determinations. b Calculated from eq 5.
The enthalpy of vaporization at 298.15'K was calculated by extrapolation with eq 4 (10.76 kcal mole-'), by use of the Clapeyron equation with eq 3 and 5 (10.78 kcal mole-'), and by use of a thermodynamic network with the thermodynamic properties of Tables I11 and XI11 (10.79 kcal mole-'). The value from the thermodynamic network was selected as the most reliable. From this value and eq 5 , the standard
PYRROLE : CHEMICAL THERMODYNAMIC PROPERTIES
Table VI:
2267
Mold Vapor Heat Capacity (cal deg-1) Temp, OK
7
388.20
C , (1.000 atm) C , (0.500 atm) C, (0.250 atm) CP"
- T(d2B/dTZ),' obsd
- T(d2B/dT2),*calcd
5
Units: cal deg-1 mole-' atm-1.
442.20
471.20
500.20
25,418
26.228
27.350
28.504
23.671 23.036 22.43
24.305 23.96
25.614 25.42
26.955 26.83
28.257 28.18
2.38 2.38
1.36 1.34
0.76 0.80
0.50 0.49
0.32 0.32
* Calculated from eq 5.
enthalpy of vaporization was calculated, AHvO~BB.~~, = 10.80 kcal mole-'. Entropy in the Ideal Gaseous State. The entropy in the ideal gaseous state a t 1 atm was calculated as shown in Table VII. Table VI1 : Molal Entropy in the Ideal Gas State (cal deg-1)
362.11
-
381.21
43.69d 27.32 0.13 -2.76 _ _ . 68.38
402.91
45.48d 25.20 0.18 -1.38 69.48
Enthalpy of Combustion and Formation. A typical determination of the enthalpy of combustion of pyrrole is summarized in Table VIII. The symbols and abbreviations are those of Hubbard, Scott, and Waddington, l a except as noted. Eleven determinations gave the following values of AEc"/M: -8369.18, -8371.08, -8370.54, -8370.98, -8371.97, -8372.22, -8370.66, -8372.50, -8371.39, -8370.24, and -8371.30 cal g-'. The average value with the standard deviation of the mean is -8371.10 0.29 cal g-'. The calorimetric apparatus and procedures were the same as used in earlier studies of pyridine.'O In seven experiments, the final contents of the bomb were analyzed for carbon dioxide to check the amount of reaction measured by the mass of sample. On the average, the amount of carbon dioxide was 99.98% of that predicted. The values of AEc"/M apply to the idealized combustion reaction at 298.15"K
*
Temp, OK--
c
Sdliq) AHv/T #(ideal) #(real). R In P b S'(obsd) ==! 0.15"
47.49d 22.98 0.23
0.00 70.70
5 The entropy in the ideal gas state minus that in the real gm state. b Entropy of compression, calculated from eq 3. c EstiBy interpolation in Table 111. mated accuracy uncertainty.
C&N(l)
m'(pyrrole), g
- t , - Aoor, deg
&(calor)(- Atc), cal &(cont)(- At(,), calb AEisn, cal A E ~ , ( H N O ~HNOZ),cal AE, cor to std states, talc -m"AEc'/M(auxiliary oil), cal m '"AEc'/.M(fuse), cal m'AEc'/M(pyrrole), cal
-
Uc'/M(pyrrole), cal g-1
-8371.08
-8445.91 -10.90 1.35 17.94 4.11 560.22 15.34 7857.85
-
5 Auxiliary data: & (calor) = 3892.61 f 0.15 cal deg-1; V(bomb) = 0.344 1.; AEc/M(auxilisry oil) = -10,984.8 cal g-l; AE'c"/M(fuse) = -3923 cal g-1; physical properties at 25': p = 0.96565 g ml-1, (dE/bP)T = -0.0074 cal g-1 atm-1, Cp = 0.455 cal dep-1 g-1. Ei(cont)(ti 25') &f(cont)(25' t t 4- At,,,). Items 81-85, inclusive, 87-90, inclusive, 93, and 94 of the computation form of ref 13.
-
+
+ S/2H20(1) + '/zN2(g)
For this reaction, the experimental value of AEc"298.16 is -561.63 f 0.08 kcal mole-' and of AHc02e8.16 is -562.07 f 0.08 kcal mole-'. The uncertainties listed are uncertainty intervals equal to twice the final "over-all" standard deviation. l4 The older value of Berthelot and Andrels for the "heat of combustion at constant pressure," 567.7 kcal mole-', has been used heretofore to calculate the resonance energy of pyrrole. The values of the resonance energy must be revised by about 6 kcal mole-' to accord with the accurate thermochemical data of this research.
0.93869 2.16973
+
+ 21/402(g) = 4co2(g)
Table VIII : Summary of a Typical Combustion Calorimetric Experiment" Ata = tt
7
415.20
-
(13) W. N. Hubbard, D. W. Scott, and G. Waddington, "Experimental Thermochemistry," F. D. Rossini, Ed., Interscience Publishers, Inc., New York, N.Y., 1956, Chapter 5, pp 75-128. (14) F. D.Rossini, ref 13, Chapter 14, pp 297-320. (15) Quoted by M. S. Kharasch, J . Res. Natl. Bur. Std., 2, 359 (1929).
Volume 71, Number 7 June 1967
D. W.SCOTT,et al.
The derived results in Table IX were computed by use of the values of AHc”, A H v O , Sa,and Sofor pyrrole and the literature values of the standard enthalpy of formation of COz(g) and HzO(l)16and of the standard entropy of graphite, hydrogen gas, and nitrogen gas,17 all at 298.15”K. Table IX: Derived Results for the Molal Chemical Thermodynamic Properties a t 298.15’K” ASS”,
kea1
cal deg-1
AQfO,
State
kcal
Kf
Liquid Gas
15.08 =t0.10 25.88&0,12
-68.95 -41.68
35.64 38.31
-26.14 -28.08
AHf’,
a For the reaction: 4C(c, graphite) C&“1 or 9).
LOP
+ ‘/ZHz(g) + l/ZNz(g) =
Table X : Observed Wavenumbers (cm-1) Liquid
560 618 649 710 733 840 867 880 1013 1048 1073 1144 1220 1235 1286 1382 1418 1467
Vapor
Appearance“
Interpretation
474
R(d), IR(C) R? R(d), IR(C) R(d) IR(C) R(d), IR(C)
Fundamental bz Fundamental a2 Fundamental bz Fundamental a2 Fundamental be Fundamental bz Fundamental bl Fundamental a1 2 X 474 = 948Al(vap) Fundamental bl Fundamental bl Fundamental a1 Fundamental a1 560 649 = 1209Ai(fiq) Fundamental a1 Fundamental bl Fundamental a1 Fundamental bl Fundamental a1 3 X 474 = 1422Bz(vap)? (Fundamental bt 733 840 = 1573Ai(liq) 721 826 = 1547Al(vap) 840 [869a~]= 1709&(liq) 826 [869a2] = 1695Bl(vap) 2 X [869a2] = 173881
601 721. 826 864 881 963 1016 1048 1074 -1144 12351 1287 138ti? 1422 1460? 1480
1530 1569
1545
1705
1693
1735
1742
3056 3104 3133 3410
+
+ + + +
(Region 1800-3000 cm-l omitted) 3058 R(-), I R 2 X 1530 = 3060A1 3115 IR ?b 312!3 R(p), I R Fundamental a1 (and bl) 3145 R(p), I R Fundamental a1 (and b1) 3531 R(p), I R Fundamental a1 (Region of higher wavenumbers omitted)
a Abbreviations: R, Raman; p, polarized; d, depolarized; IR, infrared; C, C-type band contour in vapor-state infrared spectrum indicative of bz species. a Possibly fundamental bl.
The Journal of Physical Chemaktry
Table
XI : Vibrational Assignment (cm-1) a1
bi
a1
881 1074 1144 1235 1382 1467 3129 3145 3531
864 1016 1048 1287 1422 1530 (3129) (3145)
618 710 869 bz
474 601 721 826
Chemical Thermodynamic Properties Thermodynamic functions for pyrrole were calculated by standard formulas of statistical thermodynamics. The vibrational assignment needed for that purpose was made by interpreting the available molecular spect,ral data with the aid of the calorimetric values of vapor heat capacity and entropy. The molecular spectra and vibrational assignment of pyrrole have been studied repeatedly. l8 The observed wavenumbers in the regions of interest are summarized in Table X, which also includes the interpretation based on the proposed assignment in Table XI. The selection rules, discussed in detail in several of the publications of ref 18, were used in making the assignment. Because of hydrogen bonding in liquid pyrrole, wavenumbers of some modes are significantly different in the liquid and vapor spectra, notably the modes of the bz species (16) D . D . Wagman, W. H. Evans, I. Halow, V. B. Parker, S. M. Bailey, and R. H. Schumm, “Selected Values of Chemical Thermodynamic Properties,” National Bureau of Standards Technical Note 270-1, U. S. Government Printing Office, Washington, D . C . , 1965. (17) “JANAF Thermochemical Tables,” The Dow Chemical Co., Midland, Mich. (18) W. W. Coblentr, “Investigation of Infra-red Spectra,” Part I, Carnegie Institution of Washington, Washington, D . C., 1905; S. Venkateswaren, Indian J. Phya., 5, 145 (1930); G. B. Bonino, R. Manzoni-Ansidei, and P. Pratesi, 2. Physik. Chem., BZZ, 21 (1933); G. B. Bonino and R. Manroni-Ansidei, Ric. Sci., 7, 510 (1936); A. Stern and K. Thalmayer, 2. Phyaik. Chem., B31, 403 (1936); A. W. Reitr, ibid., B33, 179 (1936); B38, 275 (1937); 0. Redlich and W. Stricks, MOnatUh., 68, 47 (1936); R. ManzoniAnsidei and M. Rolla, Atti. Accad. Nazl. Lincei, Rend., Claaae Sci. Fig. Mat. Nat., 27, 410 (1938); R. Manroni-Ansidei, Ric. Sci., 10, 328 (1939); R. C. Lord, Jr., and F. A. Miller, J. Chem. Phye., 10, 328 (1942) ; J. Lecomte, Bull. SOC.Chim. France, 415 (1946) ; H.M. Randall, R. G. Fowler, N. Fuson, and J. R. Dangl, “Infrared Determination of Organic Structures,” D. Van Nostrand Co., Inc., New York, N . Y., 1949, p 221; P.Mirone and C. Bonino, Jr., Atti. Accad. Nazl. Lincei, Rend., Claase Sci. Fis. Mat. Nut., 17, 250 (1964); P. Mirone, Gazz. Chim. Ital., 86, 165 (1956); American Petroleum Institute Research Project 44 at Texas A & M University, Catalog of Infrared Spectral Data, Serial No. 2014 and 2015; P. Mirone and G . Fabbri, Gazz. C h i n . Ital., 86, 1079 (1956); J. Morcillo and J. M. Orra, Analea Real SOC.Espan. Fig. Quim. (Madrid), B56, 231, 253 (1960); A. Kreutrberger and P. A. Kalter, J. Phya. Chem., 65, 624 (1961).
PYRROLE : CHEMICAL THERMODYNAMIC PROPERTIES
Table XI1 : Observed and Calculated Molal Properties in the Ideal Gas State
T,
Entropy, Sa, Y c a l deg-I-Calod Obsd
OK
362.11 381.21 402.91
68.38 69.48 70.70
68.34 69.45 70.70
T,OK
388.20 415.20 442.20 471.20 500.20
Heat capacity, C,", -cal deg--Obsd Cslcd
22.43 23.96 25.42 26.83 28.18
22.46 23.96 25.38 26.82 28'18
2269
band in the neighborhood of 1144 cm-l remain unexplained by the present assignment. (c) Some observed wavenumbers attributed to fundamentals have alternative explanations as sum combinations; for instance, 1235 cm-' could be the overtone of 618 cm-'. However, the present assignment is consistent with the calorimetric data, and it is unlikely that any revision of the assignment in the light of further mettroscopic studies or interpretations will have any very significant effect on the calculated thermodyu
u
Table XIII: Molal Thermodynamic Properties in the Ideal Gas State"
- H o a ) / T , ( H e- H o o ) / T , cal deg-1 cal deg -1
HO-H'o,
so
CPO,
cal deg-1
cal deg -1
AHfo,b kcal
AQf",b
kcal
0 -53.33 -54.22 -54.28 -57.62 -60.78 -63.82 -66.76 -69.60 -72.35 -75.00 -77.55 -80.01 -82.40 -84.70 -86.93
0 2.706 3.112 3.144 5.164 7.738 10.77 14.17 17.87 21.83 26.00 30.37 34.90 39.58 44.39 49.30
0 63.24 64.66 64.76 70.53 76.26 81.76 87.00 91.94 96.60 101.00 105.16 109.10 112.85 116.40 119.80
0 15.49 17.05 17.16 23.12 28.17 32.26 35.60 38.38 40.74 42.77 44.53 46.07 47.44 48.64 49.71
29.87 26.18 25.88 25.86 24.81 24.01 23.42 23.00 22.73 22.58 22.55 22.62 22.77 22.99 23.27 23.61
29.87 37.27 38.31 38.38 42.73 47.30 52.02 56.82 61.67 66.55 71.44 76.32 81.20 86.06 90.91 95.73
(Go
T,OK
0 273.15 298.15 300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500
0 9.906 10.44 10.48 12.91 15.48 17.94 20.24 22.34 24.25 26.00 27.61 29.09 30.45 31.70 32.87
kcal
Log KP
-m -29.82 -28.08 -27.96 -23.34 -20.68 -18.95 -17.74 -16.85 -16.16 -15.61 -15.16 -14.79 -14.47 -14.19 -13.95
The a To retain internal consistency, some values are given to one more decimal place than is justified by the absolute accuracy. standard enthalpy, Gibbs energy, and common logarithm of the equilibrium constant of formation by the reaction: 4C(c,graphite) '/zHz(g) '/zNz(g) C4HsN(g).
+
and the N-H stretching mode. Vapor-state values, characteristic of the unassociated molecule, are given in Table XI except for a few modes for which accurate vapor-state values are not available and for which the effect of hydrogen bonding on the wavenumber is probably insignificant. The difference in the liquidand vapor-state fundamentals was useful in identifying sum-combinations appearing for both states, including one used in obtaining the value of 869 cm-' for the unobserved highest az fundamental. Despite the wealth of molecular spectral data that has accumulated for pyrrole during the past 60 years, the vibrational assignment still cannot be made with complete certainty. Examples of remaining uncertainties are as follows. (a) The value of 618 cm-' for the lowest az fundamental comes from a very weak band reported m only one of the several investigations of the Raman spectrum. (b) Indications in the solution- and vapor-state infrared spectra of a second
+
namic functions, which are the primary concern of this research. To obtain improved agreement with the observed values of heat capacity at the higher end of the temperature range studied, an empirical anharmonicity functionlg with v = 1300 cm-' and Z = 1.6 cal deg-' mole-' was used. The contributions of this function to So and C,", in cal deg-' mole-', are only 0.0004 and 0.005 at 298.15"K and 0.03 and 0.16 at 500°K but increase to 1.14 and 2.27 at 1500°K. In actuality, there must be compensation between "positive" anharmonicity of the higher stretching modes and ('negative" anharmonicity of the lower bending modes. Evidence for extraordinary "negative" anharmonicity of the predominantly out-of-plane NH bending mode, 474 cm-', is seen not only in the value of its first over(19) R. E. Pennington and K. A. Kobe, J . Chem. Phys., 22, 1442 (1954).
Volume 71, Number 7 June 1967
D. W. SCOTT, et al.
2270
tone, which is 15 cm-1 higher than if the mode were harmonic, but also in the intensity of the overtone, which exceeds that of most of the fundamentals. Possibly the second overtone also has observable intensity; at least it is a plausible interpretation for the medium-intensity 1480-cm-' band observed only for the vapor. Similar effects are observed for the deuterium derivatives studied by Morcillo and Orza.'* In GDdNH, the N-H out-of-plane bending is more mixed among the bz modes, and not only the overtone 2 X 461 = 922 cm-1 (observed 936) but also the combinations 461 516 = 977 cm-I (observed 979) and 461 598 = 1059 cm-1 (observed 1054 cm-l) appear. For C4H4ND, the overtone of the N-D out-of-plane bending mode is masked by an intense fundamental, but for C4D4NDit appears as a moderately intense band at 740 cm-'. The empirical anharmonicity function, of course, is intended to include the smaller contributions from the other 23 modes in addition to the particularly large contributions from the N-H out-of-plane bending mode.
+
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The J O U Tof ~Physical Chemistry
Values of moments of inertia for calculating the contributions of rotation to the thermodynamic functions were taken from the work of Bak and co-workers.20 The calculated values of entropy and heat capacity are compared with the experimental values in Table XII. The calculated values of the thermodynamic functions for selected temperatures up to 1500°K are listed in columns 2-6 of Table XIII. The experimental value of ~ L H f O ~ 9 8 . 1 (Table 5 IX) and values of the thermodynamic functions of C(c, graphite), Hz(g), and Nz(g)17were used in computing values of AHJEO, AGf", and log Kf; they are listed in columns 7-9 of Table XIII.
Acknowledgment. The authors gratefully acknowledge the assistance of Thelma C. Kincheloe, Frankie R. Frow, and James P. Dawson in some of the experiments reported. (20) B. Bak, D. Chrietensen, L. Hansen, and J. RastrupAndersen, J. Chem. Phye., 24, 720 (1956).
