680
SCOTT,HUBBARD, NESLERLY, TODD, €IOSSENLOPP, GOOD,DOUSLIN, AKD MCCULLOUGH
T’ol. 67
CHEMICAL THERMODYNAMIC PROPERTIES ,4KD INTERNAL ROTATION OF METHYLPYRIDINES. I. 2-METHYLPYRIDISE’ BY D. W. SCOTT, W. K. HUBBARD, J. F. MESSERLY, S. S. TODD, I. A. HOSSENLOPP, W. D. GOOD,D. R. DOUSLIN, AND J. P. MCCULLOUGH Contribution No. 191from the ThermodynamicsLaboratory of the Bartlesvdle Petroleum Research Center, Bureau of Mines, U.S. Department of the Interior, Bartlesville, Okla. Received September 19, 1969 Thermodynamic properties of 2-methylpyridine were measured, and the results were correlated by use of spectral and molecular-structure data to obtain values of the chemical thermodynamic properties in the ideal gas state (0 to 1500’K.). Internal rotation of the methyl group was found to be free or nearly so. Experimental studies provided the following information: values of heat capacity for the solid (12°K. to the triple point), liquid (triple point to 37O0K.), and the vapor (388 t o 500°K.); the triple-point temperature; the heat of fusion; thermodynamic functions for the solid and liquid (0 to 370°K.); heat of vaporization (359 to 403°K.); parameters of the equation of state; vapor pressure (353 to 442°K.); and the standard heat of formation a t 298.15”K.
Thermodynamic studies of methylpyridines are being made by the Bureau of Mines as part of continuing research on organic nitrogen compounds. Results for 2-methylpyridine (a-picoline) are reported in this paper; results for 3-methylpyridine @-picoline) are reported in the accompanying paper2 hereafter referred to as 11. The experimental work with 2-metliylpyridine consisted of low temperature calorimetry, vapor flow calorimetry, combustion calorimetry, and comparative ebulliometry ; the detailed results of this work are reported in the Experimental section. The experimental results were correlated by using spectral and molecular structure informat’ion and were used in calculating tables of chemical thermodynamic properties for the crystal, liquid, and ideal gas states. Two significant results were obtained in correlating the calorimetric data with spectral and molecular structure information. The first was an assignment of the fundamental vibrational frequencies of the 2-methylpyridine molecule, supported by accurate experimental values of the vapor heat capacity. The second was the observation that internal rotation of the methyl group is free or very nearly so. The calculations by methods of statistical mechanics will be discussed in the next section; for convenience, the calorimetric dat’a that were used are collected in Table I. TABLE I OBSEIZVEU AND CALCULATED THERMODYNAMIC PROPERTIES O F 2-METHYLPY RIDINE
T,’ K.
359.35 379.48 402.54
Entropy, So, cal. deg. -1 mole-’ Calcd. Obsd.
T,”K.
31.02 32.91 34.72 86.10 36.76 38.84 AHj’oy~s.i6(gas)= 23.65 5 0 . 2 1 kcal. mule-’ 82.66
84.28
82.80 84.20 86.05
388.25 413.20 438.20 468.20 500.20
Heat capaoity, Cpo, cal. deg.-i mole-’ Calcd. Obsd.
31.03 32.90 34.70 36.76 38.83
Calculations by Methods of Statistical Mechanics Vibrational Assignment.-An essent,ial aspect of correlating calorimetric dat’a hy using spectral and molecular structure information is t’he assignment of the fundamental vibrational frequencies of the molecule. (1) This investigation was performed as part of American Petroleum Institute Research Project 52 on “Nitrogen Constituents of Petroleum,” which is conducted at the University of Kansas in Lawrence, Kansas, and a t the Bureau of Mines Petroleum Research Centers in Laraniie, Wyoming, and Bartlesville, Oklahoma. (2) D. W. Scott, W. D. Good, G. B. Guthrie, S. S. Todd, I. A. Hossenlopp, A. G. Osborn, a n d J. P. McCullough, J. Fhzls. Chem., 67, 685 (1963).
Therefore, the interpretation of the molecular spectra of 2-methylpyridine will be considered first. Bands observed in the Ramana and infrared4 spectra are listed in Table 11. Raman polarization datale are included. The few reported Raman bands that seem to have arisen from pyridine or 2,6-dimethylpyridine impurity were ignored. Included in Table I1 are unpublished results for the far-infrared (grating) spectra obtained at the authors’ request by Drs. F. A. Miller and W. G. Fateley of the Mellon Institute. Rough correspondence is expected between the fundamental frequencies of the methylpyridines and of toluene, the former differing from the latter by replacement of a C-H group with a nitrogen atom. However, three frequencies that involve the replaced C-H group of toluene, a stretch, an in-plane bend, and an out-of-plane bend, can have no counterpart in each methylpyridine, and the particular C-H frequencies that have no counterpart may be different depending on which C-H group is replaced. These expectations are fulfilled, as demonstrated in Table 111, in which the frequencies of toluene5 are compared with the ones of 2-methylpyridine assigned here and the ones for 3methylpyridine assigned in 11. Kote that the toluene frequencies 966 and 1155 cm.-l have no counterpart in 2-methylpyridine, whereas 842 and 1278 cm.-l have no counterpart in 3-methylpyridine. The molecular spectra of 2-methylpyridine are particularly complex in three ranges of frequencies. Between 1030 and 1060 cm.-l occur the pyridyl group frequency a t 1052 cm.-l and the two methyl rocking frequencies, which coincide a t 1042 cm.-l as in isolated methyl groups on a benzene ring.6 Between 1400 and 1500 cm.-l occur two pyridyl group frequencies (3) (a) G. B. Bonino and R. hXanaoni-Ansidei, Mem. accad scz. t s t . Bolojna, Classe scz.fis., [9] 1, Sep. 7 pp. (Feb 18, 1934); (b) S. K. K. Jatkar, Indzan J . Phys., 10, 23 (1936), (0) K. W. F. Kolilrausch, A. Ponaratz, and R. Seka, Monatsh., 70, 213 (1937), (d) R. Manaoni-Ansidel, Boll. scz. f a c . chzm znd. 7~nzz1. Bologna, 137 (1940), (e) E. Hem. L. Kahovec, and K. W.F. Kohlrausch, Z physzk Chern., B53,124 (1943); (f)D. A. Long, F. S.Jlurfin, J. L. Hales, and W Kynaston, Trans. Faraday Soc., 63, 1171 (l957), ( a ) American Petroleum Institute Research ProJect 44 a t the Carnegie Institute of Technology, Catalog of Raman Spectal Data, Serial KO.252. (4) (a) W T I Cohlentz, “Investigations of Infra-Red Spectra,” Carnegle Institution of Washington, Washington, D C., 190;; (b) J Leconlte, CoVhpt. rend , 2 0 7 , 395 (1938), (0) H. Freiser and W. L Glowacki, J . Am. Chem. Soc., 70, 2575 (1948), (d) D. P. Biddiscombe, E A. Coulson, R. Handley, a n d E. F. G. Herington, J Chzrn. Soc., 1957 (1954), (e) Reference 3f, (f) American Petroleum Institute Research ProJect 44 a t the Carnegie Institute of Technology, Catalog of Intiared Spectral Data, Serial No. 743 2020, 2021, 2129, and 2190. ( 5 ) D. W.Scott, G. B. Guthrie, J. r. Messerly, S. S. Todd, W. T. Berg, I. 4 . Hossenlopp, and J. P. McCullough, J . Phys. Chem., 66, 911 (1962). (6) R. R. Randle and D. H. Whiffen, J. Chem. SOL, 3497 (1955).
March, 1963
CHEiWCAL
THERMODYNAMIC PROPERTIES
TABLE I1 V~BRATLOSALSPECTRA O F
-Infraredliq.
Raman liq. 209 m
[0.68]
359 w
403
470 w 546 m 628 w 709 v w 728 w
404 s
0.43 0.71
194.2 s
a" fundamental
....b
a" fundamental
550 631 700 w
729 s
799 m
799 m
0.11 810 w
1x1
a' fundamental
360.6
{ '28
732 747 v s
{
a' fundamental
a' fundamental overtone (see text) a" fundamental a" fundamental
758
i8:
799 a ' fundamental
+:
",u","aie;: 820
885 w 942 N 975 m
886 w 939 w 980 w
0.07
996 s
996 s 1040 sh
1044 w
0.08
1049 s
1049 s
i / i
T'N
928 w 972 m 984
+
1194 629 = 823 A" a" fundamental combination (see text) a ' fundamental a' fundamental a ' &- a" fundamentals a' fundamental
11056
dp?
1101 N
1100 m
1147 w
0.75
1145 a
1234 m
0.14
1236 in
1284 w 1291 w
0.54
1292 s
loQ5w
a! fundamental
1107 1142
L5
::1
a' fundamentltl
-
a' fundamental
1 iZ
403
m
+ 886
1289 A'
a' fundamental
11305
1346 vw 1357 sh
1374 m
0.41
1426 w
dp?
1375
1432 s 1451 a 1458 w 1479 w 1567 m )
1589 m 1591 m 1600 m
1
r :1
1436 s
1477 B 1570 a
1468 s
1591 s
1594 s
a' fundamenta,l 550 803 = 1353 A'
+
a' fundamental a' fundamental a" fundamental a' fundamental 2 X 729 = 1458 A' OL'
fundamental
a' fundamental
0.77
Region above 1600 cm. -1
-
a' fundamental 360 1235 1595A' 2 X 803 = 1606 A' omitted.
+
TABLE 111 FUNDAMENTAL VIBRATIONAL FREQUENCIHS OF 2-METHYLPYRIDINE COMPARED WITH CORRESPONDINQFREQUENCIES O F TOLUENE AND 3-METHYLPYRIDIiYE, CM.-la 2-Methylpyridine
Toluene
a" fundamental
m
[
470 8 547 m 629 m
751 v s
811
Interpretation gas
206
360.5
VN
2-METHYLPYBlDINB, CU .-la
"Abbreviations: s, strong; m, medium; w, weak; vw, very weak; s h , shoulder. The depolarization factors of the Raman bands are listed after the intensity designations. * Not investigated.
and two methyl bending frequencies, some of which may interact with nearby overtones and combinations. The assignment of frequencies in this range is by no means certain, but is still satisfactory in a statistical sense for calculating thermodynamic functions. Between 2800 and 3200 em.-' occur the seven C-H stretching frequencies, some of which also may interact with nearby overtones and combinations. Moreover, the infrared spectra in that region are not well resolved. No attempt a t individual assignments of the C-13 stretching frequencies was made, and average or con-
681
OF 2-hrETHYLPYRIDIKE
519 785 1003 1031 1177 1209 1385 1501 1611 2922 3058 3076 3110 342 623 1041 1081 1155 1278 1329 1436 1460 1585 2954
\
3-Methylpyridine
550 803 993 1052 1148 12/16 1385 1468 1594 [2950]
536 803 1029 1041 1119 1231 1381 1472 1593 [2950]
[3050 (2)]
[3050 (2) 1
355.4 631 1042 1101
....
336.5 625 (1041) 1104 1193
1299 1346 1426 1451 1568 [2950]
1333 1419 1452 1581 [2950]
a'
*...
[3050 (2) 3090 3040 PO50 (211 401 404 405 .... 820 842 .... 942 966 194.2 205.6 205 455 462 470 71 1 720 694 a" 782 747 728 893 886 920 98 1 984 972 (1041) (1042) (1041) (1452) 1456 1486 2930 [a9501 [2950] a Parentheses denote frequencies used more than once; brackets denote average or conventional values.
ventional values were used (2950 cm.-l for methyl arid 3050 cm.-l for aromatic). The C-H stretching frequencies are unimportant thermodynamically except a t higher temperatures. The weak infrared band at 820 cm.-l observed only in the spectrum of the gas is assigned as a fundamental frequency, although there is an alternative assignment as a sum-combination. The vapor heat capacity data indicate a fundamental at about 820 cm.-l. As with toluene,6 the two lowest frequencies shift significantly between the liquid and gas states (206 to 194.2 cm.-l and 360.5 to 355.4 cm.-l). Using the two liquid-state frequencies instead of gas-state frequencies for calculating the entropy to compare with the observed values would introduce ail error of 0.16 cal. deg. -l mole-1. That error is as great as the uncertainty in the observed values. Customarily, when gas state values of frequencies are lacking, the liquid state values are assumed to be the same and are used instead. However, with 2-methylpyridine, that procedure gave an entropy discrepancy too large to dismiss as experimental uncertaiiity, and &lie discrepancy was explained and resolved only when Miller and Fateley's gas state
SCOTT, HUBBARD, MESSERLY, TODD,HOSSFKLQPP, GOOD,DOUSLIS, AKD MCCULLOCGH
682
T, -OK.
(FO - H " o ) / T , cal. deg.-l
TABLE IV THEMOLALTHERIXODYXAMIC PROPERTIES ( H 9 - H'a)/T, H a - Boo , So, Gal. d e g , P
kcal,
cal. des.-'
OB' ~-METHYLPYRIRINEa C,Q, AHfovb cal. deg.-l koal.
Vol. 67
A F ~ O , ~
kcal.
log X f b
0 0 0 0 0 29.04 29.04 Infinite 3.669 75 68 21 89 62.25 13 43 24.05 40.77 -32.62 14 22 4,241 77.68 23.90 23.65 - 63.46 42.31 -31.02 14.28 4.286 63.55 24.05 23.62 77.83 42,43 -30.91 17.72 7.090 85.84 - 68.12 31.92 22.16 48.93 -26.73 21.27 10.64 93.73 - 72.46 38.82 21.00 55.76 -24.37 24.69 14 82 101.33 44 55 76.64 20.11 -22.88 62.80 600 27.87 19,5l 108.56 49.27 - 80.69 19.44 69.97 -21.85 7m a4 65 115.41 - 84.61 30 80 53 21 18.97 -21.10 77.22 800 30 13 121 87 88.39 33 48 56 52 18.67 900 -20.52, 84.52 35 93 35 93 127 98 92.05 59.34 18 53 91.85 1000 -20.07 38 17 41.99 133.75 61.75 18.53 iiao - 95.58 -19.70 99.18 40 22 48.27 - 98.99 139 21 12QO 63.82 18,63 106.50 -19.40 42.11 54.74 144.39 65.60 18.79 102.28 113.81 -19.13 1300 - 105.47 43 84 61.38 149.31 67.16 19 00 121.12 1400 -18.91 45 44 68.17 153 99 68 51 19.26 128.40 - 108.55 1500 -18.71 T o retain internal consistency, some values are given to one more decimal place than is justified by the absolute accuracy. For the reaction 6 C(c, graphite) 7/2 Hz(g) 1/2 Nn(g) = Ot,H&(g). 0 273.15 298.15 300 400 1500
-
-
+
+
spectrum was obtained. Confirmatory evidence for &he shifts is obtained from overtone and combination bands. The sum-combination of the lowest frequency with 729 cm.-l shifts by about the expected amount from 940 cm.-l for the liquid to 928 cm.-l for the gas. Also the overtone of the second lowest frequency shifts by about the expected amount from 709 cm.-l for the liquid to 700 cm.-l for the gas. Moments of Inertia.-As the structure of the 2m&hylpyridine molecule has not been determined, the bond distances and angles were assumed to be the same as in related molecules. The pyridyl part o€ the molecule was taken to have the same dimensions a8 in pyridine.' The CH3-C part of the molecule was taken to have tetrahedral angles and bond distances the same as in acetaldehyde" For this assumed structure, the product of the principal moments of inertia is 2.137 X 8 . 3 cm.6 and the reduced moment of g. cm.2. inertia for internal rotation is 5.076 X Internal Rotation.-To obtain agreement with the observed values of entropy, internal rotation in the 2-methylpyridine molecule must be considered as free or very nearly so. In the related molecule, toluene, internal rotation also is essentially free.5 However, in toluene, a very low barrier is expected because of the sixfold symmetry of the internal rotation. I n 2methylpyridine, the internal rotation can have a threefold as well as a sixfold component. That the internal rotation is nearly free implies that the threefold component is unimportant. Thermodynamic Functions.-The molecular parameters discussed in the previous paragraphs were used in calculating the thermodynamic functions of 2methylpyridine. An empirical anharmonicity functions with v = 1130 cm.-1 and 2 = 0.75 cal. deg.-l was used to obtain better agreement urith the vapor heat capacity data. The contributions of anharmonicity (in cal. deg.-l mole-1 a t temperatures in OK.) according to this empirical function, are: for CPo,0.04 at 388.26, and 0.13 at 500.20 (the extremes of (7) B. Bak, L. Hansen, and J . Rastrnp-Andersen, J . Chem. Phys., 22, 2013 (1B.54). (8) R. W. Kilb, C. C. Lin, and E. l3. Wilson, Jr.. ibrd., a6, 1695 (1957). (9) J. P. McCullough, H. L. Finke, W. N. Hubbard, W, D. Good, R. E. Pennington, J. F. Messerly, and G. Waddington, J. Am, Chem. Soc., 76, 2661 (1934).
the experimental range), 0.01 a t 298.15 and 1.27 a t 1500; for So, 0.001 at 298.15 and 0.70 a t 1500. The calculated values of entropy and heat capacity are compared with the observed values in Table I. The satisfactory agreement is evidence of nearly free internal rotation and of the essential correctness of the vibrational assignment. Calculated values of the thermodynamic functions for selected temperatures up to 1500OK. are listed in columns 2-6 of Table IV.lo Heat, Free Energy, and Logazithm of Equilibrium calculated values of Constant of Formation.-The the thermodynamic functions, the experimental value of AHf298.16 (Table I), and values of the thermodynamic functions of C(c, graphite), H2(g), and Nz(g)ll were used in computing the values of AHf, AFf", and log Kf given in columns 7-9, Table IV. Experimental The basic experimental techniques are described in published accounts of apparatus and methods for low temperature calorimetry,12 vapor flow calorimetry,ls comparative e b ~ l l i o m e t r y , ~ ~ and combustion calorimetry.16 The reported values are based an a molecular weight of 93.124g. mole+( 1951 International Atomic WeightslG), the 1951 values of fundamental physical constants,17 and the relations: 0" = 273.15'K.18 a n d 1 oal. = 4.184 (exactly) joules. Measurements of temperature were made with platinum resistance thermometers calibrated in terms of the International (10) The vibrational and anharmonicity Contributions were computed b y the Bureau of Mines Electronic Computer Servioe, Pittsburgh, Pa. (11) D. D. Wagman, J . E. Kilpatrick, W. J. Taylor, K. S, Pitzer, a n d F. n. Rossini, J. Res. Natl. Bur. Std., 34, 143 (1945). (12) H. M. Hnffman, ChemRev., 40, l(1947); H. M. Hnffman, 9. S. Todd, and G. D. Oliver, J. Am, Chem. Soc., 71, 584 (1949); D. W. Scott, D. R. Douslin, M. E. Cross, G. D. Oliver, and H. If.Huffman, %bid.,74,883 (1952). (13) G . Waddington, S. 8. Todd, and H. M.Huffman, zbzd., 69,22 (1947); J. P. McCullough, D. W. Soott, R. E. Pennington, I. A. Hosaenlopp, a n d G. Waddington, ibid., 76, 4791(1954). (14) G. Wadding!on, J. W. Knowlton, D. W. Scott, G. D. Oliver, S. S. Todd, W. N. Hubbard, J. C. Smith, and H. & Huffman, I. zbrd., TI, 797 (1949). (15) W. N. Hubbard, F. R. Frow, and G. Waddington, J . Phys. Chem., 66, 1326 (1961). (16) E. Wichers, J . Am. Chem. Soc., 74, 2447 (1952). Use of 1962 atomic weights ( C h s n . Eng. News, Nov. 20, 1961, p. 43) would increase all molal values given herein by 0.00670. (17) F. D. Rossini, F. T. Gucker, Jr., H. L. Johnston, L. Pauling, and G. W. Vinal, zbzd.,'74, 2699 (1952). (18) Some of the results originally were computed with constants and temperatures in terms of the relation 0" = 273.16OK. Only results affected significantly by the n e s e r definition of the absolute temperature scale (H. F. Stimgon, Am. J . Phg,., 23, 614 (3955)l were recalculated. Therefore, numerical inconsistencies, much smaller than the accuracy uncertainty, may be noted in 891118 of the reported data.
March, I963
683
CHEMICAL ~ H E R M O R Y N d M I C~'ROPERTIFS OF %h!!ETHYLPYRTD1NJ'E
Temperature Scalelgbetween 90 arid 500°K. and the provisional scalez0of the National Bureau of Standards between 11and 90°K. All electrical and mass measuiements were referred to standard devices calibrated a t the National Bureau of Standards. The eneigy equivalent of the combustion calorimetric system, 8 (Calor.), was determined by combustioq of benzoic acid (NBS Sample 39 g). The Materid.-The sample of 2-methylpyridine used for low temperature calorimetry, oomparative ebulliometry, and combustion calorimetry was part of the Standard Sample of Organic Nitrogen Compound API-USBM 52-4, prepared a t the Laramie ( W y o . ) Petroleum Research Center of the Bureau of Mines.*I Samples were dried in the liquid state nrith calcium hydride befoIe use in the experimental measurements and were always transferred and handled without exposure to air. The purity, determined by calorimetric studies of melting point as a function of fraction melted; T&S 99.90 mole %. A sample of somewhat lower purity was used for vapor flow calorimetry. Heat Capacity in the Solid and Liquid States.-Low temperature calorimetric measurements were made with 0.56395 mole of sample sealed in a platinum calorimeter with helium (35 mm. pressure a t room temperature) added to promote thermal equilibration. The temperature incrementa used j n the measurements were small enaugh that corrections for non-linear variation of C, with temperature weie unnecessary. The observed values of heat capacity, C,, are listed in Table V. Above 30"K., the
Heat and Temperature of Fusion.-Three determinations of the heat af fut-hon, A H m , gave the average value 2324.1 k 0.8 cal. mole-1 with the maximum deviation from the mean taken as the uncertainty. The results of a study of the melting temperature, TF, as a function of the fraction of total sample melted, F, are listed in Table VI. Also listed in Table VI are values obtained for the triple-point temperature, TtB,the mole fraction of impurity in the sample, Nz*, and the cryoscopic constantsz2 A = A H m / R T t p z and B = 1/Tt, A C m / 2 h H m , calculated fPQm the obaerved values of Tt,, A H m , and A C m (10.29 cal. deg.-I mole-1). Thermodynamic Properties in the Solid and Liquid States.Values of thermodynamic functions for the condensed phaees were computed from the calorimetric data for selected temperatures between 10 and 370°K. The results are given in Table VII. The values a t 10qK. were computed from a Debye function for 4 degrees of freedom with e = 112.0'; these parameters were evaluated from the heat capacity data between 13 and 21'K. Corrections for the effects of premelting have heen applied to the "smoothed" data in TableVII.
TABLE V
0.1097 9.116 206. I50 206.13 2628 3.805 206.3232 206.313 . SO40 1.984" 206.3763" 206.3763 206.3965 .Pll2 1.406" 206.3965" ,9010 I . 110 206.412 208.407 1.0000 I.000 206.411 Pure 0 206.446 a A straight line through these points was extrapolated to 1 / ~ = 0 to obtain Tt,. bTemperatures from the straight line of the preceding footnote.
-
TABLE Vi 2-METRYLPYHIUINE: MELTING POINT SUMMARY Yip = 206.45 f 0.05"K.; N2* = A F / ( T ~-, T F ) = 0.0010 f 0.0002; A = 0.02744 deg.-l; II = 0.00263 deg.--l a
THE M O L A L H E A T CAPACITY O F
2-MITHYLPYRIDINE IN
CAL.DEG.-~ T,OK."
Ceb
T,OK."
CSb
T,OK.=
C,b
168.99 20.622 55.51 9 740 Crystal 171.77 2Q 844 10 503 60.43 12.37 0.810 171.77 20.855 60.92 10 519 ,873 12.65 178 21 21.371 11 350 66.38 1.070 13.78 180 25 21.580d 12 053 72.02 1,132 14.04 184.52 21.920d 12.751 77.84 1.347 15 20 13.459 188.56 22. 335OPJ 83.73 1.394 15.40 Liquid 86.95 13.829 1,619 16 52 209.90 33,881 14 099 89.68 1.722 16 07 211.97 33.911 92.76 14 393 1,972 18.11 215.52 34.017 14.647 95.38 2.144 18 87 221.09 34.159 14.913 2,424 98.35 20 10 231.03 34 487 101.41 2.592 15.191 20.84 240.87 34.881 15.459 104.28 2.928 22.24 250.59 35.294 107.77 15.769 22 R5 3,071 260.64 35.776 16.005 110.54 24.56 3.4Y3 270.98 36.321 113.91 16.289 24.94 3.584 281.19 36.883 119.89 4.132 16.785 27.24 291.24 37.456 27 26 17.301 126.18 4.133 301.16 38.051 127.54 4.759 17.399 29.89 306.24 38.363 17 814 132.78 4.875 30.38 317.13 39.043 134.91 5.623 17.973 33.64 327.84 39.725 142.07 18,512 6.403 37.20 149.05 338.37 40.413 41 16 19.074 7.208 348.75 41.089 155.85 45.29 19.601 7.988 162.49 358.95 41.828 20.110 49.89 8.809 369.01 42.443 166.22 54.97 9.652 20.323 " 7" is the mean temperature of each heat capacity measureC, is the heat capacity of the condensed phase a t satument. ration pressure. "Values of C, far crystal are not corrected for the effects of premelting caused by impurities. d T h e temperature increments of these measurements are in order of increasing T, OK.: 10.502,6.250, and6.127". accuracy uncertainty is estimated to be no greater than 0.27,. The heat capacity values for the liquid may be represented within 0.127, between 230 and 370°K. by the empirical equation
C, = 42.247 - 0.13335T
+ 5.4547 X 10-4T2 -
4.9479 X lO-'T3, cal. deg.-L mole-'
(1)
(18) H. F. Stimson, J . Res. " f a & Bur. Std., 42, 209 (1949). K.J. Hoae and E'. G . Brrckwedde, &d., 22, 351. (1939). (21) R. V. Helm, W. J. Lanum, G . L. Cook, and J. S. Ball, J . Bhys. Chew., 6 2 , 858 (1958). (20)
TP,OK.
1/F
Tcslcd.?
OK.
Vapor Pressure -The observed values of vapor pressure are listed in Table VIII. The condensation temperature of the sample was 0.008" lower than the ebullition temperature a t 1 atm. pressure. The $ntoine and Cox equations selected to represent the results are
log p
=
7.03202 - 1415.494/(t
+ 211.598)
(2)
and
log (p/760) = A(1 - 402.536/T)
log4
= 0.861242
- 6.5320 X
+ 5.6738
(3)
x
10-7~2
I n thege equations, p is in mm., t i s in "C., and T is in "K. The observed and calculated vapor pressures for both the Antoine and Cox equations are compared in Table VIII. The normal boilingpoint is 129.39" (402.54"K.). Heat of Vaporization, Vapor Heat Capacity, and Effects of Gas Imperfactim. -The experimental values of the heat of vapmimitian and vapw heat capactty are listed in Tables I X and X . The estimated accuracy uncertainties of the values oE AHv and C," are 0.1 and 0.2%, respectively, The heat of vaporisat#ionmay be represented by the empirical equation
AH@3 11213
+ 2.861T - 2.290 X 10-aT2, eal. mole-l (359-402'K.)
(4)
The effects af gas imperfection were correlated by the procedure described in an earlier paper.23 The empirical equation tor B, the seaond virial coefficient in the equation of state, PV = RT. I1 f B I V ) , is
B
=z
-1189
- 39.76 e~p(1300/T), cc. mole-l (359-500'K.)
(5)
(22) A. R. Glasgow, A . J. Streiff, and F. 1). Rossini, J. Res. Nail. Bur. Std., 35, 355 (1945). (23) J. P . M~Cul~ougki, XI. L. Rnke, J. I'. Messerly, R. E. Pennington, I. A. Hossenlopp, and G, Waddington, J . Am. Chem. Soc., 77, 6119 (1955).
684
SCOTT,RUBBARD, ~IESSERLY, TODD, HOSSEFLOPP, GOOD,DOUSLIN, AKD ~ ~ C ~ U L L O U G H
TABLE VI1 THEMOLAL T E h R M O D Y K A M I C PROPERTIES O F 2-hIETHYLPYRIDINE IN THE SOLID A N D LIQUID STATICS~ (Ha
-
Hod/T,
H B - H"o,
oal. deg.-l
Cd.
Sa, CB, cal. deg.-l cal. deg.-1
Crystal 10 15 20 25 30 35 40 45 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190 200 206.45
0.036 ,123 .274 .484 .74d 1.042 1.371 1.724 2.094 2.870 3.672 4.485 5.298 6.104 6.902 7.688 8.460 9.219 9.964 10.695 11.414 12.120 12.815 13.499 13.934
0.110 .357 .728 1.180 1.682 2.207 2.739 3.264 3.776 4.784 5.668 6.510 7,297 8.028 8.709 9.348 9.952 10.525 11.073 11.600 12.109 12.605 13.089 13.564 13.868
1.097 5.355 14.558 29.500 50.46 77.26 109.56 146.87 188.78 285.26 396.7 520.7 656.7 802.8 957.9 1121.7 1293.7 1473.5 1660.9 1855.9 2058.5 2268.8 2486.8 2712.8 2863.1
0.146 .480 1,002 1.664 2.425 3.249 4.110 4.988 5.870 7.624 9.340 10.995 12.595 14.132 15.611 17.036 18.412 19.744 21.037 22.295 23,523 24.725 25.904 27.063 27.802
0.435 1.307 2.397 3.593 4.781 6.923 6.978 7.930 8.826 j0.438 11 799 13,012 14.128 15.070 15,956 16.706 17.598 18.360 19.121 19.881 20.646 21.413 22.198 22.999 23.52
Liquid 25.326 5187.2 39.059 206.45 33 934 33.81 2rj.272 5307 39.63 210 14.363 33.88 41.21 25.668 5647 34.12 220 15.548 42.74 26.043 5989 34.45 230 16.697 44.21 26.401 6336 34.84 240 17.813 45.64 26,747 6686 35.27 250 18.898 47.03 27.084 7041 35.74 260 19.953 48.39 27.414 7401 36 26 270 20.982 48.81 27,517 7516 36.43 273.15 21.302 49.72 27,740 7767 36.81 280 21.985 51.02 28.063 8138 37.38 290 22.963 52.07 28.324 37.86 8445 298.15 23.746 52.30 37.97 28.383 8514 300 23.921 53.55 38.59 28.703 8597 310 24.856 29.022 54.79 39.22 9286 320 25.772 56.01 39 86 29.340 8652 330 26.671 57.21 40 52 29.659 10084 340 27.552 58.39 41.19 10492 29.979 350 28.416 89.56 41.87 30,300 10908 360 29.265 60.72 42.52 30.622 11330 370 30.099 a The values tabulated are the free energy function, enthalpy function, ehthalpy, entropy, and heat capacity of the condensed phases at sathration pressure. Observed values of B and -T(d*B/dP) = lim(dCp/dP)T P-CO
and the values calculated from eq. 5 are compared in Tables I X and X I The heat of vauorization at 298.15'K. was calculated by extrapolation of eq.-4 (10.03 kcal. mole-'), by use of the Clapeyron equation with eq. 3 and 5 (10.12 kcal. mole-'), and by use of a thermodynamic network with the thermodynamic functions of Table IV (10.14 kcal. mole-'). The last value was selected as most reliable. By use of eq. 5, the standard heat of vaporization (to the hypothetical ideal gas) is calculated to be 0.01 kcal. mole-' greater than the heat of vaporization (to the real gas); thus AHV'ZOS.IS = 10.15 kcal. mole-'. Entropy in the Ideal Gas State.-The entropy in the ideal gas state at 1 atm. pressure was calculated as shown in Table
XI.
'Vol. 611
'FABLE VI11 VAPOR PRESSVRE O F 2-h'IETHYLPYEIDINE --Boiling Water
point, O C . 7 2-Methyl pyridine
-
~ ( o b s d . ) , ~ ~ ( o b s d . ) p(oalcd.), mm. mm. Antoine eq. 2 Cox eq. 3
79.794 14.9.41 $0.02 0.00 60.000 187.57 .04 65 85.853 - .04 - .02 91.942 233.72 70 - .01 75 98.074 .Ql .03 289.13 104.252 80 355.22 .01 .03 433.56 .02 85 110.472 .03 90 116.736 525.86 - .01. .00 95 123.038 633.99 .02 .03 100 129.387 760.00 - .03 - .03 j- .03 .05 105 135.773 906.06 110 142.207 1074.6 .o .o 115 148.683 1268.0 - .1 .o 120 155.201 1489.1 - .2 - .1 125 161.761 1740.8 .1 - .2 130 168.356 2026.0 .2 .o ' From the vapor pressure data for water given, by X. S. Osborne, H. F. Stimson, and D. C. Ginnings, J. Res. iVatl. Bur. Std., 23,261 (1939).
-
+ +
+ + + +
+ +
+
-
+
TABLE IX THEMOLALHEATOF VAPORIZATIOK ASD SECOND VI~IAL COEFFICIENT O F 2-METHYLPYRIDINE --B,
T,OK.
P , atm.
AHu, cal.
Obsd.
cc.-
Calcd."
358.35 0.250 9284. rt 3b -1673 -1670 -1399 -1411 379.48 0.TiOO 9001 rt 1 402.54 1.000 8654 f 4 -1204 -1194 a Calculated from eq. 5 . Maximum deviation from the mean of three or more determinations.
TABLE X THE M O L A L
VAPOR
IjWAT CAPACITY O F C.41,.DxG.-'
2-hIETHYLPYRIDIXE
IN
TI "K. 388.25 413.20 438.20 468.20 600.20 C, (1.000 atrn.) 33,792 35,351 37,229 39.200 C, (0.500 atm.) 31.686 33.343 C, (0.250atm.) 31.345 33.111 34.871 36.876 38.926 C," 31.02 32.91 34.72 36.76 38.84 - T(d2K/dT2), obsd." 1..28 0.83 0.60 0.44 0.35 - T(dZR/dT'), culcd.b 1.26 .85 .63 .44 .31 Calculated from eq. 5. a Units: cal. deg.-l mole-' atm.-'. TABLE
XI
THEMOLALESTROPY o r 2-METHYLPTRIIJINE IN THE IDEAL GAS STATEIN CAL.IIEG.-' TI O I L S,( liq. )" AHu/l'
s* - S b R In Pc
359.36 59.49 25.84 0.09 -2.76
379.49 61.80 23.72 0.14 -1.88
402.55 64.40 21.60 0.20 0.00
S"(obsd.) k 0 . 17d 82. A6 84.28 86.10 * By interpolation in Table VI1 or extrapolation by use of eq. 1. b T h e entropy in the ideal gas state less that jn the real gas state, calculated from eq. 5. Entropy of compression, calEstimated accuracy uncertainty. culated from eq. 3. Heat of Combustion and Formation .-Results of a typical determination of the heat of combustion of 2-methylpyridine are given in detail in Table XII. The symbols and abbreviations are those of Hubbard, Scott, and W a d d i n g t ~ n . ~In~ three experiments, the amount of reaction determined from the mass of sample was checked by determining the amount of COS in the (24) W. N. Hubbard, D. W. Scott, and G . Waddington, "Experimental Thermochemistry," F. D. Rossini, E d . , Interscience Publishers, Inc., New York, N. P., 1956, Chapter 5 , pp. 75-128.
March, 1963
products. The COZ recovery was 100.04 f 0.01% of that calculat,ed from the mass of sample. Results of six acceptable determiaa tions are summarized in Table XI11 along with derived results calculated by using literature values of the heat of formation of carbon dioxide and water and the entropy of graphite, hydrogen, and nitrogen.11 Comparison with Earlier Work.-The results repoited here are compared with those of earlier investigators in the following paper (II).2
TABLFI
SUMMARY O F
SUMM.4RY O F A TYPIC i L COMRUSTION CALORl\fETRIC EXPERIMEXT WITH 2-METHYLPYRID1XEa
m' (2-methylpyridine), g. At, = t f - ti - Atoor,deg. G(Ca1or.) ( - Ato), cal. &(Cotit.)( - at,),* cal. AE,,,, cal. AEfdeo("0, HNO?), cal. AE, corr. to st. btates,' cal. -m"AEc","W (auxiliary oil), cal. -m"' AEc'IM (fuse), cal.
.84185 2.00078 -7788 30 -9.70 2.70 13.16 3.81 384.78 15.42 m 'A&' /'v (2-meth ylpyridine ), cal. - 7378.13 AEc" / M (2-methylpyridine), cal. g. -l -8764.10 a Auxiliary data: G(Ca1or.) = 3892.63 cal. deg.+; V(Bomb) = 0.344 1.; AEe'/iM(auxiliary oil) = -10983.7 cal. g.-I; AEco/ G1(Cont.)(tL- 25') Ef(Cont.) M(fuse) = -3923 cal. g.-l. Atoorr). Items 81-85, 87-90, 93, and 94 of the (25' - tf computation form of ref. 24.
+
+
XI11
RESULTS OF' COMBUSTION 298.15"K.
C.4LORlMETRY AT
AEc'/M (2-Methylpyridine), cal. g. -1: -8762.97, -8766. 10, -8764. I Y, -8763.05, -8765.52, -8764.99 Mean and std. dev. : -8764.45 f 0.54
TABLE XI1
+
685
CHEMICAL T H E R M O D Y N A M I C P R O P E R T I E S O F 3-MEiTHYLPYRTDfXE
Derived Results for the Liquid Statea: A&',
AHc',
AHf', ASf", AFf",
kcal. mole-' kcal. mole-' lrcal. mole-' cal. de.@;.-* mole-' kcal. mole-'
-816.18 f 0.16 -816 92 zt 0.16 13.50 & 0.18 - 88 22 39 80 29.18
-
log Kf
With uncertainty interval equal to twice the final "over-all" standard deviation [F. D. Rossini, ref. 24, Chapter 14, pp. 297-3201. a
Acknowledgment.--The assistance of W. T. Berg, J. P. Damon, F. R.Frow, wid T. C. Klncheloe in some of the experimental measurements is gratefully acknowledged. The authors thank Drs. F. A. Miller and W. G. Fateley of the Mellon Institute for obtaining the far-infrared (grating) spectrum.
CHEMICAL THERMODYNARSIC PROPERTIES AND INTERNAL ROTATION OF METHYLPYRIDINES. 11. 3-METHYLPYRIDIYE' BY D. W . SCOTT, W. D. GOOD,G. B. GUTHRIE,S. S. TODD, I. A. HOSSESLOPP, A. G. OSBORN,A N D J. P. MCCULLOUGH Contribution N o . 13%from the Therinodynamics Laboratory o,f the Bartlesville Petroleum Research Center, Bureau of Mines, U.S. Department of the Interior, Bartlesville, Okla. Received September 19, 1962
Thermodynamic properties of 3-methylpyridine were measured and the results were correlated by use of spectral and molecular-structure data to obtain valnes of the chemical thermodynamic properties in the ideal gas state (0 to 1500°K.). Internal rotation of the methyl group was found to be free or nearly so. Experimental studies provided the following information: values of heat capacity for the solid (12°K. to the triple point), liquid (triple point to 393"K.), and the vapor (404 to 500'K.); the triple point temperature; the heat of fusion; thermodynamic functions for the solid and liquid (0 to 390°K.); heat of vaporization (372 to 417'K.);, parameters of the equation of state; vapor pressure (347 to 458'K.); and the standard heat of formation at 298.15'K.
The thermodynamic studies of 3-methylpyridine (ppicoline) reported in this paper parallel the ones of 2methylpyridine reported in the accompanying paper, hereafter referred to as I. Results of the same kinds of experimental work were correlated by use of molecular data and used in calculating tables of chemical thermodynamic properties. The calorimetric data that were used in these calculations are collected in Table I. As in I, an assignment of the fundamental vibrational frequencies was obtained, and internal rotation was found to be free or nearly so. The order of presentation here is the same as in I; the calculations by methods of statistical mechanics are discussed in the next section, and the detailed experi(1) This investigation was performed as part of American Petroleum Institute Research Project 52 on "Nitrogen Constituents of Petroleum," which is conducted a t the University of Kansas in Lawrence, Kansas, and at the Bureau of Mines Petroleum Reseaich Centers i n Laiamie, Wyoming, and Bartlesville, Oklahoma. (2) D. W. Scott, W. N. Hubbard, J. F. Messerly, 9. 9. Todd, I. A. Hossenlopp, W. D. Good, D. R. Douslin, and J. P. MoCullough, J . Phus. Chen., 67, 680 (1963).
TABLE I OBSERVED AND CALCULATED THERMODYNAMICS PROPERTIES O F 3-METHYLPYRIDINE
T,OK.
372.45 393.36 417.29
Entropy, So, cal. deg. -1 mole -1 Obsd. Calcd.
83.71 85.34 87.18
133.61 85 28 87.17
T,"K.
Heat capacity, CPo, cal. deg.-i mole-1 Obsd. Calcd.
404.20 32.14 429.20 33.93 452.20 35.60 475.20 37.14 500.20 38.74 Hf0*98.1j(gas)= 25.37 =IC 0.17 kcal. mole-'
32.13 33.96 35.59 37.14 38.75
mental results are presented jn the Experimental section. Calculations by Methods of Statistical Mechanics Vibrational Assignment.-As in I, the interpretation of the molecular spectra will be considered first. Bands observed in the Raman3 and infrared4 spectra (3) (a) E. H e n , L. Xahovec, and K. W. F. ICohlrausoh, 2. physik. Chem., B53,124 (1943); (b) D.A. Long, F. S. Murfin, J. L. Hales, and W. Kynaston, T r a n s . F a r a d a y Soc., 53, 1171 (1957).
