TABLE I11 RATESO F ACIDHYDROLYSIS, MUTAROTATION AND RACEMIZATION GIVEKI N k lnitial compd.
I-&-
4289
THERMODYNAMIC PROPERTIES OF PYRIDINE
Aug. 20, 1957
(Acid)
[Co en?Cl?]+a
ki, acid
Temp., OC.
2 4 s - [Cr ennCl?]
Values from Mathieu.?O
*
30 25 25 .1 22 .1 25 Values from Basolo, et
hydrolysis
2.15 x 10-4 6.0 X 5 x 10-5 2 . 3 0 x 10-4 3 . 3 0 x 10-4
0.012 ,001 .1
d-cis- [Co enlFn] +b
FROM THE
kc, racemization
5.37 x 8.2 X 10.3 x 2.28 x 3.30 x
10-4
6.13 X 3 x 6.5 X 1.48 x 2.0 x
10-5 10-4 10-4
10-6 10-6 10-4 10-4
d.5'
mium complexes are in part responsible for (1) the general non-labile characteristics found for cobalt and chromium complexes as compared with other first row transition metal complexes, ( 2 ) the strong similarity of cobalt and chromium complexes in
[CONTRIBUTIOS K O . 62
(SEC.-')
kn, mutarotation
ease of substitution-type reactions, and (3) the ease with which Cr(I1) goes to Cr(II1) in systems which can form d2sp3 hybrid-orbital complexes with Cr(II1). ERBASA,ILLINOIS
THERMODYSAMICS LABORATORY, PETROLEUM EXPERIXEYT S T A T I O N , BUREAU O F MIXES, U. s. DEPARTMEST O F THE I N T E R I O R ]
Pyridine : Experimental and Calculated Chemical Thermodynamic Properties between 0 and 1500OK.; a Revised Vibrational Assignment1 BY J. P. MCCULLOUGH, D. R. DOUSLIN, J. F. MESSERLY, I. A. HOSSENLOPP, T. C. KINCHELOE A N D GUY WADDINGTON RECEIVEDAPRIL 22, 1957 From studies by low temperature calorimetry, comparative ebulliometry, flow calorimetry and combustion calorimetry, values were obtained for the entropy, heat capacity and heat of formation of pyridine in the ideal gaseous state. The calorimetric values of entropy and heat capacity served as guides in revising the vibrational assignments for pyridine and several deuteropyridines. T h e revised assignment for pyridine and molecular structure data were used in computing values of the thermodynamic functions a t selected temperatures between 0 and 1500°K. Values of the heat, free energy and equilibrium constant of formation were calculated a t the same selected temperatures. The experimental investigations provided t h e following information: values of heat capacity for the solid (13-224'K.), the liquid [ C s a t d = 33.633 - 9.1446 X 10-ZT 3.8478 X 10-4T2- 3.3430 X 10-'T3, cal. deg.-'mole-' (240-347'K.)], and thevapor [C," = -8.262 10.608 X 1O-*T 5.4662 X 1 0 - 5 P , cal. deg.-' mole-' (374-50O0K.)] ; the heat of fusion [1978.6 cal. mole-'] a t the triple point [231.4g°K.]; t h e entropy of the liquid a t 298.16"K. [42.52 cal. deg.-' mole-']; the vapor pressure [log," p(mm.) = 7.04162 - 1374.103/ (t 4- 215.014), (67-153")]; the heat of vaporization [ A H v = 13077 - 10.201 T - 4.7941 X 10-3T2, cal. mole-' (346388'K.)]; the second virial coefficient in the equation of state, P V = R T (1 f B / V ) , [ B = -15-84.5 exp ( 9 5 0 / T ) , cc. mole-' (346-500°K.)] ; and the standard heat of formation of t h e liquid a t 298.16'K. (23.89 kcal. mole-'].
+
Thermodynamic investigations of organic nitrogen compounds were begun recently in this Laboratory as part of American Petroleum Institute Research Project 5 2 . The objective is to provide comprehensive thermodynamic data for nitrogen compounds that are important in petroleum technology. This paper is the first of a projected series on cyclic nitrogen compounds. Results are reported for pyridine, a compound important in theoretical considerations concer=iing molecular structure as well as in practical considerations as an industrial chemical. Some thermodynamic data for pyridine have been reported previously,2 but many of the basic data are not of the accuracy that can be obtained by present-day methods. (1) (a) This investigation was performed as p a r t of American Petroleum Institute Research Project 52 on "Nitrogen Constituents of Petroleum," which is conducted a t t h e University of Kansas in Lawrence, Kansas, and a t the Bureau of Mines Experiment Stations in Laramie, Wyoming, and Bartlesville, Oklahoma. (b) Presented a t 130th American Chemical Society Meeting, Atlantic City, AT, J., September, 1956. (2) (a, C. H. Kline and J. Turkevich, J . Chem. Phrs., 12,300 (1944); (b) D. P. Biddiscombe, E. A. Coulson, R . Handley and E. F. G. Herington, J . Chem. SOL., 1957 (1954); (c) E . F. G. Herington and J. F. Martin, Trans. F a r a d a y Soc., 49, 151 (1953) [and references cited there]; (d) G. S. Parks, S. S. Todd a n d W. A. Moore, THIS JOURNAL, 68, 398 (1936); (e) J. N. Pearce a n d H. >I. Bakke, Proc. I o w a A c a d . Sci., 38B, 450 (1929).
+
The experimental part of this investigation consisted of measurements of thermodynamic properties by the methods of low temperature calorimetry, comparative ebulliometry, flow calorimetry and combustion calorimetry. Descriptions of the experiments and detailed results are given in the Experimental part of the paper. For convenience, the most important experimental results-values of the entropy, heat capacity and heat of formation for the ideal gaseous state-are collected in Table I. The entropy and heat capacity data served as TABLE I OBSERVED AXD CALCULATED MOLAL THERMODYNAMIC PROPERTIES OF PYRIDINE IN THE IDEALGASEOUS STATE T,
OK.
346.65 366.11 388.40
Entropy, S o , cal. deg. -1 Obsd. Calcd.
70.65 71.86 73.27
T,
H e a t capacity, CpO, cal. deg. -1 Obsd. Calcd.
OK.
70.65 71.89 73.30
374.20 23.79 23.79 397.20 25.23 25.24 420.20 26.65 26.65 450.20 28.43 28.40 500.20 31.12 31.21 Heat of formation, AHf0?9S16 (obsd.) = 33.50 kcal.
guides in revising the vibrational assignment for pyridine and as checks on thermodynamic properties calculated by the methods of statistical
4290
~ICCULLOUG DOUSLIN, H, MESSERLY, HOSSRNLOT, K I N C I T E AND I . ~ IT ZDDINCTON
mechanics. The experimental value of the heat of formation and the calculated thermodynamic properties were used in computing values of the heat, free energy and equilibrium constant of formation a t selected temperatures between 0 and 1500°K. These calculations are discussed in the following section.
TABLE
R E V M ~\'IRRATIONAL SOME Freq.
KO.
1 2 tia
SpecieP
Pyridine
992 30tXa 72Ob 1583 1218 1030d 305dd 1068 1483 3(133 1200 653
Vol. 7 ! )
11
ASSIGSMENT FOR
PVRIDINR
AND
DEUTEROPYRIDINES Frequency, cm. - 1 Pyri4D3Ddine-ds Pyridine Pyridine
962 2293a G90d 1530 887d 1006 2270 823 1340 2'54 908 ti25 2283 1542 1322
2DPyridine
989 3033 720b 1575 121P 1015 2285 1068 1476 3019 1212d 633' 3069 1559 1347 1121 862 1413 3069
980 989 3038 3040 717 748 Calculation of Thermodynamic Properties 8R 1570" 1570 9, a, 1195 1149 The Vibrational Assignment.-The vibrational 12 1033 1029 spectra of pyridine and several deuteropyridines 13 3053 3051 have been studied by a number of investigators3 183 1050 10.59 Corrsin, Fax and Lord (CFL) have given detailed 19'1 1468 1461 vibrational assignments for pyridine and pyridine'Od 3022 2258 d5.3a Anderson, Bak, Brodersen and RastrupA n d e r ~ e nhave ~ ~ given assignments for 4D-pyri3 1212 1217 dine, 3D-pyridine and 2D-pyridine based on the 6b 040' 630C assignments of CFL. When the published vibra7I3 30SY 3068 2289 tional assignment for pyridine was used in cal81) 1571 1570" 1570 culating thermodynamic properties, the results dis1377 14 bi 1337 1357 agreed with the experimental values of and So 13 1146 887d 1112 1108 listed in Table I (the discrepancies were about 2 18b 1086 833 848 834 and 0.3y0, respectively). Because the accuracy 1440 1911 1301 1424 1416 uncertainty of the observed values of C," is O.2yO, 20b 3080 2293" 3073 3077 a revision of the vibrational assignment for pyridine loa 885 713 890" 823 814 was required for calculating accurate thermo163 a? 360" 3 74 350' 329 365' dynamic properties. The revised assignment for 103Od 17a 1015 997 798 965d pyridine and its deuterated species is given in Table 675 633' 582 632" 638 4 bz 11. 5 981 690d 965d 968 970 The vibrational assignment of CFL is based on 1Ob 940 762 834 902 901 good spectroscopic evidence. It was considered 11 605 597 599 600 530 likely that the choice of only one fundamental fre405 16b 370 404 405 371 quency was seriously in error. T o obtain agreea The species designation is for Clv symmetry, that of ment between calculated and observed values of pyridine, pyridine-& and 4D-pyridine. b Fermi resonance both C," and S o , it was apparent that a frequency assumed between YE^ and 2 X ma. e Approximate values; near 700 cm.-' had to be eliminated and replaced see ref. 3b. Frequencies assigned t o more than one funby one near 1000 cm.-l. Corresponding changes damental.
c,"
in the assigments for the deuteropyridines had to be made to retain consistency with the product rule for isotopic substitution. There are only three observed frequencies near 700 cm.-' in the spectrum of pyridine: 675 (infrared, weak) ; 703 (infrared, very strong; Raman, very weak); 740 (infrared, strong; Raman, very weak) cm.-'. These frequencies had been assigned by CFL to v4, v11 and V10b,4 respectively. The assignment of CFL was retained for the infrared band a t 675 cm.-l, which cannot be assigned as a likely overtone or combination. The other pair of frequencies was replaced by a single ntal frequency by interpreting the 703749 i i i i . - l doublet as the result of Fermi resonance between an al mode near 720 cm.-l, taken to be Yea, and the overtone of vlfia, 2 x 37.1 (a?) = 748(&). This reinterpretation necessitated revised assignments for b? modes Vlob and vll. The fre~ , cni.-I, was quency previously assigned to v ~ 605 reassigned to vll. The assignment of the GO5 cm.-' frequency to a b2 rather than an al mode is consistent with the reported tiepolarization of the ( 3 ) (a) L. Corrsin, B. S . Fax and R. C. Lord, J . C h r n i . Phys., 21, 1170 (1953), and earlier references cited there; (b) F. A. Anderson, B. Bak, S . Brodersen and J. Rastrup-bndersen, ibid.. 23, 1047 (1955); (c) unpublished d a t a from Chemical Research Laboratory. Teddington, Middlesex. England. ( 4 ) T h e designation of normal modes (if vibration is t h a t given in ref. 3a.
Raman line.5 The frequency a t 981 cm.-', previously assigned to the a2 mode v17s in violation of the strict selection rules of C,, symmetry, was chosen for the other bz mode. However, this frequency was assigned to vg and CFL's choice for v5, 940 cm.-', was assigned instead to VlOb. (The latter change was made to obtain better over-all consistency among the assignments for pyridine, benzene and their deuterated species.3b.6 The result of the foregoing changes was to eliminate from the earlier assignment a frequency near 700 cm.-l and leave ~ 1 7 aavailable for assignment of a frequency near 1000 cm.-'. The a?mode ~1:a may be unobserved, for it should appear with very low intensity in the Raman spectrum and is forbidden in the infrared. Although the weak Raman line at 1033 cm.-' could be due to vlia, it was interpreted 673 (b,) = as the sum-combination. 374 (az) 10.19 (Bl). It was assumed that ~ 1 7 ais obscured in the Raman spectrum by the strong line of v12 a t I030 cm.-l, and that frequency was chosen fur vlia. A value of 1030 cm.-' for vlia results in a slightly more satisfactory product-rule ratio, 7&sd, for the al frequencies of pyridine and pyridine-&.
+
( 5 ) K. W. F. Kohlrausch. "Raman3pektren." Akademische Verlagsgesellschaft. Becker and Erler, Leipzig, 1943, p . 353. (6) (P) C . K. Ingold and co-workers, J . Chern. SOC. ( L o r d o n ) , 222 ff. (194fi); (b) R. I,. hIaii and D. F. Hornig, J . Chem. Phys., 17, 1236 ( 1949) .
THERMODYNAMIC PROPERTIES OF PYRIDINE
Aug. 20, 1957
Two additional minor changes have been made in the assignment for pyridine. Infrared bands a t 1200 and 1085 cm.-' were observed recently by workers a t the Chemical Research Laboratory3' and are assigned t o va and V18b. These fundamentals were previously assigned (by CFL) the same values as VSa and v18a, 1218 and 1068 cm.-'. The revision of CFL's vibrational assignment for pyridine made necessary corresponding changes in the previous assignments for the deuterated pyr i d i n e ~ . The ~ ~ ~revised ~ ~ assignments for the deuterated species, given in Table 11, were made concurrently with the revision of the assignment for pyridine. The vibrational assignments in Table I1 are as consistent internally as those of refs. 3a and 3b. The comparisons of observed and calculated product rule ratios, Tobsd and To&& in Table I11 show TABLE I11 RATIOSFOR PYRIDINE
PRODUCT-RULE
Toalod.
Symmetry class
from ref. 3a
Ref. 3a
a1 bi a2 bz
5.49 5.07 1.84 2.56
5.38 4.89 1.80 2.55
-
H%),,T, cal. deg.
( F O
T , OK.
AND PYRIDINE-& Tabad.
This work
5.45 4.90 1.82 2.54
4291
ensures that the set of fundamentals chosen is essentially correct. Uncertainties that may remain in the assigment of observed frequencies to particular modes of vibration can be removed only by additional spectroscopic evidence. It should be noted that the net effect of these reassignments is merely the replacement of fundamentals a t 703 and 749 cm.-l by fundamentals a t 720 and 1030 cm.-'-that is, the change that was found necessary to obtain agreement between calculated and experimental values of both Cpo and
so.
NOTE ADDED IN PROOF. J. K. Wilmshurst and H. J . Bernstein of the Canadian National Research Council have recently made new spectroscopic studies of pyridine and some deuteropyridines. Dr. Bernstein courteously provided us with a copy of his manuscript, which is soon to be published. The data of Wilmshurst and Bernstein require further revision of the vibrational assignment for pyridine. In their forthcoming paper, Wilmshurst and Bernstein will present a new vibrational assignment that is consistent with the available spectroscopic and calorimetric data. Use of their assignment in calculating thermodynamic properties results in no significant changes in the calculated values listed in Tables I and I11 of this paper.
The Moments of Inertia and Anharmonicity Contributions.-The moments of inertia of the pyridine molecule have been determined in several
TABLE IV THEMOLALTHERMODYNAMIC PROPERTIES O F PYRIDINE" (Ho
- H0o,)/T,
Ho
cal. deg.-1
-
so,
Hog, kcal.
cal. deg.-l
CP O, cal. deg.-l
AHf",b kcal.
AFf",b kcal.
10gioKJb
0 37.52 0 0 0 0 0 37.52 Infinite 33.82 -55.44 10.59 66.03 16.99 273.16 2.893 44.48 -35.59 298.16 -56.40 11.19 3.336 67.59 18.67 33.50 45.47 -33.33 300 -56.47 3.372 67.71 18.80 33.48 11.24 45.54 -33.18 -60.07 13.97 5.588 74.04 25.42 32.38 49.74 400 -27.18 -63.49 16.85. 80.34 31.11 31.52 8.425 54.18 500 -23.68 -66.81 19.62 11.772 86.43 35.72 30.88 600 58.77 -21.41 -70.03 22.20 15.54 92.23 39.44 30.41 700 63.47 -19.82 -73.15 24.55 19.64 97.70 42.49 30.07 800 68.21 -18.63 -76.17 26.69 24.02 102.86 900 45.04 29.86 72.99 -17.72 1000 -79.08 28.63 107.71 28.63 47.17 29.76 77.79 -17.00 1100 -81.89 33.44 112.29 30.40 48.99 29.75 82.59 -16.41 -84.62 38.42 32.02 116.64 50.54 29.82 1200 87.37 -15.91 1300 -87.23 33.49 43.54 120.72 51.88 29.92 92.18 -15.50 34.85 48.79 124.62 53.04 30.07 1400 -89.77 96.96 -15.14 1500 -92.22 36.10 54.15 128.32 54.05 30.24 101.73 -14.82 a To form an internally consistent set of values and to retain the higher accuracy of increments with temperature of a given property, some of the values in this table are given t o one more significant figure than is justified by their absolute accuracy. * The standard heat, standard free energy and common logarithm of the equilibrium constant for the formation of pyridine by the reaction: 5C(graphite) 5/2Ha(g) 1/2N2(g) + CbHeN(g).
+
+
that good agreement was retained. Also, all observed frequencies in the spectra of these compounds that were not chosen as fundamentals can be assigned readily as allowed overtones or combinations. For the most part, the intercomparison of assignments for pyridine, benzene and their deuterated species is slightly improved, although i t is apparent that some of the fundamental frequencies of pyridine and benzene differ more than in the earlier a ~ s i g n m e n t . ~Actually, ~ spectroscopic evidence alone is not sufficient to choose between the assignment in Table I1 and that of CFL. The fact, discussed later, that excellent agreement between calculated and observed values of C", and So was obtained by use of the revised assignment
recent microwave s t ~ d i e s . ~ -The ~ difference between values of the product of principal moments of inertia calculated from the results of these studies is not significant, but the value actually used in calculation of thermodynamic properties, 5.691 x was computed from the data of re' g.3 9. The symmetry number of over-all rotation is 2. The contributions of anharmonicity to the thermodynamic functions were treated by the empirical (7) K. E. McCulloh and G. F. Pollnow, J. Chsm. P h y s . , 22, 681 (1954). (8) B. B. DeMore, W. S. Wilcox a n d J. H. Goldstein, ibid., 22, 876 (1954). (9) B. Bak, L. Hansen and J. Rastrup-Andersen, ibid., 22, 2013 (1954).
4292
hxCCULLOUGH,
DOUSLIN, MESSERLY, HOSSENLOPP, KINCHELOE i i N D \f:ADDIKGTON
method described in an earlier paper from this Laboratory.lo The parameters 2 = 0.340 cal. deg.-l mole-' and Y = 750 cm.-' were selected to give agreement with the calorimetric values of C,". The contributions of anharmonicity to the thermodynamic properties are small a t 400°K., 0.03 and 0.11 cal. deg.-' mole-' in So and C,", but increase to 0.62 and 0.92 cal. deg.-l mole-' in So and Cpo a t 1500"K. The Chemical Thermodynamic Properties.The vibrational assignment, product of principal moments of inertia and anharmonicity parameters given in preceding paragraphs were used in computing values of the following thermodynamic functions a t selected temperatures between 0 and 1500°K.: ( F o - Hoo)/T,( H o - Hoo)/T,H" - HOo, So and Cpo. The results are listed in columns 2-6 of Table IV." The calculated and observed values of C," and So are compared in Table I. Agreement within 0.1% was obtained over the entire range of temperature of the experimental data. Because the observed values of So and C", are entirely independent, the excellent agreement obtained for So is another confirmation of the third law of thermodynamics. The Heat, Free Energy and Equilibrium Constant of Formation.-The calculated values of the thermodynamic functions of pyridine, the experimental value of A H f o s ~168 (Table I) and values of the thermodynamic functions of C(graphite),l 2 H2(g)l2and Nz(g)12were used in computing values of AHf O AFf and log1,Kf at selected temperatures between 0 and 1500'K. These results are listed in columns 7-9 of Table I17. ~
Experimental Physical Constants.-The 1951 International Atomic W e i g h t P and the 1951 values of fundamental physical constants14 were used. The results are based on a molecular weight of 79.098 for pyridine and the following relations: 0" = 273.16"K.; and 1cal. = 4.1840 abs. j . = 4.1833 int. j . Measurements of temperature were made with platinum resistance thermometers calibrated in terms of the International Temperature Sca1eI5 between 90 and 500'K. and the provisional scale16 of the National Bureau of Standards between 11 and 90°K. Measurements of mass, energy and resistance were made in terms of standard devices calibrated a t the National Bureau of Standards. The Material.-The sample of pyridine used in the low temperature thermal studies, vapor pressure measurements and heat of combustion experiments was part of the Standard Sample of Nitrogen Compound, A4PI-USBM-52-1,prepared and purified b y American Petroleum Institute Research Project 52b at the Laramie, Wyoming, Station of the Bu(IO) J. P. lTcCullough, H. L. Finke, \Y. 9. Hubbard,
n'.
D. Good,
R. E. Pennington, J. F. hlesserly and Guy Waddington. THIS J O U R 76, 2661 (1954). (1 1) T h e harmonic oscillator contributions to the thermodynamic
ZIAL,
functions were taken from FI. I,. Johnston, L. Savedoff and J. Belzer, "Contributions to the Thermodynamic Functions by a Planck-Einstein Oscillator in One Degree of Freedom," S A V E X O S P-646, Office of I\-aval Research, Department of the Xavy, Washington, D. C.. July, 1949. Anharmonicity contributions were computed from the tahles of R. E. Pennington and I
