Dec., 1961
HEsTs O F
COMBUSTION O F
METHANETHIOL A N D
perature must be toward the SrClz axis. Microscopic examination of the 90% PuC13 melt indicated no solid solution for compositions rich in PuC13. No polymorphic transformations were observed a t any of these compositions when thermal analysis was carried down to 25'. The PuC13-BaC12 system (Fig. 2) is quite similar to the PuC13-SrC12 system. A eutectic point occurs a t 64 mole yo PuC13 and 648', and a peritectic transformation occurs a t 38 mole % PuC13 and 758' with the accompanying production of a compound to which we have assigned the empirical formula Ba3PuC19. The compound has a refractive index of 1.76 f 0.02. Except for pure BaC12, no polymorphic transformations were observed when any of these compositions were cooled to 25'. Microscopic evidence for the existence of solid solution is based on samples from the 10% PuC13 melt. The predominant phase was cubic and was
CARBON
DISULFIDE
2229
of variable and somewhat lower refractive index than pure BaC12. A trace of Ba3PuC19was discernable along grain boundaries. It is noteworthy that below 925" the cubic structure is more stable. Evidently the cubic modification is stabilized by the solubility of PuC13 in BaC12. The duration of thermal arrests a t 759' supports the microscopic evidence for solid solution. For 30% PuC13 the thermal arrest was 70 min. per mole of melt, whereas for 10% PuC13, the thermal arrest was much less than 10 min. Acknowledgments.-The authors wish to express their gratitude to W. J. Maraman for advice and to the members of the Analytical Group under the direction of C. F. Mets for the chemical analyses involved in this investigation. This work was performed under the auspices of the U.S. Atomic Energy Commission.
METHANETHIOL AND CARBON DISULFIDE : HEATS OF COMBUSTION AND FORMATION BY ROTATING-BOMB CALORIMETRY' BY W. D. GOOD,J. L. LACINA AND J. P. MCCULLOUGH Contribution No. 108 from the Thermodynamics Laboratory, Petroleum Research Center, Bureau of Mines, U . 9. Department of the Interior, Bartlesville, Oklahoma R~ceivadJuly 17, 1961
The heats of combustion of methanethiol and carbon disulfide were measured by rotating-bomb calorimetry. For combustion calorimetry of methanethiol, normal boiling point 5.96", liquid samples were sealed in borosilicate glass ampoules rigid enough to withstand the high vapor pressure a t room temperature. Samples of carbon disulfide were sealed in polyester bags. The derived values of AHf"298.16 for formation in the gaseous state from graphite, gaseous hydrogen and rhombic sulfur are: methanethiol, - 5.46 kcal. mole-'; carbon disulfide, 27.98 kcal. mole-1.
Methods for precision combustion calorimetry of ing point method. The sample used for the combustion was dried by passing the vapors through magorganic sulfur compounds are well establi~hed.~-4 experiments nesium perchlorate. Until the present investigation, however, the The sample of carbon disulfide was obtained from a commodern methods had not been used to measure mercial source and was distilled in an efficient fractionating the heats of combustion of two common and im- column.6 The purity of the distilled sample, measured by the time-temperature freesing point method, was 99.98 portant sulfur compounds, methanethiol and car- mole %. A study by gas-liquid chromatography also indibon disulfide. These compounds presented spe- cated a purity of 99.98-99.99 mole %. The sample used for cial experimental problems because both are highly combustion calorimetry was dried by passing the vapors volatile and contain a high proportion of sulfur. through phosphorous pentoxide. Apparatus and Procedures.-The rotating-bomb calI n a continuing Bureau of Mines program of used in the study of methanethiol, laboratory thermodynamic studies of organic sulfur com- orimeter designation BMR-11, has been described.' The measurepounds, these problems were solved, and accurate ments on carbon disulfide were made in a new but essentivalues of the heats of combustion and formation ally identical calorimeter, laboratory designation BMR-111. Platinum-lined bomb Pt-3b,* internal volume 0.350 l., was were obtained. used for both compounds. Experimental Except for the methods of sample confinement discussed Materials.--The sample of methanethiol was prepared a t the Laramie Petroleum Research Center of the Bureau of Mines as part of American Petroleum Institute Research Project 48A.6 The purity of this material was 99.94 f 0.06 mole %, as determined by the time-temperature freez(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," whioh the Bureau of Mines conducts at Bartlesville, Okla., and Laramie, Wyo. (2) S. Sunner, (a1 Suenek Kem. Tidskr., 68, 71 (1946); (b) Thesis, University of Lund, 1950. (3) W. N.Hubbard, C. K a t s and G. Waddington, J . Phys. Chem., 68, 142 (1954). (4) G. Waddington, 9. Sunner and W. N. Hubbard, "Experimental Thermochemistry," F. D. Rossini, Editor, Interscience Publishers. Ine.. New York, N. Y., 1956, Chapter 7, pp. 149-179. ( 5 ) J. C. Morria, W. J. Lanum, R. V. Helm, W. E. Haines, G. L. Cook and J. 8. Ball, J . Chem. Eng. Data, 6, 112 (1960).
in the following section, experimental details were about the same as those described in ref. 3. Sample Containers.-Spherical Pyrex ampoules, weighing 100 to 200 mg., were used as sample containers for methanethiol. These ampoules had to mthstand the vapor pressure of liquid methanethiol (about 2 atm. a t room temperature) internally and the pressure of oxygen in the bomb (30atm.) externally. Empty ampoules were tested by sealing the capillary stems and subjecting them to an external pressure of 35 atm. The ends of the capillary stems were broken off those that survived this test, and the ampoules (6) The authors thank Mr. H.J. Coleman of this Center for his careful purification of the sample of carbon disulfide used in thin investigation. (7) W. D. Good, D. W. Scott and G. Waddington. J . Phyu. Chem., 60, 1080 (1956). (8) W. D. Good, D. R. Douslin, D. W. Scott, A. George, J. L. Lacina J. P. Dawson and G. Waddington, ibid.. 63,1133, (1959).
W. D. GOOD, J. L. LACINA ASD J. P. MCCULLOUGH
2230
Vol. 65
TABLE I O F IDEALIZED COMBUST1[ON REACTII ONS' Methanethiol 0.83621 0.81805 0.91328 0.90716 0.81247 0.18100 0.11602 0.16636 0.17903 0.11227 2,02022 2.02452 2.02075 2.01862 2.02400 8099.36 8084.23 -8101.44 -8086.35 -8077.83 -28.95 -28.18 -28.24 -28.16 -28.16 0.72 0.42 0.45 0.50 1.41 8.01 9.72 10.79 9.56 7.41 0.65 0.37 -0.75 -0.65 0.58 1988.10 1827.30 1966.44 1233.24 1274.37 6.00 4.50 4.78 5.03 4.09
I{NERGY m'(CHaSH), g. ' m (oil), g.
- -
tf ti Atoor., deg. AtO &(Calor.)( At,). cal. &(Cont.)(-~t,),b cal. AEien., oal. AEfdM.(HN08 4-HNOz), cal. A E , cor. to et. states,' oal. -n"AEc'/M(oil), cal. -m"'AEc'/M(fuse), cal.
0.81607 0.18052 2,02463 -8101.88 -28.19 0.78 7.44 0.64 1982.83 4.21
-
-
-6107.99 -7517.80
-4860.35 -7508.76
-
---
m'AEc'/M(CH&H), cal. -6134.17 -6146.39 -7516.72 -7513.46 AEc'/M(CH&€I), cal. g. -1 Av. value and standard dev. of the mean: -7515.64
-6867.87 -6818.67 -7520.00 -7516.50 f 1.11 cal. g.-1.
-6286.94 -7518.38
Carbon Disulfide 0.50926 0.66346d m'(CSz), g. 0.50678 0.50504 0.50056 0.51320 0.50929 .46763 .39290 m#(oil), g. .47182 .46880 .47061 .46629 .46750 .04432 .04566 m"'(polyester), g. a t .03943 .04573 .04455 .04413 .04482 (52) (55) (% rel. hum.) (52) (59) (51) (51) (51) 2.00137 Ato = t f ti A.toor., deg. 2.00087 1.99921 1.99709 2.00123 1.99963 1.99948 &(Calor.)(-At,), cal. -8054.58 -8047.90 -8039.37 -8056.03 -8049.59 -8048.99 -8056.59 -27.54 -27.56 G (Cont.) (- at,) ,* cal. -27.68 -27.65 -27.57 -27.52 -27.51 0.82 1.00 AEion., oal. 0.69 0.64 0.62 0.92 0.97 A&,. ("01 "Od, cal. 10.22 10.38 11.24 9.33 9.59 8.33 19.33 2.22 -0.46 AE. cor. t o st. states,' cal. 2.22 2.26 2.30 2.16 2.21 4315.62 -m"AW"/iU(oil), cal. 5182.55 5149.36 5169.23 5121.77 5135.02 5136.43 m"'AEco/M(pclyester), 242.12 249.40 cal. 215.41 249.74 243.39 241.09 244.86 4.54 5.07 -m""AEco/M(fuse). cal. 4.30 4.62 4.42 4.13 3.97
-
0.64729 0.29449 2.01966 8081.99 -28.81 0.68 7.22 2.56 3234.76 5.23
-
+
-
-
-----___-______-
m'AEco/M(CSz), cal. -2666.87 -2658.55 -2635.74 -2704.15 -2680.48 -2682.07 -3494.18 AEca/M(CSz),oal.g.-l -5202.38 -5204.04 -5265.58 -5269.20 -5263.18 -5266.71 -5266.01 Average value and standard dev. of the mean: -5265.26 f 0.68 csl. g.-'.
-
6852.74 -7515.21
0.66384d .39412 .04318 (59) 2.00222 8060.02 -27.56 0.97
-
-
0.91185 0.11359 2.02023 8084.27 -28.96 0.78 7.05 -0.70 1247.65 5.71
0.94488 0.09129 2.02097 8087.23 -28.98 0.55 9.27 -1.24 1002.73 5.15
-7099.75 -7513.92
0.29135 0.66013' .57062 .39610 ,04415 .04384 (56) (55) 1.99533 2.00387 8032.28 8066.66 -27.51 -27.61 1.33 0.62
-
-
23.57 -0.53 4329.12
6.81 4.77 0267.81
22.01 -0.43 4350.82
235.81 4.34
241.15 4.26
240.01 4.26
-3494.30 -5263.77
-1533.66 -3476.98 -5263.98 -5267.12
+
0 The symbols and abbreviations in this table are those used in ref. 11, except as noted. b Ei(Cont.)(ti -25') &I(Cont.) In these experiments (25" -tf At,,,,) 6 Items 81-85, incl., 87-91, incl., 93 and 94 of the computation form of ref. 11. five atmospheres of air was used in the bomb instead of the usual one atmosphere.
+
then were weighed. The ampoules were filled by a method previously described,g with the ampoule receiver cooled by an icebath. The filled ampoule6 were removed individually from the receiver, and the bulb was immediately packed in crushed ice. A stream of warm, dry air was brushed on the capillary tip extendin from the ice until all the material had evaporated from &e stem and a small bubble appeared in the bulb. The bulb was removed from the ice and immediately packed in powdered solid carbon dioxide to reduce the vapor pressure enough to permit sealing the capillary stem. The stream of dry air was kept on the capillary tip so that the chilled sample would not adsorb moisture from the laboratory air. The ampoule was sealed and then removed from the solid carbon dioxide and allowed to warm to room temperature. It was possible after a little experience to make the volume of the bubble in the ampoule negligibly small a t room temperature. Combustion reactions were initiated with the hydrocarbon oil previously deecribed (Sample USBM-P3a).' The combustion reactions were violent, a characteristic of highly volatile samples sealed in strong ampoules. In only nine experiments out of 23 was complete combustion obtained. Samples of carbon disulfide were confined in polyester bags by a technique previously described.8 The same hydrocarbon oil was used as an auxiliary kindling material. Units of Measurements and Auxiliary Quantities.-All data reported are based on the 1951 International Atomic Weights108 and fundamental constantslob and the definitions: 0 "C. = 273.15"K.; 1 cal. = 4.184(exactly) joules. The laboratory standard weights had been calibrated a t the National Bureau of Standards. In reducing weights in air to in vucuo, in converting the energy of the actual bomb process to the isothermal bomb (9) G. B. Guthrie. Jr.. D. W. Scott, W. N. Hubbard, C. Kats, J. P. McCullough, M. E. Grow, K. D. Williamson and G. Waddington, J . Am. Chem. Soc., 74, 4662 (1952). (10) (a) E. Wichera. ibid., 74, 2447 (1952); (b) F. D. Rossini. F. T. Gucker. Jr., H. L. Johnston, L. Pauling and G.W. Vinal, ibid.. 74,2699 (1952).
process, and in reducing to standard states," the following values (for 25") of density, p , specific heat, cp, and ( ~ E / ~ P ) T for the various substances were used. P,
g.
Methanethiol Carbon disulfide Auxiliary oil Polyester film
mL-1
0.861 1.255 0.87 1.38
CP,
cal. deg.-l g. -1
0.45 ,239 .53 ,315
(bE/bP)T,
cal. atm. -1
....
g. - 1
-0,0109 - ,0060 - .00069
Calibration.-During the study of methanethiol, the energy equivalent, &(Calor.),of calorimetric system BMR-I1 was determined by combustion of benzoic acid (National Bureau of Standards standard sample 39g with a certified heat of combustion of 26.4338 f 0.0026 abs. kj./g. mass under certificate conditions). Twelve calibration experiments ave the value, &(Calor.) = 4001.66 & 0.14 cal. deg.-l b e a n and standard deviation) During the study of carbon disulfide, the energy equivilent of calorimetric SI stem BMR-I11 was determined by combustion of benzoic acid (National Bureau of Standards standard sample 39h with a certified heat of combustion of 26.434 =t0.003 abs. kj ./g. mass under certificate conditions). Seven calibration experiments gave the value, E(Ca1or.) = 4025.54 i 0.19 cal. deg.-' (mean and standard deviation).
Results Calorimetric Results.-The calorimetric results for methanethiol and carbon disulfide are summarized in Table I. The experimental values of AEco/ M apply to the idealized combustion reactions 1 and 2 for methanethiol and carbon disulfide a t 298.15OK. (11) W. N. Hubbard, D. W. Scott and G. Waddington, "Experimental Thermochemistry." F. D. Rossini, Editor, Interscience Puhlishers, Ino., New York, N. Y., 1956, Chapter 5, pp. 75-128.
HEATSOF COMBUSTION OF METHANETHIOL AND CARBON DISULFIDE
Dec., 1961 CHnSH(Kq.) CSz(1iq.)
+ 7/2 O d d + 29 HeO(h.) = Cot(€$ + H2SO4*30HzO(iiq.) (1)
+ 4 Oz(g) + 92 HzO(liq.) = COz(g) +
for the reactions S(c, rhombic)
+ 3/2 02(g) + 31 HzO(liq.)= HzSOa.80Hz0(liq.) (3)
2H&304.45HzO(liq.) ( 2 )
Apart from the violence of the combustion reactions of methanethiol, no difficulty was encountered in obtaining complete oxidation of the sample to C02 and aqueous H2S04. However, complete oxidation of carbon disulfide could be obtained only if a relatively large amount of auxiliary oil was burned with the sample. Experiments were made with various ratios of carbon disulfide to auxiliary oil, and complete oxidation resulted only when less than 45% of the total measured energy came from the combustion of carbon disulfide. I n some of the experiments with carbon disulfide, 5 atmospheres of air (instead of the usual one atmosphere) was charged to the bomb before charging to a total pressure of 30 atmospheres with pure oxygen. It was hoped that fixation of more than the normal amount of nitrogen oxides would promote complete oxidation. This expedient did allow a significant increase in the ratio of carbon disulfide to auxiliary oil. As the detailed results in Table I show, the measured heat of combustion of carbon disulfide was not affected when the ratio of carbon disulfide to auxiliary oil was varied in such a way that carbon disulfide contributed between 20 and 45yo of the total measured energy. The results for methanethiol also were unaffected by relatively large changes in the ratio of that compoun to auxiliary oil (Table I). Recovery of sulfuric acid in the combustion products of both compounds was 100.0 0.1% of that expected from the stoichiometry of the combustion reaction. Quantitative recovery of sulfuric acid indicates that the compounds were pure and that the chemistry of the combustion reaction is properly described. Mass spectroscopic examination of the gaseous combustion products of both compounds did not show significant amounts of any product other than carbon dioxide. Derived Results.-Derived results for both compounds are given in Table 11. The values of AEc02g8.15and AHcO298.15 are for the idealized combustion reactions 1 and 2. To calculate the standard heats of formation of methanethiol and carbon
*
TABLE 11" DERIVED RESULTSAT 298.15"K., KCAL.MOLE-^ Property
State
Methanethiol
Carbon disulfide
-361.56 f 0.12 -400.91 f 0.12 - 3 6 3 . 0 4 f .12 - 4 0 2 . 6 9 f O 12 - 1 1 . 1 5 f .13* 2 1 . 3 7 i 0 . 1 7 b 5 . 6 9 f .02 6.61 i0.02 Gas - 5 . 4 6 f .14' 2 i . Q S f O 19' Uncertainties are the "uncertainty interval" equal to twice the final over-all standard deviation of the mean (F. D. Rossini, ref. 4,p. 319). b Reference state for sulfur is S (rhombic). AEe" AHc" AHf" AHu' AHf"
Liquid Liquid Liquid
0
disulfide, values of the heats of formation of carbon dioxide and water were taken from National Bureau of Standards Circular 50012,and AHO298.15 (12) F. D. Rossini, D. D. Wagman, W. H. Evans, 9. Levine and I. Jaffe, "Selected Values of Chemical Thermodynamic Properties," Natl. Bur. Standards Circular 500, 1952.
2231
and S(c, rhombic)
+ 3/2 Ol(g) + 46 HzO(liq.)=
H2SOa.45H20(liq.) (4)
was taken to be -143.50 and -143.63 kcal., respectively. These values were obtained by applying appropriate dilution corrections12 to the value of the heat of formation of HzSO4.115H2O(liq.) recently determined in this Laboratory. l3 The heat of vaporization of carbon disulfide is from unpublished measurements of this Laboratory. The value used for the heat of vaporization of methanethiol was obtained by a short extrapolation of the results of Russell, et ~ 1 . ' ~
Discussion The only previously published experimental value of the heat of formation of gaseous methanethiol,12 -2.97 kcal. mole-I, is from the pioneering work of T h o m ~ e n . ' ~From bond energy considerations recently predicted that the heat of formation of gaseous methanethiol should be -5.4 kcal. mole-'. This prediction is in excellent agreement with the experimental value from this research. The heat of formation of gaseous carbon disulfide has been derived from the experimental results of several investigators, including heats of combustion measured by T h ~ m s e n , 'Berthelot" ~ and Guerin, measurements of the heat of comet ~ ~ 1 . These ~ 8 bustion of carbon disulfide are quite discordant. The heat of formation given in NBS Circular 5OO,I2 27.55 kcal. mole-', apparently was calculated directly from the results of Terres and We~emann's'~ studies of the equilibria of the reactions COS COS
+ HzS = COS + HzO + H2S = CSs + H20
(5) (6)
Values of AH0298.16 for these reactions, computed from the meamred equilibrium constants and free energy data, show significant trends with reaction temperature. For example the three for reaction 6 that may be values of AH0298.15 calculated from Terres and Weseniann's results show a trend with reaction temperature of almost 0.5 kcal. mole-'. These and other uncertainties in the result obtained from the equilibrium studies account for the discrepancy between the earlier value of the heat of formation of carbon disulfide and the more accurate result of this investigation. (13) W. D. Good, J. L. Lacinaand J. P. McCullough, J. Am. Chem. floc., 83, 5589 (1960).
(14) H. Russell, Jr., D. W. Osborne and D. S L Yost, {bid., 64, 165 (1942~. (15) J. Thonisen. "Thermochemische Untersuchungen," Barth, Leipzig (1882-1886). (le) T. L. Allen, J . Chem. Phye., 31, 1039 (1959). (17) (a) hl. P. E. Berthelot, Ann. chtm. phys.. 23, 209 (1881); (b) as, 126 (1893). (18) H. Guerin, M. Bastick, J. Bastick and J. Adam-Gironne, Compt. rend., 228, 87 (1949). (19) E. Terres and H. Wesemann. Angew. Chem., 45,795 (1932).
