614
W. N. HUBBARD, W. D. GOODAND GUYWADDINGTON
The probable error in the values reported in Tables 111 and I V is estimated at f10 kcal./mole, based partly upon the assumptions made in the calculations and partly upon the errors in temperature measurement, pressure calibration and intensity determination for some of the very small ion peaks involved. I n the single instance where comparison of two experimental methods was available (Lac2) the
Vol. 62
agreement between the results from the ClausiusClapeyron equation and those from the third law were within this estimated experimental error. The concentration of Al2C2 in the vapor above the A1-C system is insufficient to account for the large mass transport of carbon observed by Ruff, et aE.4b Their carbon loss may be attributable to oxidation of the graphite and s@equent evolution of co.
THE HEATS OF COMBUSTION, FORMATION AND ISOMERIZATION OF THE SEVEN ISOMERIC C4HloSALKANE THIOLS AND SULFIDES BY WARDN. HUBBARD, WILLIAMD. GOODAND GUYWADDINGTON Contribution No. 69 from the Thermodynamics Laboratory, Petroleum Experiment Station, Bureau of Mines, U.S. Department of the Interior, Bartlesville, Oklahoma Received January 10, 1068
The heat of combustion of each of the seven C~HIOS isomers-1-butanethiol, 2-butanethiol, 2-methyl-1-propanethiol, 2determined in a rotating-bomb methyl-2-propanethiol, 2-thiapentane, 3-thiapentane and 3-methyl-2-thiabutane-was calorimeter. The combustion and calibration experiments were performed in a single unified series. The results, supplemented by experimental values of the heat of vaporization of each compound and the heat of formation of HzS.Od-?OHzO from rhombic sulfur, oxygen and water, gave values of the standard heat of formation and standard heat of isomerization at 25” for each compound in the liquid and gaseous states.
Improved procedures have been developed for determining the heat of combustion of organic sulfur compound~.~-4The new procedures are being applied in this Laboratory to “Standard Sample” sulfur compounds prepared as part of the program of American Petroleum Institute Research Proj ect 48A.6.6 An earlier publication’ reported studies of the three isomeric CsHsS compounds in a unified series in which combustion experiments for each isomer were distributed appropriately among those for the others. This paper reports similar studies of the seven isomeric C4H10S compounds : l-butanethiol (n-butyl mercaptan), 2-butanethiol (sec-butyl mercaptan), 2-methyl-1-propanethiol (isobutyl mercaptan), 2-methyl-2-propanethiol (t-butyl mercaptan), 2-thiapentane (methyl n-propyl sulfide), 3thiapentane (diethyl sulfide) and 3-methyl-2-thiabutane (methyl isopropyl sulfide). Experimental Materials.-The seven samples were prepared at the Laramie, Wyo., station of the Bureau of .Mine!. Various supplemental data for the substances are listed in Table I. The values of specific heat ( c ~ ) , density ( p ) and d V / b T ) p were used in correcting the energy of the actual bomb process to the isothermal process, reducing weights in air to
in vacuo, and correcting to standard states.8~8 The purities (except for 2-butanethiol) and specific heats were determined by low-temperature calorimetry in this Laboratory.10-15 The sample of 2-butanethiol could not be crystallized to permit cryoscopic purity determinations; so, the purity was estimated from infrared and mass spectra observed during the purification process. The relatively low value and high uncertainty imply only that there is considerable uncertainty in the estimated purity and not that there is any reason to believe the sample was less pure than the others. Density data, from which the values of ( b V / d T ) palso were derived, were obtained at the Laramie station.6s6JB Apparatus and Method.-The rotating-bomb calorimeter used in these studies and the experimental procedures for organic sulfur compounds were described in an earlier publication.a The ampules to contain the volatile compounds were of Pyrex instead of soft glass because there is evidence that reaction between the hot combustion gases of sulfur compounds and molten soft glass can introduce thermochemical uncertainty. Bomb Pt-4 was used. The value of A E c o / M for the auxiliary oil, USBM-P3a, empirical formula CH1.891, had been determined to be -10983.8 cal. g.-’. Other experimental details were the same as described in ref. 3. Units.-Energy quantities are expressed in terms of the
(8) W. N. Hubbard, D. W. Scott and G. Waddington, “Experimental Thermochemistry,” F. D. Rossini, Editor, Interscience Publishers, Inc., New York, N. Y., 1956, Chapter 5, pp. 75-128. (9) W. N. Hubbard, D. W. Scott and Guy Waddington, THIB JOURNAL, 58, 152 (1954). (1) This investigation waB part of American Petroleum Institute (10) D. W. Scott, H. L. Finke, J. P. McCullough, J. F. Messerly, Research Project 48A on “The Production, Isolation and Purification R. E. Pennington, I. A. Hossenlopp and G. Waddington, J . Am. of Sulfur Compounds and Measurement of their Properties,” which the Chem. SOC.,79, 1062 (1957). Bureau of Mines conducts a t Bartlesville, Okla., and Laramie, WYO. (11) D. W. Scott, J. P. McCullough, J. F. Messerly, R. E. Penning(2) S. Sunner, Thesis, University of Lund, Carl Bloms Boktryckeri, ton, I. A. Hossenlopp, H. L. Finke and G. Waddington, ibid., 80, 55 Lund, Sweden, 1949. (3) W. N. Hubbard, C. Kats and G. Waddington, THISJOURNAL, (1958). (12) J. P. McCullough, D. W. Scott, H. L. Finke, W. N. Hubbard, 68,142 (1954). M. E. Gross, C. Kats, R. E. Pennington, J. F. Messerly and G. Wad(4) G. Waddington, S. Sunner and W. N. Hubbard, “Experimental dington, ibid., 7 6 , 1818 (1953). Thermochemistry,” F. D. Rossini, editor, Interscience Publishers, (13) D. W. Scott, H. L. Finke, W. N. Hubbard, J. P. MoCullough, Inc., New York, N. Y.,1956, Chapter 7, pp. 149-179. (5) W. E. Haines, R. V. Helm, C. W. Bailey and J. 9. Ball, THIS G. D. Oliver, M. E. Gross, C. Katz, K. D. Williamson, G. Waddington and H. M. Huffman, ibid., 74,4656 (1952). JOURNAL, 58, 270 (1954). (14) J. P. McCullough, H. L. Finke, J. F. Messerly, R. E. Penning(6) W. E. Haines, R. V. Helm, G. L. Cook and J. 9. Ball, ibid., 60, ton, I. A. Hossenlopp and G. Waddington, ibid., 77, 6119 (1955). 549 (1956). (15) Unpublished results for 2-butanethiol. (7) W. N. Hubbard and G . Waddington, Rec. trav. chim., 78, 910 (16) Unpublished results for 2-methyl-1-propanethiol. 11954).
HEATSOF COMBUSTION OF ISOMERIC ALKANETHIOLS AND SULFIDES
May, 1958
615
TABLEI SUPPLEMENTAL DATAFOR SAMPLES Standard sample Designation
Compound
1-Butanethiol 2-Butanethiol 2-Methyl-1-propanethiol 2-Methyl-2-propanethiol 2-Thiapentane 3-Thiapentane 3-Methyl-2-thiobutane
API-USBM API-USBM API-USBM NBS 905 API-USBM NBS 903 API-USRM
Purity, mole %
14 19 24 18 20
cp
99,990 f 0.005 99.9 f O . l 99.993 & 0.003 99.989 f 0.005 99.98 i 0.01 99.995 2t 0.002 99.98 f 0 01
defined calorie equal to 4.1840 abs. joules. The 1951 International Atomic Weights17used throughout give 90.186 as the molecular weight of C4HtoS. Calibration.-The energy equivalent of the calorimetric system &(Calor.), was determined by combustion of benzoic acid (National Bureau of Standards standard sample 39g) with a certified heat of combustion of 26.4338 i 0.0026 abs. kj. (6317.83 2t 0.62 cal.)/g. mass under certificate conditions.'* Conversion from cert,ificate conditions to standard conditions by the method of ref. 8 gives -6312.91 o.62 cal,/g. mass for aEcolnl, the energy of the idealized combustion reaction. Six satisfactory calibration experiments distributed among the combustion experiments for the CIHIOScompounds gave for €(Calor.), the energy equivalent of the calorimetric system, 3009.27, 3909.55, 3909.76, 3909.73, 3910.33 and 3909.57 cal. deg.-l The average value with the standard deviation of the mean iB 3909.70 =k 0.14 cal. deg.-l.
-
*
(259,
cal. deg.-l g . 3
0.4566 ,4538 .4555 .4640 ,4548 ,4543 .4568
1nL-l
( b V / h T ) P (25O), 1. deg. -1 g.
0.83676 ,82480 .8293 1 .79472 .83741 ,83120 ,82486
1.38 X 1.49 X 1.44 X 1.73 X 1.41 X 1.45 X low6 1.49 x 10-6
P (25'1,
g.
and AHf0298.16, the standard heat of formation, for both liquid and gas, according to the equation 4C(c, graphite)
+ 5Hz(g) + S(c, rhombic)
=
CaHloS(liqor 9) (3)
The values of uncertainty in Table Iv, except as noted, are uncertainty intervals equal to twice the final 'over-all" stalldard deviation.19 To calculate the standard heat of formation of the thiols and sulfides, AH'298.16 for the reaction rhombic) + 3/202(g) 71Hz0(1iq) = HzS04.70Hz0(liq) (4)
was taken to be -143.58 kcal. This datum was determined by bomb calorimetry under conditions substanti.ally identical with those of the combusResults tion experiments.4 The standard heat of formation Heat of Combustion, Formation and h m e r i z a - a t 2 9 8 . 1 6 0 ~of. &O(liq) and COz(g) were taken to tion.-Sixty-seven combustion experiments with the be - 68,317420 and - 94.051821 kcal, mole-i, reseven isomers and the calibration experiments spectively. with benzoic acid were performed within 15 days. The heat of isomerization referred to l-butalleThe unified series was planned so that the experi- thiol, H o i - HO,, is the differencebetween the heat ments for each isomer and the calibration experi- of formationof the isomer and that of l-butanements extended over the same period of time, in thiol.. The values of H O ~ - HO,for the liquid state order that effects due to variation of ambient con- could have been calculated directly from the approditions would tend to be the same for the different priate values of A E ~ ~ ~f~the ~ experiments ~ . ~ ~ on . sets of experiments. It is impractical to report all the isomers are carried out under identical condisatisfactory experiments in detail, but data for sin- tions, it is necessary to measure only the mass of gle experiments for each of the isomers are summa- sample used and to know only an approximate value rized in Table 11. These experiments were selected of the heat of combustioll of one of the isomers.7,zz,23 as typical of all the combustion experiments for the The many other measurements and calculations particular The Of the actually made (all necessary for accurate values of factory combustion experiments are listed in Table ~ $ 7 16,~ A0 ~ c~~ 2 ~g 8 .~1 and e A H ~ O ~ ~ ~ , ~ in ~ )de111. The values of AEco/M in Tables I1 and I11 termin$tions of H O ~- HO, only the purpose of corapply to the reaction recting for known small deviations from identical C&"iq) SO&) 66HzO(liq) = 4COz(g) conditions among the many experiments. HZSO*.~OHZO( liq) (1) Discussion The Of 18 experiments that It is difficult to assess the absolute accuracy of were unsatisfactory are not included in Table 111. bomb calorimetric data since there may be systemThe presence of carbon smudges on the walls of the atic errors that defy detection. However, bebomb and/or odor in the discharge gas indicated cause this unified series of was conthat, in most of the unsatisfactory experiments, the ducted in such a way as to that not only reaction did not proceed to complet'ion because of physical and procedural conditons, but any premature or violent rupture of the ampoule. variations of ambient conditions, were nearly Derived results are in Table IV. These include identical for each compound, the accuracy of the values of AEC'298.16 and AHc'298.16 for the idealized heat-of-isomeri~ation data should be indicated by combustion reactio11, eq. 1 AHv0298.16/the standard because most of heat of vaporization; H o i - H O n , the shndard heat the precision of the measurements, (19) F. D. Rossini, "Experimental Thermochemistry," F. D. Rosof isomerization, for both liquid and gas, according sini, ed., Interscience Publishers, Inc., New York, N. Y.,1956, Chap. to the equation 14, pp. 297-320.
+
+
CdHloS( 1-butanethiol, liq or
+
g) =
CdH,oS (isomer, liq or g) (2)
(17) E. Wichers, J . A m . Chem. Soc., 74,2447 (1952). (18) (a) National Bureau of Standards certificate for standard sample 39g; (b) R. S. Jessup, J . Research Natl. Bur. Standqrdg, 86, 431 (1848).
(20) D. D.Wagman, J . E. Kilpatrick, W. J. Taylor, K. 8. Pitzer and F. D. Rossini, J . Research N a t l . Bur. Standards, 84, 143 (1945). (21) E. J. Prosen, R. S. Jessup and F. D. Rossini, ibid., SS, 447
(1944). (22) F. D.Rossini, J . Chem. Phzls. 3, 438 (1935). (23) E. J. Prosen and F. D. Rossini, J . Research N u t ( . B q , Sfandarda, $7, 289 (1941).
W. N. HUBBARD, W. D. GOODAND GUYWADDIXGTON
616
TABLE V Hoi -
REACTIONS AT 298.1G°K., KCAL.MOLE-' -2.05 ~t 0.1224 n-Butane = 2-methylpropane 1-Propanethiol = 2-propanethiol -2.00 f .09' n-Pentane = 2-methylbutane -1.93 f .2626 1-Butanethiol = 2-methyl-1-propanethiol -2.19 f .29" 2-Thiapentane = 3-methyl-Zthiobutane -2.07 f .24" 1-Butanethiol = 2-butanethiol -2.1~k .27" This investigation. H"n
F O R S I M I L A R ISOnlERIZATION
Vol. 62
May, 1958
REACTION BETWEEN PLUTONIUM(VI) AND (111) IN PERCHLORATE SOLUTION
the systematic errors should cancel. An exception to that statement occurs if any samples contain significant impurity. In the present investigation the least pure samples, except 2-butane-thiol for which an accurate value of the purity is unknown, are 2-thiapentane and 3-methyl-2-thiabutane1 each containing 0.02 mole yoimpurity. On the assumption that the impurity is hydrocarbon and the ratio of heat of combustion per gram for hydrocarbon and sulfur compound is 11:8, the 0.02 mole % impurity would cause an error of 0.0075% or 0.06 kcal. mole-' in the heat of combustion. If the . precision of the measurements is considered, an error of such magnitude (probably a maximum estimate) is scarcely significant. Some support for the accuracy of the heat-ofisomerization data is provided by the close agreement of the values for several similar isomerization reactions tabulated in Table V. Two are for hydrocarbons24B25and four are for sulfur compounds studied in this Laboratory. I t is apparent that all '
617
the values agree within the assigned uncertainty. The values of the heat of formation of 2methyl-2-propanethiol and 3-thiapentane that were reported in earlier p u b l i c a t i ~ n s ~were ~ J ~ based on heat-of-combustion data obtained by methods in which all of the current refinements, particularly the change to Pyrex ampoules, had not been incorporated. Although the old and new values agree within the combined uncertainty, the values presented here are deemed more reliable and, hence, supersede the previous ones, A revision of the values of the heat, free energy and equilibrium constant of formation that were given prevlously is necessary t o make them consistent with the new values of the heat of formation. The revised values are not given here but will appear in a later paper on the isomerization equilibria of the seven C4HlOS isomers as a function of temperature. (24) E. J, Prosen, F. W. Maron and F. D. Rossini, ibid., 46, 108 (1951). (25) J. PI. Knowlton and F. D. Rossini, ibid., %a,415 (1939).
KINETICS OF OXIDATION REDUCTION REACTIONS OF PLUTONIUM. THE REACTION BETWEEN PLUTONIUM(V1) AND PLUTONIUM(II1) IN PERCHLORATE SOLUTION1 BY SHERMAN W. RABIDEAU AND ROBERT J. KLINE Contribution from the University of California, Los Alamos Scientific Laboratory, Los Alamos, New Mexico Received Januar~18,1068
+
The rapid, reversible reaction, P u + + + 3- PUOZ++ +Pu++++ PuOz+,W P S studied spectrophotometrically by.following the rate of disappearance of PuOz++ through the absorption peak at 8304 8. The reaction rates were found to be conveniently measurable even at temperatures of 35" with concentrations of PuOz++and P u + + +in the and 10-3 M ranges, respectively. The reaction is first order in each of the reactants and is independent of the hydrogen ion concentration over the ranges of acidity investigated: namely, 0.1 to 1.0 M . Specific reaction rate constants as functions of temperature have been obtained for both the forward and the reverse reactions in deuterium oxide and in ordinary aqueous perchloric acid solutions of unit ionic strength. Heats, free energies and entropies of activation have been obtained for both forward and reverse reactions in the two solvents. The observation was made that the specific reaction rate constant for the Eorward reaction decreased by a factor of 1.7 upon changing the solvent from ordinary water to deuterium oxide; however, the specific reaction rate constant for the back reaction was greater bv a factor of 1.5 in the deuterium oxide solvent. Thus a t comparable acidities, the value of the equilibrium quotient, [PuOz4+][Pu+++]/[Pu++++][PuOz+],increases approximately threefold upon changing the solvent from ordinary water to deuterium oxide. Addition of chloride ion to an extent threefold greater than the total plutonium concentration did not bring about a measurable change in either the forward or the reverse specific reaction rate constants.
Introduction Although the rapid reversible equilibrium among the four oxidation states of plutonium can usually be considered t o be maintained at all times,z the demonstrable slowness of the reaction between Pu+++and PuOz++has been reported in a previous communication. In these preliminary experiments the spectrophotometric recording equipment available did not permit the concentration of PuOz++ to be followed through its absorption peak at 8304 k. With the approximately ten-fold increase in sensitivity attendant upon the use of this peak (molar absorptivity of PUOZ++a t 8304 A. ca. 550 M-' cm.-l) the plutonyl ion concentrations could be in the lod4 M range to give reaction rates which were conveniently measurable without loss ( 1 ) This work was done under the auspices of t h e U. S. Atomia Energy Commission. (2) R. E. Conniak, J . Am. Cham. Soe., 71, 1528 (1949). (3) A. E.Ogard and 9. W. Rabidesu, THISJOURNAL, 60, 812 (1956).
of precision. The reaction between PuOz+ and Pu++++, the back reaction, must be considered even in the early stages of the experiment.
Experimental The spectrophotometric measurements were made with the Cary Model 14 recording instrument. The experimental procedure was similar to that described in a previous communication. The plutonium solutions were prepared from samples of an especially selected lot of high purity metal. The P u + + + stock solutions of known concentration were made by dissolution of the metal in the requisite weight of standardized Mallinckrodt 71 % perchloric acid. Fresh solutions of P u + + + were prepared daily to avoid interference from the gradual oxidation of the plutonium by the a-particle oxidation process. The stock solutions of plutonyl ion were prepared by prolonged ozonization of the perchloric acid solutions of Pu+++. All dilutions of the plutonium stock solutions were carried out on a weight aliquot basis. All solutions were prepared with distilled water which had been redistilled from alkaline permanganate in an all(4) 8. W. Rabideau, ibid., 62, 414 (1958).
