March, 1960
NOTES TABLE VI1 HEATSOF SOLUTION
STANDARD
Sult
KMnOr K~MoO~ KClOI KaC103 Na2Cr04 Na2Cr20,(re,xction 2)
A.H(kcnl./mole)
10.41 i 0.06 - 0 . 9 5 i .10 9.89 f .06 5.18 f .Of3 -4.57 f . l o -21.37 f .18
Thermodynamic Calculations Brown, Smith and Latimers have determined the entropy of KMn04(c) a t 298°K. to be 41.04 cal./deg. mole :tnd have calculated from solubility data that the standard free energy of solution of KMn04(c')is 1710 cal./deg. mole. We have combined these data with our heat of solution and the NBSs standard partial 'molal entropy of K+(aq) to obtain ASQ = 29.2 cal./deg. mole for the entropy of solution of KMn04(c) and 45.7 cal./deg. mole for the standard partial molal entropy of Mn04-(aq). This latter entropy differs from the NBSs value (45.4) because .we have used our heat of solution rather than that, of Roth and Becker' whose work was carried out a t 16.6 and 21.6' and with more concent,rated solutions. The heat of formation of K2Mo04(c)has been calculated to be -357.3 kcal./mole from our heat of solution and the heats of formation of Moo4(aq)2and :K+ The standard free energy of solution of KC103(c) has been calculated to be 1.19 kcal./mole from the s o l ~ b i l i t y *and ~ ~ the activity coefficientDin saturated solution. We have used this AFO with our AHo to calculat,e the entropy of solution, ASo = 29.1 cal./deg. mole. This ASo and the entropies of KC1O3(c)Ioand K+(aq)blead to 38.8 cal./deg. mole for the standard partial molal entropy of C103-(aq). Earlier heats of solutionb were carried out at temperatures lower than 25" and with solutions more concentrated than ours. Standarmd heats of formation of NanCr04(c)and Na2Cr20,(c) have been calculated to be -318.6 and - 468.8 kcal./mole, respectively, from our heat of solution of Na2Cr04(c) and our heat of solution of Xa&r2O7(c) in OH -(aq) as in equation 2. Heats of formation of Cr04'(aq),11 Na+(aq),6 OH-(aq)b and H20(l)bhave been used in these calculations. The stmdard partial molal entropies of MnOa(as) and c103-(aq) may be combined with other thermodynamic data6 to obtain standard free energies of formation and oxidation potentials and the heats of solution of KMnOl(c), KC103(c) and NaClOs(c) may be combined with other heat databto obtain heats of formation. Acknowledgment.-We are grateful to the National Science Foundation for financial support, to (6) 0. L. 1. Brown, W. V. Smith and W. M. Latimer, f.A m . Chem. Soc., 68, 2144 (1936). (7) W. A. Hoth and G . Becker, 2. phurik. Chem., A169, 27 (1932).
(8)A. Seidell. "Solubilities of Inorganic and Metal Organic Compounds," D. 'Jan Nostrand Co.. Inc., New York, N . Y.. 1940. (9) J. H. Jones and H . R . Froning, J . A m . Cham. Soc., 66, 1672 (1944). (10) W. M . Latimer, P. W. Schutz and J. F. G. Hicks, Jr.. tbid., 16, 88 (1934). (11) L. G. Heder. ibid.. 80, 6181 (1958).
377
the Alfred P. Sloan Foundation for a research fellowship for one of us, to Mr. Richard Jesser for doing much of the work on K2Mo04and to Mr. Merritt Birky for assistance with some of the calorimetric experiments. SEPARATION O F WAXES FROM PETROLEUM BY ULTRACENTRIFUGATION BYC. W. DWIGGINS AND H. N. DUNNING U. S. Department of the Interior, Bureau of Mines, Bartlesville, Oklahoma Received October 2.9, 1969
The colloidal properties of asphalts have long been recognized. More recently, the colloidal nature of crude petroleum has been established by ultracentrifugation.2 The results of these studies emphasized the presence of asphaltic materials and of some inorganic residues in the sediment. Other studies have shown that asphaltenes are sedimented during ultracentrifugation and contribute largely to the viscosities of the ultracentrifugal fraction^.^ However, studies in this Laboratory show that the sediment from several crude oils contains relatively large amounts of waxes. Although the presence of microcrystalline waxes in crude oils has been known for several years,4 there have been no reports of the sedimentation of these waxes during ultracentrifugation. Four crude oils, from Oklahoma, Texas, and Kuwait, were ultracentrifuged for 3 hours at an average force of 60,OOO times gravity in a Beckman Model L ultracentrifuge equipped with a No. 40 angle-head rotor. The shortest practical period waa used to minimize asphdtene sedimentation. The sediments were drained of oils and suspended in chloroform with ultrasonic agitation. Then the chloroform suspensions were centrifuged for 2 hours at an average force of 40,000 times gravity. During this centrifugation, waxy materish accumulated at the top of the tubes, most of the residual oils were dissolved in the chloroform, and inorganic materials sedimented to the bottom of the tubes. This purification process waa repeated. The waxy materials thus obtained were dried, melted, and allowed to cool for X-ray diffraction studies. Softening points ranged from 80 to 90". The waxy material obtained from Texas Wilcox oil was only slightly colored; those from the other oils were darker but still translucent.
X-Ray diffraction patterns of the waxy materials from the four crude oils are similar and resemble those of waxes reported in the literature. In Fig. 1, the X-ray diffraction pattern of the waxy material centrifuged from the Kuwait crude oil is compared to that of a carefully purified, highmelting-point, microcrystalline wax stock, "190 Special," similar to Petrolite C-1035 produced by the Bareco Wax Co., division of Petrolite Corp. The X-ray diffraction pattern of the waxy material is distinct and in good agreement with that of the pure wax. These X-ray diffraction data (1) J. Pfeiffer and R. N. Saal. THIB JOURNAL, 44, 139 (1940). (2) B. R . Ray, P. A. Witherspoon and R . Grim. ibid., 61, 1296 (1957).
(3) H. N. Dunning, I. A. Eldib and R. J. Bolen, presented at the Diviaion of Colloid Chemistry, Am. Chem. Soc. Meeting, Atlantin City, N. J. (September 16, 1959). (4) J. W. Home and J. W. Watkina. Bureau of Minw Tenhnical Paper 715, 1949, 47 pp.
NOTES
378
90
il
I
'oo/-
-05
10
,
,
15
20
28,
COPPER
1 25
30
35
K,.
Fig. 1.-X-Ray diffraction patterns of wax ultracentrifuged from crude oil and of commercial, high-melting point wax.
are rather positive proof that the materials centrifuged from crude oils, as described above, are waxes. Their softening points and lack of solubility in solvents such as hydrocarbons and chloroform indicate that they are of relatively high molecular weight. The ease with which these waxes were ultracentrifuged from petroleum indicates that they were present as unstable colloids, probably in a, suspended microcrystalline form. These results indicate that the sediment obtained from ultracentrifugation of petroleum often contains relatively large amounts of wax in addition to the asphaltic materials previously identified.2.3 Such waxes must be taken into account during interpretation of ultracentrifuge data based on sediment obtained. Because the centrifugal forces used axe in the range of supercentrifuges, the centrifugd method may prove commercially applicable for clarification of crude oils or refinery stocks and for the preparation of high-molecularweight waxes.
THE HEATS OF COMBUSTION OF SOME COBALT AMMINE AZIDES B Y TERENCE M.
DONOVAN, c. HOWARD SHOMATE AND TAYLOR B. JOYNER
Chcmislry Divisron, Research Department, U. S., Naval Ordnance Station. Chrna Lake, Cali/ornta. Received October SO, 1960
1881
There has lbeen recent interest in the thermodynamics and kinetics of metallic azides. Previously the heat of formation of thallium azide was determined in this Laboratory.2 During the (1) B. L. Evans. A. D. Yoffe and Peter Gray, Chcm. RwB.. S9, 51.5 (1859).
Vol. 64
course of a study of the thermal decomposition of some cobalt ammine azides it was thought desirable to have values of their heats of formation and the present study resulted. Experimental Materials.-The compounds were prepared and purified by previously described methods.3- X-Ray powder pattrrns were used to identify all compounds except [Co(NH&(N&]. Corroborating evidence of the composition of [Co("&I( N3)3 end .[Co(NH&N3]( N 3 ) 2 was obtained during t.he course of kinet,ic studes of their thermal decomp~sition.~ Explosions prevented similar studies of the remaining compounds. The very explosive [Co(NH3)3(N&] wsw obtained by individual preparations each yielding enough material (a). 400 mg.) for a single combustion. This was carefully washed but, not recrystallized because of the rapid hydrolysis in warm water.' In view of these difficulties, some uncertainty must be attached to the reported AH+ of this compound. Measurements.-The measurements were made with calorimetric equipment described previously.s*9 Bcnzoic acid (N.B.S. sample No. 39g) was used in determining the energy equivalent of the calorimeter which was 2789.36 i 0.43 cal. deg.-' for all determinations. All weighings were reduced to vacuum and all heat values are expressed in defined calories ( I cal. = 4.1&10 abs. joules). X-Ray powder patterns of the solid residues showed the lines of COO and COaOc only, except in the case of [Co(NH3),(N&] where t8he lines of cobalt metal also were evident. Average values of the 0:Co ratios as determined by reducing the residue samples in a stream of HP a t 700" are: [ CO(NHJ)G]( N3)3. 1.1232; [Co[NHs)sNs](N3)2, 1.1577; n's1.1285; tram- [ CO(NH3)4(NB)&s, CO(NH3)4(NI)P]N3, 1.1253; and [Co(NHa)3(Na)s],0.8401. All the energy values were corrected to correspond to cobalt aa the free metal in the final product using 57.1 kcal. mole-' as the heat of formRt,ionof COOand 35.7 kcal. g. atom-' as t.he energy of combination of the excess oxygen.l0 The exhaust gases were tested for oxides of nitrogen and carbon monoxide spectrographically and the bomh washings were tested for soluble cobalt with KOCN. Observat,ion of the bomb wmhings showed no starting material which in all cases except the [Co(NH,)&N3)3] consisted of highly colored water -soluble matenal. A 360-ml. Parr double-valve oxygen bomb with 1 ml. of water waa flushed for 15 minutes m t h oxygen a t slightly greater than atmospheric pressure and then filled to 30 atmospheres for the combust,ions. Corrections were made for the ignition wire and fuse material. The observed values for the heat of the bomb process were corrected to obtain values for the energy of the idealized combustion reaction in which all the reactants and products were in their standard states a t 25" and no external work was performed. The corrections, which included those for the formation of nitric acid, were made as described by Huhbard, Scott and Waddingt0n.l'
Results The determined heats of combustion are: [Co(NHs)~] (Nd3, -645.5 0.3; [Co(",)i"I (N3)z: -562.8 f 0.4; ~ ~ u ~ ~ - [ C O ( N H ~ ) ~ ( N -500.3 ~)Z]~CT~, 0.8; ~ ~ s - [ C O ( N H , ) ~ ( N ~-500.8 ) ~ ] N ~ ,f 0.4,
*
(2) W. S. McEwan and M. M. Williams, J. Am. Chem. Soc., 76, 2182 (1954). (3) M. Linhard and H . Flygare, Z. anorg. allgem. Chem., 262, 328 (1950). (4) M. Linhard and M. Weigel, ibad., 463, 245 (1950). (5) M. Linhard, M . Weigel and H. Flygare, &bid..268, 233 (1950~. (6) T. B. Joyner, D. A. Stewart and L. A. Burkardt. Anal. Chcm., SO, 194 (1958). (7) To he reported by Taylor B . .Ioyner and Frank Verhoek. (8) W. S. McEwan and M . W. Rigg, J. Am. Chem. Soc., 73. 4725 (1951). ( Y ) M. M. Williams, W. S. M c E r a n and R . A Henry, THISJ O U R N A L , 61, 2G1 (1957). ( 1 0 ) B. J. Boyle, F . G. King and K . C. Conway, J. Am. Chem. Sor., 76. 3835 (1954). (11) W. N. Hubbard. D. W. Scott and G . Waddington. THISJonaN L L . 68. 152 (1954).
