Sept., 1958
1145
XOTES
TABLE I1 VAPORPRESSURE OF LIQUIDTHORIUM TETRAFLUORIDE BY THE QUASI-STATIC METHOD Temp., OK.
Pressure, atm.
Temp.,
1437 1450 1466
x 10-3 x 10-3 3 . 0 7 x 10-3 2.64: x 10-3 3.91 x 10-3 3.96 x 10-3 4.09 x 10-3 5.03 x 10-3 5.88 x 10-3
1.501 1529 1532 1535 1555 1575 1575 1595
2.03
:$. 15
1466
1460 1470 1477 1484 1499
OK.
Pressure, atm.
6.07 x 9.34 x 8.77 x 9.71 X 1.33 x 1.72 X 1.71 X 2.44 X
10-3
10-3 10-3 10-3
10-2
squares treatments of the log P us. 1/T data. The equations are sublimation log
Phtrn) =
-
+
(16,860 f 190) T (9.105 i 0.160), (1055-1297°1C.)
(2)
(15,270 zk 310) T (7.940 f 0.206), (1427-1595'K.)
(3)
vaporization log P ( s t m ) =
-
+
Vapor pressure measurements were not carried out a t the melting point because neither method is applicable in this pressure range. Comparison of the results was made by extrapolating equations 2 and 3 to the melting point (1383°K.); vapor presatmosphere, sures of 8.2 X lop4 and 7.9 X respectively, were obtained. The heats of sublimation and vaporization a t the mid-temperatures in each set of experimental data are AH11,6(subl)= 77.1 f 0.9 koal./mole AHlr18(vap) = 69.9 f: 1.5 kcal./mole
(4) (5)
The AC, of vaporization (- 19 cal./deg./niole) estimated for the other tetrahalides of thorium by L. Brewer, and reported in N.B.S. Circular 5OOj9 was used in the free energy of vaporization equation
-.
I xi04 T OK
Fig. 1.-Plot
of log P us. 1/T for thorium tetrafluoride.
and 232 also were observed. These masses are attributed t o ionization of ThF4(,, to ThF3+, ThF2+, T h F + and Th+. Corresponding peaks for the dimer of ThF, mere not observed over the temperature range of these measurements. Acknowledgments.-The authors wish to thank Dr. T. A. Milne and Dr. S. J. Yosim for the helpful discussions concerning these results, Mr. W. A. McCollum for assistance in performing the experiments and Mr. L. Silvernian for carrying out the cheinical analyses.
- ACpT In T + I T (6) The constants AHo and I are evaluated from (3) T H E ABSORPTION SPECTRUM OF THE A P T = AH0
as 98,660 and - 194.50, respectively. Equation G gives a normal boiling point of 1953°K. for ThF4. Application of this AC, correction to (5) yields AH1963(vap) = 61.6 kcal./mole, AS1953(vap) = 3 1.5 cal./deg./mole. Some conclusions may be drawn regarding the vapor species of ThF4 by comparing the vapor pressure data from the two methods. The quasi-static method gives the total pressure above the salt. The results from the effusion method were calculated by assuming the salt vaporized as the monomer. The agreement of the two sets of data on extrapolation t o the melting point represents good evidence that ThF4 vaporizes as the monomer. This conclusion is substantiated by mass spectrographic studies made on ThF4effusing from a Knudsen cell. The predominant peak mas due t o mas8 289; smaller peaks representing masses of 270, 251 (9) F. D. Rossini. D. D. Wagman, W. H. Evans, S. Levine and I. Jaffe, Selected Values of Chemical Thermodynamic Properties, National Bureau of Standards, Circular 500 (1952).
TITANIUM(1V)-HYDROGEN PEROXIDE COMPLEX BY DAVIDLEWIS Department o f Chemistry, The City College, New York SI, N . Y Receaved March 26, 1958
The colored complex formed by the reaction 01 Ti(1V) and hydrogen peroxide in strong acid solution, usually AI sulfuric acid, is characterized by an absorption band with a maximum a t 405-10 mp and a molar absorptivity of ca. 730. Most measurements of this spectrum have been made on solutions or less in Ti(IV), since this is the analytically useful range of the colored complex. Reeves and Jonassen' have examined the spectral behavior of more concentrated solutions; they report that above a concentration of 1.2 X 10-8M Ti(IV) the maximum shifts progressively toward (1) R. E. Reeves and H. B. Jonassen, J . Am. Cham. SOC.,76, 5354 (1 954).
1146
NOTES
lower wave lengths and lower molar absorptivities with increasing concentration of the complex. Results obtained in this Laboratory on solutions in the same concentration range studied by Reeves and Jonassen show no change in the maximum wave length and only a slight decrease-3.5Y0--in molar absorptivity compared to the value for more dilute solut,ions. The curves in Fig. 1 show the
Vol. 62
rather than of Ti(IV) when treated with hydrogen peroxide. The simplest explanation of their results would be to attribute the decrease in molar absorptivity t o incomplete complex formation; and, since uncomplexed Ti(1V) does not absorb in the spectral region reported, the shift in the maximum wave length would be due to the increasing contribution of the organic species to the spectrum.
A THERMODYNAMIC INVESTIGATION OF '
DIBORON TETRACHLORIDE
BY M I L T ~J. S LISEVSKYA N D THOMAS WARTIK Contribution f r o m The Pennsylvania Stale University, College of Chemist r y and Physics, Department of Chemistry, University Park, Penna. Received M a y 9, 1958
Diboron tetrachloride is one of the relatively few boron compounds which contain a boron-to-boron single bond. Although reasonable progress has been made toward its chemical characterization1-3 and although its structure has been determined by X-ray diffraction4 and by spectroscopic a n a l y s i ~ , ~ its thermodynamic properties have not previously been investigated. The principal deterrent t o its thermodynamic investigation is its low stability. Although decomposition in the vapor phase is J 1 apparently not too rapid, liquid BzC14begins t o de320 350 400 450 500 compose almost immediately at room temperature. Wave length, mp. The authors have measured heat capacities of Fig. l.-Absorbance of solutions of the Ti(IV)-H202 B&14 in the region from 13.42 t o 214.51°K., in complex in M HzS04 and 0.20 M H202: up er curve, 2.28 x M Ti: lower curve 1.14 X loM2M $i. Crosses (+) which range no abnormalities were observed. indicate location of maxima reported by Reeves and Jonas- The heat of fusion was found t o be 2579 f 4 cal. sen. per mole, and, using a correction for liquid-soluble, solid-insoluble impurities, the temperature of fusion spectra for two solutions, the upper curve cor- of pure BzC14 was estimated to be 180.21"K. responding to the highest concentration reported by and Purification of B2Cl4.-B2Cl4was prepared Reeves and Jonassen. The data are plotted on an byPreparation the method of Wartik, Moore and Schlesinger,' and was absorbance scale; on the molar absorptivity scale purified by fractional distilhtion in a low temperature used by Reeves and Jonassen the two curves would column similar to that described by Simons.6 With the be identical within experimental error. The crosses pressure in the column a t about 10 mm., distillation occurred t -20". The vapor pressure of the compound at 0" indicate the location of the maxima estimated from aagreed with the reported value of 44 mm. By this method, their data. This region was examined a t 2 nip 19.7 g. of purified B2C14was obtained and kept in an ampoule intervals but no evidence of any discontinuity in a t -78.5' until ready for use. To eliminate the effects of the inevitable decomposition the curve was found. The spectra were obtained occ,urred during the weighing of the sample, the latter with a Beckman DU Spectrophotometer using which was weighed after, instead of before, the heat capacities 1.00 cm. cells and inserts t o give a -1.00 mm. path were measured. Through careful handling and rapid length. Replicate measurements gave for the transfers, a purity of 98.50 mole yowas realized in the sample maximum a = 705 =I= 1, 707 =I= 5, X 405-10 mp, studi.ed. This purity, although far below that usually in this Laboratory, is probably close t'o the maxiTi(1V) and for the achieved 405-IOmp for the 2.28 X mum which can be espected.in view of t,he fact t,hat t.he 1.14 X 10+ 14 Ti(IV) solut,ions, respectively. sample had to be introduced int>othe calorimeter through R The only significant difference in the experi- relatively long filling tube of very small diameter. Measurement of the Heat Capacities .-The heat capacimental procedure of Reeves and Jonassen and that of B2C14 were measured in isothermal calorimeter "C" reported here lies in the method of preparing the ties (with thermocouples S, and S,) of the Cryogenic LaboraTi(IV) solutions. The former hydrolyzed tetra- t,ories. The apparatus, method, and temperature scale isopropyl titanate with cold 5 N sulfuric acid and were as described by Messerly and Aston.? One defined used the resulting hydrolysis mixture for their calorie was taken as equal to 4.1833 international joules. Bethe sample was introduced, the calorimeter was exposed measurements ; in this work titanium metal sponge fore - - .___ (du Pont, assay 99.63%) was dissolved by boiling (1) T. Wartik, R. Moore and H. I. Schlesinger, J . Am. Cham. Sac.. with concentrated sulfuric acid and the addition, 11, 3265 (1949). (2) G . Urry, T. Wartik, R. Moore and H. I . Schlesinger, ibid., 76, a t intervals, of 30% hydrogen peroxide to oxidize (1954). the accumulated Ti(II1) salts to Ti(1V). I9'ince 5293 (3) A. Stock, G. Brandt and A. Fisher, Ber., 58, 653 (1925). the latter solutions gave identical spectra with hy(4) A. Atoji, W. Lipscornb and R. Wheatley, J . Chem. Phvd., 23, drogen peroxide in the entire concentration range 1176 (1955). ( 5 ) D. E. Mann and L. Fano, ibid., 26, 1Gfi5 (1957). investigated, it must be concluded that the varying (6) J. H. Simons, I n d . E n g . Chem., Ana2. E d . , 10, 29 (1938). spectra obtained by Reeves and Jonassen reflect the (7) J. G. Aston and G. Messerly, J . A m . Chem. Sac., 68, 2354 behavior of their mixture of hydrolysis products (1937); 62, 886 (1940).
