August, 1.962
DIPOLEMOMENT AND ~TAGNETIC SUSCEPTIBILITY OF DECABORANE
1449
THE DIPOI,E MOMEKT AND MAGNETIC SUSCEPTIBILITY OF DE CABORANE' BY
RUDOLPH 8. BOTTEL AND A. w. LAUBENGa4YER
DPpartment of Chemistry, Cornell University, Ithacn, New York Received Pebruavy 81, 1968
The dipole moment of decaborane has been determined by measuring the dielectric constants of benzene, cyclohexane, and carbon disulfide solutions. The data have been treated by the Debye method and by the method proposed by Guggenheim. The dipole moment varies from 3.17 in carbon disulfide to 3.62 in benzene. The magnetic suspectibility of decaborane has been determined by the Gouy method. Decaborane is diamagnetic; its gram molar susceptibility is -116 i 1.5 X
Introduction In a previous communicatioii,2 we reported the dipole moment of decaborane, BI0Hl4,as determined from measurements of the dielectric constants of benzene solutions and calculated by the Debye method. In this paper, additional data for benzene solutions are report?d, as well as data for cyclohexane and carbon disulfide solutions. The dipole moment has been calculated by the Debye method and by the method proposed by Guggenheim.3 The magnetic susceptibility of B10H14 as determined by the Gouy method also is reported. Experimental Purification of Solvents.-Benzene, Baker C.P., was dried with sodium, distilled, and fractionally crystallized four times, each time freezing out about two-thirds of the benzene and pouring off the remainder. It then was fractionally distilled over sodium through a 1-m. Schneider column. The middle fraction was redistilled and a new fraction that boiled a t 79.5-79.8' (uncorrected) was collected. The purified benzene was stored over sodium for a week before it waq used (dZ60.87360, lit. 0.873604 and 0.8736V; n2bo 1.4980, lit. 1.4981E). Cyclohexane, Matheson C.P., was treated in the same way as benzene. The final fraction collected had a boiling point of 79.8-80.1" (uncorrected). The purified cyclohexane was stored ovcr sodium (dZ60.77385, lit. 0.773837 and 0.7738g8; n z 5 1.4236, ~ lit. 1.423548). Carbon disulfide, Baker and Adamson C.P., was purified by two methods. One method9 involved extensive treatments with potassium permanganate solution, mercury, and mercury( 11) sulfate solution, followed by distillation in a nitrogen atmosphere. The carbon disulfide obtained was unsatisfactory. When decarborane was added to it, the decaborane was dispersed and a very cloudy liquid was produced. Carbon disulfide then was purified by first distilling over ceresin wax.l0 A middle fraction was distilled over phosphorus pentoxide in a nitrogen atmosphere. The purified material was stored in a brown bottle over phosphorus pentoxide and kept in the dark. Its purity was checked by determination of its critical solution temperature (c.s.t.) in (1) Taken in part from a thesis submitted b y R. S. B. in partial fulfillment of the requirements for the M.S., September, 1952, Cornell University. ( 2 ) A. W.Laubengayer and R. Bottei, J . Am. Chem. Soc., 74, 1618 (1952). (3) E. A. Guggenbeim, Trans. Faraday Roc., 47, 573 (1951). (4) A. L. Olsen and E. R . Washburn, J . A m . Chem. SOC.,57, 303 (1935). ( 5 ) D. R. Simonsen and E. R. Washburn, ibid., 68, 235 (1946). (6) A. V. Few and J. W. Smith, J. Chem. Soc., 753 (1949). (7) G. Scatchard, S. E. Wood, and J. M . Mochel, J . Am. Chem. Soc., 61, 3206 (1939). (8) A. F. Forziati, A. R. Glasgow, Jr., C. E. Willingham, and F. D. Rossini, .I. Res. Natl. Bur. Sfd., 36, 129 (1946). (9) D. L. Hammick and J. Howard, J . Chem. S o c . , 2915 (1932). (10) E. C. hIcKelvey and D. FI. Simpson, J . Am. Chem. SOC.,44, 108 (1922).
methyl alcohol; 80.24% CSz, c . 8 . t . 35.45", lit. 35.4°,10,11 85.32% CSZ, c.s.t. 35.56", lit. 35.6°.*0J1 Methyl alcohol, Baker and Adamson C.P., was dried with magnesium and distilled over sulfanilic acid'z (dZ60.7865, lit. 0.786613). Purification of Decaborane.-Decaborane was purified by sublimation under high vacuum at room temperature, m.p. 99.6-99.7 lit. 99.6-99.7.14 Preparation of Solutions.-The solvents were distilled under high vacuum a t room temperature from a suitable drying agent into weighed flasks. The flasks containing solvent were stored in a desiccator and reweighed juvt prior to the preparation of solutions. The sublimator, containing purified decaborane under high vacuum, was opened in a drybox through which dry nitrogen had been passed for a t least 1 hr. The drybox was equipped with a glass bulb through which liquid nitrogen was passed to condense the last traces of moisture before opening the sublimator. Decaborane was put into weighed screw-cap vials which were removed from the drybox and reweighed. After the vi& were returned to the drybox, dry nitrogen again was passed through i t for about 45 min. The last traces of moisture were removed as previously described. The caps then were removed from the vials and the vials slipped into flasks rontaining weighed solvent. The flasks were well shaken to ensure that all of the decaborane had dissolved arid the solutions were homogeneous. The solutions were transferred to the dielectric cell using a special siphoning apparatus so that there was very little exposure t o air during the transfer. Measurements.--The dielectric constants of the solutions were mesmred a t 25.0 f 0.02", using a heterodyne beat oscillator operated at a frequency of 1.57 Me. The dielectric constants a t 26" of the solvents used were taken to be: benzene, 2.2750,15 cyclohexane, 2.015,16 and carbon disulfide, 2.634.17 Refractive indices for the sodium+ line were measured at 25 It 0.10" with an Abbe refractometer (Bausch and Lomb). Densities of solutions were determined after the dielectric constants of the solutions had been measured. Measurements were made using standard Ostwald-Sprengel pycnometers which were calibrated a t 25" with pure standard water.'* The pycnometers were thermostated for about :1 hr. in a well stirred water bath regulated at 25 i: 0.002 . To standardize the effect of the adsorption of moisture, the pycnometers were wiped with a moist chamois and remained in the balance cape for 20 min. before each weighing. A tare was treated in the same way. After the initial weighing, the weight was rechecked after 10 min. more to ensure that thermal equilibrium had been attained. Weight8 ralibrated O,
(11) Interpolated values. (12) W. Heruld and K. L. Wolf, 2. pnysik. Chem., U B , 182 (1931). (13) H. T. Briscoe and W. T. Rinehart, J. Phys. Chem., 46, 387 (1952). (14) A. Stook, "Hydrides of Boron and Silicon," Cornell University Press, Ithaca, N. Y., 1933. (15) A. S. Brown, P. M. Levin, and E. W. Abrahamson, J . Chem. Phys., 19, 1226 (1951). (16) M. A. Govinda Rau and E. N. Narayanaswamy, Proc. I n d i a n Acad. Sci., 1, 14 (1934). (17) M. G. Nalone and A. L. Ferguaon, J . Chern. Phys., 2, 99 (1934). (18) A. Weissberger, "Physical Methods of Organic Chemistry," Vol. I, Interscience Publishers, Inc., New York, N. Y., 1945, p. 256.
R,UDOLPH8. ROTTEI
1450
AR‘D
according to the method of Richards were used. For each weighing?the pressure, temperature of the balance case, and the humidity were recorded. Densities were calculated as shown in Weissberger, page 275. No vapor correction was necessary because the gas space above the liquid in the capillary arms of the pycnometers was kept free of vapor by making them long and narrom.. A correction was made for the buoyancy effect of air. The densities were reproducible to & l x 10-8. The magnetic susceptibility was determined by the Gouy aethod, using a solution of KiCh whose volume susceptibility was 6.208 X 10-6 a3 a standard. The apparatus and method of measurement have been described by Coaroy and 8ienkoP The sample of decaborane was packed in the same recision bore Pyrex tube that was used in the calibration. &he packing was done in a drybox through which dry nitrogen was passed for 1 hr. The tube was sealed with a Lucite cap to protect the sample from moieture. The height of the same was measured with a cathetometer. The change of weight of the sample with changes in field strength was determined at the same temperature at which the calibration was made. The usual precautions were taken to ensure thermal equilibrium was attained and that a dry nitrogen atmosphere surrounded the sample throughout the measurements. Two sets of mearuiements were made on the same sample. Calculations.-Polarizations at infinite dilution, OPZ, were calculated by the Debye method and by the Guggenheim method. In the Debye method, oP2 was corrected for electronic polarization, P E , and atomic polarization, P A . The sum of PE and P A was assumed to be 1.15 times MRD, the molar refraction for the D-sodium line, which for RIOHI~ was 46 1. The dipole moment was calculated by the usual equation
w.IJAURENGBYER
,4.
Vol. 66
against Fc’ and the best value of [ ( e - GI)/W]W+O was estimated. Likewise, the best value of [(n9- ~ I ~ ) / W I U - O , where n is the refractive index of the solution and ni that of the solvent, was estimated. The value of [(nz- n ~ ~ ) / W l l*-to was subtracted from [ ( E G ~ ) / W ]toWobtain ~ O (A/W)2L1+o, m-here A is equal to [(e - € 1 ) - (nz - n l z ) ] . Polarizations at infinite dilution were calculated using the equation
-
here M z is the molecular weight of the solute and d1 is the density of the solvent. Polarizations at infinite dilution were corrected for atomic polarization (0.15 P E ) and the dipole moment was calculated in the usual manner.
Results The molar polarizations of Bl0H14as determined by the Debye method are listed in Table I In Table I1 are listed the data for the calculation of the dipole moment by the Guggeiiheinz method. The dipole moments of BI0Hl4are listed in Table 111. Decaborane is diamagnetic; the gram molar susceptibility is -116 i 1.5 X
*
TABLE I1 EXPERIVEKTAL DATA9 K D CALCULATED AIOLAR POLARIZATION OF B l o H 1 4 - G ~ METHOD ~ ~ ~ ~ ~ ~ ~ ~ ~ e - €1 __
where T is the absolute temperature. In the Guggenheim method,20 the data E - Q / W ,where e is the dielectric constant of solution, el, that of the solvent, and W is the weight fraction of the solute, were plotted
TABLE I MOLEFRACTIONS AND MOLARPOLARIZATIONS OF B10H14DEBYEMETHOD Mole fraction
Molar polarization
I n benzene 0 0071345 0073878 0078698 014133 .017660 018691
OPz
307 306 304 297 293 290 315
4 2 3 5 3 4 3
In cyclohexane 0 0037279 0093958 0094486 011287 014205
021043
291.0 287 7 286 3 286 6 287 9 291 1 oPz = 288 0
In carbon disulfide 0 0024542 0048692 0085013 0095470 .010818 oPs 119) L. E. Conroy and
256 262 259 262 257 = 259
9 9 6 8 5 0
M. J. Sienko, J . Am. Chem. Soc., 74, 3250
( 1952).
(20) This method is most advantageous since densities need not be determined.
‘w
-
n2
W
€
1212
W
n
In benzene 2 2 2 2 2 2 2 2
0 0 011127 011520 012268 021662 021954 027533 028964
2750 40736 41223 42222 53054 53819 60466 61931
(7) T*-0
0 0,0054087 ,013697 ,013673 ,016319 ,020512 ,030222
= 12.12
11 899 11 910 12 011 11 796 11 887 11 701 11 987
1 4980 1 4989 1 4989 1 4990 1 4998 1 4998 1 5002 1 5503
rq)
W+O
=
0 242 234 245 249 240 240 238
0.24 OPz = 272.7
I n cyclohexane 2,015 1,4236 2.0605 8,412 . . .. 1,4254 8.856 2,1354 2.1354 9.806 1,4255 1.4258 8,860 2,1596 1,4264 8.994 2,1995 2.2962 9.304 1.4274
... 0,382 ,397 ,380 ,390 ,397
=
$9
0
0 0039371 0077999 013588 015250 017266
2 2 2 2 2 2
In carbon diwlfide 634 1 6235 1 6231 I6 133 6975 1 6226 15 595 7556 1 6221 15 519 8503 1 6219 16 041 8786 1 6217 16 085 9117
=
16.12
r?)
w-0
=
233.2
-0 432 - 385
-
-
338 341 349
-0.45 oP2
=z
225.0
SPECTRA OF CHEMISORBED ETHYLEKE ON ALTJMISUM OXIDE
August, 1962
1451
prepared as described in the Experimental part of this paper. The longer the exposure, the greater was the molar polarization. The extent of reSolvent Debye method Guggenheim method action, however, was very small, because if 3.36 Ilt 0.02 D. Cyclohexane 3.39 f 0.02 D. Bl0H14 which had been exposed to moist air for 3.62 =t . 0 2 D . 3.61 f .03 D. Benzene a short time was sublimed, the amount of non3.17 i .03 I). 3.26 =t .04 D. Carbon disulfide sublimable residue from a charge of about 2 g. Discussion was barely enough for a melting point determinaThe dipole moments as calculated by both tion. The amount of residue increased with inmethods are in rather good agreement. There creased exposure, but it was never very much. is no c'orrelatiosi between the dipole moment and The residue was orthoboric acid as determined the dielectric constant of the solvent in which the from its melting point, microscopical observation, dipole moment was measured. It was, therefore, and X-ray powder pattern, The increased polarity not possible, as originally planned, to use the probably is due to a rather rapid surface reaction equation proposed by SmythZ1for the ratio of the which introduces the very polar OH group into the dipole moment' in solution to that of hhe gas. BI0Hl4molecule. If the diamagnetic atomic susceptibility of The high value of the dipole moment has been 2 3 and that of boron is taken to be -6.7 x rationalized by molecular orbit,al treatmentz2 of boroln hydride structures using a three-center- hydrogen as -2.93 X 10-6,24the calculated gram molar susceptibility is -108 X The difbond approximation. Although it has been reported that' Bl0Hl4is ference between the experimental and calculated quite stable to oxidation and hydrolysis by moist values probably is due to the value that has been air a t room temperature, preliminary experiments assumed for hydrogen. The value used is for a showed that even short, exposure to moist' air led singly-bonded hydrogen and probably will not hold to variable results. Molar polarizations were for the four bridge-bonded hydrogens. The calalways greater for solutions prepared using BIaH1* culated value would be in closer agreement with which had been exposed to moist air than for those the experimentValvalue if a constitutive correction for this bonding were available. TABLE I11 DIPOLE MOMENTS OF BIOHI,
(21) W. P. Conner, R. P. Clarke, and C. P. Smyth,
J. Am. Cham.
Soc., 64, 1379 (1942).
(22) W. B. Eberhardt, B. Crawford, Jr.. and W. N. Lipscomb, J . Chem. P h y s , , 22, 989 (1954).
(23) L. Klemm, 2. Elektrochem., 46, 434 (1939). (24) P. W. Selwood, "Magnetochemlstry," Interscience Publishers, Inc., New Yolk, N. Y., 1943, p. 52.
AN INFRARED STUDY OF THE CHEMISORPTION OF ETHYLENE ON ALUMISURII OXIDE BY P. J. LUCCHESI, J. L. CARTER, 4ND D. J. C. YATES Esso Research and Engineering Company, Linden, New Jersey Receised March 1. 1.962
An infrared study of the adsorption of ethylene on aluminum oxide shows several interesting features about the nature, orientation, and reactivity of the adsorbed s ecies. On some oxides, room temperature adsorption leads to the slow formaInation of ethyl groups S-CH2CH8 (9 is a surface site). The formation of C2H,involves self-hydrogenation, as the oxide contributes no hydrogen. The surface species reacts with hydrogen at 450' to give CH4, CsH6, and C3H8in the gas phase. This In contrast, on another crystallographicallv similar oxide, ethylene adsorption leads to the formation of S-CH&Hn-S species reacts with hydrogen a t 450' t o yield first S-CHZCHI and then gaseous C2H,. The results are discussed in terms of their significance in the general problem of elucidating the nature of the chemisorption and catalytic hydrogenation of ethylene on aluminum oxides. KOchemisorption of ethylene was found to occur on silica at room temperature.
Introduction The advent of the infrared method for studying the adsorption of gases 011 solids has provided a new tool for probing the det!ails of cat,alysis. Thjs met8hod can give direct information about the nature wid orientation of the adsorbed species. A fairly substantial literature has developed on this subject,, and has been reviewed recently.1r2 One of t8he catalytic reactions that has 'been studied in some detail is the hydrogenation of ethylene. A central problem h.as been the elucidation of the details of ethylene chemisorption on various surfaces. Data on nickel films314 showed (I) (2) (3) (1)
R. P. Eischens a n d W. A. Pliskin, Adsan. Catalysis,10, 2 (1958). V. Crawford, Quart. Rev. (London), 14, 378 (1960). 0 . Beeck. Discussisns Faraday ,Sot., 8 , 118 (1950). G. I. Jenkins and E. I
