XOTES
42 1
Regeneratioin consisited of heating the spent catalyst to 650' in a muffle furnace and holding a t that temperature for 13 hr.
Results and Discussion A fresh catalyst sample was used for each treatment to give the r e d t s shown in Table I[. The theoretical adsorption based upon 0.88 CO molecule per Pd atom4 was calculated to be 0.654 cc./g. The results of Table I show that there is no crystal growth of palladium a t 450' under vacuum, since practically the theoretical adsorption was obtained. The 90% of theoreticad obtained on the fresh catalyst was perhaps caused by previously adsorbed CO from the atm.osphere.
-~
--
Table I : Effect of Catalyst Treatment on CO Adsorption Conditions
Hz treatment, 'C;.
J. J. F. Scholten and A. Van Montfoort, J . Catalysis, 1, 86 (1962). ( 5 ) N. V. Sidgwick, "The Chemical Elements and Their Compounds," Val. 11,Oxford University Press, London, 1950, p. 1558
Cc. STPCO/g.
100 0 496 f 0.O2lcL 100 0.524 i 0.029'L 100 0 , 1 9 1 f 0.042'L 100 0.441 i 0.034" 100 0 . 55* 100 0 . 2Ob 100 0.267 f a) 023" 300 0 .34b 350 (24 hr.) 0.25* * Single detera Average deviation on triplicate analyses. mination. 25 300 300 450 450 450 650 650 650
Acknowledgment. The authors wish to express their appreciation to the Harshaw Chemical Co. for their cooperation and assistance in sample preparation and analytical problems. (4)
Temp., O C .
palladium alumina compound, which is not reducible with hydrogen, has not been eliminated, crystal growth is the preferred explanation for the data observed. I t is also concluded that crystal growth of the palladium metal particles can occur a t temperatures below 4001' and that oxygen is an accelerator for this process. ThLe exact nature of the reactions involved is not understood a t this time, but it is believed that palladium oxide may be considerably more mobile than the metal itself, leading to increased crystallite formation as the oxygen severity is increased.
Air, 1 atm. Air, 1 atm. Oxygen, 1 a t m Air, 1 atm. Vacuum Oxygen, 1 a t m . Air, 1 atm. Air, 1 atm. Air, 1 atm.
-
That oxygen is the major cause of the decrease in palladium surface is demonstrated by a comparison of the results obtained using air a t 1 atm. us. oxygen a,t 1 atm. a t a given temperature. For example, a t 450' under vacuum, essentially theoretical adsorption oocurred, while in air the adsorption dropped to 80% and in oxygen to 36y0. This effect of oxygen cannot be attributed to the formation of higher oxides of pallndium, since these are known to be unstable and readily reduced with hydrogen a t room temperature.6 It is possible, however, that a palladium oxide-alumina complex exists which is difficult to reduce, since a 300° reduction temperature on the 650' catalyst gave 60% of theoretical adsorption as compared with 50% when reduced at 100'. Additional time of hydrogen treatment, as shown by that which wa13 treated 24 hr. a t 350°, did not show any benefit. In view of the data presented, it is concluded that far greater differences exist between palladium and platinum-alumina catalysts than might be inferred from differences in Tamman temperature and other physical properties. Although the possibility of a
The Electric Dipole Moment and Molecular Conformation of the Heterocycle Boron-
Oxygen-Ni trogen-Boron-Oxygen-Nitrogen
by H. Bradford Thompson,' Lester P. Kuhn, and Masahiro Inatome Alfred AVobel Science Laboratories, Gustavus Adolphus College. St. Peter, Minnesota, and the Ballistics Research Laboratories, Aberdeen Proving Ground, ,Maryland (Receiaed J u l y 31, 1963)
Synthesis and structural proof of two compounds having the cyclic structure I have been reported,a and the name Bon-:Bon proposed for this ring system.
This structure should be nonpolar if the chair form prevails. Accordingly, we have measured the electric dipdle moments in solution for the two knov7n BonBons, the dimers of (aminooxy)di-n-butylborane and (n-buty1aminooxy)di-n-butylborane. Results are surnmarized in Table I. (1) Department of Chemistry, Iowa State Cniversity, Ames, Iowa. (2) L. P. Kuhn and M. Inatome, J . Am. Chem. Soc., 8 5 , 1206
(1963).
Volume 68, iVumber 2
February, lB64
422
?rTOTES
electric moment of 2.4 D. and the form lIb, 5.4 D. The moment of IIc would be 2.6 D. and forms inter-
Table I : Electric Dipole Moment Data and Results Concn. X 105, mole/ml.
Sa
c
n26D
Moment, D.
(R2BONHz)z in CC14 ( R = n-butyl), Solvent 0.160 0.315 0.470
1 ,45783 1 ,45786 1.45790 1.45790
2.20820 2.20824 2.20817 2.20829
(R2BONHR)Z in CC14 ( R Solvent 0.150 0.337 0,582
‘ Slope for ( e
1,45786 1 ,45783 1 ,45783 1.45780
-
2.20847 2.20847 2.20863 2.20832
0.0 =
0.0 f 0. 2
n-butyl)
0.0
+ 2)(n* + 2) c’s. concn.
n2)/(~
0 . 0 i0 . 2 See ref. 7.
Discussion It is apparent that both Bon-Bons have very small electric dipole moments. Since the moment is proportional to the square root of the orientation polarization, the uncertainty (both relative and absolute) in a dipole moment is quite large when the moment is small. Nonetheless, the data clearly suffice to establish a nonpolar conformation. This should be either a chair or a flexible form; a planar structure seems most unlikely for tetracovalent nitrogens and borons. It is clear that the chair form will have a small or zero moment, since, ignoring possible orientations of the butyl groups, it has a center of symmetry. The moment of the flexible form is somewhat more difficult to predict; to estimate this we have assumed the bond parameters in Table II.3-5
Table I1 : Bond Lengths and Momenta Assumed Bond
Moment
Ref.
R-B R-h’ B-0
0.0 0.6
S-0
0.30 2.55 I. . 3 1
Estimate” 3 Estimate” 3 5 3
K-B H-B a
I .o
Length
Ref.
1.36 1.36 1.55
4b 4b 4c
From electronegativity differences and by analogy with data
in ref. 3.
Bond angles about boron, oxygen, and nitrogen atoms have been assumed to be tetrahedral. In each case this seems to be a reasonable mean between published values in analogous corn pound^.^^ On this basis, the boat form IIa should have an The Journal of Phlisical Chemietra
mediate between I I a and IIc could have moments somewhat lower, but IIc involves very close approach of the side chains in the “flagpole” positions and is thus sterically an unlikely contributor. Consequently, a flexible form would have a moment in excess of 2 D, at the very least. It thus appears that the Bon-Bon ring system is chair form. Experimental Electric moments were determined by Guggenheim’s methodJ6 using procedure’ and apparatus8 described previously. The solvent carbon tetrachloride was fractionally distilled from analytical reagent grade using a column of about eight theoretical plates, dried over CaCL, again fractionated, collected, and stored over CaC12. The fraction used boiled over a range of less than 0.03’: n 2 51.4578. ~ Purity check by vapor chromatography indicated no detectable volatile impurity a t the 0.01% level or above. Solutes prepared as described previously* were again recrystallized from dry CCl, before preparing the solutions. Errors in n and E as reported in Table I are estimated to be less than 0.0001 and 0.0002, respectively. The internal consistency of the data is somewhat better, corresponding to errors of 0.00003 and 0.0001, respectively. In view of the startlingly small variation in E and in n over the concentration range, two of the (aminooxy)di-n-butylborane solutions were evaporated after the measurements, and the presence of the solute was verified.
C. P. Smyth, “Dielectric Behavior and Structure,” McGrawHill Book Co., Inc., New York, N . Y., 19.55, p. 244. (4) (a) “Tables of Interatomic Distances and Configuration in Molecules and Ions,” L. E. Sutton, Ed., The Chemical Society, London, 1958; (b) from “Table of Selected Bond Lengths”; (e) mean of four molecules containing analogous B-N single bonds. (5) H. J. Becher, 2. anorg. allgem. Chem., 270, 273 (1952). (6) E. A. Guggenheim, Trans. Faraday Soc., 45, 714 (1948). (7) €1. B. Thompson, L. Everson, and J. V. Dahlen, J . Phus. Chem.. 66, 1634 (1962). (8) H. B. Thompson and C. C. Sweeney, ibid., 64, 221 (1960). (3)
