1212
NOTES
netics suggested by Griehl and Schnock or single second-order kinetics t o make a decision possible. An example of a reaction which proceeds with distillation has been given. The method is applicable to many other reactions in which an appreciable volume change occurs. Except for the case of a single second-order reaction with unequal initial reactant concentrations, the rate equations must be modified to include a function of the initial concentrations in the normal rate constant. Reactions which could be analyzed in this fashion include those where a gas is liberated, a liquid vaporized or distilled, or a precipitate formed which effectively removes the product from the locus of reaction. Examples of types of reactions which might be studied in this way are the polymerization of a monomer to an insoluble polymer
Vol. 63
(if the polymer does not enter into further reaction) ; certain pyrolysis reactions; and of course reactions similar to the present case. If this approach is not used when an appreciable volume change occurs, then incorrect material balances will occur, which may not be recognized due to inability to carry the reaction to completion, and incorrect rate constants will be obtained, as may be seen from equations 28 and 32-34. Acknowledgments.-The authors wish to express their thanks to Dr. T . W. DeWitt and Dr. P. H. Hobson for many helpful discussions during the course of this work, to Mr. J. B. Cox for assistance in using the Bendix G15D Computer, to Messrs. R. F. Crafts and W. S. Ward for assistance in the experimental study, and to The Chemstrand Corporation for permission to publish this paper.
NOTES CHROMATOGRAPHY OF DECABORANE AND SUBSTITUTED DECABORANES BY BERNARD S I E ~ E LA’N D JULIUS L. MACK Research and Development Department, U. 8. Naval Propellant Plant, Indian Head, M d . Received December 67, 1068
Recent advances in decaborane chemistry have developed new methods for the preparation of substituted decaboranes. A vexing problem often encountered in these investigations has been the extreme difficulty in isolating decaborane derivatives from complex reaction mixtures. This is attributable to the low volatility of decaborane derivatives2 and their extreme susceptibility to air and many solvents. Chromatography was considered an ideal solution to this problem, provided a system could be developed that would minimize the decomposition of decaborane and its derivatives. An anhydrous system was deemed necessary since these compounds are readily hydrolyzed when in contact with organic solvents containing water. While most adsorbents ordinarily used in chromatography cannot be made anhydrous without losing their effectiveness3s4Florisil can be heated to high temperatures without destroying its surface.6 Initial experiments with this “Anhydrous” adsorbent resulted in extensive loss of decaborane ; in one experiment only 180 mg. of decaborane was eluted from 1.0 g. put onto a column of Florisil. It was subsequently found that losses could be minimized by previous overnight evacuation of the florid column a t 500”; this treatment removed (1) Aerojet-General Corporation, Azusa, California. ( 2 ) Decaborane has a vapor pressure of 0.3 mm. a t 55’ (A. Stock and E. Pohland, Ber., 6’2, 90 (1929)) and substituted decaboranes are generally considerably less volatile. (3) L. H. Milligan, THrs JOURNAL, Z6, 247 (1922). (4) F. E. Bartell and E. G. Almy, ibid., 36,475 (1932). (5) Florisil-a synthetic adsorbent, Floridin Co., Tallahassee, Florida.
20-23 g. of water from the 500 g. of adsorbent used in each column and contributed to the effectiveness of the separations by preventing break-up of the column during chromatography by rising gas bubbles. Sharp separations were obtained on mixtures of decaborane-biphenyl, decaborane-iododecaboPane and decaborane-benzyldecaborane. A previously reported reaction mixturea was chromatographed ; benzyldecaborane had previously been isolated from the reaction mixture by high vacuum distillation, but the distillation had resulted in significant decomposition. With chromatography, a larger yield of benzyldecaborane was recovered, in addition to a new benzylated product. These separations were based on simply adsorption-type chromatography. It appeared interesting to investigate also the possibility of partition-type chromatography. Using the same adsorbent as a support for diethyl ether, decaborane was sharply separated from biphenyl, with petroleum ether serving as the mobile phase. A mixture of mono and di-iododecaboranes was also separated by this type of process. Experimental General Procedure.-The adsorbent used was 100/200 mesh Florisil. The column was 31 mm. Pyrex glass, packed with adsorbent to a height of four feet, and was bounded nt the bottom by a frit,ted disc and greaseless stop-cock. The head consisted of a solvent reservoir below which was an exit to the atmosphere through a stopcock. After the column was packed to the desired height, the head was closed off and the column was wrapped with a heating jacket. The latter was heated overnight a t 500’ with evacuation through the bottom. The heating jacket was then removed and dried solvent was poured on the cooled column, rigidly excluding air. The sample was then introduced, followed by eluent. The eluents used were dried petroleum ether (b.p. 38-43’) and methylene chloride, (6) B. Siegel, J. Mack, J. Lowe and J. Gallaghan, J. A m . Chem. Soc., 80, 4523 (1958).
1
m
NOTES
July, 1959 chosen for volatility and inertness. The eluate was collected at a rate of 30-40 cc./hr. Separations (Adsorption) .-A petroleum ether solution of 1.0 g. of decaborane and 0.5 g. of biphenyl was chromatographed with petroleum ether as eluent. The initial 600 cc. of eluate contained no solute. Decaborane was eluted over the next 500 cc. of eluate. After 200 cc. of further eluate without solvent, biphenyl was eluted quantitatively. The separations of mixtures of decaborane-benzyldecaborane and decaborane-iododecaborane’ were similar except that in these cases, after the elution of decaborane with petroleum ether, the substituted decaboranes could not be eluted with the latter and methylene chloride was used as the eluent. A petroleum ether extract (8.8 9.) of the benzyl chlorideBloH13MgI reaction6 was chromatographed after distilling the volatile material. This yielded a trace of decaborane, eluted with petroleum ether; this was followed by 2.95 g. of bensyldecaborane, eluted with 25% methylene chloride; the last fraction (1.9 9.) was eluted with methylene chloride and had a cryoscopic molecular weight of 298 and a composition of 72.6% C, 14.7% B and 7.8T0 H. The latter was rechromatographed with gradually increasing concentrations of methylene chloride as eluent but no further separation was noted. Separations (Partition).-A decaborane-biphenyl mixture was chromatographed on a column prepared with diethyl ether, using petroleum ether as eluent. Biphenyl was eluted quantitatively first, followed by decaborane. In a similar manner, a mixture of iododecaborane-di-iododecaborane’ was chromatographed on a column prepared with methylene chloride, using petroleum ether as eluent. Iododecahorane was eluted first, followed by diiododecaborane .a (7) The latter was prepared by an unpublished method. Details were made available to us by a private communication from the Reaction Motors Division, Thiokol Chemical Corp. (8)The melting point of this compound was 268O. Since the diiododecaborane reported by Stock (A. Stock, “Hydrides of Boron and Silicon,” Cornell Univ. Press, Ithaca, N. Y., 1933) melted at 2.30°, the compound isolated in this paper is apparently another isomer.
DISSYMMETRY OF DISCS OF NEGLIGIBLE THICKNESS
1213
0.00
1.00
2.00
d 3.00
4.00
5.00 1.00
0.80
0.60
0.40
0.20
0.00
P(@). Fig. 1.-Scattering
function,
P(q)as
a function of
2.
6.00
5.00
4.00 i
3.00
BY PAULBECHER Chemical Research Dept.. Atlas Powder Cn., Wdmington, Delaware Receiped November 10, 1968
The scattering functions and the corresponding dissymmetry corrections for a variety of molecular shapes, such as spheres, rods and coils, have been tabulated, e.g., by Doty and Steiner.’ Recently, however, we required such information for a discshaped scattering unit. Although no such tabulation apparently exists, Debye2 has shown that the scattering function for a disc of negligible thickness (ie., negligible with respect to the wave length employed) is given by P(8)=
Z”
- x2/6 +
n=m
[x2(‘-l) COS (n
+ l)n]/bn
n=3
where the coefficients b, are given by the recursion formula and where bl = 1 and b2 = 6. The quantity x is defined in the usual maimer x =
2rD
7 sin
x
8
2-
(1) P. Doty and R. F. Steiner, J . Chem. Phvs., 18, 1211 (1950). (2) P. Debye and E. W. Anacker, THISJOURNAL, 55, 644 (1951); Cf. also 0.Kratky snd G. Porod, J . Colloid Sei,, 4, 35 (1948).
2.00
1.00 0.00
0.20
0.40 0.60 0.80 D/Xl. Fig. 2.-Dis~ymmetry, 14j/1135,as a function of D/X’
TABLE I SCATTERING FACTOR FOR THINDISCS z
p (6)
5
0.10 .20 .30 .40 .50 .60 .70 .80 .90 1.00 1.10 1.20 1.30 1.40
0.998 .993 ,985 ,973 .961 ,942 .921 .899 ,874 ,846 ,817 ,787 .756 .722
1.50
,687
2.60 2.70 2.80 2.90 3.00 3.10 3.20 3.30 3.40 3.50 3.60 3.70 3.80 3.90 4.00
P
(8)
0.335 .309 ,286 .263 ,242 .225 ,205 .191 .174 .162 .152 ,143 .132 .124
,116
