NOTES
June, 1961 lines in the studied temperature range. The ratio of the two pressures at a given temperature is 1.51:1, indicating the degree of dissociation of CdSe in the vapor. Hence, within our experimental error, the data prove the existence of the equilibrium CdSe(s) = C d W
+ '/zSedg)
(1)
Diatomic selenium is known to be the dominant species and generally used as a reference state' above the boiling point of selenium 958°K. On the other hand, t'here is no evidences for diatomic cadmium in the vapor phase; therefore this possibility was ruled out as an alternate of equation 1. The heat for the reaction can be calculated from the van't Hoff equation d In K dT
- AH0 RT2
One can express the equilibrium constant in terms of the total pressure, with the use of the law of partial pressures, as K
=
(gP ) ( $
P)"'
=
O.385Pah
(3)
If one assumes that AHo is constant over the studied temperatureg range, direct integration yields (4)
AHo = 68.5 kcal./mole a t 1100°K. The vapor pressure of CdSe may be expressed from the data as a function of the temperature as IogP,,
=
-l0O2O + 9.8 T'K.
(5)
From the heat of reaction and the heat of evaporation of liquid Cd metal,' the standard heat of formation of CdSe was calculated to be 44.6 kcal./mole at 1000°K. P. G~ldfinger's~value of 73.1 f 1.5 kcal./mole for the heat of evaporation of CdSe at 900°K. according to eq. 1 is somewhat larger than the value reported in the present paper. The author wishes to thank V. J. Lyons and T. G. Dunne for helpful discussions, J. Kucza for help with the experimental work and C. L. Fisher for constructing the quartz Bourdon gauge. (7) D. R. Stull and G. C. Sinke, "Thermodynamic Propertied of the Elementa," A.C.S. Publication, 1956. (8) K. E. Kelley, U. S. Bur. Minea. Bull. 383, 1935. (9) S. Glasstone, "Thermodynamics for Chemists," D. Van Nostrand Co., New York, N. y., 1947.
2,4-DIMETHYLENETETRABORANE: STRUCTURE FROM N.M.R. SPECTRA BY I. SHAPIRO,~ ROBERTE. WILLIAMSAND SIDNEY G. GIBBINS Research Laboratorv, Olin Mathieson Chemical Corporation, Pasadena, CaliJornia Received November 14, 1960
The compound formed by the reaction of ethylene and tetraborane had been tentatively identified as dimethylenetetraborane on the basis of its infrared spectrum and by chemical analysis.2 (1) Hughw Tool Company-Aircraft fornia.
Divieion, Culver City, Cali-
1061
The "cyclic" bridge structure of this compound now is confirmed by proton and B"-n.m.r. spectra obtained in this Laboratory. In addition the polyisotopic mass spectrum and vapor pressure data for this compound are reported. Experimental The reaction of ethylene with tetraborane to form dimethylenetetraborane has been carried out by both the lowtemperature (70") sealed tube method and the hot-cold reactor method.* The latter method is preferred for preparing larger samples of the compound. I n either case, the compound is purified by fractionation2 in standard highvacuum apparatus. The mass spectrum was obtained with a Consolidated Model 21-103 mass spectrometer operating a t an ionizing potential of 70 v., and the n.m.r. spectra were obtained with a Varian V-4300 high resolution nuclear magnetic resonance spectrometer operating at 12.8 and 40 Mc. Vapor pressure values over the temperature range of -20 to 20" were obtained in an isoteniscope.
Discussion polyisotopic mass spectrum of dimethylenetetraborane is given in Table I. There were no peaks observed above m/e 80. The reduction of the data (calculated on the basis of 80% Bl1 and 20% B10)3 for the parent grouping (m/e 67-80) to a monoisotopic spectrum leads to the conclusion that the molecule contains four boron atoms. The reduction of the spectrum on the basis of five boron atoms leads to significant negative values and, on the basis of three boron atoms, to appreciable residues. Consequently, the molecule must contain two carbon atoms with a balance of twelve hydrogen atoms, in agreement with the stoichiometry of the reaction2
Mass Spectrum.-The
+ C2H4 +BiCzHiz + Hz
From Table I the peak intensities at m/e 79 and 80 are considerably less than those a t m/e 78 and immediately lower mass units; nevertheless, these peaks are real. Only 2% of m/e 78 can be attributed to m/e 79 for the C13 contribution, i.e., C12C1acombination species. I n this connection it is pointed out that in the case of tetraborane the mass spectral cut-off peak occurs a t two mass units lower than the corresponding molecular weight. B"-N.M.R. Spectrum.-The B"-n.m.r. spectrum of dimethylenetetraborane consists of a low-field doublet (J = 130 c./s.) centered at 6 4 = -4 and a high-field doublet ( J = 145 c./s.) centered a i 6 = -39. The peaks of the high-field doublet are about half the height but broader than the peaks of the low-field doublet. From a comparison of the B"-n.m.r. spectra of dimethylenetetraborane and tetraboranes it is readily apparent that the low field triplet in tetraborane, representing BH2 groups, has been transformed into a doublet (BH group) in the dimethylenetetraborane, thus indicating that substitution has occurred on the sites 2 and 4 boron nuclei. Alkyl substitution has shifted the low-field doublet (6 = -4) to lower field than the corresponding (2) B. C. Harrison, I. J. Solomon, R. D. Hitea and M. J. Klein, J . Inore. Nucl. Chem., 14, 195 (1960). (3) See ref. 10, I. Shapiro and J. Ditter, J . Chem. Phys., 2 6 , 798 (1957). (4) T. P. Onak, H. Landesman, R. E. Williams and I. Shapiro, J . Phyd. Chem., 63, 1533 (1959). (6) B E. Willirtms, S. G. Gibbins and I. Shapiro, J. Am. Chem. Soe.. 81, 6164 (1969).
1062
Yol. 63
VALUEOF 100 FOR m/e 41 4
6
80 79 78 77 76 75 74 73 72 71 70 69 68 e7 66 65 64 63 62 61 60 59 58
[ntensity
0.7 1.9 28.6 33.4 57.9 50.0 34.0 29.0 19.8 13.7 9.5 10.8 8.2 3.6 5.5 6.1 47.5 54.8 49.0 37.6 20.6 15.6 12.0
m/e
57 56 55 54 53 52 51 50 49 48 47 46 45 41 43 42 41 40 39 38 37 36.5 36
Intensity
m/e
Intensity
6.6 2.6 1.2 0.5 4 .O 14.6 33.4 35.9 45.4 43.7 35.2 21.6 10.7 4.8 2.0 2.7 100 31 .O 19.8 17.7 55.0 0.4 34.5
35.5 35 34.5 34 33 32 31 30 29 28 27 26 25 24 23 22 21 20 15
0.8 17.2 0.3 7.6 2.4 0.6 .2 .1 .7 2.4 19.5 14.0 6.9 6.0 2.9 1.0 0.2
14
13 12 11
..
1.0 0.6 31.8 13.0 28.1
triplet of tetraborane (6 = +6.54). The highfield doublet (BH group) corresponding to sites 1 and 3 boron nuclei in the dimethylenetetraborane is shifted only slightly to lower field (less than 1 &unit) when compared to the corresponding doublet in tetraborane. The spin-coupling (JH-B) in the high-field doublet (each member of the doublet actually is a septet due to spin-coupling with the 20% BO ' isotope5) is less in the case of dimethylenetetraborane than in tetraborane, which probably accounts for an overlapping of the inner peaks of the septets to create a slight central peak between the members of the high-field doublet. H1-N.M.R. Spectrum.-The proton spectrum (40 Mc.) was obtained a t different power intensity levels in order to get proper resolution of the various peaks. The general contour of the spectrum is that of a very sharp, narrow and intense peak located off-center (toward low-field side) of a broad diffuse peak, with a number of small intensity peaks spaced throughout the spectrum but predominantly located on the low-field side of the broad diffuse peak. The large [single spike is attributed to the CH2 groups. The other peaks can be assigned to a pair of quartets representing the dissimilar B-H groups and to a bridge proton component (broad diffuse peak). The total width of this bridge component is fairly well defined ( J = -35 c./s.) and is similar to that in other boron hydride^.^ The peak position relatiomhip of the bridge component to the quartet representing the hydrogens attached to the 1 and 3 boron nuclei is similar to that in tetraborane5; however, the quartet representing the 2and 4-positions is shifted slightly more toward the low-field side than in the case of tetraborane.6
borane. Vapor Pressure.-The vapor pressure data over the temperature range of -20 to 20" is given in Table 11. The calculated vapor pressures are obtained from the equation log P,,
3077 509 T
= 10.22289 - A
162748.8 + ___ T2
This equation, obtained from the experimental data by the method of least squares, represents the data with an average deviation of 0.2 mm. The boiling point derived from this equation is approximately 84". The heat of vaporization a t 298°K. is found to be 9083 cal. The single vapor pressure value at 0" reported previously2 is in good agreement with the present data. TABLE I1 VAPORPRESSURES OF DIMETHYLENETETRABORANE ~~
~~
t, "C.
~~
V.p. obs., mm.
V.p. calcd.,
mm.
-23.1 3.30 3.30 -18.1 4.55 4.56 -12.6 6.35 6.44 -10.1 7.75 7.52 - 3.7 11.2 11.0 13.7 0 13.9 3.0 16.1 16.3 6.9 20.0 20.4 23.6 9.9 24.1 30.7 14.3 30.9 18.3 38.5 38.0 Extrapolated boiling point -84'
Dev., mm.
0.0
.o
+ .1
- .2 - .2 - .2
+ .2 + + .5 .4
-
.2 .5
A THERMODYNAMIC STUDY OF HOMOPIPERAZIKE, PIPERAZINE AND N(2-AMIN0ETHYL)-PIPERAZIIRJE AND THEIR COMPLEXES WITH COPPER(I1) IOh' BY
JOSEPH
M. PAG.4;\-0,' DAVIDE. GOLDBERG AND W. COXARD FERNELIUS~
Department of Chemzatry, The Pennsyluanza State rnwersity, T'nzuersaty Park, Pennsyluanza Recezued November 17, 1960
The effects of a number of factors on equilibria involving metal ion-amine complexes have been investigated.3 However, none of these studies has included the coordination of a polyamine which, in order to coordinate, must shift from a more to a less stable conformation. Piperazine and some of its derivatives present an opportunity to study this situation. Although piperazine in its normal or "chair" conformation4 would not be expected to act as a chelate group, a solid complex of S,N1dimethylpiperazine in the "boat" conformation has been rep0rted.j (1) Holder of a National Science Foundation Research Partacipation award f o r the summer of 1960, State College a t Bridgewater, Bridgewater. Massachusetts. ( 2 ) Koppers Company, Inc., Pittsburgh 19, Pennsylvania. (3) For references and discussion see C. R. Bertsch, W. C. Fernelius and B. P. Block, J. Phys. Chsm., 62, 444 (1958). (4) P. Anderaen and 0. Haasel, A d a Chem Scand. 8 , 1181 (1949), and later unpublished data aa reported in ref. 5 .
