3.eoe
NOTES
viously.e The ethyl ether (Mallinckrodt, C.P. anhydrous) was dried and distilled in vacuo over lithium borohydride. Standard high vacuum apparatus and techniques were used in the preparation and handling of all materials. The Bll n.m.r. spectra were obtained by a Varian high resolution n.m.r. spectrometer operating a t 12.8 mc. The infrared samples were prepared by placing a few drops of the liquid samples between two sodium chloride plates in a nitrogen filled dry box and spectra taken with a PerkinElmer Model 21 spectrophotometer. In the preparation of dichlorohorane ethyl etherate, a mixture of 10.00 mmole of ethyl ether, 3.72 mmoles of boron trichloride and 0.93 mmole of diborane was allowed to react a t room temperature until all the diborane had been absorbed. Excess ether, 4.42 mmoles, was umped off leaving dichloroborane etherate. Deuteriodiciloroborane ethyl etherate was prepared in the same manner as described above for the dichloroborane etherate. The melting poinot of both etherates occurred in the range -27 to -23 The purity of both compounds was found to be better than 95% based on the stoichiometry of the reaction and n.m.r. and infrared analyses of the products. Difficulty was experienced in transferring dichloroborane ethyl etherate and deut,erodichloroborane ethyl etherate in the high vacuum system because of the low vapor pressures of the etherates. Dichlorohorane etherate decomposed slowly a t room temperature to give small amounts of ethane, diborane, ethyl chloride and boric oxide.
.
Results and Discussion Using stoichiometric amounts of diborane, boron trichloride and ether, dichloroborane etherate was formed as 4BCla
A
+ BzHe + 6(CzH5)20 +6HBClz(CzHs)zO
I n the infrared spectra dichloroborane etherate and deuteriodichloroborane etherate exhibit single absorption bands in the B-H(D) terminal stretching frequency region a t 3.98 p (B-H) and 5.31 p (B-D), respectively. Also, dichloroborane etherate does not exhibit any absorption band in the B-HPridge frequency range.3 Aside from the above mentioned infrared absorption and C-H band at 3.36 p the remainder of the spectra for both compounds is complex. On several occasions when excess diborane was used in the above reaction a small infrared absorbance was observed a t slightly lower frequencies than the B-H (or B-D) stretching frequency in dichloroborane. This band, attributed to the BH2 symmetric stretching of monochloroborane, disappeared on standing, leaving the spectrum of dichloroborane etherate. The Bll n.m.r. spectrum of dichloroborane etherate exhibits only a symmetrical doublet, which is indicative of either a B-H unit or two nonequivalent boron atoms not bonded t o hydrogen. The latter interpretation can be ruled out since the BI1-D spectrum of deuteriodichloroborane exhibits a singlet occurring midway between the two parts of the dichloroborane doublet. This collapse of a B-H doublet by deuteration without observing any B”-D coupling already has been reported for deuter~decaborane.~Additionally, the separation of peaks for the dichloroborane etherate due to B”-H spin-spin coupling is found to be approximately the same as the analogous separation in pentaborane, again confirming the B-H unit assignment for the doublet. (2) I. Shapiro, H. G . Weiss, M. Schmioh, S. Skolnik and G . B. L. Smith, ibid., ‘74,901 (1952). (3) I. Shapiro, C . 0. Wilson and W. J. Lehmann, J . Chem. Phys., 29, 237 (1958).
Vol. 62
The Bll n.m.r. spectrum of boron trichloride etherate exhibits a singlet a t a lower magnetic field than dichloroborane etherate. The expected spectrum of monochloroborane would be a triplet. When diborane and boron trichloride in ether in varying proportions are mixed, only the singlet and/or the doublet are observed; no monochloroborane is detected. I n contrast to this situation, evidence of a triplet in the n.m.r. spectrum due to monochloroborane is obtained when the “diglyme” solvent is used. The fundamental structure (I) for dichloroborane etherate is implied by the above spectral studies. C1
\d
H
Alto
PH5 \
I
C2H5
Although the possibility of dimer, trimer, etc., formation is not ruled out, any such structure in which the boron atoms do not have the same chemical environment appears unlikely. Thus a dimer ( [HBCl(OEt&!+[HBCl3]-) which is structurally similar to the diammoniate of diborane6 is regarded as improbable. Likewise, dimers involving hydrogen bridging cannot be considered because there is no infrared absorption in the B-Hbridge frequency range.a Structure I could account for the observation that dichloroborane etherate decomposed to give small amounts of ethane, ethyl chloride and diborane. This decomposition is analogous to that of boron trichloride etherate, reported by Wiberg and Sutterlin t o give ethyl chloride.6 The formation of ethane and diborane in the former case is not surprising in view of the presence of the hydridic hydrogen. Acknowledgment.-The authors appreciate the assistance given by Drs. R. E. Williams and W. J. Lehmann in the preparation and interpretation of the n.m.r. and infrared spectra. (4) R. E. Williams and I. Shapiro, ibid., a9, 677 (1958). (5) 9.G.Shore and R. W. Parry, J . A m . Chem. Soc., 77,6084 (1955): D. R. Schultz and R. W. Parry, ibid., BO, 4 (1958). (6) Wiberg and Sutterlin, Z . onoro. allgem. Chem., 202, 21 (1931).
T H E MOLAR REFRACTION OF METHYL ISOCYANATE BY WILLIAMM. TOLLES A N D JEROME R. TICHY~ Contribution from the Deportment of Chemistry, The University of Connectzcut, Storre, Connectacut Received August 7 , 1868
In connection with another problem, the occasion arose to prepare some methyl isocyanate. A search of the literature indicates the physical constants of this compound are not well established. Aside from the b.p. 43-45’, no values exist for the density or refractive index. We have determined these latter constants and ~ and dzT4 0.9230. found them t o be n Z 7 1.3630 With these values, the molecular refraction is found to be 13.73. The molecular refraction calculated for CHsNCO is 13.68 while that for CHsOCN is (1) Maine Medical Center, 22 Bramhall St., Portland, Maine.
COMMUNICATION TO THE EDITOR
Dee., 1958
1607
12.93. Hence the experimentally found molecular refraction confirms the isocyanate structure for this substance. Initial attempts to purify the crude product, from the reaction of (CH3)2S04and KOCN, by fractional distillation at atmospheric pressure, did not give satisfactory results. The main difficulty under these conditions is that extensive decomposition and polymerization occur.
The material can be purified, however, by distilling under a vacuum of 10-12 mm. a t room temperature. A capillary b.p. determination shows that a small quantity of some volatile material comes off at 29-30' and the main product boils a t 44-45' with decomposition. The CHINCO is difficult f o burn in a standard C and H combustion train and consistently gives low carbon values.
(2) The molecular refractions were calculated from atomic refractivities in: A. I. Vogel, "Textbook of Practical Organic Chemistry, 3d Ed., Longmans, Green & Co., New York, N. Y.,1956,p. 1036.
Calcd. for CHyNCO: C, 42.11; H, 5.26; N, 24.56. Found: C, 40.03, 40.23; H, 5.38, 5.24; N, 24.14, 24.32.
COMMUNICATION TO THE EDITOR THEORY OF T H E TRANSIENT STATE I N T H E ULTRACENTRIFUGE
Sir: Although Archibald has presented both exact' and approximate2treatments of the ultracentrifuge differential equation
ac D - - w2srC = 0,r ar
where p =
An =
r1, r2
(r - r l ) / H ;
T
=
(w2s?/H)t; a = w2s?H/2D
and =
2
[I
+
-
l ) l u n ( ~ eXp(-ap)C(p,O)dp )
(C)
(3)
recent investigator~~.~,5 have preferred to adapt The perturbation treatment has been carried to the centrifuge the more manageable solution through first order for un and second order for En, of Mason and Weaver6 obtained for the case of corrections to the latter vanishing in first order; gravity sedimentation from h2€,(2) .. .; U n = U,(O) + Xu,(" + . . .; e, = En(0)
+
A, bC
D dX - - KC
= 0,x = XI,52
(G)
The results are Un(W = B , -I/ z[f,(k)(p) B,
= 1
cos
=
An(0)
m p
+ hA,(I) + . . .
+ (a/n.)gn'k'(p)
+ (a/n?r)2;f,@) = g,(O)
+
(4)
sin nrp]
= 1
I n order to determine the validity of this proce- fn(') = Bn[ap(l - p) - ( p - l / 2 ) ] - a/4; g,(l) = dure the centrifuge equation (C) has been solved Bn [ l / a ( P - 1/2)1 - a/4 by a perturbation treatment7 which in zero order ento) = B , ( n ~ ) ~ / 2 a en(1) ; = 0 yields the Mason-Weaver result. The findings en(2)/cn(0) = 3(n?r)-'[l (az/9)(1 15/n2?r2)] (5) are. presented in this preliminary report. If X is defined by the relation For the usual case of interest, C(p, 0) = Coand
+
+
- rI)/(rz + r1) = H/2? (1) B.A.(0)/Co then equations (C) for X = 0 (a2?= const.) have 4A,(')/An(") the same form as equations (G) and it is possible X = (rz
to obtain the transient concentration distribution in the ultracentrifuge as a power series expansion in X. I n the usual ultracentrifuge Y = 5 em. and H = 1 cm. so that X = 0.1 and the series converges rapidly. The form of the solution is (1) W. J. Archibald, Phys. Rev., 6 4 , 371 (1938); Ann. N . Y . Acad. Sci., 43, Art. 5, 211 (1942). (2) W. J . Archibald, J . A p p l . Phus., 18,362 (1947). (3) D.A. Yphantis, and D. F. Waugh, THISJOURNAL, 60, 623,630 (19563. (4) R. A. Pasternak, G . M . Nazarian, and J. R. Vinograd, Nature, 179, 92 (1957). (5) K. E. Van Holde, and R. L. Baldwin, THISJOURNAL, 62, 734
(1958).
M.Mason and W. Weaver, Phys. Rev., 23,412 (1924). (7) G. M. Nazarian, doctoral dissertation, Department of Chemis-
(6)
try, California Institute of Technology, 1957.
= =
+
4B,-%a[l ( - l ) n + l exp(-a)]/n2?r2 a[32/n2?r2Bn- 11 - 2[3 [tanh CY/^) ] (6)
The availability of the extremely accurate formula for en provides the basis for an experimental method of determining diffusion constants since for a fixed location in the cell, we have from (2) C ( t ) = C,,
+ KI exp(-ht) + KZexp(--k2t) + . . .
-
(7)
where kn = 2 a ( D / H 2 ) e n . For a of order of magnin2 so that kp = 4k1, k3 = 9kl. tude unity, En Also, if we choose the fixed location to be in the vicinity of p = 1/4 this makes uz = 0 whereas u1 is close to its maximum value giving iKzl
