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Cyclopentadienylboranes.

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permit differentiation into sulfides with a greater similarity
to alloys and the more salt-like complex compounds of the
transition metals. The more metallic structural units are
distinctly separated from the ionic ones by formation of
layers or chains.
account, Corasil and Zipax appear to be equal as regards
the possible speed of analysis at equal pressure drop.
Comparable values were obtained for the Corning glass
beads only with substances that were very strongly retarded
on the other carriers.
Lecture at Aachen on January 22,1971 [VB 286 IE]
German version : Angew. Chem. 83,413 (1971)
Corasil and Zipax are active adsorbents because a silica
gel with a large specific surface area is used for the porous
surface layer. This activity is evidenced in a variety of ways:
The relative retention is a function ofthe amount of stationary phase on the support. The uncoated carrier adsorbs
stationary phase from the solvent saturated with the
stationary phase until a steady state is reached. Reproducible results cannot be obtained with loadings lower than
that corresponding to this steady state. Only with the
Corning glass beads are the values of relative retention
independent of the amount of loading.
[l] J . W Boon and C. H . Mac Gillary, Recl. Trav. Chim. Pays-Bas 61,
910 (1942).
[Z] W Bronger, 2. Anorg. Allg. Chem. 359,225 (1968).
[3] W Bronger, Angew. Chem. 78,113 (1966); Angew. Chem. internat.
Edit. 5, 134 (1966).
[4] W Bronger and P . Bottcher, unpublished work.
[5] W Bronger and J . Huster, J. Less. Common Metals 23, 67 (1971).
[6] W Bronger and 0.Giinther, unpublished work.
Problems of High Speed Liquid Chromatography
By Heinz Engelhardt“
The theoretical relations derived for gas chromatography
are valid also for liquid chromatography. However, the
differences in the relative numerical values of the physical
quantities (viscosity, diffusion coefficient, etc.) concerned
in, for instance, the equation for zone spreading as a function of flowrate cause a shift in the relative influences of
the various terms of this equation.
Thus the longitudinal diffusion term (the B term) has very
little influence in liquid chromatography, since the rate of
diffusion in the mobile phase is slower than in gases by a
factor of lo4. On the other hand, this same slow diffusion
leads to preponderance of the term (the C , term) for resistance to mass transfer in the mobile phase,‘namely that
between the moving mobile phase between the particles
and the stagnant mobile phase in the pores of the carrier.
This band broadening can be overcome to some extent by
decreasing the depth of the pores; this can be effected by
decreasing the diameter of the particles (< 10 Fm), since
then the pore depth also becomes smaller, or by using
thin-layer particles (porous layer beads) in which a thin
porous surface layer (- 1 pm) is placed on an inpenetrable
core. This surface layer can be produced either by etching
the surface of the particles, as in the carrier material Corning GLC 100 (Corning Glass Works, Coming, N. y.)or by
precipitating a thin porous layer of silica gel as in the
carrier materials Corasil (Waters Assoc., Framingham,
Mass.) and Zipax (Dupont, Wilmington, Del.). If the
particle diameter is increased, then, in order to obtain the
same flowrate, a higher pressure must be applied, the
limits being set by the apparatus. Such particles were compared by observing the band broadening in relation to
velocity (H. vs. velocity) and the number of effective plates/
sec (measure of the speed of analysis).
The carriers differ in their loading capacity for the stationary phase. Surface-etched particles give sticky fillings even
with light loading (0.4%of 3,3’-oxydipropionitrile),whereas
the others can be much more heavily loaded (up to 2.6% of
3,3’-oxydipropionitrile)without appearing sticky. The
number of effective plates/sec created is largest with Zipax.
If, however, the difference in particle size is taken into
If all of the pores on a porous carrier are almost completely
filled with stationary phase (e.g., Porasil A with 100% wjw
of 3,3’-oxydipropionitrile),band broadening in the stationary phase preponderates and lower plate heights are found
for strongly retarded substances than for those eluted at
the beginning. With these heavily loaded columns there is
no reasonable loss of stationary liquid phase (using completely saturated eluants) due to mechanical erosion which
limits the life of columns with porous layer beads. On
these columns the sample size can be very large without
overloading.
Lecture at Erlangen on January 22,1971 [VB 285 IE]
German version: Angew. Chem. 83,411 (1971)
Cyclopentadienylboranes
By Hans Grundke and P. I . Paetzold (lecturer)[‘’
o-Cyclopentadienyl compounds XCp are subject to, inter
a h , two types of equilibration, namely, valence tautomerism (I) and sigmatropic hydrogen shift (2):
X
WhenX=R,AI only reaction(l)isobserved, whenX=R,Si
both reactions occur, but when X =R,C only reaction (3)
takes place. How do cyclopentadienylboranes R,BCp
behave?
We prepared cyclopentadienyldiethylborane Et,BCp ( I )
[and analogously diethyl(methylcyclopentadieny1)borane
(211 by reaction of chlorodiethylborane-pyridine with
NaCp and subsequent removal of the pyridine by BF, :
The by-way through the pyridine adduct is necessary since,
in the presence of Lewis acids such as free Et,BCl, ( I )
rapidly dimerizes by a Diels-Alder reaction ;this dimeriza-
[*] Dr. H. Engelhardt
Institut fur Organische Chemie der Universitat
Erlangen-Numberg
852 Erlangen, Henkestrasse 42 (Germany)
Angew. Chem. internat. Edil. / Vol. I0 (1971) 1 No. 6
p] Dr. H. Grundke and Prof. Dr. P. I. Paetzold
Institut fur Anorganische Chemie der Technischen Hochschule
51 Aachen, Templergraben 55 (Germany)
423
tion occurs slowly at room temperature, but in one minute
at 75°C even in absence of a catalyst.
H@
0-C=NI,
xa
R,
HO'
-
/CO-NHR~
R-C-C+
N-RZ
8
1
R'
(2)
R'
( 1)
=H
x
=R~-COO
/CO-NHR2
c=c,
N - ~2
R3-C6
-
R,
,CO-NHR2
S-v
o /N-R~
R~-CO
(4)
(5)
1
R'=BrCH?
The fission of the signals of two olefinic protons in the
ratio 1:1 in the spectrum of (2) then accords with expectation.
The 'H-NMR spectrum of the dimers of ( I ) contains
signals for only two olefinic protons, at - 6.35 and - 6.55
ppm, together with signals of 28 other protons at higher
shifts; hence follows that the two bulky boryl groups are
bound to olefinic centers and, as expected, not to the
junction centers of the cycloaddition. However, the diene
components then cannot have structure (6) but must be
(c) -an indication that there is an equilibrium between
(b) and (c) in which the more stable (b) preponderates
greatly.
R~
1.9 I
R-C-c
PI
=N- R~
The 'H-NMR spectrum of ( I ) contains signals with the
following shifts from TMS (relative intensities in parentheses): s=O.7 to -1.6 (lo), -3.17 (2), -6.79 (2),and -7.50
(1);on general experience these signals can be ascribed to
the two ethyl groups, a CH, group, and two olefinic CH
groups. Reaction (1) is excluded by the CH, signal, and
similarly isomer (a) in equilibrium (2) can be excluded. (c)
is excluded because it is known that with boron the nuclear
resonance frequency of ortho-ligands is lowered (e.g., with
compounds C,H,BX, and C6F,BX,), so that the spectrum
shows the existence of only one ortho-olefinic proton, as in
(b). Moreover, a CNDO-MO calculation[" shows (b) to
be about 7 kcal more stable than (c).
YH3 C O - N H R ~
H2C=C -C'
*
0
R-c
CO-NHR~
9 - R '
N-R~
0
(3)
(6)
HX = HC1, H B r . R3-COOK
then to the acyl-carbon, yielding compounds such as (7)
(with hydroquinone/boron trifluoride). (7) easily splits
off hydroquinone, giving the ketene imine (8)I4J.
Lecture at Aachen on January 22,1971 [VB 287 IE]
German version: Angew. Chem. 83,447 (1971)
[I]We thank Dr. J. Fleischhauer, Aachen, for the MO data
H3C-CO-C=C=N-C(CH3)3
I
(CH3)3
NH-C
New Synthesis of Heterocycles by means of
Isocyanides
By H.-J. KabbeCg1
(8)
In the presence of approximately equimolar amounts of
boron trifluoride, oxetanes ( I b) prepared from aromatic
aldehydes and tert-butyl isocyanide split off isobutene and
pass into the cinnamonitriles (9).
Numerous aliphatic aldehydes and ketones, as well as
aromatic aldehydes, react with isocyanides in the presence
of catalytic amounts of boron trifluoride, to give 2,3-bis(alky1imino)oxetanes( I ) " ] :
Lecture at Tiibingen on January 29,1971 [VB 288 IE]
German version: Angew. Chem. 83,448 (1971)
These oxetanes are remarkably stable both thermally and
towards bases but can be cleaved by acids HX. This normally affords the P-addition products (2), but occasionally
unsaturated amides such as (3) are formed by isomerization[*'.
When the oxetanes ( I a) are derived from aldehydes their
reaction with carboxylic acids leads to acyl migration and
formation of a-(acy1amino)-P-hydroxyacrylamides( 4 ) ; if
bromoacetic acid is used as addend, hydrogen bromide is
split off from the tautomeric keto form ( 5 ) and the plactam (6) is obtainedc3].
Neutral, weakly acidic, or basic compounds HY add to
( I a) only under the influence of an additional acid and
[l]
[2]
[3]
[4]
H.-J. Kabbe, Chem. Ber. 102,1404 (1969).
H . - J . Kabbe, Chem. Ber. 102, 1410 (1969).
H.-J. Kabbe and N . Joop, Liebigs Ann. Chem. 730,151 (1969).
H . 4 . Kabbe, Chem. Ber. in the press.
Rheological and Boundary Layer Problems
in Printing
By W Kunz"
All printing processes involve the transference of printing
ink onto substrate and, at least in the classical processesletterpress, offset, and gravure printing- interaction takes
[*] Dr. H.J. Kabbe
Farbenfabriken Bayer AG, Chemisch-wissenschaftliches
Laboratorium, Pharma
56 Wuppertal-Elberfeld (Germany)
424
[*] Dr. W. Kunz
Burda GmbH, Forschungsleitung
76 Offenburg, Postfach 360 (Germany)
Angew. Chem. internal. Edit. / Vol. I 0 (1971)
No. 6
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