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Isolation of Benzoyl Radicals.

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to this compound is again based largely o n its NMR spectrum (see Figure), in which the signals for the ring- and bridge
protons exhibit the expected large shifts to lower (0.4-1.7 7 )
and higher fields (10.3 and 11.8 T, J = 10 cps),respectively,reIative to the signals in the spectrum of (2). Compound (2)
and the salt ( 3 ) must have the same carbon skeleton, for on
catalytic hydrogenation both give the same saturated hydrocarbon C12H~2,which we consider to be bicyclo[5,4, Ildodecane.
The N M R and ultraviolet spectra of ( 3 ) resemble those of the
benzotropylium cation 151.
Received: January 29th, 1965
[ Z 914/738 IEI
German version: Angew. Chern. 77, 348 (1965)
[ I ] E. Vogel and H. D . Roth, Angew. Chem. 76, 145 (1964);
Angzw. Chem. internst. Edit. 3, 228 (1964); E. Vogel and W. A.
BiiN, Angew. Chem. 76, 784 (1964); Angew. Chem. internat.
Edit. 3. 642 (1961).
121 For the synthesis of aromatic carbanions with 10 x-electrons, see T. J . Kutz et al., J . Amer. chem. SOC. 86, 5194
(1964), and earlier publications; E. A . LaLancette and R. E. Benson, ibid. 85, 2853 (1963).
[3] H. J. Daoben, Jr., I;. A . Gadecki, K. M. Hurinon, and D. I-.
Peorson, J . Amer. chem. SOC.79, 4557 (1957).
[41 [ C I Z H I ~ ~ ~ Cm.p.
I O ~194
~ ,"C (decomp.), was obtained
analogously.
(51 H. H. Rennhard, E. Heilbrotmeu, and A . Estltetrnroser, Chem.
and Ind. 1955, 415; G. Nm~ille,H. Srrriuss, and E. Heilbronner,
Helv. chim. Acta 43, 1221 (1960).
Reaction of Triphenylaluminum with
Cyclohexyl Isonitrile
lnstitut fur Organische Chemie
der Universitat Erlangen-Nurnberg (Germany)
When triphenylaluminum and cyclohexyl isonitrile are
heated in xylene at 5O-6O0C, compound (I) - the first
representative of a new class of organoaluminum derivatives
- is formed; it crystallizes out of the solution at -20 OC after
removal of most of the xylene and addition of anhydrous
petroleum ether.
0
3
i 1)
11
The product is colorless and is stable under pure nitrogen.
I t dissolves readily in benzene, ether, or carbon tetrachloride
but is only slightly soluble in petroleum ether. It decomposes
in air with liberation of cyclohexyl isonitrile. When heated,
it begins to soften and to decompose slowly above 75 "C. Its
structure was verified by its elemental analysis and infrared
8
spectrum (sharp band due t o the -C=N group at 2215 cm-1;
;j-N=c for cyclohexyl isonitrile is at 2125 cm-1).
The same compound was obtained by the following quantitative metathesis reaction:
0
b
(C6H.c)jB- C - - N = C ~ H I[ II] -k A I ( C ~ H S )+
~
8
0
( C ~ H S ) ~ A I - C ~ N - C ~fHB(C2Hj)j
II
Here the method described by Koster 121 for the preparation
of triethylboron from boric esters was used; the reaction
product was crystallized and purified with petroleum ether.
Received: January 29th, 1965; supplemented- March 5th, 1965
[ Z 9301756 1El
German version: Angew. Chem. 77, 380 (1965)
[*I P. Mischke, Diploma Thesis, Universitiit Erlangen-Niirnberg, 1965.
[ I ] G. Hesse, H . Witte, and G . Bittner, Liebigs Ann. Chem., in
the press; G. Birtner, Diploma Thesis, Universitiit ErlangenNiirnberg. 1964.
[21 R. Kiister, Liebigs Ann. Chem. 618, 38 (1958).
Angew. Chem. inreriiut. Edit. / Vol. 4 (1965)
/ No. 4
By Prof. Dr. LJlrich Schmidt, Dr. K. H. Kabitzke, and
Dipl.-Chem. K. Markau
Chemisches Laboratorium der Universitat Freiburg/Brsg.
and Institut fur Elektrowerkstofte der Frauenhofer-Gesellschaft, Freiburg/Brsg. (Germany)
The formation of aldehydes, diketones, and numerous acyl
compounds on irradiation of acyl chlorides and acyl bromides
in solution [1,2] can be explained only by the photochemical
formation of free acyl radicals. We have now succeeded in
capturing the free acyl radicals formed o n irradiation of aromatic acyl bromides in Y ~ C U Oby condensation in a cold trap
behind the site of exposure.
Despite its extremely low resonance energy (about 10 kcal/
mole), the orange-red free benzoyl radical is stable at 7 0 OK
and combines only above 140'K with a bromine radical to
yield benzoyl bromide within a few minutes. The free-radical
nature of the condensate was proved by measurement of its
strong electron spin resonance signal. The color and ESR signal disappear simultaneously on warming. The benzoyl radical
was also detected and captured following photolysis of benzaldehyde. Homolytic cleavage of the C-H bond in aldehydes
resulting from attack by a radical former has previously been
assumed in order to explain the course of radical additions of
aldehydes onto olefinic double bonds [3]. The ESR signals for
the benzoyl radicals made from benzoyl bromideor from benzaldehyde were identical.
When p-chlorobenzoyl bromide and p-methoxybenzoyl bromide were photolysed, red-brown p-chlorobenzoyl and green
p-methoxybenzoyl radicals, respectively, were caught in the
cold trap. The ESR signals have a width (peak-peak) of about
15 gauss and exhibit slight anisotropy. The average g factors
are about 2.006.
By Prof. Dr. G . Hesse, Dr. H. Witte, and
cand. chem. P. Mischke [*]
(C~-CHS)~AIN -CsH
Isolation of Benzoyl Radicals [I]
Received: February 1st. 1965
[ Z 908/732 IEI
German version: Angex,. Cheni. 77, 378 (1965)
[ I ] Photoreactions of Carboxylic Acid Derivatives, Part 4.
Part 3 : U.Schmidt, Angew. Chem. 77, 216 (1965); Angew. Chem.
internat. Edit. 4 , 239 (1965).
[2] U. Schmidt, Angew. Chem. 77, 169 (1965); Angew. Chem.
internat. Edit. 4, 146 (1965).
[3] Reviewed by Ch. Walling: Free Radicals in Solution. Wiley,
New York 1957, p. 273.
Thermolysis of Cycloalkyl Esters
Yielding Cycloalkanones
By Ing. Hansdieter Hofman
[*I
Forschungslaboratorien der H. J. Zimmer A G . ,
Frankfurt/Main (Germany)
Cycloalkyl esters are cleaved at 330-450°C on dehydrogenating catalysts to produce good yields of the corresponding
cycloalkanones; cycloalkanols and cycloalkenes are formed
as by-products. The rate of the reaction depends mainly
upon the nature of the acyl group and decreases in the order
formyl9acetyl >propionyl> butyryl, valeryl. In the presence
of hydrogen, the yield of cycloalkanone is 8-20 %, higher.
The catalyst used was zinc oxide containing 6.7 % CaO,
4.5 % A I z O 3 , and 1.6 % Cr203.
Cyclohexanol/cyclohexanone mixtures containing cyclohexyl
esters such as are obtained by oxidation of cyclohexane with
air can also be dehydrogenated to cyclohexanone by this
procedure. For example, a mixture consisting of 64.3 :L
cyclohexanol, 28.3 :4 cyclohexanone. and 2.7 % cyclohexyl
esters (calculated as acetate) were pyrolysed at 370°C. The
conversion of cyclohexanol and cyclohexyl ester was 80.3 %.
The yield of cyclohexanone based o n the amount of mixture
355
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