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Direct Detection of Dicyanoketene in the Gas Phase.

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Received: April 18, 1980 [ Z 561 b IE]
German version: Angew. Chem. 92,750 (1980)
The high intensity of band @ is attributable to superposition
of several ionizations. PERTCI calculations[61with MNDO
wave functions['] permit assignment of the bands a / ' B , ( ~ r )
and @/2B2(a), 'A,(a), 2A2(7r),and 'B2(o) to ionizations of
dicyanoketene (2).
111 a) R. Bussas. G. Kresze, Angew. Chem. 92, 748 (1980);Angew. Chem. Int.
Ed Engl. 19, 732 (1980); b) K. B. Sharpless, K. M. Gordon, J. Am. Chem.
Soc. YX. 300 (1976);L. M . Stephenson, D. R. Speth, J. Org. Chem. 44,4683
(1979).
121 Fluoride ions catalyze the reaction of hexafluoropropanone with N-sulfinylaniline: Yu V. Zeifman, E. G. Ter. Gabrielyan, D. P. Del'rsora, N. P Gamberyan. Izv. Akad. Nauk SSSR 2, 396 (1979); aldehydes and a-diketones react
with evolution of SO2 to give imines:
with N-sulfinyl-pp-toluenesulfonamide
G. Kresze, R. Albrechl, Angew. Chem. 74, 781 (1962);Angew. Chem. Int. Ed.
Engl 1. 595 (1962); R. Albrechr, G. Kresze, B Mlakar, Chem. Ber. 97,483
(1964): G. Kresze, D. Sommerfeld, R. Albrecht, ibid. 98. 601 (1965);R. AIbrechr, G. Kresze, ibid. 98, 1431 (1965).
131 F. G. Bordwell, Pure Appl. Chem. 49, 963 (1977).
[4]G. Kresze, W. Wucherpfennig, Angew. Chem. 79. 109 (1967);Angew. Chem.
Int Ed. Engl. 6. 149 (1967)
151 R. Block. P. LePerchec, F. Rouessac, J.-M. Conia, Tetrahedron 24, 5971
(1968).
161 Y. Bessiere-Chrelien, H. Serne, J. Heterocycl. Chem. //, 317 (1974).
[7] K. Kociolek, M . T. Leplawy, Synthesis 1977, 778; K. Kociolek, M. Leplawy,
Rocz. Chem. 49. 1841 (1975).
[8] J. Sander, K . Clauss, Angew. Chem. 92, 138 (1980);Angew. Chem. Int. Ed.
Engl. 19, 131 (1980),cf. also K. Clauss, H. Jensen, ibid. 85,965 (1973)and 12,
869 (1973).
191 a) E. J. Corey, T. Dursr, J. Am. Chem. SOC.90, 5548 (1968);b) R. P. Gupru. J.
S. Pizey, Phosphorus Sulfur 7, 325 (1979).
Direct Detection of Dicyanoketene in the Gas
Phase'"'
By Alfred Hotzel, Richard Neidlein, Reinhard Schulz, and
Armin Schweig1'I
Cyanoketenes are exceptionally reactive and are therefore
regarded as highly unstable['I. Evidence for their existence
could only be gained indirectly by trapping reactions, except
in the case of sterically stabilized tert-butyl- and tert-pentylcyanoketenes. Dicyanoketene itself was also postulated in
1978 on the basis of trapping products['].
We now wish to report the generation of free dicyanoketene (2) in the gas phase and its characterization by UV photoelectron spectroscopy and mass spectrometry.
On slow warming of 2,5-diazido-3,6-dicyano-1,4-benzoquinone
to 60°C in vacuo @<S x
mbar) a gas
mixture could be pumped off over a longer period of time
whose PE spectrum (Fig. 1) showed it to contain not only nitrogen and a small amount of carbon dioxideI41 but also a
further compound having the vertical ionization energies @
10.56 eV, @ 13.25 eV and 13.49 eV. Band @ is split into partial vibrational bands separated by 1150 cm - ' and its shape
resembles that of the lowest-energy 'B, PE band of ketenel51.
1'1 Prof. Dr. A. Schweig, DipLChem. R. Schulz
Fachbereich Physikalische Chemie der Universitat
Hans-Meerwein-Strass, D-3550 Marburg 1 (Germany)
Prof. Dr. R. Neidlein, Dr. A. Hotzel
Pharmazeutisch-chemisches Institut der Universitat
Im Neuenheimer Feld 364, D-6900 Heidelberg (Germany)
["I Part 89 of Theory and Application of Photoelectron Spectroscopy. This
work was supported by the Deutsche Forschungsgemeinschaft and the Fonds der
Chemischen 1ndustrie.-Part 88: R. Schulz, A . Schweig, C. Wentmp, H . - W Winter, Angew. Chem., in press
Angew. Chem. Ini. Ed. Engl. 19 (1980) No. 9
1
10
12
I
14
16
I
I
IPleV
-
Fig. 1. a) He-I photoelectron spectrum of the gaseous product mixture obtained
(1) to 60"C/ < 5 x 10 on heating 2,5-diazido-3,6-dicyano-1,4-benzoquinone
mbar: b) experimental, and c) calculated (MNDO-PERTCI) vertical ionization
energies of dicyanoketene (2).
'
In view of the unusual reaction conditions-the highly
reactive dicyanoketene is pumped off from the surface of the
decomposing quinone (1) which does not itself go into the
gas phase even in a high vacuum-further independent evidence appeared desirable.
28
100
'"1iiI
0
I
6L
92
50
100
150 mie
Fig. 2. 100-eV mass spectrum of the dicyanoketene (2) obtained together with ni(/) to 85 "C in the
trogen on heating 2,5-diazido-3,6-dicyano-l.4-benzquinone
ion source.
To this end we slowly heated the quinone (1) in the ion
source of a mass spectrometer until vigorous evolution of nitrogen occurred (85 "C). The mass spectrum (Fig. 2) unequivocally confirms the formation of dicyanoketene (2). High
resolution spectra of the two characteristic peaks at the mass
numbers 92 ( M ' ) and 64 (M' - CO) afforded the empirical
formula C4N20(calc. 92.0011, exp. 92.0011) and C3N2(calc.
64.0061,exp. 64.0060).Fragmentation of the molecular cation with loss of CO is characteristic of ketenesl'] and rules
out the two C4N20isomers (3) and (4) as possible competing
products in the decomposition of (1). This is in agreement
with MNDO calculations (standard enthalpies of formation:
(2) 52 kcal/mol; (3) 118 kcal/mol; (4) 101 kcal/mol).
0 Verlag Chemie, GmbH, 6940 Weinherm, 1980
0570-0833/80/0909-0739
S 02.50/0
739
NC-E-0-CN
NC
(4)
CN
Thus dicyanoketene (2), like di~yanothioketene~'],is stable
at low pressure in the gas phase.
Received: February 29. 1980 [Z 562a IE]
German version: Angew. Chem. YZ, 751 (1980)
CAS Registry numbers:
( I ) , 66563-24-4; (2). 4361-47-1; (3), 74408-85-8; (41, 74408-84-7
[ f ] R. C. De Selms, Tetrahedron Lett. 1969. 1179 H. W. Moore, W Weyler, H.
R . Shelden, rbid. 196Y, 3947; H. W. Moore, W Weyler, J. Am. Chem. SOC.92.
4132 (1970); W. Weyler, W. G Duncan, H. W. Moore, rbid. 97, 6187 (1975).
(21 R. Neidlein, E. Bernhard, Angew. Chem. 90. 395 (1978); Angew. Chem. Int.
Ed. Engl 17, 369 (1978).
[3j We are grateful to Dr. R. Gurtner for the preparation of 2,5-dichloro-3,6-dicyano-l,4-benzoquinone, from which ( I ) was obtained according to 121. The
premature deflagration of ( I ) in the experiments described could be suppressed by preparation of (I) in the presence of roughly twice the amount of
finely divided calcium carbonate ("solid state dilution"). The mixture of (/)
and CaCO, was thoroughly dried at 0 ° C and l o - * mbar prior to each experiment.
141 It could be demonstrated by mass spectrometry that carbon dioxide is formed
on thermal decomposition of the (di- or polymeric?) byproducts. This reaction becomes increasingly pronounced with rising temperature, hut plays
only a minor role below 100 "C. Increasing temperature considerably
strengthened the mass peak at m / e = 44 after that at m / e = 92 bad disappeared almost completely.
[5] D. Hall, J. P. Maier. P. Rosmus, Chem. Phys. 24, 373 (1977).
161 H. L. Hose, G. Lauer, K: W. Schulre, A. Schweig, Theor. Chim Acta 48, 47
(1978); the geometry was optimized by MNDO 171
171 M. J. S. Dewar, W. Thiel, J. Am. Chem. SOC.9Y. 4899 (1977).
181 J. Seiblr Massenspektrometrie Akademlsche Verlagsgesellschaft. Frankfurt
am Main 1974.
191 R. Schulz, A . Schweig. Angew. Chem. Y2, 752 (1980); Angew. Chem. Int. Ed.
Engl. IY, 740 (1980).
directly above the ionization region of a modified PS 18 photoelectron spectrometer and went to completion at 470 "C.
The PE spectrum of the starting material (1) (Fig. la ) shows
bands at @ 10.00 eV/'B,(n), @ 10.95-1 1.10 eV/2Az(T) and
'Bz(n), @ 12.80 eV/'B,(n), @ 13.08 eV/'B,(a) and 'Ai(a)
and @ 13.70 eV/2A,(n)151.The PE spectrum of the pyrolysis
products (Fig. Ib) contained not only the known bands of
carbon oxide sulfideI61but also the new bands at @ 9.94 eV/
'B,(n), @ 12.79 eV/'Bz(o), @ 13.00-13.8 eV/*B,(n),
'Bz(o), 'A,(o) and 2A2(~)15a1.
Band @ is split into vibrational
partial bands separated by 1500 cm - I and e xpe ~tedly[~]
cos
cos
Direct Detection of Dicyanothioketene in the Gas
Phase'"]
By Reinhard Schulz and Armin Schweig[*l
Dedicated to Professor Karl Dimroth on the occasion of
his 70th birthday
Dicyanothioketene (2) has been formulated as an intermediate on several occasions[l1; however, all attempts to isolate
this species or to detect it by spectroscopy have so far failed.
Not even monocyanothioketenes have yet been identified directly''].
We have now succeeded in directly detecting this apparently highly reactive molecule by variable temperature photoelectron spectroscopy (VTPES)r31o n gas phase pyrolysis of
2-(4-oxo-1,3-dithietan-2-ylidene)malonitrile( l ) ~ ' a l . A previous attempt to generate (2) in the gas phase by this reaction
and to isolate it in solution at low temperature afforded only
dimeric and polymeric material[41.
NC
x ) o
NC
(1)
47O0C
NC,
c=c=s+ cos
NC'
(2)
The reaction (1)-+(2) was performed in a flash pyrolysis
reactor (stainless steel tube, 20 x 0.6 cm; ca. 5 x lo-' mbar)
"3 Prof. Dr. A. Schweig, DiplLChem. R. Schulz
Fachbereich Physikalische Chemie der Universitat
Hans-Meerwein-Strasse, D-3550 Marburg 1 (Germany)
I"] Part 90 of Theory and Application of Photoelectron Spectroscopy. Tbls
work was supported by the Deutsche Forschungsgemeinschaft and the Fonds der
Chemischen 1ndustrie.-Par1 89: [101.
I40
0 Verlag Chemie. CmbH, 6940 Wernheim, 1980
d)
I
I
1
10
12
11111 ,
1
I
I
16
IP/eV-
Fig. 1. He-I photoelectron spectrum of a ) the starting material ( I ) and b) its pyrolysis products at 470OC; c) experimental and d ) calculated (MNDO-PERTCI)
vertical ionization energies of dicyanothioketene (2).
shows the same fine structure as the energetically lowest-lying 'Bi(n) band in the PE spectrum of thioketenel*". The
identity of dicyanothioketene (2) follows not only from the
extremely clear-cut reaction but also from the good agreement between the experimental vertical ionization energies
and those predicted by MND0[9"1-PERTCI[9b1
calculations
(Fig. 1). The ionization energies are expectedly smaller than
for dicyanoketene"''. The energy difference between the
'Bi(n) states of dicyanoketene and dicyanothioketene (0.7
eV) is in excellent agreement with the corresponding difference in the case of the ketene/thioketene pair[*].
0570-0833/80/0909-0740
$02.50/0
Angew. Chem. Inr. Ed. Engl. 19 (1980) No. 9
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