вход по аккаунту


Electrochemical Reduction of (2 2) Paracyclophane.

код для вставкиСкачать
Results from cyclic voltmetry on mercuiy electrode are Eathered in table 1.
Table 1
This manuscript is
to be cited as
Angew. Chem. Suppl.
Dieses Manuskript ist
zu zitieren als
Angew. Chem. Suppl.
0 Verlag Chemie GmbH, 0-6840 Weinheim. 1982
0721-4227/82/0404CSO8 02.5010
Cyclic voltmetry on mercury electrode, for (2.2)paracyclophane
= 7 x
mol/L in DMF and 0.2 M tetrahutylmnim perchlorate.
Potential scan from - 2.5 to - 3.3 V(SCC1.
of (2.2)l'aracyclophane
_ ~
v/ 5
Rodolphe Jund, Paul Lemoine, Maurice Gross* -
Indirect detennination of the half-wave reduction potentials of
benzene and (2.l)paracyclophane was obtained by Gerson et al./l/ at respectively ElI2 = - 3.31 2 0.12 L'(SCE) and El,2 = - 3.05 ? 0.12 V(SCE) in
1,2-dimethoxyethane and 0.1 M tetrabutylamnoniun perchlorate. These estimated values are in agreement with previous results / 2 / showing that
(2.2)paracyclophane has a higher electron affinity in comoarison to that
of henzene. During the course of our polarographic investigations at
very cathodic potentials / 3 / , the following medim : N,N-dimethylformamide containing O . Z M tetrabutylamnoniun perchlorate exhibited a current
density of 4.35 uiVmn2 at - 3V(SCE) at 22°C in D.C. polarography (capillary characteristics at this potential : m = 0.077 mg/s, t = 0.3 s ,
mercury height 35cm). In these experimental conditions, the polamgraphic reduction have of (2.2)paracyclophane is accessible, as shown on
fipre 1. Its half-wave potential is E l / * = 3.0020.05 V(SCE). This
experimental value agrees very well with the value predicted by Gerson
et al./l/. All experiments were undertaken at mom temperature (ZOOC).
The only effect of decreasing temperature ( from 20-C to OaC) was to
diminish the (2.L)paracyclophane solubility, with formation of crystals
into the solution.
* Pmf.
Dr. M. Gross, Prof. D r . P. Lemoine, Dr. R. Jund
Laboratoire d'Electrochimie et de Chimie Physique du Corps Solide,
E.R.A. au C.H.R.S. no 468
UniversitE Louis Pasteur, 4 rue Blaise Pascal, F - 67000 Strasbourg.
- 3.080
- 3.134
- 2.889
- 2.883
- 3.193
Peak potentials are given with
a) No anodic peak at these rates.
= ? 0.030
At mderate scan rates ( 5 V/s to 20 V/s) no anodic pea); is observed.
However, at higher potential scan rates (beyond 50 V/s ) an anodic peak
is observed (figure 2). the difference between the cathodic and the anodic peak potentials ( B E = Epa Epc ) being then higher than 280 mi'.
The plot of Ip (Ip = current peak) versus vl/' (ptential
scan rate) is not linear, whereas Epc = f(1og v) is a straight line
with a slope of -0.075 V. The above results are consistenr with an irreversible reduction process.
On mercury electrode, attempts to carry out potentiostatic coulometry at very negative potential ( > -3V(SCE) failed : the stirr&
mercury did not reach a stationary hydrodynamic behaviour at such cathodic potentials. Previous investigations revealed that, whilst cyclophanes usually undergo m-electrons reductions at moderately negative potentiah /5/, (2.2)paracyclophane exhihited enhanced basicity and was
very stable towards reduction M that the nmber of electrons involved
in the electrochemical reduction step could not be ascertained / 6 / .
- 654 -
Figure 2
12.2) paracyclophane, on mercury electrode,
Potential scan : 100 V/s.Triangular sweep from -2.5V to - 3.3 V(SCE)
Same solution than figure 1.
. Cyclic voltaometry of
Figure 1
Polamgraphic cathodic wave of (2.Z)paracyclophane,
in [MF + 0.2M tetrabutylmnium perchlorate.
Curve A : solvent and supporting electrolyte
Curve B : after addition of 7 x
m1/L (?.Z)paracyclophane,
In the concentration range studied ( ~ O - ~ m o l /I S~X- 10-~mol/~)
the luniting current is proportional to the concentration of the
(2.2)paracyclophane. In normal pulse polarography, the plot
log Icorr = f ( l o g tPl) /4/, is a straizht line with a slope of -0.470
( I corr = corrected current, tpol is the duration of polarization)
The experimental slope (-0.47 ) is close to the value ( - 0 . 5 ) corresponding to 3 limiting current controlled hy diffusion /4/. The logarithmic analysis of the polarographic wave, respectively in D.C. polarography and in n o m l pulse polarography, leads to identical values of the
slope : 73 m V .
655 -
The remaining possibility to determine the nmber of electrons exchanged
in the reduction step was to compare the height of the polarographic reduction wave with'the height of the well know polarographic reduction
wave of similar compounds /7/, whose size and several properties are
comparable to those of (2.2)paracyclophane. In the present experimental
conditions, naphtalene exhibits a polarographic monoelectronic h'ave at
klI2 I - 2.58 t 0.01 V(SCE). Assuming that the diffusion coefficients of
naphtalene and of (2.2)paracyclophane are of the same order of magnitude,
the comparison of their respective wave heights in the Illkovic equation
leads to n = 2 for the nmber of electrons exchanged in the electrochemical reduction of (2.2)paracyclophane (calculated values are between
1.90 and 2.18). We reached similar conclusions, when comparing the polarographic wave height of (2.2)paracyclophane with the wave heights of,
respectively phenanthrene ( n = 1 ) and anthracene ( nglohal = 2) obtained
- 657
in the same experimental conditions. This result, compared with the
monoelectronic reduction of naphtalene, phenanthrene and biphenyl / 7 / / 9 /
/15/ is quite consistent with previous observations obtained by chemical reactivity /2//10/ and by esr /2//8/111/,
on the radical anions
produced by chemical reduction of (2.Z)paracyclophane hy Na , K in a
n d e r of solvents /2//8/. Indeed, hy brominatlon (electrophilic substition) of (2.2)paracyclophane, Reich and Cram / l o / so as Gerson and
Martin /2/ identified the dibromo 1.
- derivative as the main product
of the reaction. We might expect from that result, the possible generation of a diradkal during the chemical substitution and this is in
excellent agreement with the now observed two electrons electrochemical
On the other hand, from the ohsergation made by Gerson and
Martin /?/ that, in the chemically generated radical anion of (?.?)paracyclophane "both moieties contribute to the hypzrfine structure", the
chemical identity of the generated species in the electrochemical twoelectrons reduction of (2.2)paracyclophane may be either a dianion,
either a diradical, depending on the splitting of the two mast stable
unoccupied molecular orbitals. Indeed, it has been showm that these two
orbitals are quite close, so that secondary effects may intervert their
sequence, as demonstrated by Gerson and Martin /Z/. Should the two K O .
be almost degenerated, a dianion would he obtained, whereas a diradical
would result in case of significant splitting.
Oieses Manuskript ist
zu zitieren als
Angew. Chem. Suppl.
This manuscriptis
to be cited as
Angew. Chem. Suppl.
Q Verlag Chemie GmbH, D-6940 Weinheim, 1982
0721-4227/82/040406758 02.50/0
Vinyldiazide: Potentielle Vorstufen funktronalisiertLAlkylidencarbene
Synthese und Umsetzungen von 3.3-Diazido-Z-cyan-acrylsaurernethylester * *
Von Robert carrl'e, Daniel Danion, Erich Ackermann und
Rolf W. Saalfrank*
Prof. Dr. R. Carri'e, Dr. D. Danion, GrouTe de Recherches
des Physicochimie Structurale, Dacult'e des Sciances de
l'universiti?, B.P. 25 A, F-35042 Rennes ("rankreich)
Prof. Dr. R.W.
Attempts for electrochemical reduction of benzene in the
same conditions failed, even at - 35'C , the corresponding reduction
potential being too cathodic to he reached.
1.. F. Gerson, H. Ohya-Nishiguchi, C. Wydler, Angew. Chem. g
3 (1976) 617;
Saalfrank, Dip1.-Chem. E. Ackermann
Institut fur Organische Chemif der Universitat ErlangenNurnberg, HenkestraRe 42, D-8520 Erlangen
Geminale Vinyldiazide, 1 . Mitteilunq, Teil der Dissertation von E. Ackermann, Erlangen 1 9 8 1 , Diese Arbeit wurde
Angew. Chem. Int. Ed. Engl. 15 (1976) 552.
2 . F. Gerson, W.B. Martin Jr., J. Am. Chem. SOC.91 (196911883.
von der Deutschen Forschungsgemeinschaft und dam Fonds
3. P. Lemoine, M. Gross, C.R. Acad. Sc. Paris, 290 (1980) C-231.
der Chemischen Industrie gefordert. R.W. Saalfrank dankt
4. M. Gross, J . Jordan, J . Electroanal. Chem.,
der Universitat Rennes fiir eine Gastyrofessur.
- 65%
(1977) 163.
- 660 -
5. K. Anher, B. L a m , B. Thulin, 0. Wennerstrh, Acta Chem. Scan. 8 2
(1978) 155 ; ihid. B 3 3 (1979) 391 ; J. Chem. SOC. Perkin I1 (1980)
Soc. Japan, 52 (1979) 2420.
gut untersuchte reaktive Zwischenstufen und
Bisher wurde zwar uber BeisTiele
der ersten Glieder der homologen ungesattigten Carbene
S. Nagakura, Molecular Physics, g (1967) 1.
M.E. Peover, J. Chem. Soc., (1960) 385.
Reich and D.J. Cram, J . her. Chem. SOC., 90 (1968) 1365.
17. H.M. McConnell,
lichkeiten dieser Carhene sind jedoch weitgehend unerforscht.
Noch weniger ist uber heterosubstituierte / 4 / bzw. funktionalisierte /5/ ungesattigte Carbene bekannt. Versuche zur Darstellung der Diazoethenvorstufe / 6 /
11. S.I. Weissman, J. her. Chem. SOC., &3
richtet /2. 3/, Eigenschaften und yraparative Anwendungsmoq-
7. P.H. Given, J. Chem. Soc., (1957) 2684.
8 . A. Ishitani and
9. P.H. Given and
1 sind
finden bereits seit langem in der organischen Synthese XuBerst
vielseitige Verwendung / l / .
6 . T. Sato, K. Torizuka, M. Shimizu, Y. Kurihara, N. Yoda, Bull. Chun.
10. H.J.
des Diethoxyvinylidens
(1958) 6462.
aus 2,2-Diethoxy-l-ethendiazonium-hexachloroantimonat
J. Chem. Physics, 2 (1961) 508.
1 3 . A . Streitwieser Jr., I. Schwager, J. Am. Chem. SOC., 66 (1962) 2316.
fliissigem Ammoniak mit Natriumamid als Base schlugen fehl.
Anstelle des durch "0nium'-Umlagerung
zu erwarten-
den Diethoxyacetylens entstand 5-Ethoxy-l~-l,2,3-triazol / l / .
Aufgrund der
Received May 29,
1981 /Z 53 S /
(CN)2-Analoqie kann Dicyanvinyliden
teresse /a/.
als CO-
Wir haben nun 3,3-Diazido-2-cyan-acrylsaure-
als potentielle Vorstufe von Cyan(methoxy-
n2c=(=c ~c :
- 659 -
Equivalent aufgefaRt werden und ist daher von besonderem In-
- 661 -
Без категории
Размер файла
182 Кб
paracyclophane, reduction, electrochemically
Пожаловаться на содержимое документа