these of the literature. Primary alcohols were oxidized to acidic
derivatives, as it was already observed for alcohols in homoge-
of the electrode to the oxidation of benzaldehyde to benzoic
acid. The investigation of the electrocatalytic activity of the
1
neous electrocatalysis on platinum electrode. However, it has
II
2þ
grafted complex [Ru (tpy)(bpy)(O)] also revealed the poor
activity of the immobilized catalyst toward compounds with
C–H bonds adjacent to unsaturated bonds. This result can
be promising to achieve selective oxidations of unsaturated
alcohols.
been reported that electrocatalysis of benzenemethanol led
selectively to benzaldehyde when the catalyst was covalently
attached to a polymer film.
1
5
Kinetic analysis of the oxidation of benzenemethanol with
an oxidized graphite felt revealed a slow oxidation to benzalde-
ꢀ1
hyde (k
acid (k
the oxidation performed with the [Ru (tpy)(bpy)(OH
2
¼ 0.0028 min ) and a faster oxidation to benzoic
ꢀ
1
1
¼ 0.01 min ). We used the same kinetic model for
2þ
2
II
)]
Acknowledgements
modified electrode, considering that the volume concentration
of catalyst in the felt was constant during electrolysis. The
curves calculated from this kinetic model fit well with the
experimental data and confirm the hypothesis that the volume
concentration of catalyst in the felt does not decrease signifi-
cantly during the electrolysis (4 h). However, cyclic voltamme-
try analyses showed a very strong decrease in the volume
concentration of the catalyst after electrolyses. The measure-
ment of the volume concentrations of catalyst during the elec-
trolysis of benzenemethanol (Fig. 3) highlights a dramatic
decrease during the first 30 minutes of the reaction. After this
period, the concentration remains almost constant. Curiously,
when the electrolysis is performed without substrate, the
volume concentration of the catalyst decrease during the first
We are grateful to Prof. De Giovani for helpful discussions.
References
1
2
3
4
5
6
7
8
9
0
1
M. Navarro, W. F. De Giovani and J. R. Romero, Synth.
Commun., 1990, 20, 399.
M. Navarro, W. F. De Giovani and J. R. Romero, Tetrahedron,
1991, 47, 851.
M. Navarro, W. F. De Giovani and J. R. Romero, J. Mol. Catal.
A: Chem., 1998, 135, 249.
B. A. Moyer, M. S. Thompson and T. J. Meyer, J. Am. Chem.
Soc., 1980, 102, 2310.
M. S. Thompson, W. F. De Giovani, B. A. Moyer and T. J.
Meyer, J. Org. Chem., 1984, 49, 4972.
J. M. Madurro, G. Chiericato, Jr., W. F. De Giovani and J. R.
Romero, Tetrahedron Lett., 1988, 29, 765.
M. S. Thompson and T. J. Meyer, J. Am. Chem. Soc., 1982, 104,
1
5 minutes to reach a practically constant value. A possible
2
1
explanation would be that the initial volume concentrations
measured by cyclic voltammetry are overestimated, perhaps
due to a contribution of the capacitive current. Thus, the con-
centration of the catalyst would be almost constant during the
5
070.
K. J. Takeuchi, M. S. Thompson, D. W. Pipes and T. J. Meyer,
Inorg. Chem., 1984, 23, 1845.
L. A. Gallagher and T. J. Meyer, J. Am. Chem. Soc., 2001, 123,
5308.
M. S. Thompson and T. J. Meyer, J. Am. Chem. Soc., 1982, 104,
4106.
L. K. Stultz, M. H. V. Huynh, R. A. Binstead, M. Curry and T. J.
Meyer, J. Am. Chem. Soc., 2000, 122, 5984.
ꢀ
8
ꢀ3
.
electrolysis, most probably around 0.2–0.4 ꢁ 10 mol cm
ꢀ
1
The comparison of the rate constants k
and k1 ¼ 0.027 min , clearly shows that the presence of the
1
¼ 0.0028 min
0
ꢀ1
1
1
catalyst on the graphite felt increases significantly the reaction
0
ꢀ1
rate. In contrast, the rate constant k ¼ 0.009 min is similar
2
ꢀ
1
to k
hyde is oxidized into the corresponding acid directly on the
2
¼ 0.01 min . These results seem to show that benzalde-
12 R. C. McHatton and F. C. Anson, Inorg. Chem., 1984, 23, 3935.
13 W. J. Vining and T. J. Meyer, J. Electroanal. Chem., 1987,
2
2
electrode and that the catalyst only oxidizes the benzene-
methanol to benzaldehyde. This would be in agreement with
the selective oxidation of benzenemethanol to benzaldehyde
observed when the modified electrode is covered by a polymer
film.
2
37, 191.
J. P. Collin, A. Jouaiti and J. P. Sauvage, J. Electroanal. Chem.,
990, 286, 75.
W. F. De Giovani and A. Deronzier, J. Electroanal. Chem., 1992,
37, 285.
1
4
5
1
1
3
The oxidations of compounds with C–H bonds adjacent to
unsaturated bonds (1 to 5), already described in homogeneous
16 F. Geneste, C. Moinet and G. J e´ z e´ quel, New J. Chem., 2002, 26,
1539.
4
,6
17
18
19
F. Geneste, M. Cadoret, C. Moinet and G. J e´ z e´ quel, New
J. Chem., 2002, 26, 1261.
catalysis,
II
surprisingly could not be achieved with the
Ru (tpy)(bpy)(OH )] modified electrode. These results need
2þ
[
to be confirmed using a smaller amount of substrate in the
2
The potential was calculated as follows: (E
c
þ E
a c
)/2, where E and
E
a
are the cathodic and anodic potentials, respectively.
P. W. Atkins, Physical Chemistry, ed. Oxford University Press,
2
3
electrolysis medium. Indeed, most of the reactions performed
in homogeneous catalysis were described with a ratio of sub-
strate to catalyst of around 10–15. Nevertheless, the oxidation
of compounds 1 and 2 was quantitative after 100 catalytic
cycles when the catalyst was in solution whereas we did not
observe any formation of oxidized compounds with the mod-
ified electrode. These results stress the lower reactivity of the
catalyst immobilized on the electrode, compared to the catalyst
in solution. This property of the grafted catalyst could be very
interesting to achieve selective oxidations of alcohols contain-
ing unsaturated bonds.
Oxford, 5th edn., 1994, ch. 25, pp. 883–884.
20 The solution of toluene and cyclohexene was not concentrated
enough to be monitored by HPLC.
2
1
The initial waveshape could be obtained again when after electro-
II
catalysis the felt was treated with Ru Cl
2 3 3
(DMSO)(tpy), CF SO H
and H O. We are currently studying this phenomenon.
2
2
2
The oxidation of benzenemethanol to benzoic acid on a reference
graphite felt (non-oxidized) was very low. But the reaction was
improved on an oxidized electrode, probably due to the formation
of oxides at the surface of the fibres. See, for example: D. C.
Alsmeyer and R. L. McCreery, Anal. Chem., 1992, 64, 1528;
P. Chen and R. L. McCreery, Anal. Chem, 1996, 68, 3958; F.
Regisser, M.-A. Lavoie, G. Y. Champagne and D. B e´ langer, J.
Electroanal. Chem., 1996, 415, 47. Thus, the oxidation of water
was observed at more anodic potential using a reference felt com-
pared to an oxidized one and the difference of reactivity between
the two felts could be explained by the oxidation of alcohols by
water oxidation intermediates..
Conclusion
In conclusion, this work shows that the oxidation of alcohols
II
2þ
can be achieved using [Ru (tpy)(bpy)(O)] covalently attached
to the surface of a graphite felt. Kinetic analyses of the
electrolysis of benzenemethanol highlighted the contribution
2
3
To allow UV detection in the HPLC analyses, the concentration
of substrates in the electrolysis medium could not be reduced.
T h i s j o u r n a l i s Q T h e R o y a l S o c i e t y o f C h e m i s t r y a n d t h e
C e n t r e N a t i o n a l d e l a R e c h e r c h e S c i e n t i f i q u e 2 0 0 4
7
26
N e w . J . C h e m . , 2 0 0 4 , 2 8 , 7 2 2 – 7 2 6