An organic catalytic system for dehydrogenative oxidation

Full text of DOI:10.1021/jo980884t

7534
J . Org. Chem. 1998, 63, 7534-7535
Ta ble 1. Oxid a tion of 2,6-Di-ter t-bu tylp h en ol
An Or ga n ic Ca ta lytic System for
Deh yd r ogen a tive Oxid a tion
Toshikazu Hirao* and Shinya Fukuhara
Department of Applied Chemistry, Faculty of Engineering,
Osaka University, Yamada-oka, Suita,
Osaka 565-0871, J apan
Received May 8, 1998
Organic compounds possessing relevant redox func-
tions may potentially serve as catalysts in oxidation
reactions, but stoichiometric amounts of the oxidant are
usually required. In a previous paper,1 derivatives of
coenzyme PQQ were shown to participate in a reversible
redox cycle with oxygen in dehydrogenative oxidation.
Furthermore, a synthetic metal catalytic system has been
devised that makes use of the redox properties of
π-conjugated polymers such as polyanilines.2 This find-
ing suggests that an aniline oligomer may function as
an oxidation catalyst. We herein report the catalytic
action of N,N′-bis(4′-aminophenyl)-1,4-benzoquinone di-
imine derivative 1 as an aniline trimer.3
Treatment of 2,6-di-tert-butylphenol with a catalytic
amount of N,N′-bis(4′-aminophenyl)-1,4-benzoquinone di-
imine (1a ) under atmospheric oxygen resulted in oxida-
tion to the diphenoquinone 2 as a major product and the
benzoquinone 3 (eq 1). This result is in sharp contrast
found to serve as a catalytic oxidant. N,N′-Bis(acryloyl)
derivative 4d worked similarly. The catalytic activity
was also observed with the corresponding polymer of 4d ,
although 4d is not soluble in DMF. It should be noted
that the selectivity for 2 was higher with the heteroge-
neous catalyst 4d .
to the fact that such efficient catalytic activity was not
observed with N,N′-diphenyl-1,4-benzoquinone diimine
(1b) as shown in Table 1. This difference is probably
attributable to the redox potentials of 1.4 A better result
was obtained by use of the tetramethyl-substituted
catalyst (1c).
This method is applied to the dehydrogenative oxida-
tion of benzylamine to N-benzylidenebenzylamine (eq 2).
The reaction under argon drastically decreased the
yield without formation of the quinone 3, indicating that
the catalytic cycle is achieved under oxygen. The reduced
form of the oxidant is considered to be the N,N′-bis(4′-
aminophenyl)-1,4-phenylenediamine 4a or 4c, which was
The latter formation is explained by dehydrogenation to
benzylideneamine and subsequent transamination with
benzylamine. A distinct difference in catalytic activity
was observed between 1a and 4a as shown in eq 2. This
difference is probably due to the presence of the amine
protons of 4a , which is consistent with the result that a
proton is required for the formation of a reversible redox
cycle of polyanilines.5 In the case of oxidation of the
phenol, a proton source is available from the substrate.
As mentioned above, the catalysis appears to depend
on a reversible redox cycle of 1 under oxygen. The broad
(1) Ohshiro, Y.; Itoh, S.; Kurokawa, K.; Kato, J .; Hirao, T.; Agawa,
T. Tetrahedron Lett. 1983, 24, 3465.
(2) Hirao, T.; Higuchi, M.; Ikeda, I.; Ohshiro, Y. J . Chem. Soc., Chem.
Commun. 1993, 194. Higuchi, M.; Ikeda, I.; Hirao, T. J . Org. Chem.
1997, 62, 1072.
(3) Wei, Y.; Yang, C.; Ding, T. Tetrahedron Lett. 1996, 37, 731. The
suggestion of Prof. Wei is acknowledged.
(4) The redox potential was measured with the reduced phenylene-
diamine derivative 4 because the quinone diimine moiety of 1 was
inactive for CV measurement (see ref 5): E1/2 ) 0.19, 0.39, 0.57 V for
4a and 0.47, 0.98 V for N, N′-diphenyl-1,4-phenylenediamine (4b)
versus Ag/Ag+. These potentials are not corrected for the junction
potential. For 1.0 mM dichloromethane solution of ferrocene, the E1/2
value is 0.51 V with 0.13 V for the peak separation.
(5) Higuchi, M.; Imoda, D.; Hirao, T. Macromolecules 1996, 29, 8277.
S0022-3263(98)00884-6 CCC: $15.00 © 1998 American Chemical Society
Published on Web 09/11/1998

Notes
J . Org. Chem., Vol. 63, No. 21, 1998 7535
In conclusion, the above-mentioned results indicate
that the π-conjugate molecules possessing a reversible
redox function contribute to the construction of an
efficient organic and complex catalytic system under
oxygen.
Exp er im en ta l Section
Syn th esis of 1 a n d 4. The preparation of 1a , 1c, 4a , and
4c was carried out according to the reported method.3 4d was
prepared as follows. To a solution of 4a (290 mg, 1.00 mmol) in
DMF (25 mL) was added dropwise a solution of acryloyl chloride
(181 mg, 2.00 mmol) and pyridine (313 mg, 4.00 mmol) in DMF
(5 mL) at 0 °C under argon. Stirring was continued for an
additional 5 h. The reaction mixture was concentrated under
reduced pressure. Methanol (20 mL) was added to the obtained
residue, which was filtered to remove the insoluble black solid.
Reprecipitation of the concentrated filtrate from a saturated
aqueous solution of NaHCO3 was carried out three times.
Further reprecipitation from hexane (200 mL) gave 235 mg (59%
yield) of 4d . mp 213-214 °C (uncorrected, dec); IR (KBr) 3300,
1659, 1613, 1510, 1384, 1307, 822 cm-1 1H NMR (600 MHz,
;
DMSO-d6) δ 9.91 (s, 2H), 7.80 (s, 2H), 7.48 (dd, 4H, J ) 7.2, 1.8
Hz), 6.98 (s, 4H), 6.92 (dd, 4H, J ) 7.2, 1.8 Hz), 6.40 (dd, 2H, J
) 17.1, 10.5 Hz), 6.20 (dd, 2H, J ) 17.1, 2.1 Hz), 5.69 (dd, 2H,
J ) 10.5, 2.1 Hz); MS (FAB) m/z, 398 (M+). Anal. Calcd for
C24H22N4O2‚1.25H2O: C, 68.47; H, 5.87; N, 13.31. Found: C,
68.20; H, 5.41; N, 13.66.
F igu r e 1. UV-vis spectra. (a) [1a ] ) 5.0 × 10-5 M; solvent
MeCN. (b) (1) treatment with benzylamine at 70 °C for 5 h
under argon; (2) treatment at room temperature for 9 h under
atmospheric oxygen.
Polymerization was carried out by treatment of 4d (40 mg,
0.10 mmol) in dichloromethane with benzoyl peroxide (2.4 mg,
0.01 mmol) at 80 °C for 24 h under argon in a sealed glass tube.
The blue solid polymer (28 mg) was washed with dichlo-
romethane and methanol and dried; mp >300 °C; IR (KBr) 3313,
absorption around 540 nm in the UV-vis spectrum of
1a (Figure 1a), which is possibly assigned to the CT band
between the benzenoid and quinoid moieties, disappeared
on treatment with benzylamine at 70 °C under argon.
This spectral change implies the reduction of 1a to 4a .
The absorption reappeared to some extent upon contact
with atmospheric oxygen (Figure 1b). The phenylenedi-
1658, 1603, 1536, 1503, 1319, 1250, 823 cm-1
. Anal. Found:
C
24H22.46N4.15
.
A Rep r esen ta tive P r oced u r e for th e Ca ta lytic Oxid a -
tion of 2,6-Di-ter t-bu tylp h en ol. A mixture of 2,6-di-tert-
butylphenol (206 mg, 1.00 mmol) and 1a (29 mg, 0.10 mmol) in
DMF (1 mL) was stirred at 70 °C for 40 h under atmospheric
oxygen. Ether (50 mL) was added to the reaction mixture, which
was filtered and concentrated. The yields of 2 and 3 were
determined by GLC as shown in Table 1.2
1
amine 4a was also detected by H NMR in the reaction
mixture obtained similarly in acetonitrile-d3. These
results support the catalytic cycle of 1 or 4 shown in
Scheme 1.
A Rep r esen ta tive P r oced u r e for th e Ca ta lytic Oxid a -
tion of Ben zyla m in e. A mixture of benzylamine (107 mg, 1.00
mmol) and 1a (29 mg, 0.10 mmol) in acetonitrile (1 mL) was
stirred at reflux for 24 h under atmospheric oxygen. Ether (50
mL) was added to the reaction mixture, which was filtered and
concentrated. The yield of N-benzylidenebenzylamine was
determined by GLC as shown in eq 2.2
A Rep r esen ta tive P r oced u r e for th e Ca ta lytic Oxid a -
tion of Ben zyl Alcoh ol. To a mixture of 1a (29 mg, 0.10 mmol),
copper(I) chloride (9.9 mg, 0.10 mmol), and potassium carbonate
(553 mg, 4.00 mmol) in toluene (2 mL) was added benzyl alcohol
(216 mg, 2.00 mmol). The mixture was stirred at 90 °C for 24
h under atmospheric oxygen. Ether (50 mL) was added to the
reaction mixture, which was filtered and concentrated. The yield
of benzaldehyde was determined by GLC as shown in eq 3.
Benzoic acid was not detected by GLC.
Sch em e 1
The combination of polyanilines and a copper or iron
salt is revealed to form an efficient complex catalytic
system,2 and the imine moiety of 1c is capable of
coordinating to transition metals.6 Benzyl alcohol was
allowed to undergo the dehydrogenation to benzaldehyde
on treatment with a catalytic amount of copper(I) chloride
and 1a or 1c in the presence of potassium carbonate (eq
3). Both catalytic components are essential for the
Mea su r em en t of UV-Vis a n d 1H NMR Sp ectr a in th e
Red ox P r ocess of 1a . The oxidation reaction of benzylamine
was carried out similarly as mentioned above at 70 °C for 5 h
under argon. The obtained solution was diluted to ca. 5 × 10-5
M with acetonitrile for the measurement of the UV-vis spec-
trum. The solution was contacted with atmospheric oxygen at
room temperature for 9 h to give the spectrum shown in Figure
1
1. For the measurement of the H NMR spectrum, acetonitrile-
d3 was used as a solvent.
effective conversion. Since the azodicarboxylate has been
reported to serve as a hydrogen acceptor,7 1 might also
play a similar role in the present oxidative transforma-
tion.
J O980884T
(7) Marko´, I. E.; Giles, P. R.; Tsukazaki, M.; Brown, S. M.; Urch, C.
J . Science 1996, 274, 2044; Angew. Chem., Int. Ed. Engl. 1997, 36,
2208.
(6) Moriuchi, T.; Bandoh, S.; Miyaishi, M.; Hirao, T., to be published.