Synthesis of aromatic aldehydes by aerobic oxidation of hydroaromatic compounds and diarylalkanes using N-hydroxyphthalimide (NHPI) as a key catalyst

Article abstract of DOI:10.1016/j.tet.2005.12.048

Aerobic oxidation of hydroaromatic compounds and diarylalkanes by N-hydroxyphthalimide (NHPI) under mild conditions afforded the corresponding hydroperoxides in high selectivity. Treatment of the resulting hydroperoxides with sulfuric acid followed by neutralization by a base resulted in phenol and aromatic aldehydes in high selectivity. This method provides a convenient synthetic route to aldehydes involving an aromatic moiety.

Full text of DOI:10.1016/j.tet.2005.12.048

Tetrahedron 62 (2006) 2497–2500
Synthesis of aromatic aldehydes by aerobic oxidation
of hydroaromatic compounds and diarylalkanes using
N-hydroxyphthalimide (NHPI) as a key catalyst
Yasuhiro Aoki, Satoshi Sakaguchi and Yasutaka Ishii
*
Department of Applied Chemistry and High Technology Research Center, Faculty of Engineering,
Kansai University, Suita, Osaka 564-8680, Japan
Received 24 November 2005; revised 20 December 2005; accepted 21 December 2005
Available online 18 January 2006
Abstract—Aerobic oxidation of hydroaromatic compounds and diarylalkanes by N-hydroxyphthalimide (NHPI) under mild conditions
afforded the corresponding hydroperoxides in high selectivity. Treatment of the resulting hydroperoxides with sulfuric acid followed by
neutralization by a base resulted in phenol and aromatic aldehydes in high selectivity. This method provides a convenient synthetic route to
aldehydes involving an aromatic moiety.
q 2005 Elsevier Ltd. All rights reserved.
1. Introduction
2. Results and discussion
Aerobic oxidation of alkylbenzenes is an important
commercial process for the production of alkyl aromatic
hydroperoxides, which are used as oxidants for epoxidation
of alkenes like propene as well as raw materials for the
We first examined the aerobic oxidation of tetralin (1) under
dioxygen atmosphere (1 atm) in the presence of a catalytic
amount of AIBN and NHPI (Eq. 1). Table 1 shows the result
for the oxidation of 1 with atmospheric dioxygen catalyzed
by NHPI followed by treatment with triphenylphosphine.
1
production of phenols. The Hock process is well known as a
typical method for the concomitant synthesis of phenol and
acetone from cumene hydroperoxide obtained by the aerobic
oxidation of isopropylbenzene. Currently, most phenols are
Table 1. Oxidation of tetralin (1) with O
conditions
2
(1 atm) by NHPI under various
2
a
manufactured by this method worldwide. Resorcinol and
hydroquinone are also prepared by the aerobic oxidation of
the m- and p-diisopropylbenzenes, respectively. However,
there is little work reported on the aerobic oxidation of
hydroaromatic compounds and diphenyl alkanes to prepare
phenols and aldehydes, probably because of the difficulty in
b
Entry
Temperature (8C) Time (h) Conv. (%)
Select. (%)
3
4
1
2
75
65
50
75
75
5
6
6
5
5
61
52
50
22
20
80
87
92
77
30
8
8
4
nd
nd
c
3
4
d
3
carrying out the oxidation selectively. In previous papers,
e
5
we have reported the aerobic oxidation of hydrocarbons
catalyzed by NHPI in the presence or absence of transition
metals such as cobalt and manganese salts. This oxidation
provides a novel efficient catalytic method for the trans-
formation of alkanes to oxygen-containing compounds like
alcohols, ketones and carboxylic acids in high conversion
a
Compound 1 (2 mmol) was reacted with O (1 atm) in the presence of
2
AIBN (3 mol%) and NHPI (10 mol%) in CH
treatment with PPh (ca. 10 mmol) at room temperature for 2 h.
3
CN (5 mL) followed by
3
b
c
d
e
GC yield based on 1 reacted.
BPP was used instead of AIBN.
In the absence of AIBN.
In the absence of NHPI.
4
and selectivity under mild conditions. In continuation of our
study, the present methodology was extended to the synthesis
of various aromatic aldehydes by the aerobic oxidation of
hydroaromatic compounds and diphenyl alkanes to hydro-
peroxides upon treatment with sulfuric acid.
Compound 1 was oxidized with O (1 atm) in the presence
2
of AIBN (3 mol%) and NHPI (10 mol%) in acetonitrile at
7
5 8C for 5 h. The resulting hydroperoxide (2) was treated
with excess triphenylphosphine to give 1,2,3,4-tetrahydro-
-naphthol (a-tetralol) (3) and a-tetralone (4) in 80 and 8%
1
Keywords: Aerobic oxidation; Hydroaromatic compounds; Hock process.
*
selectivity, respectively, at 61% conversion of 1 (entry 1).
The same reaction at 65 8C gave almost the same results as
Corresponding author. Tel.: C81 6 6368 0793; fax: C81 6 6339 4026;
e-mail: ishii@ipcku.kansai-u.ac.jp
0040–4020/$ - see front matter q 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2005.12.048

2498
Y. Aoki et al. / Tetrahedron 62 (2006) 2497–2500
that at 75 8C except for a slight decrease of the conversion
entry 2). In order to carry out the reaction at lower
after 8 h. This is believed to be due to the decomposition of
the NHPI by a side-reaction with a radical species
generated from the resulting hydroperoxide 2. It is
known that an increase in the concentration of hydroper-
oxides causes their steep self-decomposition.
(
temperature, t-butyl peroxypivalate (BPP), which decom-
poses at 55 8C was employed as a radical initiator instead of
AIBN. The oxidation can be performed at 50 8C to lead to 3
in high selectivity (92%) along with 4 (4%) at 50%
conversion of 1 (entry 3). The reaction of 1 by NHPI alone
at 75 8C took place at low conversion (22%) to give 3 (77%
selectivity), but the reaction by AIBN in the absence of
NHPI resulted in a complex mixture of products (entries 4
and 5). Quite recently, Xu et al. reported the oxidation of 1
We next tried the conversion of the resulting hydroperoxide
into aldehyde by treating with some acids (Table 2).
2
Table 2. Oxidation of 1 with O
with sulfuric acid
2
(1 atm) by NHPI followed by treatment
a
with O in the presence of anthraquinones and NHPI at
2
b
5
Entry
Temperature
8C)
Time
(h)
Conv.
(%)
Select. (%)
8
0 8C to give 4 (88%) and 3 (12%).
(
3
4
5
+
O
2
1
2
3
4
5
75
75
75
75
50
3
6
3
3
3
49
64
40
52
31
2
3
!1
17
nd
4
8
7
46
nd
94
89
92
2
1
(
2 mmol)
(1 atm)
c
d
NHPI (10 mol%)
AIBN (3 mol%)
CH CN (5 mL)
3
Temp., Time
e
87
a
Compound 1 (2 mmol) was reacted with O (1 atm) in the presence of
AIBN (3 mol%) and NHPI (10 mol%) in CH
2
mixture was treated with H SO (ca. 20 mg) at room temperature for 2 h
followed by adding pyridine (ca. 6 mL).
GC yield based on 1 reacted.
2
Pyridine conc.H
SO
OOH
OH
O
2
4
PPh
3
CN (5 mL). The reaction
3
OH
(ca. 6 mL)(ca. 20 mg)
(excess)
O
4
+
rt 2 h
rt 2 h
H
b
c
d
e
5
2
3
4
InCl$4H
2
O (50 mg) was used in place of H
CeCl$7H O (50 mg) was used in place of H SO .
2 4
SO .
3
(
1)
3
2
2
4
BPP (3 mol%) was used in place of AIBN.
In order to obtain further insight into the present reaction,
the oxidation was followed by using NHPI/AIBN at 65 8C
and using NHPI/BPP at 50 8C, respectively (Fig. 1). The
time-conversion curves of 3 and 4 by both systems are
similar. The oxidation proceeded smoothly for about 3 h,
but it became very slow and was practically terminated
The oxidation of 1 in the presence of AIBN and NHPI at
75 8C for 3 h followed by treatment with sulfuric acid at
room temperature afforded 3-(2-hydroxyphenyl)butanal (5)
(94%), 4 (4%), and 3 (2%) at 49% conversion of 1 (entry 1).
When the reaction was prolonged to 6 h, the conversion was
increased to 64% but the selectivity to 5 was slightly
decreased (entry 2). Treatment of 2 with a Lewis acid like
1
00
8
6
4
2
0
0
0
0
0
InCl , which does not decompose in aqueous medium, gave
3
almost the same result as that of sulfuric acid (entry 3).
However, when CeCl3 was employed instead of InCl3,
tetralone 4 (46%) was formed as the principal product along
with tetralol 3 (17%), but the desired 5 was formed in only
Select. of 3
Conv. of 1
Select. of 4
2% yield (entry 4). This shows that CeCl serves as a metal
3
ion, which promotes the redox decomposition of the
hydroperoxide 2. The reaction using BPP instead of AIBN
at 50 8C led to 5 in 87% selectivity at 31% conversion of 1
(entry 5).
0
3
6
9
12
15
18
Time (h)
1
00
On the basis of these results, we examined the synthesis of
aldehydes having an aromatic moiety from several
hydroaromatic compounds and diphenyl alkanes (Table 3).
8
6
4
2
0
0
0
0
0
Indane (6) was reacted under the same conditions as entry 1
in Table 2 to afford 3-(2-hydroxyphenyl)propanal (8) (81%)
and indanone (7) (10%) at 42% conversion of 6 (entry 1). In
this reaction, a trace amount of 1-indanol was formed. sym-
Octahydroanthracene (9) was easily oxidized under these
conditions to give 1,2,3,4,6,7,8,9-octahydroanthracen-1-one
Select. of 3
Conv. of 1
Select. of 4
(
10) (13%) and 4-(5,6,7,8-tetrahydro-3-hydroxy-2-
naphthyl)butanal (11) (73%) at higher conversion (85%)
entry 2). In this oxidation, however, no products in which
0
3
6
9
12
15
18
Time (h)
(
both cyclohexyl rings in 9 are oxidized were obtained. It
was found that diphenyl methane (12) was less reactive than
1. Hence, benzonitrile, which is capable of raising the
Figure 1. Time-dependence curves for aerobic oxidation of 1 (2 mmol)
under O (1 atm): (a) NHPI (10 mol%)/AIBN (3 mol%) in CH CN (5 mL)
at 65 8C. (b) NHPI (10 mol%)/BPP (3 mol%) in CH CN (5 mL) at 50 8C.
2
3
3

Y. Aoki et al. / Tetrahedron 62 (2006) 2497–2500
2499
a
Table 3. Conversion of hydroaromatic compounds and diphenyl alkanes into aldehydes
b
Entry
Substrate
Temperature (8C)/Time (h)
Solvent)
Conv. (%)
Product (select. (%))
(
OH
O
H
O
1
75/3 (CH
3
CN)
CN)
42
6
9
O
7
(10)
8
(81)
O
OH
2
3
75/3 (CH
3
85
H
1
1 (73)
1
0 (13)
O
Ph
Ph
100/5 (PhCN)
100/3 (PhCN)
30
37
PhOH 14 (99)
14 (62)
Ph
H
12
1
3 (98)
H
Ph
Ph
4
5
Ph
O
6 (97)
15
1
15
15
75/3 (CH
3
CN)
CN)
23
33
16 (96)
16 (99)
O
14 (83)
14 (97)
c
6
50/18 (CH
3
c
7
50/3 (CH
3
CN)
24
14 (67)
Ph
Ph
Ph
17
1
8 (O99)
a
Substrate (2 mmol) was reacted under the same conditions as entry 1 in Table 2.
GC yield based on substrate reacted.
BPP (t-butyl peroxypivalate) was used instead of AIBN.
b
c
reaction temperature to 100 8C, was used as a solvent. The
reaction gave benzaldehyde (13) and phenol (14) in
excellent selectivity at moderate conversion of 12 (entry
plate or KBr press disk. A GLC analysis was performed with
a flame ionization detector using a 0.2 mm!25 m capillary
column (OV-17). Mass spectra were determined at an
ionizing voltage of 70 eV. All starting materials, catalysts,
and initiators were purchased from commercial sources and
used without further treatment. The yields of products were
estimated from the peak areas based on the internal standard
technique.
3
). 1,2-Diphenylethane (15) reacted in the same way as 12 to
give the corresponding aldehyde, phenylacetaldehyde (16),
in high selectivity (97%) at 37% conversion (entry 4).
Although long reaction time is needed for the oxidation of
1
5 at lower temperature (75 or 50 8C), 15 was found to be
slowly oxidized even at 50 8C to give 16 in high selectivity
entry 6). However, oxidation of 1,1-diphenylethane (17)
having a methine group more easily proceeded than that of
(
3.2. General procedure for the oxidation of tetralin (1)
to 1,2,3,4-tetrahydro-1-naphthol (a-tetralol) (3)
and a-tetralone (4)
1
2
5 to give acetophenone (18) in high selectivity (99%) at
4% conversion (entry 7).
An acetonitrile (5 mL) solution of tetralin (1) (2 mmol),
AIBN (3 mol%), and NHPI (10 mol%) was placed in a two-
necked flask equipped with a balloon filled with O at
2
In conclusion, we have developed a method for aerobic
oxidation of hydroaromatic compounds and diarylalkanes to
the corresponding hydroperoxides selectively. Further
treatment of the resulting hydroperoxides with sulfuric
acid followed by neutralization with a base produced phenol
derivatives and aromatic aldehydes in high selectivity. This
method provides a convenient synthetic route to aldehydes
involving an aromatic group.
50–75 8C for 5–6 h. The reaction mixture was treated with
an excess amount of PPh at 25 8C for 2 h.
3
3.3. General procedure for the oxidation of various
substrates to aldehyde and ketone derivatives
An acetonitrile (5 mL) solution of substrate (2 mmol),
AIBN (3 mol%), and NHPI (10 mol%) was placed in a two-
necked flask equipped with a balloon filled with O at 75 8C
3. Experimental
2
3
.1. General procedure
for 3 h. The reaction mixture was treated with H
(ca. 20 mg) in CH CN (1 mL) at 25 8C for 2 h. The mixture
was neutralized by adding pyridine (ca. 6 mL). The solvent
was removed under reduced pressure, and the residue was
purified by column chromatography on silica gel (n-hexane/
SO
2 4
3
1
13
H and C NMR were measured at 270 and 67.5 MHz,
respectively, in CDCl with TMS as the internal standard.
3
Infrared (IR) spectra were measured as thin films on NaCl

2500
Y. Aoki et al. / Tetrahedron 62 (2006) 2497–2500
AcOEtZ10:1) to give aldehydes and ketones. Products
were characterized by H and C NMR, IR, and GC–MS.
and ‘High-Tech Research Center’ Project for Private
Universities: matching fun subsidy from the Ministry of
Education, Culture, Sports, Science and Technology, 2005–
2009.
1
13
6
1
.3.1. 4-(2-Hydroxyphenyl)butanal (5). H NMR d 9.79
3
(
s, 1H), 7.09–6.79 (m, 4H), 5.66 (br, 1H), 2.62 (t, JZ7.2 Hz,
1
3
2
2
3
1
1
H), 2.55 (t, JZ6.7 Hz, 2H), 1.95–1.90 (m, 2H); C NMR d
03, 130, 127, 120, 115, 42.9, 29.3, 22.1; IR (NaCl) 3420,
066, 3034, 2937, 2723, 1716, 1593, 1503, 1454, 1231,
K1
175, 1107, 755 cm ; MS m/eZ40, 51, 65, 77, 91, 107,
20, 133, 145, 164.
References and notes
1
. Landau, R.; Sullivan, G. A.; Brown, D. Chem. Tech. 1979, 602.
$
7
3
.3.2. 1,2,3,4,6,7,8,9-Octahydroanthracen-1-one (10).
2. (a) Hock, H.; Lang, S. Ber. Dsch. Chem. Ges. 1944, B77, 257.
(b) Sheldon, R. A.; Kochi, J. K. Metal-catalyzed Oxidations of
Organic Compounds; Academic: New York, 1981. (c)
Jordan, W.; Van Barneveld, H.; Gerlich, O.; Boymann, M. K.;
Ullrich, J. In Ullmann’s Encyclopedia of Industrial Organic
Chemicals, Vol. A9; Wiley-VCH: Weinheim, 1985;
pp 299–312.
1
H NMR d 7.74 (s, 1H), 7.26 (s, 1H), 2.87 (t, JZ6.2 Hz,
H), 2.77 (t, JZ6.4 Hz, 4H), 2.60 (t, JZ6.4 Hz, 2H), 2.09
2
1
3
(
q, JZ6.2 Hz, 4H); C NMR d 198, 152, 143, 141, 135,
1
1
4
29, 128, 75; 53, 39, 29, 23; IR (NaCl) 2934, 2850, 1727,
K1
727, 1679, 1436, 1265, 1041, 894, 747 cm ; MS m/eZ
0, 51, 63, 77, 91, 103, 115, 129, 144, 158, 172, 185, 200;
C
HRMS (EI, M ) calcd for C H O: 200.1201, found:
1
2
3. (a) Shimizu, I.; Matsumura, Y.; Inomata, Y.; Uchida, K.;
Arai, Y.; Iwamoto, K. JP 03031231, 1991. Shimizu, I.;
Matsumura, Y.; Inomata, Y.; Uchida, K.; Arai, Y.;
Inomata, K. JP 03031221, 1991. (b) Baba, N.; Oda, J.;
Kawahara, S.; Hamada, M. In Bulletin of the Institute for
Chemical Research, Vol. 67; Kyoto University: Kyoto:, 1989;
pp 121–127.
4 16
00.1204.
3.3.3. 4-(5,6,7,8-Tetrahydro-3-hydroxy-2-naphthyl)bu-
tanal (11). H NMR d 9.74 (s, 1H), 6.75 ppm (s, 1H),
1
6
1
1
2
8
1
.48 (s, 1H), 2.63–2.48 (m, 8H), 1.89 (m, JZ6.8 Hz, 2H),
13
.70 (m, JZ7.3 Hz, 4H), C NMR d 204, 152, 136, 131,
28, 124, 115, 43, 29, 28, 23, 22; IR (NaCl) 3412, 3004,
927, 2855, 1712, 1620, 1517, 1424, 1247, 1191, 1094, 918,
58, 777 cm ; MS m/eZ40, 55, 65, 77, 91, 105, 115, 133,
46, 161, 174, 187, 200, 218; HRMS (EI, M ) calcd for
4. (a) Ishii, Y.; Sakaguchi, S.; Iwahama, T. Adv. Synth. Catal.
2001, 343, 809. (b) Yoshino, Y.; Hayashi, Y.; Sakaguchi, S.;
Ishii, Y. J. Org. Chem. 1997, 62, 6810. (c) Backvall, J.-E.
Modern Oxidation Methods, Wiley-VCH:Weinheim 2004 pp
119–163.
K1
C
C H O : 218.1307, found: 218.1332.
14 18 2
5
. Yang, G.; Zhang, Q.; Miao, H.; Tong, X.; Xu, J. Org. Lett. 2005,
, 263.
7
Acknowledgements
6. The product 5 has been reported; Wolf, P. F.; McKeon, J. E.;
Cannell, D. W. J. Org. Chem. 1975, 40, 1875.
This work was supported by a Grant-in-Aid for Scientific
Research on Priority Areas ‘Advanced Molecular Trans-
formations of Carbon Resources’ from the Ministry of
Education, Culture, Sports, Science and Technology, Japan,
7. The product 10 has been reported; Sambaiah, T.; Li, L.-P.;
Huang, D.-J.; Lin, C.-H.; Rayabarapu, D. K.; Cheng, C.-H.
J. Org. Chem. 1999, 64, 3663. Burford, C.; Cooke, F.; Roy, G.;
Magnus, P. Tetrahedron 1983, 39, 867.