Alkane oxidation with air catalyzed by lipophilic N-hydroxyphthalimides without any solvent

Full text of DOI:10.1021/jo0158276

J . Org. Chem. 2001, 66, 7889-7891
7889
Alk a n e Oxid a tion w ith Air Ca ta lyzed by
Sch em e 1. P r ep a r a tion of NHP I Der iva tives
Lip op h ilic N-Hyd r oxyp h th a lim id es w ith ou t
An y Solven t
Naoko Sawatari, Takahiro Yokota,
Satoshi Sakaguchi, and Yasutaka Ishii*
Department of Applied Chemistry, Faculty of Engineering,
Kansai University, Suita, Osaka 564-8680, J apan
ishii@ipcku.kansai-u.ac.jp
Received J une 8, 2001
is difficult to dissolve in nonpolar solvents such as
hydrocarbons. Therefore, it is interesting to develop
NHPI derivatives that easily dissolve in hydrocarbons
such as cyclohexane. If such a catalyst can be prepared,
the aerobic oxidation of alkanes can proceed without any
solvent. This study is focused on the preparation of NHPI
derivatives not requiring the use of solvents for the
oxidation of alkanes with dioxygen under mild conditions.
In tr od u ction
Although there have been major advances in the
oxidation of saturated hydrocarbons with molecular
oxygen, the development of effective and selective meth-
ods for the catalytic functionalization of hydrocarbons
still remains a major challenge in oxidation chemistry.
In particular, selective oxidation of alkanes with dioxygen
to oxygen-containing compounds such as alcohols, ke-
tones, and carboxylic acids is a very important industrial
process from both economical and environmental as-
Resu lts a n d Discu ssion
To employ NHPI derivatives as catalysts, it is impor-
tant to use cheap starting materials readily available
from commercial sources. Thus, we chose trimellitic
anhydride (TA) available from Aldrich Chemical Co. as
the starting material and prepared a series of 4-alkyl-
oxycarbonyl N-hydroxyphthalimides 1a -d (Scheme 1).
Treatment of TA with hydroxylamine afforded N-hydrox-
yphthalimide 4-carboxylic acid (1a ) on which subsequent
esterification with hexyl alcohol led to 4-hexyloxycarbonyl
N-hydroxyphthalimide (1b) in good yield. Similarly, a
series of NHPI derivatives substituted by 4-alkyloxycar-
bonyl moieties having a different alkyl chain were
prepared and used for the aerobic oxidation of cyclohex-
ane (2b).
1
pects. Traditional alkane oxidation with dioxygen, which
is referred to as autoxidation, often suffers from relatively
harsh conditions and limited conversion and selectivity.2
For instance, autoxidation of cyclohexane to a mixture
of cyclohexanone and cyclohexanol (K/A oil) is now carried
out using a soluble cobalt catalyst in industrial scale
worldwide. The drawback of this process is that the
oxidation must be operated in 3-6% conversion of
cyclohexane to maintain higher selectivity (75-80%) to
the K/A oil. In the 1940s, DuPont first industrialized this
process for the purpose of the production of adipic acid
3
from the K/A oil. Although much effort has been made
Table 1 shows the representative results for the
oxidation of 2b catalyzed by 4-laulyloxycarbony N-
hydroxyphthalimide (1c) under various reaction condi-
tions. As expected, 1c anchoring a long alkyl chain was
cleanly dissolved in the substrate 2b under the reaction
conditions to form a transparent solution. The reaction
of 2b (4 mL, ca. 37 mmol) under air (10 atm) in the
to develop an effective oxidation system of cyclohexane
with molecular oxygen, the DuPont process is currently
employed without major modification.
Recently, we have developed a novel method for alkane
oxidation with dioxygen using the N-hydroxyphthalimide
NHPI) as a catalyst under mild conditions.4 Thus,
(
cyclohexane can be converted into adipic acid in higher
conversion (70%) and selectivity (70%) by a combined
presence of 1c (30 µmol), Co(acac)
2
(3 µmol), and Mn-
(
OAc) (0.3 µmol) in the absence of solvent at 100 °C for
2
3
catalyst of NHPI with Mn(OAc) under normal pressure
5
14 h gave cyclohexanone (3b), cyclohexanol (4b) and
adipic acid (5b) in a ratio of 61:28:7 with 56 turnover
number (TN) (Table 1, run 1). It is interesting to note
that the sum of these oxidation products, 3b, 4b, and 5b,
was very high (96%). Removal of 3b, 4b, and 5b from
the reaction mixture under reduced pressure left a white
solid involving 1c. It was found that a part of the catalyst
of dioxygen in acetic acid at 100 °C. Previous work from
our laboratory focused on the aerobic oxidations of
hydrocarbons must be carried out in an appropriate
solvent such as acetic acid or benzonitrile, since NHPI
(1) (a) Sheldon, R. A.; Kochi, J . K. Metal-Catalyzed Oxidations of
Organic Compounds; Academic Press: New York, 1981. (b) Mennier,
B. Chem. Rev. 1992, 92, 1411. (c) Busch, D. H.; Alcock, N. W. Chem.
Rev. 1994, 94, 585.
1
c was changed to the corresponding phthalimide, but
(
2) (a) Parshall, G. W.; Ittel, S. D. Homogeneous Catalysis, 2nd ed.;
about 50% of 1c was recovered unchanged. The oxidation
of the alkyl chain contained in 1c was not observed at
all. The oxidation of 2b by NHPI under these conditions
proceeded very slowly to afford 3b, 4b, and 5b in a 51:
J ohn Wiley and Sons: New York, 1992; p 246. (b) Simandi, L. Catalytic
Activation of Dioxygen by Matal Complexes; Kluwer Academic Pab-
lisher: Dordrecht, The Netherlands, 1992; p 84.
(
3) Davis, D. D. In Ullman’s Encyclopedia of Industrial Chemistry,
th ed.; Gerhartz, W., Ed.; J ohn Wiley and Sons: New York, 1985;
Vol. A1, 270.
5
4
3:3 ratio in lower conversion (11.7 TN) (Table 1, run 2).
In a previous paper, we showed that the NHPI-catalyzed
oxidation of 2b with dioxygen in acetic acid produced 3b
and 5b as major products, but cyclohexanol 4b was
scarcely formed (Scheme 2). In this oxidation, however,
a considerable amount of 4b was obtained. This is
(
4) Ishii, Y.; Sakaguchi, S.; Iwahama, T. Adv. Synth. Catal. 2001,
3
43, 393.
(
5) (a) Iwahama, T.; Shojyo, K.; Sakaguchi, S.; Ishii, Y. Org. Proc.
Res. & Dev. 1998, 2, 255. (b) Ishii, Y.; Nakayama, K.; Takeno, M.;
Sakaguchi, S.; Iwahama, T.; Nishiyama, Y. J . Org. Chem. 1995, 60,
934.
3
1
0.1021/jo0158276 CCC: $20.00 © 2001 American Chemical Society
Published on Web 10/18/2001

7
890 J . Org. Chem., Vol. 66, No. 23, 2001
Notes
Ta ble 1. Aer obic Oxid a tion of Cycloh exa n e (2b) by 1c
a
u n d er Va r iou s Con d ition s
product distribution/%
run
catalyst
TNb
56
3b
4b
5b
othersc
1
2
3
4
5
6
1c/Co(II)/Mn(II)
NHPI/Co(II)/Mn(II) 11.7
1c/Co(II)
1c/Mn(II)
1c/Co(II)/Mn(II)
1c/Co(II)/Mn(II)
61
51
65
57
53
2
28
43
25
35
20
1
7
3
7
4
26
85
4
3
3
4
1
41
7.7
33
28
d
e
12
a
2
b (37 mmol) was reacted in the presence of 1c (30 µmol),
Co(acac)2 (3 µmol), and Mn(OAc)2 (0.3 µmol) under air (10 atm) at
b
c
1
00 °C for 14 h. Turnover number. Others contain glutaric acid
as a major compound. 2b (19 mmol) was used. e 2b (9 mmol) was
d
used.
Sch em e 2
F igu r e 1. Aerobic oxidation of cyclohexane (2b) by NHPI
derivatives. Compound 2b (37 mmol) was reacted in the
presence of NHPI derivatives (30 µmol), Co(acac)
2
(3 µmol),
and Mn(OAc) (0.3 µmol) at 100 °C for 14 h.
2
Ta ble 2. Aer obic Oxid a tion of Va r iou s Alk a n esa
believed to be due to the presence of a large excess of
2
b, although the alcohol 4b is much more reactive than
alkane 2b. Therefore, when the amount of 2b employed
was reduced from 37 to 9 mmol under these conditions,
the formation of 3b and 4b decreased markedly, and
adipic acid 5b, which is a further oxidation product of
3
b and 4b, was crystallized as a white solid from the
reaction solution in high selectivity (85%), although the
TN of the catalyst decreased from 56 to 28 (Table 1, run
6
2
). Removing the Mn(OAc) from the catalytic system
resulted in a slight decrease of the total yield of the
oxygenated products, but the product distribution was
almost the same as that by the 1c/Co(acac)
system. By contrast, oxidation lacking Co(acac)
2
/Mn(OAc)
in the
2
2
catalytic system led to a considerably lower amount of
the oxidation products (Table 1, run 4). In a previous
paper, we showed that the aerobic oxidation of 2b by
NHPI in the absence of a Co species was not induced,
since the Co(II) species reacts with dioxygen to give a
Co(III)-oxygen complex that assists the hydrogen atom
abstraction from the NHPI to form phthalimide N-oxyl
(
PINO), which is a key species in the alkane oxidation.5
In this oxidation of 2b by 1c, the generation of the
corresponding PINO from 1c is necessary to promote the
oxidation.
a
Substrate (37 mmol) was reacted in the presence of 1c (30
µmol) or NHPI (30 µmol), Co(acac)2 (3 µmol), and Mn(OAc)2 (0.3
µmol) at 100 °C for 14 h.
Figure 1 shows the oxidation results of 2b by several
alkoxycarbonyl NHPI derivatives 1a -d having different
alkyl chains. It is attractive that the total yields of
oxygenated products increased with increasing the alkyl
chain length in 1a -d .
It is rather difficult to explain rationally the effect of
the alkyl chain length of 1a -d on the oxidation of 2b.
Although the catalytic activity of 1a -d is not fully
explained by the solubility of these in 2b, the solubility
seems to be an important factor governing the oxidation
activity. The reaction solution involving 1b bearing the
hexyl moiety became turbid under the operated reaction
conditions. As a result, the catalytic activity of the 1b
was undoubtedly low compared with that of the 1c.
Table 2 summarizes a comparison of the oxidation of
various alkanes catalyzed by 1c in the presence of small
amounts of Co(acac) and Mn(OAc) with that by NHPI
under the same conditions.
2
2
The oxidation of cyclopentane (2a ) occurred in lower
yield than that of 2b to give cyclopentanone (3a ), cyclo-
pentanol (4a ), and glutaric acid (5a ) in 31:13:46 ratio with
20 TN. The low TN in the oxidation of cyclopentane 2a
by 1c may be due to the easy cleavage of the C-C bond
to glutaric acid 5a . Replacing 1c with NHPI under these
conditions, the TN of the catalyst decreased to 9. Large-
membered cycloalkanes such as cyclooctane (2c) and
cyclododecane (2d ) were easily oxidized by 1c to afford
the corresponding cyclic ketones, 3c and 3d , and alcohols,
4c and 4d , respectively in good yields. The TN of the
catalyst 1c for the oxidation of 2c and 2d reached 110
and 140, respectively. In the oxidation of large-membered

Notes
J . Org. Chem., Vol. 66, No. 23, 2001 7891
cycloalkanes by 1c, cleavage to R,ω-dicarboxylic acids, 5c
and 5d , was considerably suppressed compared with the
oxidation of cyclopentene 2a . 2-Methylpentane (6) led to
precipitate was filtered and washed with water. The solid was
filtered off and dried under vacuum to give 1a (5.2 g) in 70%
yield.
1
a : 1H NMR (CD
3
OD/TMS) δ 7.05 (d, 1H), 8.31 (s, 1H), 8.40
2
-methyl-2-pentanol (7) in which the tertiary C-H bond
13
(
1
d, 1H); C NMR (CD OD/TMS) δ 167.4, 164.9, 137.7, 136.7,
33.8, 130.7, 124.7, 124.2; IR (neat) 2793, 1726, 1191, 709 cm
3
was exclusively oxidized. The TN of the NHPI in the
oxidation of these alkanes decreased to 1/5 to 1/2 of those
of 1c.
-1
.
P r ep a r a tion of 4-Alk yloxylca r boxyl-N-h yd r oxyp h th a l-
im d es 1b-d . Compound 1a (10 mmol) and p-toluenesulfonic
acid (0.1 equiv) were dissolved in lauryl, hexyl, or myristyl
alcohol (30 mL) and n-hexane (10 mL). The mixture was stirred
under refluxing temperture for 6 h and cooled to 10 °C. The
product was obtained as a white crystal. Recrystallization from
methanol gave pure 1b-d .
In conclusion, we have succeeded in the oxidation of
alkanes with air under mild condition in the absence of
any solvent by the use of the lipophilic NHPI derivatives,
which are easily dissolved in alkanes. This method would
provide an interesting approach to alkanes oxidation with
air in industrial chemistry.
1
1b: H NMR (CD OD/TMS) δ 0.82 (t, 3H), 1.37 (m, 8H), 1.79
3
(q, 2H), 4.37 (t, 2H); 13C NMR (CD
37.7, 136.5, 134.1, 131.0, 124.5, 124.3, 67.2, 32.0, 29.7, 26.8,
OD/TMS) δ 166.4, 164.9,
3
1
2
-
1
3.6, 14.4; IR (neat) 2915, 2361, 1786, 1738, 1188, 711 cm
.
Exp er im en ta l Section
1
1
c: H NMR (CD
3
OD/TMS) δ 0.88 (t, 3H), 1.2 (m, 18H), 1.8
13
(
1
3
q, 2H), 4.37 (t, 2H), C NMR (CD
3
OD/TMS) δ 166.4, 164.9,
37.4, 136.6, 134.1, 131.0, 124.5, 124.2, 67.2, 33.0, 30.7, 30.6,
0.4, 30.3, 29.7, 27.1, 23.7, 14.4; IR (neat) 2915, 2361, 1786, 1728,
Gen er a l P r oced u r e. The starting materials were com-
mercially available and used without purification. GC analysis
was performed with a flame ionization detector using a 0.2 mm
-
1
1
13
1188, 711 cm
.
×
30 m capillary column (OV-17). H and C NMR spectra were
measured at 270 and 67.5 MHz, respectively, in methanol-d
with Me Si as the internal standard. Infrared (IR) spectra were
1
1
d : H NMR (CD
3
OD/TMS) δ 0.88 (t, 3H), 1.27 (m, 22H), 1.8
4
1
3
(
q, 2H), 4.37 (t, 2H), C NMR (CD
3
OD/TMS) δ 166.4, 164.9,
37.7, 136.7, 134.1, 131.1, 124.6, 124.4, 67.2, 33.0, 30.7, 30.6,
0.5, 30.4,30.3, 29.7, 27.1, 23.7, 14.4; IR (neat) 2915, 2361, 1786,
4
1
3
1
measured using NaCl or KBr pellets. GC-MS spectra were
obtained at ionization energy of 70 eV. The yields of products
were estimated from the peak areas on the basis of the internal
standard technique by the use of GC.
-
1
728, 1188, 711 cm
.
Typ ica l P r oced u r e for th e Oxid a tion u n d er Air (10 a tm ).
Cyclohexane (4 mL, ca 37 mmol), NHPI derivatives (30 µmol),
Ack n ow led gm en t. This work was partly supported
by Daicel Chemical Co. and a Grant-in-Aid for Scientific
Research (S) (No.13853008) from J apan Society for the
Promotion of Science (J SPS).
2 2
Co(acac) (3 µmol) and Mn(Oac) (0.3 µmol) were placed in a 50-
mL Teflon-coated autoclave, and 10 atm of air was charged. After
removal of the solvent under reduced pressure, a catalytic
amount of conc. sulfuric acid and ethanol (10 mL) were added
to the resulting mixture, and the solution was stirred at 100 °C
for 15 h. The resulting solution was extracted with diethyl ether
J O0158276
(6) (a) Wentzel, B.; Donners, M.; Alsters, P.; Feiters, M.; Nolte, R.
(
5 mL × 3). Removal of the solvent afforded a clean liquid which
Tetrahedron 2000, 56, 7797. (b) Einhorn, C.; Einhorn, J .; Marcadal-
Abbadi, C.; Pierre, J . J . Org. Chem. 1999, 64, 4542. (c) Gorgy, K.;
Lepretre, J . Saint-Aman, E.; Einhorn, C.; Einhorn, J .; Marcadel, C.;
Pierre, J . Electrochem. Acta 1998, 44, 385. (d) Rougny, A.; Daudon,
M. Bull. Soc. Chem. Fr. 1976, 156. 833. (e) Ranadive, V. B.; Samant,
S. D. Indian J . Chem. 1995, 34b, 102. (f) Banks, A. R.; Fibiger, R. F.;
J ohnes, T. J . Org. Chem. 1977, 42, 3965. (g) Pfeffer, P. E.; Foglia, T.
A.; Barr, P. A.; Schmeltz, I.; Silbert, L. S. Tetrahedron Lett. 1972, 40,
4063. (h) Taschner, E.; Rzeszortarska, B. Angew. Chem., Int. Ed. 1965,
4, 594.
was subjected to column chromatography on silica gel (n-hexane/
AcOEt ) 5/1) to give the corresponding oxygenated products.
P r ep a r a tion of Ca ta lysts. N-Hyd r oxylp h th a lim d e-4-ca r -
6
boxylic Acid (1a ). To a pyridine (50 mL) was added NH
2
OH/
HCl (44 mmol) under stirring followed by TA (40 mmol). The
mixture was stirred 15 h at 90 °C and poured into 50 mL of
water. After cooling, the mixture was acidified by slowly adding
hydrochloric acid (50 M) until it becomes acidic to pH 2-3. The