Baeckvall J.-E. (ed.) Modern Oxidation Methods
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78 Steinhoff, B.A. and Stahl, S.S. (2002) Org.
Lett., 4, 4179–4181.
79 Schultz, M.J., Park, C.C., and
Sigman, M.S. (2002) Chem. Commun.,
3034.
80 Hallman, K. and Moberg, C. (2001)
Adv. Synth. Catal., 343, 260.
81 ten Brink, G.-J., Arends, I.W.C.E., and
Sheldon, R.A. (2000) Science, 287, 1636.
82 ten Brink, G.-J., Arends, I.W.C.E., and
Sheldon, R.A. (2002) Adv. Synth. Catal.,
344, 355.
83 Bianchi, D., Bortolo, R., DAloisio, R.,
and Ricci, M. (1999) Angew. Chem. Int.
Ed., 38, 706; Bianchi, D., Bortolo, R.,
DAloisio, R., and Ricci, M. (1999)
J. Mol. Catal. A: Chemical, 150, 87.
84 ten Brink, G.J., Arends, I.W.C.E.,
Hoogenraad, M., Verspui, G., and
Sheldon, R.A. (2003) Adv. Synth. Catal.,
345, 1341.
85 Mifsud, M., Parkhomenko, K.V., Arends,
I.W.C.E., and Sheldon, R.A. (2010)
Tetrahedron., 66, 1040.
86 Kovtun, G., Kameneva, T., Hladyi, S.,
Starchevsky, M., Pazdersky, Y.,
Stolarov, I., Vargaftik, M., and
Moiseev, I.I. (2002) Adv. Synth. Catal.,
344, 957; Moiseev, I.I. and Vargaftik,
M.N. (1998) New J. Chem., 22, 1217;
Pasichnyk, P.I., Starchevsky, M.K.,
Pazdersky, Y.A., Zagorodnikov, V.P.,
Vargaftik, M.N., and Moiseev, I.I. (1994)
Mendeleev Commun.,1–2; Moiseev, I.I.,
Stromnova, T.A., and Vargaftik, M.N.
(1994) J. Mol. Catal., 86, 71.
87 Mori, K., Hara, T., Mizugaki, T.,
Ebitani, K., and Kaneda, K. (2004)
J. Am. Chem. Soc., 126, 10657.
88 For an example in toluene see
Keresszegi, C., Burgi, T., Mallat, T.,
and Baiker, A. (2002) J. Catal., 211, 244.
89 Nishimura, T., Kakiuchi, N., Inoue, M.,
and Uemura, S. (2000) Chem. Commun.,
1245; see also Kakiuchi, N., Nishimura,
T., Inoue, M., and Uemura, S. (2001) Bull.
Chem. Soc. Jpn., 74, 165.
90 Mori, K., Yamaguchi, K., Hara, T.,
Mizugaki, T., Ebitani, K., and Kaneda, K.
(2002) J. Am. Chem. Soc., 124, 11573.
91 Kwon, M.S., Kim, N., Park, C.M.,
Lee, J.S., Kang, K.Y., and Park, J. (2005)
Org. Lett., 7, 1077.
92 Uozumi, Y. and Nakao, R. (2003) Angew.
Chem. Int. Ed., 42, 194.
93 Hou, Z., Theyssen, N., Brinkmann, A.,
and Leitner, W. (2005) Angew. Chem. Int.
Ed., 44, 1346.
94 Prati, L. and Rossi, M. (1997) Stud. Surf.
Sci. Catal., 110, 509; Prati, L. and Rossi,
M. (1998) J. Catal., 176, 552; Bianchi, C.,
Porta, F., Prati, L., and Rossi, M. (2000)
Top. Catal., 13, 231; Comotti, M., Della
Pina, C., Matarrese, R., Rossi, M., and
Siani, A. (2005) Appl. Catal. A: General,
291, 204; Prati, L. and Porta, F. (2005)
Appl. Catal. A: General, 291, 199.
95 Christensen, C.H., Jørgensen, B.,
Rass-Hansen, J., Egeblad, K.,
Madfsen, R., Klitgaard, S.K.,
Hansen, S.M., Hansen, M.R.,
Andersen, H.C., and Riisager, A. (2006)
Angew. Chem. Int. Ed., 45, 4648.
96 Taarning, E., Nielsen, I.S., Egeblad, K.,
Madsen, R., and Christensen, C.H.
(2008) ChemSusChem, 1,75–78; see also
Taarning, E., Madsen, A.T., Marchetti,
J.M., Egeblad, K., and Christensen, C.H.
(2008) Green Chem., 10, 408.
97 Abad, A., Concepcion, P., Corma, A., and
Garcia, H. (2005) Angew. Chem. Int. Ed.,
44, 4066.
98 See also Tsunoyama, H., Sakurai, H.,
Negishi, Y., and Tsukuda, T. (2005) J. Am.
Chem. Soc., 127, 9374.
99 Enache, D.I., Edwards, J.K., Landon, P.,
Solsona-Espriu, B., Carley, A.F.,
Herzing, A.A., Watanabe, M., Kiely, C.J.,
Knight, D.W., and Hutchings, G.J. (2006)
Science, 311, 362.
100 Carrettin, S., McMorn, P., Johnston, P.,
Griffin, K., and Hutchings, G.J. (2002)
Chem. Commun., 696.
101 Ito, N., Phillips, S.E.V., Stevens, C.,
Ogel, Z.B., McPherson, M.J., Keen, J.N.,
Yadav, K.D.S., and Knowles, P.F. (1991)
Nature, 350, 87.
102 Drauz, K., and Waldmann, H. (1995)
Chapter 6, in Enzyme Catalysis in Organic
Synthesis, VCH, Weinheim.
103 For example see: Skibida, I.P. and
Sakharov, A.M. (1996) Catal. Today, 27,
187; Sakharov, A.M. and Skibida, I.P.
(1988) J. Mol. Catal., 48, 157;
Feldberg, L. and Sasson, Y.L. (1994) J.
Chem. Soc. Chem. Commun., 1807;
References
j
183
Capdevielle, P., Sparfel, D., Baranne-
Lafont, J., Cuong, N.K., and Maumy, D.
(1993) J. Chem. Res. (S), 10;
Munakata, M., Nishibayashi, S., and
Sakamoto, S. (1980) J. Chem. Soc. Chem.
Commun.,219;Bhaduri,S.andSapre,N.Y.
(1981) J. Chem. Soc. Dalton Trans., 2585;
Jallabert, C. and Rivi
ere, H. (1977)
Tetrahedron Lett., 1215; (1980)
J. Mol. Catal., 7, 127; Jallabert, C.,
Lapinte, C., and Rivi
ere, H. (1986)
J. Mol. Catal., 14, 75; Jallabert, C.
and Rivi
ere, H. (1980) Tetrahedron,
36, 1191.
104 Wang, Y., DuBois, J.L., Hedman, B.,
Hodgson, K.O., and Stack, T.D.P. (1998)
Science, 279, 537.
105 Chauhuri, P., Hess, M., Fl
€
orke, U., and
Wieghardt, K. (1998) Angew. Chem. Int.
Ed., 37, 2217.
106 Chauhuri, P., Hess, M.,
Weyherm
€
uller, T., and Wieghardt, K.
(1998) Angew. Chem. Int. Ed., 38, 1095.
107 Mahadevan, V., Klein Gebbink, R.J.M.,
and Stack, T.D.P. (2000) Curr. Opin.
Chem. Biol., 4, 228.
108 Whittaker, M.M., Ekberg, C.A.,
Peterson,J., Sendova, M.S., Day, E.P., and
Whittaker, J.W. (2000) J. Mol. Catal. B:
Enzymatic, 8,3.
109 Marko, E.I., Giles, P.R., Tsukazaki, M.,
Brown, S.M., and Urch, C.J. (1996)
Science, 274, 2044; Marko, I.E.,
Tsukazaki, M., Giles, P.R., Brown, S.M.,
and Urch, C.J. (1997) Angew. Chem. Int.
Ed. Engl., 36, 2208.
110 Marko, I.E., Giles, P.R., Tsukazaki, M.,
Chell
e-Regnaut, I., Gautier, A.,
Brown, S.M., and Urch, C.J. (1999)
J. Org. Chem., 64, 2433.
111 Marko, I.E., Gautier, A.,
Chell
e-Regnaut, I., Giles, P.R.,
Tsukazaki, M., Urch, C.J., and
Brown, S.M. (1998) J. Org. Chem., 63,
7576.
112 Semmelhack, M.F., Schmid, C.R.,
Cort
es, D.A., and Chou, C.S. (1984)
J. Am. Chem. Soc., 106, 3374.
113 Dijksman, A. (2001) Thesis Delft
University of Technology, Delft.
114 Betzemeier, B., Cavazzine, M., Quici, S.,
and Knochel, P. (2000) Tetrahedron Lett.,
41, 4343.
115 Ansari, I.A. and Gree, R. (2002) Org. Lett.,
4, 1507.
116 Gamez, P., Arends, I.W.C.E., Reedijk, J.,
and Sheldon, R.A. (2003) Chem.
Commun., 2414; Gamez, P., Arends,
I.W.C.E., Sheldon, R.A., and Reedijk, J.
(2004) Adv. Synth. Catal., 346, 805.
117 Fiegel, P.J., Leskela, M., and Repo, T.
(2007) Adv. Synth. Catal., 349, 1173; see
also Geislmeir, D., Jary, W.G., and Falk, H.
(2005) Monatsh. Chem., 136, 1591.
118 Mitsudone, T., Mikami, Y., Ebata, K.,
Mizugaki, T., Jitsukawa, K., and
Kaneda, K. (2008) Chem. Commun., 4804.
119 Minachev, Kh.M., Antoshin, G.V.,
Klissurski, .D.G., Guin, N.K., and
Abadzhijeva, N.Ts. (1979) React. Kinet.
Catal. Lett., 10, 163.
120 Kirihara, M., Ochiai, Y., Takizawa, S.,
Takahata, H., and Nemoto, H. (1999)
Chem. Commun., 1387.
121 Fiegel, P.J. and Sobczak, J.M. (2007)
New J. Chem., 31, 1668.
122 Iwahama, T., Sakaguchi, S.,
Nishiyama, Y., and Ishii, Y. (1995)
Tetrahedron Lett., 36, 6923.
123 Yoshino, Y., Hanyashi, Y., Iwahama, T.,
Sakaguchi, S., and Ishii, Y. (1997)
J. Org. Chem., 62, 6810; Kato, S.,
Iwahama, T., Sakaguchi, S., and
Ishii, Y. (1998) J. Org. Chem., 63, 222;
Sakaguchi, S., Kato, S., Iwahama, T.,
and Ishii, Y. (1988) Bull. Chem. Soc.
Jpn., 71,1.
124 see also Minisci, F., Punta, C.,
Recupero, F., Fontana, F., and
Pedulli, G.F. (2002) Chem. Commun., 7,
688.
125 Choudary, B.M., Lakshmi Kantam, M.,
Ateeq Rahman, Ch., Reddy, V., and
Rao, K.K. (2001) Angew. Chem. Int. Ed.,
40, 763.
126 (a) D
€
obler, C., Mehltretter, G., and
Beller, M. (1999) Angew. Chem. Int. Ed.,
38, 3026; (b) D
€
obler, C., Mehltretter, G.,
Sundermeier, G.M., and Beller, M.J.
(2000) J. Am. Chem. Soc., 122, 10289.
127 D
€
obler, C., Mehltretter, G.M.,
Sundermeier, U., Eckert, M.,
Militzer, H.-C., and Beller, M. (2001)
Tetrahedron Lett., 42, 8447.
128 Barak, G., Dakka, J., and Sasson, Y. (1988)
J. Org. Chem., 53, 3553.
184
j
5 Modern Oxidation of Alcohols using Environmentally Benign Oxidants
129 Jacobsen, S.E., Muccigrosso, D.A.,
and Mares, F. (1979) J. Org. Chem., 44,
921; see also Bortolini, O., Campestrini,
S., Di Furia, F., and Modena, G. (1987)
J. Org. Chem., 52, 5467.
130 Trost, B.M. and Masuyama, Y. (1984)
Tetrahedron Lett., 25, 173.
131 Bortolini, O., Conte, V., Di Furia, F., and
Modena, G. (1986) J. Org. Chem., 51,
2661.
132 Sato, K., Aoki, M., Takagi, J., and
Noyori, R. (1997) J. Am. Chem. Soc., 119,
12386.
133 Sato, K., Takagi, J., Aoki, M., and Noyori,
R. (1998) Tetrahedron Lett., 39, 7549.
134 Ishii, Y., Yamawaki, K., Yoshida, T.,
Ura, T., and Ogawa, M. (1987)
M. J. Org. Chem., 52, 1868; Ishii, Y.,
Yamawaki, K., Ura, T., Yamada, H.,
Yoshida, T., and Ogawa, M. (1988)
J. Org. Chem., 53, 3587; Yamawaki, K.,
Nishihara, H., Yoshida, T., Ura, T.,
Yamada, H., Ishii, Y., and Ogawa, M.
(1988) Synth. Commun., 18, 869;
Yamawaki, K., Yoshida, T., Nishihara, H.,
Ishii, Y., and Ogawa, M. (1986) Synth.
Commun., 16, 537.
135 Venturello, C. and Gambaro, M. (1991)
J. Org. Chem., 56, 5924.
136 Neumann, R. and Gara, M. (1995)
J. Am. Chem. Soc., 117, 5066.
137 Zauche, T.H. and Espenson, J.H. (1995)
Inorg. Chem., 37, 6827.
138 Espenson, J.H., Zhu, Z., and Zauche,
T.H. (1991) J. Org. Chem., 64, 1191.
139 Arends, I.W.C.E., Sheldon, R.A.,
Wallau, M., and Schuchardt, U. (1997)
Angew. Chem. Int. Ed. Engl., 36, 1144.
140 Maspero, F. and Romano, U. (1994)
J. Catal., 146, 476.
141 Zondervan, C., Hage, R., and
Feringa, B.L. (1997) Chem. Commun.,
419; Brinksma, J., Rispens, M.T.,
Hage, R.H., and Feringa, B.L. (2002)
Inorg. Chem. Acta, 337, 75.
142 Shi, F., Tse, M.K., Pohl, M.-M.,
Br
€
uckner, A., Zhang, S., and Beller, M.
(2007) Angew. Chem. Int. Ed., 46, 8866.
143 For recent reviews see: Kroutil, W.,
Mang, H., Edegger, K., and Faber, K.
(2004) Adv. Synth. Catal., 346, 125;
de Wildeman, S.M., Sonke, T.,
Schoemaker, H.E., and May, O. (2007)
Acc. Chem. Res., 40, 1260–1266;
Moore, J.C., Pollard, D.J., Kosiek, B., and
Devine, P.N. (2007) Acc. Chem. Res., 40,
1412.
144 Stampfer, W., Kosjek, B., Moitzi, C.,
Kroutil, W., and Faber, K. (2002) Angew.
Chem. Int. Ed. Engl., 41, 1014;
Stampfer, W., Kosjek, B., Faber, K., and
Kroutil, W. (2003) J. Org. Chem., 68, 402;
Edegger, K., Mang, H., Faber, K., Gross, J.,
and Kroutil, W. (2006) J. Mol. Catal. A:
Chemical, 251, 66.
145 Forneris, F., Heuts, D.P.H.M.,
Delvecho, M., Rovida, S., Fraaije, M.W.,
and Maltevi, A. (2008) Biochem., 47, 978;
van Hellemond, E.W., Leferink, N.G.H.,
Heuts, D.P.H.M., Fraaije, M.W., and
van Berkel, W.J.H. (2006) Adv. Appl.
Microbiol., 60, 17.
146 Masutani, K., Uchida, T., Irie, R., and
Katsuki, T. (2000) Tetrahedron Lett., 41,
5119.
147 Jensen, D.R., Pugsley, J.S., and
Sigman, M.S. (2001) J. Am. Chem. Soc.,
123, 7475.
148 Ferreira, E.M. and Stolz, B.M. (2001)
J. Am. Chem. Soc., 123, 7725.
References
j
185
6
Aerobic Oxidations and Related Reactions Catalyzed
by N-Hydroxyphthalimide
Yasutaka Ishii, Satoshi Sakaguchi, and Yasushi Obora
6.1
Introduction
The development of the petrochemical industry has led to a situation in which over
90% of organic chemicals are derived from petroleum. These include a wide range of
oxygen-containing molecules such as alcohols, aldehydes, ketones, epoxides, and
carboxylic acids which are starting materials for the production of, in particular,
plastics and synthetic fiber materials for polyamides, polyesters, polycarbonates, and
so on. For instance, ethylene oxide, acrolein, acrylic acid, and methacrolein are
produced by the vapor-phase partial oxidation of lower alkenes like ethylene,
propylene, and butenes [1], while acetic acid, KA oil (a mixture of cyclohexanone
and cyclohexanol), benzoic acid, terephthalic acid, and phenol accompanied with
acetone are manufactured by the liquid-phase catalytic oxidation of alkanes such as
butane, cyclohexane, and alkylbenzenes, for example [2]. Liquid-phase aerobic
oxidation, which is generally referred to as autoxidation, is extensively practiced in
industry worldwide, although the efficiency of this oxidation methodology is not
necessarily as high [2a,3]. As a result, nitric acid is still widely used as a useful
oxidizing agent for manufacturing carboxylic acids like adipic acid, nicotinic acid,
pyromellitic acid, and so on [2a,4]. Nowadays, however, environmentally unaccept-
able traditional oxidation methods using high-valent metal oxo complexes, halogens,
and nitric acid are being replaced by cleaner oxidation methods.
Although the partial aerobic oxidation of alkanes leading to alcohols and carbonyl
compounds has considerable potential from both ecological and economical view-
points, current oxidation technology is not always fully feasible, as it incurs extensive
oxidative cleavage or concomitant combustion of alkanes. The most important liquid-
phase oxidation methods include the transformation of p-xylene to terephthalic acid,
and cyclohexane to KA oil [2a]. However, the reaction conditions are often harsh,
the reagent mixture is corrosive, and the reaction is often unselective. Therefore, it is
apparent that selective transformation of hydrocarbons, especially saturated hydro-
carbons like alkanes, to valuable oxygenated compounds is an extremely important
area of contemporary industrial chemistry. Thus, considerable research effort has
been undertaken aimed at the development of selective oxidations of alkanes with
j
187
molecular oxygen, leading to alcohols, ketones, and carboxylic acids [5, 6]. A number
of oxidations of alkanes with dioxygen, catalyzed by transition metals, in the presence
of reducing agents such as aldehydes have appeared in the literature, but these are
mainly on a laboratory scale [6]. In recent years, there has been a growing demand
for the development of fundamentally new and environmentally benign catalytic
systems, for the oxidation of hydrocarbons, that are operative on an industrial scale
under moderate conditions in the liquid phase with a high degree of selectivity.
Recently, we have developed an innovative strategy for the catalytic generation of a
type of carbon radical from hydrocarbons. This is a phthalimide N-oxyl (PlNO) radical
generated in situ from N-hydroxyphthalimide (NHPI) and molecular oxygen in the
presence (or absence) of a cobalt ion under mild conditions. The carbon radicals,
derived from a variety of hydrocarbons under the influence of molecular oxygen, lead
to oxygenated products like alcohols, ketones, and carboxylic acids in good yields. The
development of NHPI-catalyzed reactions has been reported in review papers [7].
Here we show a novel methodology for the functionalizations of hydrocarbons,
including oxygenation, nitration, sulfoxidation, epoxidation, carboxylation, and
oxyalkylation through generation of the catalytic carbon radical. In particular, the
NHPI-catalyzed aerobic oxidations of alkanes, which are very important in industry
worldwide, are described in detail.
6.2
NHPI-Catalyzed Aerobic Oxidation
NHPI (Scheme 6.1) was first used as a catalyst by Grochowski et al. [8a] for the
addition of ethers to diethylazodicarboxylate, and as an efficient mediator by Masui
et al. [8b,c] for the electrochemical oxidation of alcohols. A patent has been granted for
a process involving the oxidation of allylic hydrogen of isoprenoid with dioxygen
using NHPI in the presence of a radical initiator [8d]. In 1995, the authors of this
chapter found that NHPI serves as a carbon radical-producing catalyst (CRPC) from
hydrocarbons in both the presence and the absence of transition metals like Co and
Mn ions under dioxygen [9].
6.2.1
Alkane Oxidations with Dioxygen
During the past several decades, a number of catalytic systems have been developed
for the oxidation of alkanes with dioxygen in the presence of reducing agents, for
Scheme 6.1 Structure of NHPI.
188
j
6 Aerobic Oxidations and Related Reactions Catalyzed by N-Hydroxyphthalimide
example, H
2
, metals, and aldehydes, among others, under mild conditions [10–14].
In 1981 Tabushi et al. reported the oxidation of adamantane to l- and 2-adamantanols
by the Mn(III)porphyrin/Pt/H
2
system under a dioxygen atmosphere at room
temperature [11]. Barton developed a family of systems, the so-called Gif systems,
for aerobic oxidation and oxidative functionalization of alkanes under mild condi-
tions using Fe and Zn as reductants [12a–c]. Alkane oxidation using aldehydes as
reducing agents was reported by Murahashi et al., who attempted the aerobic
oxidation of cyclohexane and adamantane by ruthenium or iron catalysts in the
presence of acetaldehyde [13a–c]. There have been several reports on the photo-
oxidations of alkanes with O
2
catalyzed by polyoxotungstates [15], heteropolyoxome-
talates [16], and FeCl
3
[17]. Shulpin et al. carried out the vanadium-catalyzed
oxidation of alkanes to alcohols, ketones, and hydroperoxides by O
2
in combination
with H
2
O
2
[18]. Lyon and Ellis reported that halogenated metalloporphyrin com-
plexes are efficient catalysts for the oxidation of isobutane with dioxygen [19]. Mizuno
et al. have shown that heteropolyanions containing Fe catalyze the aerobic oxidation
of cyclohexane and adamantane into the corresponding alcohols and ketones [20].
An Ru(III)-EDTA system [25], Ru-substituted polyoxometalate [22], and [Co(NCMe)
4
]
(PF
6
)
2
[23] have been reported to catalyze the aerobic oxidation of cyclohexane and
adamantane. However, effective and selective methods for the catalytic oxygenation
of alkanes with dioxygen still remain a major challenge.
Adipic acid, which is used as a raw material for nylon-6,6 and polyester, is the most
important of all the aliphatic dicarboxylic acids manufactured at present. The current
production of adipic acid consists of a two-step oxidation process involving the
aerobic oxidation of cyclohexane in the presence of a soluble Co catalyst at 150–170
C
to a KA oil, and the nitric acid oxidation of the KA oil to adipic acid [2a,24]. The
drawbacks of this process are that the oxidation in the first step must be operated to
give 3–6% conversion of cyclohexane to keep a high selectivity (80%) of the KA oil,
and that the nitric acid oxidation evolves a large amount of undesired global-warming
nitrogen oxides, in particular N
2
O. Therefore, the direct conversion of cyclohexane to
adipic acid with molecular oxygen has long been sought, as this would be a desirable
and promising method in industrial chemistry worldwide. Tanaka et al. succeeded in
achieving conversion of cyclohexane to adipic acid under 30 atm of O
2
by the use of a
higher concentration of Co(III) acetate combined with acetaldehyde or cyclohexa-
none, which serves as promoter [26]. More recently, Noyori and coworkers reported
the oxidation of cyclohexene to adipic acid with aqueous hydrogen peroxide by a
polyoxometalate having a phase-transfer function as an alternative clean route [27].
The direct conversion of cyclohexane to adipic acid was successfully achieved by
the use of a combined catalyst of NHPI with Co and Mn ions [28]. The oxidation of
cyclohexane (1) in the presence of a catalytic amount of NHPI (10 mol%) and Mn
(acac)
2
(1 mol%) under dioxygen atmosphere (1 atm) in acetic acid at 100
C for 20 h
gave adipic acid (4) in 73% selectivity at 73% conversion (Eq. (6.1)). This is the first
example of a one-step oxidation of 1 to 4 under normal pressure of dioxygen at a
reasonably low reaction temperature with high conversion and selectivity. The
oxidation using the NHPI/Co(OAc)
2
system in acetonitrile, on the other hand, gave
cyclohexanone (2) in good selectivity (Eq. (6.1)) [29]. The oxidation by the NHPI/Co
6.2 NHPI-Catalyzed Aerobic Oxidation
j
189
system in acetonitrile provides an alternative direct route to cyclohexanone, although
the autoxidation of cyclohexane leads to a KA oil mixture with cyclohexanol as a
main product [2a,25]. The present catalytic system can be extended to the oxidation of
large-membered cycloalkanes to the corresponding dicarboxylic acids. Cyclooctane,
cyclodecane, and cyclododecane were oxidized to suberic acid, sebacic acid, and
dodecanedioic acid, respectively.
ð6:1Þ
The aerobic oxidations of 1 must be carried out in an appropriate solvent such as
acetic ac id or acetonitrile because of the lower solubility of NHPI in nonpolar
solvents such as hydrocarbons. It is noteworthy that the NHPI-catalyzed reaction
of 1 could procee d w ithout any solvent by the use of a lipophilic NHPI derivative.
Of a series of 4-alkyloxyc arbonyl N-hydroxyphtha limid es examined as lipophilic
NHPI catalysts, 4-lauryloxycarbonyl N -hydroxyph thalimide was found to be a n
efficient catalyst for the aerobic oxidation of 1 under solvent-free conditions
(Figure 6 .1) [30].
Figure 6.1 Oxidation of 1 catalyzed by NHPI derivatives under solvent-free conditions.
190
j
6 Aerobic Oxidations and Related Reactions Catalyzed by N-Hydroxyphthalimide
The oxidation of 1 by fluorinated NHPI (F
15
- and F
17
-NHPI) catalysts was consid-
erably accelerated by the addition of a small amount of [Zr(acac)
4
]inafluorinated
solvent like trifluorotoluene (TFT) to afford selectively KA oil (2 and 3). The formation
of adipic acid (4) was markedly suppressed in TFT, and the solvent used is a crucial
factor to determine the product selectivity (Figure 6.2) [31].
Methane and ethane, which are the main components of natural gas, have been used
for a long time as a clean fuel worldwide. Since ethane comprises 5–10% of the natural
gas, a vast amount of it is obtained when methane is produced. If a new methodology
for converting ethane to useful oxygen-containing compounds like ethanol and acetic
acid could be developed, it would vastly contribute to the efficient use of feedstock.
Previously, Sen et al. reported liquid-phase oxidation of ethane to acetic acid and formic
acid by Pd/Cwith H
2
O
2
generatedin situ from H
2
, arising from a metal-catalyzed water
gas shift reaction with CO, water, and O
2
. [32]. Ethane can be converted into N,N-
dimethylpropylamine by the reaction with N,N-trimethylamine N-oxide in using Cu
(OAc)
2
as the catalyst [33]. Ethane oxidation with H
2
O
2
catalyzed homogeneously by
V-containing polyphosphomolybdates has been carried out by Shulpin et al. [34].
Catalytic aerobic oxidation of ethane to acetic acid was successfully performed
through a catalytic radical process using NHPI derivatives combined with a Co(II) salt
in acetonitrile or propanoic acid. Among the catalysts examined, N,N-dihydroxypyr-
omellitimide (NDHPI) was found to be the best. For instance, when a mixture of
ethane (20 atm) and air (20 atm) in acetonitrile was allowed to react in the presence of
NDHPI (100 mmol) and Co(OAc)
2
(30 mmol) at 150
C for 15 h, 830 mmol of acetic acid
was obtained, and the turnover number (TON) of NDHPI reached 8.3 (Eq. (6.2)). In
this reaction, other products such as ethanol or acetaldehyde were not detected at all.
Figure 6.2 Oxidation of 1 catalyzed by F-NHPI derivatives in TFT.
6.2 NHPI-Catalyzed Aerobic Oxidation
j
191
In the oxidation of ethane using NHPI as a catalyst under these conditions, the
amount of NHPI used was twice that of NDHPI, but the yield of acetic acid and the
TON of the catalyst were 530 mmol and 2.7, respectively. The highest TON (15.3) was
obtained when the reaction was carried out using NDPHI combined with CoCl
2
in
propanoic acid [35].
ð6:2Þ
The autoxidation of isobutane is now mainly carried out to obtain tert-butyl
hydroperoxide [36]. Halogenated metalloporphyrin complexes are reported to be
efficient catalysts for the aerobic oxidation of isobutane [18, 37]. It was found that the
oxidation of isobutane by air (10 atm) catalyzed by NHPI and Co(OAc)
2
in benzoni-
trile at 100
C produced tert-butyl alcohol in high yield (81%) along with acetone
(14%) (Eq. (6.3)) [38]. 2-Methylbutane was converted into the carbon-carbon bond-
cleaved products, acetone and acetic acid, rather than the alcohols, as principal
products. These cleaved products seem to be formed via b-scission of an alkoxy
radical derived from the decomposition of a hydroperoxide by Co ions. The extent of
the b-scission is known to depend on the stability of the radicals released from the
alkoxy radicals [39]. It is thought that the b-scission of a tert-butoxy radical to acetone
and a methyl radical occurs with more difficulty than that of a 2-methylbutoxy radical
to acetone and an ethyl radical. As a result, isobutane produces tert-butyl alcohol as
the principal product, while 2-methylbutane affords mainly acetone and acetic acid.
ð6:3Þ
192
j
6 Aerobic Oxidations and Related Reactions Catalyzed by N-Hydroxyphthalimide