Singlet oxygen oxidation of organic substrates

Details Singlet oxygen oxidation of organic substrates Singlet oxygen oxidation of organic substrates

2001-09-28

2002-11-26

Richter, Johann (Department: 1621)

Organic compounds -- part of the class 532-570 series

Organic compounds

Oxygen containing

C568S469900, C568S558000, C568S567000, C568S568000, C568S577000

Reexamination Certificate

active

06486360

ABSTRACT:

The only singlet oxygen oxidation (
1
O
2
-Ox) which is currently carried out industrially is the photochemical
1
O
2
-Ox in which the
1
O
2
is generated by a photochemical route. The disadvantage of this process is given by the high costs of the photochemical equipment required, and by a limited service life. The required lamps degenerate relatively rapidly during the oxidation as a result of soiling of the glass surface. In addition, this process is not suitable for colored substrates. The process is actually suitable only for fine chemicals which are prepared on a relatively small scale. (La Chimica e l'Industria, 1982, Vol. 64, page 156).
For this reason, attempts have been made to find other process variants for the
1
O
2
-Ox which are suitable for the
1
O
2
-Ox of non-water-soluble, hydrophobic organic substrates.
J. Am. Chem. Soc., 1968, 90, 975 describes, for example, the classical “dark”
1
O
2
-Ox in which
1
O
2
is not generated photochemically, but chemically. In this process, hydrophobic substrates are oxidized by means of a hypochlorite/H
2
O
2
system in a solvent mixture of water and organic solvent. However, this process has only found a few synthetic applications since many substrates are only sparingly soluble in the required medium. In addition, the use possibility is rather limited because of secondary reactions between hypochlorite and substrate or solvent. In addition, a large part of the
1
O
2
is deactivated in the gas phase. In addition, this process is not suitable for industrial scale since in the organic medium addition of the hypochlorite on H
2
O
2
results, and a large excess of H
2
O
2
is required to suppress the secondary reaction of substrate with hypochlorite. An additional disadvantage arises as a result of the formation of stoichiometric amounts of salt.
A variant of the “dark”
1
O
2
-O
x
, which is not based on hypochlorite and thus should partly avoid the above disadvantages, is known, for example, from J. Org. Chem., 1989, 54, 726 or J. Mol. Cat., 1997, 117, 439, according to which some water-soluble organic substrates are oxidized with H
2
O
2
and a molybdate catalyst in water as solvent. According to Membrane Lipid Oxid. Vol. II, 1991, 65, the
1
O
2
-Ox of water-insoluble, organic substrates with the molybdate/H
2
O
2
system is difficult since it was assumed that none of the customary solvents is suitable for maintaining the disproportionation, catalyzed by molybdate, of H
2
O
2
into water and
1
O
2
. However, the use of molybdenum catalysts also brings other disadvantages with it. For example, in addition to the H
2
O
2
disproportionation, they also catalyze other undesired oxidations of some substrates. For example, allyl alcohols cannot be effectively peroxidized with the molybdate/H
2
O
2
system since this group of substances is epoxidized by molybdenum in the presence of H
2
O
2
. A further disadvantage of these catalysts is the relatively low pH range in which they function. These catalysts can only be used in the basic range between pH9 and pH 12, the use of this system is accordingly unsuitable for acidic conditions.
Accordingly, it was an object of the present invention to catalysts for the H
2
O
2
disproportionation for “dark”
1
O
2
-Ox which are effective in a broad pH range, in particular including in the acidic range and which do not catalyze undesired secondary reactions, such as, for example, the epoxidation of allylic alcohols, in addition to the H
2
O
2
disproportionation.
Unexpectedly, it has now been found that lanthanides are effective as catalysts both in the basic and also in the acidic range, with undesired secondary reactions not arising or arising only to a considerably lesser degree when said lanthanides are used. Unexpectedly, these catalysts are also active in heterogeneous form, meaning that their recovery from the reaction mixture can be carried out in a simple way.
Accordingly, the present invention provides a process for the oxidation of organic substrates by means of
1
O
2
, which comprises adding 30-70% strength H
2
O
2
to organic substrates which react with
1
O
2
in water, in an organic solvent or in water/solvent mixtures in the presence of a lanthanide as catalyst, whereupon, following the catalytic decomposition of H
2
O
2
to give water and
1
O
2
, oxidation to give the corresponding oxidation products takes place.
The process according to the invention is suitable for the oxidation of organic substrates which react with
1
O
2
.
Accordingly, substrates which may be used are the following compounds: olefins which contain one or more, i.e. up to 10, preferably up to 6, particularly preferably up to 4 C═C double bonds; electron-rich aromatics, such as C
6
-C
50
, preferably up to C
30
, particularly preferably up to C
20
, phenols, polyalkylbenzenes, polyalkoxybenzenes; polycyclic aromatics having 2 to 10, preferably up to 6, particularly preferably up to 4 aromatic rings; sulfides, such as, for example, alkyl sulfides, alkenyl sulfides, aryl sulfides which are either mono- or disubstituted on the sulfur atom, and heterocycles having an O, N or S atom in the ring, such as, for example, C
4
-C
50
, preferably up to C
30
, particularly preferably up to C
20
, furans, C
4
-C
50
, preferably up to C
30
, particularly preferably up to C
20
, pyrroles, C
4
-C
60
, preferably up to C
30
, particularly preferably up to C
20
, thiophenes. In this connection, the substrates may have one or more substituents, such as halogen (F, Cl, Br, I), cyanide, carbonyl groups, hydroxyl groups, C
1
-C
50
, preferably up to C
30
, particularly preferably up to C
20
, alkoxy groups, C
1
-C
50
, preferably up to C
30
, particularly preferably up to C
20
, alkyl groups, C
6
-C
50
, preferably up to C
30
, particularly preferably up to C
20
, aryl groups, C
2
-C
50
, preferably up to C
30
, particularly preferably up to C
20
, alkenyl groups, C
2
-C
50
, preferably up to C
30
, particularly preferably up to C
20
, alkynyl groups, carboxylic acid groups, ester groups, amide groups, amino groups, nitro groups, silyl groups, silyloxy groups, sulfone groups, sulfoxide groups. In addition, the substrates may be substituted by one or more NR
1
R
2
radicals in which R
1
or R
2
may be identical or different and are H; C
1
-C
50
, preferably up to C
30
, particularly preferably up to C
20
, alkyl; formyl; C
2
-C
50
, preferably up to C
30
, particularly preferably up to C
20
, acyl; C
7
-C
50
, preferably up to C
30
, particularly preferably up to C
20
, benzyl, where R
1
and R
2
may also together form a ring, such as, for example, in a phthalimido group.
Examples of suitable substrates are: 2-butene; isobutene; 2-methyl-1-butene; 2-hexene; 1,3-butadiene; 2,3-dimethylbutene; &Dgr;
9,10
-octalin, 2-phthalimido-4-methyl-3-pentene; 2,3-dimethyl-1,3-butadiene; 2,4-hexadiene; 3-methyl-2-buten-1-ol; 4-methyl-3-penten-2-ol; 2-amino-4-methyl-3-pentene; 2-chloro-4-methyl-3-pentene; 2-bromo-4-methyl-3-pentene; 1-trimethylsilylcyclohexene; 2,3-dimethyl-2-butenyl-para-tolylsulfone; 2,3-dimethyl-2-butenyl-para-tolyl sulfoxide; N-cyclohexenylmorpholine; 2-methyl-2-norbornene; terpinolene; &agr;-pinene; &bgr;-pinene; &bgr;-citronellol; ocimene; citronellol; geraniol; farnesol; terpinene; limonene; trans-2,3-dimethyl-acrylic acid; &agr;-terpinene; isoprene; cyclopentadiene; 1,4-diphenylbutadiene; 2-ethoxybutadiene; 1,1′-dicyclohexenyl; cholesterol; ergosterol acetate; 5-chloro-1,3-cyclohexadiene; 3-methyl-2-buten-1-ol; 3,5,5-trimethylcyclohex-2-en-1-ol; phenol, 1,2,4-trimethoxybenzene, 2,3,6-trimethylphenol, 2,4,6-trimethylphenol, 1,4-dimethylnaphthalene, furan, furfuryl alcohol, furfural, 2,5-dimethylfuran, isobenzofuran, dibenzyl sulfide, (2-methyl-5-tert-butyl)phenyl sulfide etc.
As a result of the oxidation according to the invention, the corresponding oxidation product is obtained from the substrates. Alkenes, (polycyclic) aromatics or heteroaromatics give, in particular, hydroperoxides or peroxides which are able to further react under the reaction conditions to give alcohols, epoxides, acetals or ca

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