U.S. patent application number 09/759503 was filed with the patent office on 2001-11-08 for method and composition for hydroxylation of aromatic substrates.
Invention is credited to Barnhart, Terence Michael.
Application Number | 20010039365 09/759503 |
Document ID | / |
Family ID | 22985811 |
Filed Date | 2001-11-08 |
United States Patent
Application |
20010039365 |
Kind Code |
A1 |
Barnhart, Terence Michael |
November 8, 2001 |
Method and composition for hydroxylation of aromatic substrates
Abstract
A method and composition are disclosed for the hydroxylation of
aromatic substrates in the presence of oxygen, hydrogen, and a
catalyst. In a preferred embodiment, benzene is oxidized to phenol
in the presence of oxygen, a vanadium catalyst, and hydrogen. The
method is economical, safe, and amenable to commercial
scale-up.
Inventors: |
Barnhart, Terence Michael;
(Pattersonville, NY) |
Correspondence
Address: |
GENERAL ELECTRIC COMPANY
CRD PATENT DOCKET ROOM 4A59
P O BOX 8
BUILDING K 1 SALAMONE
SCHENECTADY
NY
12301
US
|
Family ID: |
22985811 |
Appl. No.: |
09/759503 |
Filed: |
January 16, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09759503 |
Jan 16, 2001 |
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09259652 |
Feb 26, 1999 |
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6265622 |
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Current U.S.
Class: |
568/629 ;
562/465; 568/733; 568/735; 568/771 |
Current CPC
Class: |
C07C 39/04 20130101;
C07B 41/02 20130101; C07C 37/58 20130101; Y02P 20/52 20151101; C07C
37/58 20130101 |
Class at
Publication: |
568/629 ;
562/465; 568/771; 568/733; 568/735 |
International
Class: |
C07C 037/58 |
Claims
1. A method of hydroxylating an aromatic substrate, which comprises
reacting an aromatic substrate having at least one active aromatic
hydrogen in the presence of oxygen, hydrogen and a catalyst.
2. The method of claim 1, wherein the aromatic substrate is
selected from the group consisting of benzene, naphthalene,
anthracene, phenanthrene, and derivatives of the foregoing having
one or more substituents.
3. The method of claim 2, wherein the substituents are selected
from the group consisting of aryl groups, alkyl groups, functional
groups, and combinations thereof, wherein the functional groups are
carboxylic acids, carboxylic acid alkyl esters, carboxylic acid
aryl esters, aldehydes, hydroxyls, olefins, alkyl ethers, or aryl
ethers.
4. The method of claim 3, wherein the substituents are substituted
by one or more moieties selected from the group consisting of aryl
groups, alkyl groups, functional groups, or combinations thereof,
wherein the functional groups are carboxylic acids, carboxylic acid
alkyl esters, carboxylic acid aryl esters, aldehydes, hydroxyls,
olefins, alkyl ethers, or aryl ethers.
5. The method of claim 2, wherein the aromatic substrate is
benzene, or benzene substituted by at least one alkyl group, aryl
group, alkyl ether, aryl ether, hydroxyl, or combinations
thereof.
6. The method of claim 5, wherein the aromatic substrate is
benzene, biphenyl, phenyl phenol, toluene, cumene, phenol, or
para-cumyl phenol.
7. The method of claim 2, wherein the aromatic substrate is
benzene.
8. The method of claim 1, wherein the oxygen and hydrogen are
provided as a mixture of oxygen and hydrogen with at least one
inert gas, or as a mixture of hydrogen with air.
9. The method of claim 8, wherein the mixture of oxygen and
hydrogen in inert gas comprises up to about 90% inert gas.
10. The method of claim 1, wherein the oxygen and hydrogen are
provided at a pressure between about 0.1 MPa and about 36 MPa.
11. The method of claim 1, wherein the catalyst is formed in
solution from a vanadium, niobium, or tantalum precursor or mixture
thereof; at least one anionic ligand precursor; and at least one
neutral, electron-donating ligand precursor.
12. The method of claim 11, wherein the stoichiometric ratio of
anionic ligand precursor to vanadium, niobium, or tantalum, or
mixture thereof, and the stoichiometric ratio of neutral,
electron-donating ligand precursor to vanadium, niobium, or
tantalum, or mixture thereof are each about 500-2:1.
13. The method of claim 11, wherein the stoichiometric ratio of
anionic ligand precursor to vanadium, niobium, or tantalum, or
mixture thereof, and the stoichiometric ratio of neutral,
electron-donating ligand precursor to vanadium, niobium, or
tantalum, or mixture thereof are each about 100-2:1.
14. The method of claim 11, wherein the stoichiometric ratio of
anionic ligand precursor to vanadium, niobium, or tantalum, or
mixture thereof, and the stoichiometric ratio of neutral,
electron-donating ligand precursor to vanadium, niobium, or
tantalum, or mixture thereof are each about 50-2:1.
15. The method of claim 11, wherein the anionic ligand precursor is
at least one member selected from the group consisting of halides,
carboxylic acids, acetic acid, trifluoroacetic acid, propionic
acid, butyric acid, benzoic acid, beta-diketones, acetylacetone,
conjugate bases of carboxylic acids, acetate, trifluoroacetate,
propionate, butyrate, benzoate, beta-diketonates, acetylacetonate,
carboxylic acids in a position alpha to a heteroaromatic nitrogen
atom, picolinic acid, substituted picolinic acids, picolinic acid
N-oxide, substituted picolinic acid N-oxides, conjugate bases of
carboxylic acids in a position alpha to a heteroaromatic nitrogen
atom, picolinate, substituted picolinates, picolinate N-oxide, and
substituted picolinate N-oxides; and the neutral ligand precursor
is at least one member selected from the group consisting of water,
acetonitrile, nitrogen in a heteroaromatic ring, pyridine,
substituted pyridines, picolinic acid, substituted picolinic acids,
alcohols, hydroxyaromatic compounds, phenol, substituted phenols,
ethers, furan, tetrahydrofuran, phosphines, amines, amides,
ketones, esters, Schiff bases, and imides.
16. The method of claim 11, wherein the catalyst is formed in
solution from a vanadium, niobium, or tantalum precursor, or
mixture thereof; a carboxylate precursor; and a pyridyl
precursor.
17. The method of claim 11, wherein the catalyst is formed in
solution from a combination of picolinic acid, and at least one of
sodium metavanadate, VO(picolinate).sub.2 or
VO(acetylacetonate).sub.2.
18. The method of claim 1, wherein a catalyst in solution has the
formula MO(O.sub.2)(L.sup.1).sub.n(L.sup.2).sub.m, wherein M is
vanadium, niobium or tantalum, n is an integer from 0 to 1, m is an
integer from 1 to 3, L.sup.1 is an anionic, mono- or bi-dentate
ligand, and L.sup.2 is a neutral, electron-donating ligand.
19. The method of claim 18, wherein L.sup.1 is at least one member
selected from the group consisting of halides, conjugate bases of
carboxylic acids, acetate, trifluoroacetate, beta-diketonates,
acetylacetonate, propionate, butyrate, benzoate, conjugate bases of
carboxylic acids in a position alpha to a heteroaromatic nitrogen
atom, picolinate, substituted picolinates, picolinate N-oxide, and
substituted picolinate N-oxides; and L.sup.2 is at least one member
selected from the group consisting of water, acetonitrile, nitrogen
in a heteroaromatic ring, pyridine, substituted pyridines,
picolinic acid, substituted picolinic acids, alcohols,
hydroxyaromatic compounds, phenol, substituted phenols, ethers, fu
ran, tetrahydrofuran, phosphines, amines, amides, ketones, esters,
Schiff bases, and imides.
20. A method of hydroxylating an aromatic substrate, comprising
reacting the aromatic substrate in the presence of oxygen,
hydrogen, and an effective amount of a catalyst formed from
vanadium, niobium, or tantalum precursors, an anionic, mono- or
bi-dentate ligand precursor, and a neutral, electron-donating
ligand precursor.
21. The method of claim 20, wherein the aromatic substrate is
benzene, naphthalene, anthracene, phenanthrene, or the foregoing
substituted by at least one alkyl group, aryl group, hydroxyl,
alkyl ether, aryl ether, or combinations thereof.
22. A method of making phenol from benzene, comprising reacting
benzene in the presence of oxygen, hydrogen, and an effective
amount of a catalyst formed from vanadium, niobium, or tantalum
precursors, an anionic, mono- or bi-dentate ligand precursor, and a
neutral, electron-donating ligand precursor.
23. A composition for hydroxylating an aromatic substrate having at
least one active aromatic hydrogen, comprising oxygen, hydrogen, a
vanadium, niobium, or tantalum precursor or mixture thereof, at
least one anionic ligand precursor, and at least one neutral,
electron-donating ligand precursor.
24. The composition of claim 23, further comprising at least one
inert gas.
25. The composition of claim 23, wherein the stoichiometric ratio
of anionic ligand precursor to vanadium, niobium, or tantalum, or
mixture thereof, and the stoichiometric ratio of neutral,
electron-donating ligand precursor to vanadium, niobium, or
tantalum, or mixture thereof are each about 500-2:1.
26. The composition of claim 23, wherein the stoichiometric ratio
of anionic ligand precursor to vanadium, niobium, or tantalum, or
mixture thereof, and the stoichiometric ratio of neutral,
electron-donating ligand precursor to vanadium, niobium, or
tantalum, or mixture thereof are each about 100-2:1.
27. The composition of claim 23, wherein the stoichiometric ratio
of anionic ligand precursor to vanadium, niobium, or tantalum, or
mixture thereof, and the stoichiometric ratio of neutral,
electron-donating ligand precursor to vanadium, niobium, or
tantalum, or mixture thereof are each about 50-2:1.
28. The composition of claim 23, wherein the anionic ligand
precursor is at least one member selected from the group consisting
of halides, carboxylic acids, acetic acid, trifluoroacetic acid,
propionic acid, butyric acid, benzoic acid, beta-diketones,
acetylacetone, conjugate bases of carboxylic acids, acetate,
trifluoroacetate, propionate, butyrate, benzoate, beta-diketonates,
acetylacetonate, carboxylic acids in a position alpha to a
heteroaromatic nitrogen atom, picolinic acid, substituted picolinic
acids, picolinic acid N-oxide, substituted picolinic acid N-oxides,
conjugate bases of carboxylic acids in a position alpha to a
heteroaromatic nitrogen atom, picolinate, substituted picolinates,
picolinate N-oxide, and substituted picolinate N-oxides; and the
neutral ligand precursor is at least one member selected from the
group consisting of water, acetonitrile, nitrogen in a
heteroaromatic ring, pyridine, substituted pyridines, picolinic
acid, substituted picolinic acids, alcohols, hydroxyaromatic
compounds, phenol, substituted phenols, ethers, fu ran,
tetrahydrofuran, phosphines, amines, am ides, ketones, esters,
Schiff bases, and imides.
29. The composition of claim 23, wherein the catalyst is formed in
solution from a vanadium, niobium, or tantalum precursor, or
mixture thereof; a carboxylate precursor; and a pyridyl
precursor.
30. The composition of claim 29, wherein the catalyst is formed in
solution from a combination of picolinic acid and at least one of
sodium metavanadate, VO(picolinate).sub.2 or
VO(acetylacetonate).sub.2.
31. The composition of claim 23, wherein a catalyst in solution has
the formula MO(O.sub.2)(L.sup.1).sub.n(L.sup.2).sub.m, wherein M is
vanadium, niobium or tantalum, n is an integer from 0 to 1, m is an
integer from 1 to 3, L.sup.1 is an anionic, mono- or bi-dentate
ligand, and L.sup.2 is a neutral, electron-donating ligand.
32. The composition of claim 31, wherein L.sup.1 is at least one
member selected from the group consisting of halides, conjugate
bases of carboxylic acids, acetate, trifluoroacetate,
beta-diketonates, acetylacetonate, propionate, butyrate, benzoate,
conjugate bases of carboxylic acids in a position alpha to a
heteroaromatic nitrogen atom, picolinate, substituted picolinates,
picolinate N-oxide, and substituted picolinate N-oxides; and
L.sup.2 is at least one member selected from the group consisting
of water, acetonitrile, nitrogen in a heteroaromatic ring,
pyridine, substituted pyridines, picolinic acid, substituted
picolinic acids, alcohols, hydroxyaromatic compounds, phenol,
substituted phenols, ethers, furan, tetrahydrofuran, phosphines,
amines, amides, ketones, esters, Schiff bases, and imides.
33. The composition of claim 23, wherein the aromatic substrate is
benzene, naphthalene, anthracene, phenanthrene, or the foregoing
substituted by at least one alkyl group, aryl group, hydroxyl,
alkyl ether, aryl ether, or combinations thereof.
34. A composition for making phenol from benzene, comprising
oxygen, hydrogen, a vanadium, niobium, or tantalum precursor or
mixture thereof, at least one anionic ligand precursor, and at
least one neutral, electron-donating ligand precursor.
35. The composition of claim 34, further comprising at least one
inert gas.
Description
BACKGROUND OF THE INVENTION
[0001] This invention relates to methods for the hydroxylation of
aromatic substrates. In particular, this invention relates to a
method for producing hydroxyaromatic compounds by the oxidation of
aromatic substrates in the presence of oxygen, hydrogen, and a
catalyst. The invention also relates to catalyst compositions for
effecting said hydroxylation.
[0002] Phenol is among the most important industrial organic
chemical intermediates, being used for the manufacture of
thermoplastics and other resins, dyestuffs, explosives,
agrochemicals, and pharmaceuticals. It is particularly important in
the manufacture of phenol-formaldehyde resins used in the
construction, appliance, and automotive industries, and in the
manufacture of bisphenol A for epoxy and polycarbonate resins.
[0003] Despite its industrial importance, prior art methods for the
production of phenol are non-selective, multi-step, and/or
expensive. For example, benzene may be alkylated to obtain cumene,
which in turn is oxidized to form cumene hydroperoxide. The
hydroperoxide is cleaved using an acid catalyst to form phenol and
acetone. Another industrial process using oxidation of toluene
requires expensive starting materials. Older industrial processes
such as the Raschig Hooker process require high energy input, and
result in corrosive or difficult to dispose of wastes.
[0004] More recent processes for the production of phenols include
the hydroxylation of aromatic substrates using hydrogen peroxide in
the presence of a titanoaluminate molecular sieve, as disclosed in
U.S. Pat. No. 5,233,097 to Nemeth et al., or in the presence of a
hydrogen fluoride-carbon dioxide complex as disclosed in U.S. Pat.
No. 3,453,332 to Vesely et al. U.S. Pat. No. 5,110,995 further
discloses hydroxylation of phenol or phenol derivatives in the
presence of nitrous oxide and zeolite catalyst. A multi-step
process requiring partial hydrogenation of benzene, separation of
the reaction products, oxidation of some of the reaction products,
dehydrogenation, and other steps is disclosed in U.S. Pat. No.
5,180,871 to Matsunaga et al. U.S. Pat. No. 5,001,280 to Gubelmann
et al., U.S. Pat. No. 5,110,995 to Kharitonov et al., and U.S. Pat.
No. 5,756,861 to Panov et al. disclose oxidation of benzene to
phenol by nitrous oxide in the presence of a zeolitic catalyst,
with yields of up to about 16%.
[0005] While certain of these methods provide good yields, they
still suffer from various drawbacks and disadvantages. In
particular, nitrous oxide is expensive, and it is also a greenhouse
gas that presents significant environmental concerns. Thus, despite
the number of methods available to synthesize hydroxyaromatic
compounds, there still remains a need for a process that is simple,
high-yield, environmentally friendly, economical, and amenable to
commercial scale-up.
SUMMARY OF THE INVENTION
[0006] The above-described drawbacks and disadvantages are
alleviated by the method described herein, which is a method of
hydroxylating an aromatic substrate, which comprises reacting an
aromatic substrate having at least one active aromatic hydrogen in
the presence of oxygen, hydrogen and a catalyst. The method is
environmentally friendly, economical, safe, and amenable to
commercial scale-up.
[0007] In another embodiment the invention comprises a catalyst
composition for hydroxylating an aromatic substrate having at least
one active aromatic hydrogen, comprising oxygen, hydrogen, a
vanadium, niobium, or tantalum precursor or mixture thereof, at
least one anionic ligand precursor, and at least one neutral,
electron-donating ligand precursor.
DETAILED DESCRIPTION OF THE INVENTION
[0008] The present method is directed to hydroxylation of aromatic
substrates in the presence of oxygen, hydrogen, and a catalyst. One
preferred embodiment comprises hydroxylation of benzene in the
presence of oxygen, hydrogen, and a vanadium catalyst.
[0009] One or more of a range of aromatic substrates may be
hydroxylated in the practice of this method. Preferably the
aromatic substrate is benzene, naphthalene, anthracene,
phenanthrene, or the like, or substituted derivatives thereof. The
substituents may be the same or different. The number of
substituents may vary, as long as at least one active aromatic
hydrogen is available for substitution, where an active aromatic
hydrogen is one capable of being replaced by hydroxyl to produce a
hydroxyaromatic compound. Benzene, for example, may have from one
to five substituents, which may the same or different.
[0010] Suitable substituents include one or more aryl groups, for
example phenyl, naphthyl, anthracyl, and phenanthryl. The aryl
substituents may themselves be substituted by various functional
groups, providing that such functional groups do not interfere with
the hydroxylation. Suitable functional groups include, but are not
limited to, alkyl groups as described below, carboxylic acids,
carboxylic acid alkyl and aryl esters, aldehydes, hydroxyls,
olefins, and alkyl and aryl ethers. Mixtures of different aryl
groups and/or substituted aryl groups as substituents are also
within the scope of the invention.
[0011] Other suitable substituents include one or more alkyl
groups, wherein the alkyl groups are straight- or branched-chain,
or cyclic, and typically have from one to twenty six carbons. Some
illustrative non-limiting examples of these alkyl groups include
methyl, ethyl, propyl, isopropyl, butyl, tertiary-butyl, pentyl,
neopentyl, hexyl, cyclobutyl, cyclopentyl, cyclohexyl,
methylcyclohexyl, cycloheptyl. Exemplary alkyl-substituted benzenes
include, but are not limited to, toluene, xylene, and cumene. The
alkyl groups may themselves be substituted by various functional
groups, providing that such functional groups do not interfere with
the hydroxylation. Suitable functional groups include, but are not
limited to, aryl groups as described above, carboxylic acids,
carboxylic acid alkyl and aryl esters, aldehydes, hydroxyls,
olefins, and alkyl and aryl ethers. Mixtures of different alkyl
groups and/or substituted alkyl groups as substituents are also
within the scope of the invention.
[0012] Other suitable substituents include, but are not limited to,
one or more functional groups, providing that such functional
groups do not interfere with the hydroxylation. Suitable functional
groups include, but are not limited to, carboxylic acids,
carboxylic acid alkyl and aryl esters, aldehydes, hydroxyls,
olefins, and alkyl and aryl ethers. Mixtures of different
functional groups as substituents are also within the scope of the
invention. Mixtures of substituents comprising combinations of
functional groups, aryl groups, alkyl groups and/or their
functionalized derivatives are also within the scope of the
invention.
[0013] Preferred aromatic substrates are benzene, and benzene
substituted by alkyl groups, aryl groups, alkyl ethers, aryl
ethers, or combinations thereof. Especially preferred are biphenyl,
phenyl phenol, toluene, cumene, phenol, and para-cumyl phenol.
[0014] Molecular oxygen may serve as both oxidant and source of
hydroxyl oxygen in the present hydroxylation method. Hydrogen may
serve as a reductant. The compositional ratio between oxygen and
hydrogen is preferably outside the explosive range from the
viewpoint of safety. The hydroxylation advantageously proceeds in
the presence of a mixture of oxygen, hydrogen, and up to about 90%
of at least one inert gas, e.g., nitrogen, argon, helium and the
like. A preferred hydrogen source is molecular hydrogen, which may
be used directly or in a mixture, especially, e.g., as a mixture
with the oxygen source. A preferred oxygen and hydrogen source
comprises air, or mixtures comprising the components of air. The
partial pressure of oxygen is preferably in the range from about
0.02 megaPascals (MPa) to about 7.1 MPa, and the partial pressure
of hydrogen is preferably in the range from about 0.002 MPa to
about 1.42 MPa. The absolute total pressure of the reaction is
within the range of about 0.1 MPa to about 36 MPa, and preferably
within the range of about 1 MPa to about 8 MPa.
[0015] Preferred catalysts are based on precursors which under the
reaction conditions produce a catalyst effective in the
hydroxylation of an active aromatic hydrogen. Such precursors
include precursors giving rise to a metal complex, such as a
vanadium, niobium or tantalum complex or mixtures thereof;
precursors giving rise to an anionic ligand; precursors giving rise
to a neutral, electron-donating ligand, and precursors comprising a
combination of vanadium, niobium or tantalum with either an anionic
ligand or a neutral, electron-donating ligand, or both. The anionic
and/or neutral, electron-donating ligands may be present in the
same molecule, for example as bidentate or tridentate ligands.
[0016] Suitable metal precursors include, but are not limited to,
the oxides or the alkali metal salts of vanadium, niobium, or
tantalum, for example sodium metavanadate; substituted oxides of
vanadium, niobium and tantalum, for example
VO(acetylacetonate).sub.2 and VO(picolinate).sub.2, and alcoholates
such as tantalum trisethoxide and niobium trisethoxide. Mixtures of
metal precursors are also within the scope of the invention. In
particular, mixtures of precursors containing either the same or
different metals are suitable.
[0017] Suitable anionic ligand precursors include, but are not
limited to, halides, carboxylic acids and/or their alkali metal or
other salts, for example, sodium acetate, trifluoroacetate,
beta-diketonates, acetylacetonate, propionate, butyrate, benzoate,
or their corresponding acids; carboxylic acids and/or their alkali
metal or other salts in a position alpha to a heteroaromatic
nitrogen atom, such as, but not limited to, picolinic acid and
substituted picolinic acids; picolinate and substituted
picolinates, and their corresponding N-oxides. Suitable
substituents for picolinic acid and picolinate include, but are not
limited to, carboxylic acid, carboxylate, halogen, alkyl,
heteroaryl, and aryl. Suitable beta-diketonates include those known
in the art as ligands for the metal precursors of the present
invention. Examples of betadiketones (from which beta-diketonates
are derived) include, but are not limited to, acetylacetone,
benzoylacetone, dibenzoylmethane, diisobutyrylmethane,
2,2-dimethylheptane-3,5-dione, 2,2,6-trimethylheptane-3,5-dione,
dipivaloylmethane, trifluoroacetylacetone, hexafluoroacetylacetone,
benzoyltrifluoroacetone, pivaloyltrifluoroacetone, he
ptafluorodimethyloctanedione, octafluorohexanedione,
decafluoroheptanedione, 4,4,4-trifluoro-1-phenyl-1- ,3-butanedione,
2-furoyltrifluoroacetone, 2-theonyltrifluoroacetone,
3-chloro-2,4-pentanedione, 3-ethyl-2,4-pentanedione,
3-methyl-2,4-pentanedione, methyl 4-acetyl-5-oxohexanoate. Mixtures
of anionic ligand precursors are also within the scope of the
invention. Metal complexes of the anionic ligands are also usable,
e.g., VO(acetylacetonate).sub.2 and VO(picolinate).sub.2.
[0018] Suitable neutral, electron-donating ligand precursors
include, but are not limited to, water; acetonitrile; nitrogen in a
heteroaromatic ring, such as, but not limited to, pyridine,
substituted pyridines, picolinic acid or substituted picolinic
acids; alcohols; hydroxyaromatic compounds; phenol; substituted
phenols; ethers; furan; tetrahydrofuran; phosphines; amines;
amides; ketones; esters; Schiff bases; or imides. Mixtures of
neutral, electron-donating ligand precursors are also within the
scope of the invention.
[0019] The above precursors may be supplied to the solution
separately or as metal complexes with at least one ligand. For
example, one preferred formulation comprises the combination at low
pH (e.g., less than about 4, and preferably less than about 3) of
sodium metavanadate, a carboxylic acid, and a compound containing
heteroaromatic nitrogen, e.g., picolinic acid, substituted
picolinic acids, pyridine, substituted pyridines, or their
corresponding N-oxides. Another preferred formulation comprises the
combination of VO(acetylacetonate).sub.2 with a compound containing
heteroaromatic nitrogen, e.g., a pyridyl compound. Still another
combination comprises the combination of VO(picolinate).sub.2 with
a carboxylate and/or a compound containing heteroaromatic nitrogen,
e.g., a pyridyl compound. In each of the above formulations, the
catalyst is formed in solution from a vanadium, niobium, or
tantalum precursor; a carboxylic acid precursor (which may be in
the form of a carboxylic acid or acid salt, or which may also
function as the metal precursor); and a precursor compound
containing heteroaromatic nitrogen, e.g., a pyridyl precursor
(which may be in the form of the pyridyl compound itself, or which
may also function as the metal precursor).
[0020] The stoichiometric ratio of the anionic ligand precursor to
metal (i.e. vanadium, niobium, or tantalum, or mixture thereof) in
the composition and stoichiometric ratio of the neutral,
electron-donating ligand precursor to metal in the composition are
not particularly limited so long as there is a sufficient molar
quantity of anionic ligand and of neutral, electron-donating ligand
to satisfy the vacant valency sites on the metal in the active
catalyst species effective in the hydroxylation of an aromatic
compound having at least one active aromatic hydrogen. In addition,
the quantities of anionic ligand and neutral, electron-donating
ligand are preferably not such that they interfere either with the
hydroxylation reaction itself or with the isolation or purification
of the product mixture, or with the recovery and reuse of catalyst
components (such as metal).
[0021] When a ligand precursor is also a hydroxyaromatic compound
produced by the reaction, then the stoichiometric ratio of ligand
precursor to metal precursor may be directly related to the
turnover number of the reaction, which is the yield of moles of
product per moles of metal (or mixture of metals). The turnover
number of the reaction determines the moles of hydroxyaromatic
compounds produced. For optimum efficiency the turnover number is
desired to be as high as possible. Preferred turnover numbers for
the present invention are greater than 1, more preferably greater
than about 10, and most preferably greater than about 50. Typically
turnover numbers may be between about 5 and about 50.
[0022] In preferred embodiments of the present invention the
stoichiometric ratio of both the anionic ligand precursor to metal
and the neutral, electron-donating ligand precursor to metal in the
composition are about 500-2:1, more preferably about 100-2:1, and
still more preferably about 50-2:1. When the catalyst composition
comprises metal precursor (or mixture of metal precursors) in which
the metal is supplied in the form of, for example, a complex with
either the anionic ligand precursor, or the neutral,
electron-donating ligand precursor, or both, then the
stoichiometric ratio of ligand precursor to metal is essentially
2:1, as for example in VO(acetylacetonate).sub.2 and in
VO(picolinate).sub.2. It is also contemplated that additional,
uncomplexed anionic ligand precursor, or uncomplexed neutral,
electron-donating ligand precursor, or both, may be added to the
reaction mixture when the metal is supplied in the form of a
complex with either the anionic ligand precursor, or the neutral,
electron-donating ligand precursor, or both.
[0023] Without being bound by theory, it is hypothesized that
suitable catalyst precursor combinations may give rise in the
presence of molecular oxygen or a molecular oxygen precursor to
catalysts having the general structure
MO(O.sub.2)(L.sup.1).sub.n(L.sup.2).sub.m
[0024] wherein M is a metal such as vanadium, niobium or tantalum;
n is an integer from 0 to 1; m is an integer from 1 to 3; L.sup.1
is an anionic, mono- or bi-dentate ligand; and L.sup.2 is a
neutral, electron-donating ligand. Suitable anionic ligands
include, but are not limited to, halides or the conjugate base of a
carboxylic acid, for example, acetate, trifluoroacetate,
beta-diketonates, acetylacetonate, propionate, butyrate, benzoate,
and the conjugate base of a carboxylic acid in a position alpha to
a heteroaromatic nitrogen atom, such as, but not limited to,
picolinate, and substituted picolinates, and their corresponding
N-oxides. Suitable neutral, electron-donating ligands include, but
are not limited to, water; acetonitrile; nitrogen in a
heteroaromatic ring, such as, but not limited to, pyridine,
pyridyl, picolinic acid or a substituted picolinic acid; alcohols;
hydroxyaromatic compounds; phenol; substituted phenols; ethers;
furan; tetrahydrofuran; phosphines; amine; amides; ketones; esters;
Schiff bases; or imides.
[0025] The catalyst is present in an effective amount, which is
readily determined empirically by one of ordinary skill in the art,
depending on the starting aromatic substrate, the desired reaction
rate, the cost of the catalyst, and like considerations. Generally,
the catalyst will be present in amounts of up to about 10 mole
percent of the aromatic substrate.
[0026] The reaction temperature is generally within the range of
about 25.degree. C. to about 200.degree. C., preferably in the
range of about 40.degree. to about 150.degree. C. Although the
reaction time depends upon reaction conditions, the reaction time
is generally several seconds to several hours.
[0027] Although the reaction may be run neat in benzene, toluene,
or other aromatic substrate, at least one inert solvent may also be
used where desirable to provide at least some degree of miscibility
or microhomogeneity with respect to the catalyst, the aromatic
substrate, oxygen and/or hydrogen. Solvents which enhance
solubility and/or reactivity of the reactants are especially
desirable, but the solvent will optimally solubilize, at least in
part, the aromatic substrate, the catalyst, and oxygen and/or
hydrogen without significantly decreasing the utilization
efficiency of the catalyst. Exemplary solvents include, but are not
limited to, acetonitrile, fluorinated hydrocarbons, freons,
chloroform, dichloromethane, carbon tetrachloride, or combinations
thereof.
[0028] Hydroxylation may be practiced either in a batch,
semi-continuous, or continuous process. In a batch reaction
catalyst and ligands are dissolved in the aromatic substrate or
substrate/solvent mixture, preferably under an inert atmosphere,
and a gaseous mixture comprising oxygen, hydrogen, and at least one
inert gas is introduced into the reaction vessel. Although not
necessary, it is preferred that the gas mixture be sparged or
vigorously mixed with the reaction liquor in order to enhance
transport into the liquor and thus increase reaction rate. In this
instance, the use of a homogenous feedstock is advantageous in
ensuring adequate contact between the catalyst and the aromatic
substrate. The hydroxyaromatic compound or other products produced
by the method of this invention may be separated and isolated by
conventional techniques.
[0029] The following Examples are provided by way of example only,
and should not be read to limit the scope of the invention.
EXAMPLE 1
[0030] 0.01 grams (g) of VO(acetylacetonate).sub.2, 0.02 g of
picolinic acid, and 50 milliliters (mL) of benzene were added to a
stainless steel bomb. The bomb was sealed with a cap containing a
gas-sparging stir shaft and reactor cooling coils. The reactor was
then brought to 100.degree. C. with stirring, and pressurized with
2.1% hydrogen gas in air at 6.9 MPa. Stirring was continued at this
temperature and pressure for about 18 hours. The reaction was then
cooled, and analysis by gas chromatography indicated the presence
of 0.012 g of phenol and no other reaction products, indicating a
turnover number (yield of moles of product per moles of catalyst)
of 3.5.
EXAMPLE 2
[0031] VO(picolinate).sub.2 or catalyst precursors which in
solution produce VO(O.sub.2)(picolinate)(L).sub.n, (as described
above) and benzene are added to a stainless steel bomb. The bomb is
sealed with a cap containing gas-sparging stir shaft and reactor
cooling coils. The reactor is then brought to reaction temperature
(approximately 100.degree. C.) with stirring, and pressurized with
a mixture of hydrogen in air (approximately 6.9 MPa of 2.1%
hydrogen gas). Stirring is continued at this temperature and
pressure until no more gas uptake is observed. The reaction is then
cooled, and analyzed by gas chromatography to show the presence of
phenol in benzene.
[0032] While preferred embodiments have been shown and described,
various modifications and substitutions may be made thereto without
departing from the spirit and scope of the invention. Accordingly,
it is to be understood that the present invention has been
described by way of illustration and not limitation.
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