U.S. patent application number 09/759505 was filed with the patent office on 2001-06-07 for method and composition for hydroxylation of aromatic substrates.
Invention is credited to Barnhart, Terence Michael.
Application Number | 20010003139 09/759505 |
Document ID | / |
Family ID | 22985814 |
Filed Date | 2001-06-07 |
United States Patent
Application |
20010003139 |
Kind Code |
A1 |
Barnhart, Terence Michael |
June 7, 2001 |
Method and composition for hydroxylation of aromatic substrates
Abstract
A method and composition are disclosed for the oxidation of
aromatic substrates in the presence of oxygen, a catalyst, a proton
source, and a non-gaseous reductant. In a preferred embodiment,
benzene is oxidized to phenol in the presence of oxygen, a vanadyl
catalyst, trifluoroacetic acid as a proton source, and ferrocene as
a reductant. 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: |
22985814 |
Appl. No.: |
09/759505 |
Filed: |
January 16, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09759505 |
Jan 16, 2001 |
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09259653 |
Feb 26, 1999 |
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Current U.S.
Class: |
568/802 |
Current CPC
Class: |
C07C 37/58 20130101;
Y02P 20/52 20151101; C07C 39/04 20130101; C07C 37/58 20130101 |
Class at
Publication: |
568/802 |
International
Class: |
C07C 037/00 |
Claims
1. A method of hydroxylating an aromatic substrate, which comprises
reacting the aromatic substrate in the presence of oxygen, a
catalyst, at least one proton source, and at least one non-gaseous
reductant.
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 is provided as a
mixture with at least one inert gas, or as air.
9. 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.
10. The method of claim 9, 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.
11. The method of claim 9, 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.
12. The method of claim 9, 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.
13. The method of claim 9, 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.
14. The method of claim 9, wherein the catalyst is formed in
solution from a vanadium, niobium, or tantalum precursor, or
mixture thereof; at least one organic acid; a carboxylate
precursor; and a pyridyl precursor.
15. The method of claim 14, wherein the catalyst is formed in
solution from a combination of picolinic acid, trifluoroacetic
acid; and at least one of sodium metavanadate, VO(picolinate).sub.2
or VO(acetylacetonate).sub.2.
16. 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.
17. The method of claim 16, 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.
18. The method of claim 1, wherein the proton source is a mineral
acid or an organic acid.
19. The method of claim 1, wherein the proton source is
trifluoroacetic acid.
20. The method of claim 1, wherein the reductant is a
dicyclopentadiene metal complex, zinc, iron, tin, or cooper.
21. The method of claim 1, wherein the reductant is ferrocene.
22. A method of hydroxylating an aromatic substrate, comprising
reacting the aromatic substrate in the presence of oxygen; 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; a
proton source; and a non-gaseous reductant.
23. The method of claim 22, wherein the aromatic substrate is
benzene, naphthalene, anthracene, phenanthrene, or the foregoing
substituted by at least one alkyl group, aryl group, hydroxyl
group, alkyl ether, aryl ether, or combinations thereof.
24. A method of making phenol from benzene, comprising reacting
benzene in the presence of oxygen; 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; a proton source; and a
non-gaseous reductant.
25. A composition for hydroxylating an aromatic substrate having at
least one active aromatic hydrogen, comprising oxygen; a vanadium,
niobium, or tantalum precursor or mixture thereof; at least one
anionic ligand precursor; at least one neutral, electron-donating
ligand precursor; at least one proton source; and at least one
non-gaseous reductant.
26. The composition of claim 25, 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.
27. The composition of claim 25, 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.
28. The composition of claim 25, 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.
29. The composition of claim 25, 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.
30. The composition of claim 25, wherein the catalyst is formed in
solution from a vanadium, niobium, or tantalum precursor, or
mixture thereof; at least one organic acid; a carboxylate
precursor; and a pyridyl precursor.
31. The composition of claim 30, wherein the catalyst is formed in
solution from a combination of picolinic acid, trifluoroacetic
acid, and at least one of sodium metavanadate, VO(picolinate).sub.2
or VO(acetylacetonate).sub.2.
32. The composition of claim 25, 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.
33. The composition of claim 32, 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.
34. The composition of claim 25, wherein the proton source is a
mineral acid or an organic acid.
35. The composition of claim 25, wherein the proton source is
trifluoroacetic acid.
36. The composition of claim 25, wherein the reductant is a
dicyclopentadiene metal complex, zinc, iron, tin, or cooper.
37. The composition of claim 25, wherein the reductant is
ferrocene.
38. The composition of claim 25, wherein the aromatic substrate is
benzene, naphthalene, anthracene, phenanthrene, or the foregoing
substituted by at least one alkyl group, aryl group, hydroxyl
group, alkyl ether, aryl ether, or combinations thereof.
39. A composition for making phenol from benzene, comprising
oxygen, a vanadium, niobium, or tantalum precursor or mixture
thereof, at least one anionic ligand precursor, at least one
neutral, electron-donating ligand precursor, at least one proton
source; and at least one non-gaseous reductant.
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, a catalyst, a proton
source, and a non-gaseous reductant. The invention also relates to
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, a catalyst, a proton source, and a
non-gaseous reductant. The method is environmentally friendly,
economical, safe, and amenable to commercial scale-up.
[0007] In another embodiment the invention comprises a composition
for hydroxylating an aromatic substrate having at least one active
aromatic hydrogen, comprising oxygen; a vanadium, niobium, or
tantalum precursor or mixture thereof; at least one anionic ligand
precursor; at least one neutral, electron-donating ligand
precursor; a proton source; and a non-gaseous reductant.
DETAILED DESCRIPTION OF THE INVENTION
[0008] The methods described herein comprise oxidation of an
aromatic substrate in the presence of oxygen, a catalyst, a proton
source, and a non-gaseous reductant. One preferred embodiment
comprises oxidation of benzene in the presence of oxygen, a vanadyl
catalyst, trifluoroacetic acid as a proton source, and ferrocene as
a reductant.
[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. The
hydroxylation advantageously proceeds in the presence of a mixture
of oxygen and up to about 90% by volume of at least one inert gas,
e.g., nitrogen, argon, helium and the like. A preferred mixture is
nitrogen with from about 5% to about 30% by volume oxygen. A
preferred oxygen source is 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. 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 aromatic compound having at least one active
aromatic hydrogen, oxygen, a proton source, and a non-gaseous
reductant. 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 mono- or
bi-dentate 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.
[0016] Suitable metal precursors include, but are not limited to,
the oxides 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 or their
corresponding N-oxides include, but are not limited to, carboxylic
acid, carboxylate, halogen, alkyl, heteroaryl, and aryl. Suitable
betadiketonates include those known in the art as ligands for the
metal precursors of the present invention. Examples of
beta-diketones (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,
heptafluorodimethyloctanedione, 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 3, and preferably less than about 2) 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. 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 an acid species (added as a
proton source) or a hydroxyaromatic compound produced by the
reaction, then the stoichiometric ratio of either or both ligand
precursors 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. In addition, the turnover number is directly
proportional to the quantity of proton source which is added to the
reaction mixture and consumed during the course of the reaction.
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 may be
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 bases of
carboxylic acids, for example, acetate, trifluoroacetate,
beta-diketonates, acetylacetonate, propionate, butyrate, benzoate,
and conjugate bases of carboxylic acids in a position alpha to a
heteroaromatic nitrogen atom, such as, but not limited to,
picolinate, 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 substituted picolinic acids; alcohols;
hydroxyaromatic compounds; phenol; substituted phenols; ethers;
furan; tetrahydrofuran; phosphines; amines; 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 proton source is at least one mineral acid (such as
hydrochloric acid) or organic acid (such as trifluoroacetic acid).
The proton source is preferably at least partially soluble, and
more preferably wholly soluble in the reaction mixture, and its
corresponding ion does not significantly interfere with or inhibit
the reaction. The proton source is present in the reaction mixture
as a co-reactant which is consumed in the course of the reaction.
The stoichiometric ratio of the proton source to non-gaseous
reductant in the reaction mixture is no greater than about 10:1,
preferably no greater than about 2:1, and most preferably no
greater than about 1.2:1. In especially preferred embodiments of
the present invention the stoichiometric ratio of the proton source
to non-gaseous reductant is about 1.10-1.01:1. Depending upon the
catalyst composition, the proton source may serve both as
co-reactant and as an anionic ligand precursor. For example,
trifluoroacetic acid and other organic acids may serve as both
co-reactant and as anionic ligand precursor.
[0027] Any method known in the art may be used to add the proton
source or mixture of proton sources. Most frequently the proton
source or mixture is added in the form of a solid or a liquid, or a
solution or slurry, alone or in combination with another reaction
component or inert solvent. It is within the scope of the invention
to add the proton source or mixture either in a single reaction
charge or incrementally during the course of the reaction.
[0028] The reductant in the method is at least one non-gaseous
reductant, and includes those compatible with the catalyst and
known in the art. A suitable non-gaseous reductant within the
context of the present invention is one which is serves as a
reductant only in the presence of a proton source, and which may be
added to the reaction mixture in a physical form other than a gas.
Any method known in the art may be used to add the non-gaseous
reductant or mixture of non-gaseous reductants. Most frequently the
non-gaseous reductant or mixture is added in the form of a solid or
a liquid, or a solution or slurry, alone or in combination with
another reaction component or inert solvent. It is within the scope
of the invention to add the non-gaseous reductant or mixture either
in a single reaction charge or incrementally during the course of
the reaction. Suitable reductants include, but are not limited to,
dicyclopentadiene-metal complexes such as ferrocene; zinc, iron,
tin, copper, and the like. Preferred reductants are ferrocene and
zinc. Effective quantities of proton source and reductant are
readily determined empirically by one of ordinary skill in the art,
depending on the starting aromatic substrate, the desired reaction
rate, and like considerations.
[0029] 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.
[0030] 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, the proton source, oxygen and/or the non-gaseous
reductant. 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
non-gaseous reductant, the catalyst, the proton source, and oxygen
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.
[0031] Hydroxylation may be practiced either in a batch,
semicontinuous, 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 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. Hydroxylation may also be
effected in a continuous mode by passing a mixture of the reactants
over a fixed bed of the catalyst. 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.
[0032] The following Example is provided by way of example only,
and should not be read to limit the scope of the invention.
[0033] 0.0099 grams (g) (0.0373 mmol) of VO(acetylacetonate).sub.2,
0.0201 g (0.1632 mmol) of picolinic acid, 2.0 g (17.54 mmol) of
trifluoroacetic acid, and 50 milliliters (mL) of benzene were added
to a stainless steel bomb fitted with a gas liner. 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 3.45 MPa of a gas mixture containing 28% oxygen gas
in nitrogen was introduced into the bomb. A mixture of 1.2 g (10.75
mmol) of ferrocene in 20 mL benzene was then slowly introduced into
the bomb by means of a high pressure pump while stirring was
continued. Upon completion of the ferrocene addition, the bomb was
cooled to room temperature and the reaction mixture was analyzed by
gas chromatography. Yield of phenol was 0.015 g (0.1593 mmol) for a
turnover number (yield of moles of product per moles of vanadium)
of about 40.
[0034] 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.
* * * * *