Organic compounds -- part of the class 532-570 series – Organic compounds – Oxygen containing
Reexamination Certificate
2001-01-16
2001-11-27
Shippen, Michael L. (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Oxygen containing
C252S182120, C252S182300, C252S182330, C502S160000, C502S167000, C502S170000, C502S155000
Reexamination Certificate
active
06323378
ABSTRACT:
BACKGROUND OF THE INVENTION
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.
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.
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.
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%.
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
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.
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
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.
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.
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.
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.
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.
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.
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.
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 includ
Brown S. Bruce
General Electric Company
Johnson Noreen C.
Shippen Michael L.
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