Organic compounds -- part of the class 532-570 series – Organic compounds – Heterocyclic carbon compounds containing a hetero ring...
Reexamination Certificate
1996-06-10
2001-04-24
Ramsuer, Robert W (Department: 1626)
Organic compounds -- part of the class 532-570 series
Organic compounds
Heterocyclic carbon compounds containing a hetero ring...
C548S310700, C548S148000, C562S804000, C564S419000
Reexamination Certificate
active
06222044
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a process for making 2-aryl benz(ox, thi, imid)azoles and 2-aminoaryl amino-benz(ox, thi, imid)azoles. The term “benz(ox, thi, imid)azole” is used herein as a shorthand term to designate an oxazole, thiazole or imidazole group which is fused to an aromatic ring at the 4 and 5 positions.
Polyimide benz(ox, thi, imid)azole (PIBX) polymers can be prepared by reacting a dianhydride with a diamine containing one or more benz(ox, thi, imid)azole groups. See, for example U.S. Pat. No. 4,087,409 to Preston, incorporated herein by reference. Among the useful benz(ox, thi, imid)azole-containing diamines are those in which the 2 position of the oxazole ring is substituted with an aminoaryl group. Among the diamines of the latter type are those represented by the structure:
wherein X is —O—, —S—, or —NH—.
These latter amines can be prepared by reacting an amino benzoic acid with 2,4- or 2,5-diamino phenol, 2,4- or 2,5-diamino phenyl mercaptan, or 1,2,4-triaminobenzene (when X is —O—, —S—, and —NH—, respectively). For example, it is known to prepare 2-(m-aminophenyl)-aminobenzoxazole (DAMBO) by reacting 2,4-diaminophenol with meta- or para-aminobenzoic acid in the presence of polyphosphoric acid. Unfortunately, however, this process suffers from several drawbacks. The reaction mixture requires extensive neutralization, and thus forms large volumes of aqueous phosphate salts as a waste stream. The product must be purified extensively through repeated sublimations in order to be useful as a monomer. In addition, the diaminophenol and aminobenzoic acid starting materials are expensive and not readily available.
For these reasons, it would be desirable to provide an alternate method for making DAMBO as well as other 2-aminoaryl aminobenz(ox, thi, imid)azoles.
SUMMARY OF THE INVENTION
In one aspect, this invention is a process for preparing a 2-(aryl)-benz(ox, thi, imid)azole, comprising:
(a) contacting an aromatic aldehyde with hydroxylamine in substantially the absence of caustic under conditions such that an aromatic aldehyde oxime is formed;
(b) contacting said aromatic aldehyde oxime with a halogenating agent under conditions such that an aromatic hydroxamoyl halide is formed; and
(c) contacting the aromatic hydroxamoyl halide with an aromatic amine compound which has a primary amine group ortho to a hydroxyl group, a thiol group or another primary amine group to form a 2-(aryl)-benz(ox, thi, imid)azole.
In this process, both the aromatic aldehyde and the aromatic amine compound may be nitro-substituted. In such case, the nitro group or groups may be reduced to primary amine groups after step (c). In the case where neither, or only one of the aromatic aldehyde and the aromatic amine compound is nitro-substituted, the benz(ox, thi, imid)azole may be nitrated after step (c) so that following the nitration, both the benz(ox, thi, imid)azole and the aromatic substituent at the 2-position contain a nitro group. These nitro groups may be then reduced to amines.
Steps (a), (b), and (c) can be performed under mild conditions to obtain high yields of benz(ox, thi, imid)azole at essentially 100% selectivity, and do not require the use of polyphosphoric acid. Moreover, the process of this invention makes use of relatively inexpensive starting materials.
DETAILED DESCRIPTION OF THE INVENTION
In the first step of this process, an aromatic aldehyde is contacted with hydroxylamine under conditions such that an aromatic aldehyde oxime is formed. By “aromatic aldehyde oxime”, it is meant a compound in which a group represented by the structure:
—CH═N—OH
is bonded directly to an aromatic nucleus of an aromatic ring structure.
The aromatic aldehyde is a compound having a —CHO group directly bonded to an aromatic nucleus of an aromatic ring structure. Suitable aromatic ring structures to which the —CHO group is bonded include pyridine, benzene and fused ring systems such as anthracene, naphthalene and the like. The aromatic ring structure may be unsubstituted or substituted. However, any substituted ring structure must contain either a hydrogen or a nitro group attached to an aromatic nucleus, or else at least one of the substituent groups must be capable of being replaced by a nitro group after the benz(ox, thi, imid)azole is formed. In addition, any substituent group should not react under the conditions of the reaction with hydroxylamine with the aromatic aldehyde, or of the subsequent reactions with a halogenating agent and with the aromatic amine compound. Suitable substituents include phenyl, phenoxyl, —SO
2
—(C
6
H
5
) and the like. It is preferred, but not necessary, that the aromatic aldehyde contain a nitro group bonded to an aromatic ring. Benzaldehyde and mononitrobenzaldehyde are preferred aromatic aldehydes, with m- and p-nitrobenzaldehyde being especially preferred.
The hydroxylamine (H
2
NOH) may be and preferably is used in the form of a salt of a protic acid, such as the HCl salt. The hydroxylamine is preferably used in a slight excess relative to the aromatic aldehyde.
The aromatic aldehyde and the hydroxylamine are advantageously contacted in the presence of a solvent or diluent. Preferred solvents are polar materials in which both the aldehyde and the hydroxylamine are soluble. Alternatively, nonsolvents can be used as diluents. It is also preferred that the solvent be one which boils within the preferred or more preferred temperature range described below, so the reaction may be conducted under refluxing conditions. Suitable solvents include, for example, ethanol, methanol, isopropanol, 1,4-dioxane, tetrahydrofuran, and polar aprotic solvents that are inert to the reactants and the products, as well as toluene and benzene.
The reaction is preferably conducted at an elevated temperature at which the aromatic aldehyde does not degrade. A preferred temperature is from about 30 to about 120° C., with a temperature from about 50 to about 95° C. being more preferred. At the more preferred temperature, a reaction time of from about 1/2 hour to about 8 hours is generally sufficient to essentially complete the reaction.
In the formation of the aromatic hydroxamoyl halide, the contacting of the aromatic aldehyde with hydroxylamide is preferably carried out under conditions substantially in the absence of caustic or base, such as a tertiary amine (e.g., triethylamine), wherein substantially, in the absence of caustic or base, is an amount of at most about 5% equivalent weight of the hydroxamoyl halide formed from the aldehyde oxime. Preferably the amount of caustic or base is at most about 2%, even more preferably at most about 1%, and most preferably at most about 0.2% equivalent weight of the hydroxamoyl halide.
The resulting aromatic aldehyde oxime is then reacted with a halogenating agent under oxidizing conditions to form the corresponding aromatic hydroxamoyl halide. By “aromatic hydroxamoyl halide”, it is meant a compound in which a group represented by the structure:
—CA=N—OH
is bonded directly to a nucleus of an aromatic ring structure. In the foregoing structure, A represents a halogen atom, preferably chlorine or bromine.
The halogenation proceeds well even under mild conditions, and for that reason it is preferable to use mild halogenating agents and conditions in order to avoid halogenation at other sites on the aromatic aldehyde oxime molecule. Suitable halogenating agents include chlorine (Cl
2
), bromine (Br
2
), hypochlorous acid (HOCl), hypobromous acid, and materials which generate hypochlorous or hypobromous acid in situ. Chlorine, bromine, hypochlorous acid and hypobromous acid are advantageously used as dilute solutions, preferably as aqueous solutions. Materials which produce hypochlorous acid in situ include, for example, aqueous mixtures of sodium hypochlorite and a mineral acid, especially HCl; mixtures of a peroxysulfate salt such as potassium peroxysulfate with HCl; and mixtures of N-chlorosuccinamide with aqueous HCl. In analogous fashion, hypobromous acid may be formed in situ from aqueous mixtures o
Ramsuer Robert W
The Dow Chemical Company
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