Chemistry of hydrocarbon compounds – Aromatic compound synthesis – By isomerization
Reexamination Certificate
2000-03-21
2002-08-13
Griffin, Walter D. (Department: 1764)
Chemistry of hydrocarbon compounds
Aromatic compound synthesis
By isomerization
C585S025000, C585S027000, C568S722000, C568S723000, C568S729000, C568S730000, C568S783000
Reexamination Certificate
active
06433236
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a method of isomerization of substituted diaryl compounds by treating the diaryl compounds with a strong acid. The invention is further related to a method of isomerizing a mixture of isomers, selectively removing one or more desired isomers and re-isomerizing the remaining isomers.
BACKGROUND OF THE INVENTION
Substituted diaryl compounds, such as dimethylbiphenyls, and other various substituted diphenyl derivatives can be easily functionalized to produce other compounds such as bibenzoic acid, or converted to monomers for production of various high performance polymers such as polyesters or polyamides. While all of the isomers of substituted diaryl compounds can be functionalized, certain isomers are preferred due to their geometry that gives them certain structural advantages over the other isomers. For example, the 3,4′- and 4,4′-isomers of disubstituted biphenyl are strongly preferred to the other four isomers due to their linearity. Linearity and symmetry are very important when diaryl compounds are used as monomers for high performance polymers because it is the geometric structure of monomer repeat units that defines several physical properties of the resulting polymers, such as melting point, crystallinity, glass transition point and modulus. Therefore, there is a need for development of methods for selective production of certain desired monomers of substituted diaryl compounds in high yields while minimizing yields of other isomers.
Substituted diaryl compounds can be obtained directly from petroleum refining operations, or functionalization of refinery products, but more commonly are produced by coupling of substituted monoaryl compounds.
Coupling various substituted monoaryl compounds in the presence of catalytic amounts of palladium (II) acetate or aluminum chloride to obtain mixtures of biaryl isomers is reported by Iataaki et al in
J. Org. Chem.
Vol., 76-79 (1973). The reference also discloses selective separation of a single isomer from a mixture of isomers. H. Yashimoto et al,
Bull. Chem. Soc. Japan,
46, 2490-92 also reported oxidative coupling of substituted monoaromatic compounds in the presence of catalytic amounts of palladium salts. The reaction yields a mixture of isomers, and is conducted in 2,4-pentanedione.
Oxidative dimerization of disubstituted monoaromatic compounds such as dimethylphthalate is reported by A. Shiotani in
J. Mol. Catal.
18, 23 (1983) and
J. Mol. Catal.
34, 57 (1986). The references disclose a catalytic reaction, requiring palladium-based catalyst, that yields mixture of isomers of tetramethylcarboxylates. No further isomerization of the mixtures is reported.
Co-pending U.S. application Ser. No. 09/111,487 to White, et al. discloses a process of coupling various monoaromatic compounds in the presence of catalytic amounts of palladium (II) compounds and a strong acid. The coupling process produces mixtures of isomers and can be adjusted to selectively produce higher amounts of desired single isomers. The process requires the presence of a palladium catalyst. No steps of isomerization subsequent to the coupling reaction, separation of a single compound or subsequent re-equilibration of the mixture of isomers are disclosed in the application.
Substituted biaryl compounds obtained by any of the above-mentioned coupling methods, from petroleum refining operations, or from functionalization of refinery products, may contain mixtures of isomers comprising some, but usually a small amount of the desired isomers with a linear or nearly linear structure.
To increase the amount of the desired isomers, several methods of isomerization of isomeric mixtures of substituted biaryl compounds have been proposed. Isomerization of dimethylbiphenyl in the presence of silica, alumina or silica-alumina catalysts is disclosed in Japanese Patent publication JP 76038710. Dimethylbiphenyl mixtures having a low content of 4,4′-dimethylbiphenyl isomer are contacted with the catalyst in the liquid phase to increase the content of the 4.4′-dimethylbiphenyl isomer. The resulting product comprises a mixture of all six isomers with about 7% of 4,4′-product.
Isomerization of single isomers of dimethylbiphenyl by photo-irradiation of the isomers is reported by Mende et al in
Tetrahedron Lett.
(43), 3747-50 (1970). The isomerization of 2,X′-isomers is possible by irradiation of the isomers at 254 nm. However, 3,X′-, and 4,4′-isomers are photostable and do not undergo photoinitiated isomerization. Isomerization of 2,X′-isomers results in a mixture of several isomers but does not produce the linear 4,4′-isomer in any measurable quantity.
Isomerization of dimethylbiphenyl is reported in Japanese Patent publication JP 08099914, published Apr. 16, 1996. In this reference, a mixture of dimethylbiphenyl isomers is isomerized in the presence of ZSM-5 and/or ZSM-11 catalysts in the vapor phase to produce a mixture with higher amounts of 3,3′-, 3,4′- and 4,4′-products.
The present invention provides a method for isomerization of a single isomer of substituted diaryl compounds or a mixture of isomers of substituted diaryl compounds to produce an equilibrium isomeric mixture with a high content of desired isomers by treating the isomer or the mixture of isomers with a strong acid. The isomerization reaction is acid catalyzed and does not require any additional catalysts. The isomerization reaction conditions can be adjusted to produce an equilibrium mixture comprising different isomers in different amounts. One or more desired isomers can be selectively removed from the equilibrium mixture and the mixture can be re-isomerized or re-equilibrated subsequent to the removal of the desired isomers. The isomerization process may be used to: 1) substantially reduce the amount or yield of at least one isomer substituted in the 2-position, or 2) substantially increase the amount of at least one isomer substituted in at least the 3-position, the 4-position or the 4′-position to obtain monomers or reactants for the production of at least substantially linear or crystalline polymers.
SUMMARY OF THE INVENTION
Isomerization of one or more substituted diaryl compounds, such as disubstituted biaryl compounds to produce high yields of substantially linear isomers, such as 4,4′- and 3,4′-substituted isomers, is achieved by treating the substituted diaryl compounds with a strong acid. The isomerization process may also be used to substantially reduce or eliminate the amount of less linear isomers such as 2-substituted isomers. Acids useful for the isomerization have a Hammett Acidity less than −12.6, preferably less than −14. Hammett Acidity, H
0
, is defined as Ho
0
=pK
BH+
−log(C
BH+
/C
B
); where K
BH+
is the ionization constant for the indicator, C
BH+
is the concentration of the protonated indicator and C
B
is the concentration of unprotonated indicator. (see,
Van Nostrand's Scientific Encyclopedia,
5th Ed.)
Diaryl compounds that may be isomerized according to the process of the present invention include one or more electron donating groups as substituents on each of the aromatic rings. Exemplary substituted diaryl compounds which may be isomerized to linear or substantially linear diaryl compounds are represented by the general formula (A):
wherein both n and m are integers from 1 to 4 and may be the same or different, p is an integer from 0 to 10, each R
1
can be the same or different and each R
2
can be the same or different. Each R
1
and each R
2
is selected from groups donating electron density to the ring, or electron donating groups, such as an alkyl, aryl, amino, alkoxy, or a hydroxy group. R
1
and R
2
may be the same or different. Preferably, at least one of the substituents is selected from a hydrocarbon electron donating group, such as alkyl or aryl groups. The optional bridging group may be a branched or straight chain alkylene group. Diaryl compounds where p=0 are
Iretski Alexei Viktorovich
Schiraldi David Anthony
Sherman Sheldon Christopher
Tolbert Laren Malcolm
White Mark Gilmore
Arteva North America S.A.R.L.
Clements Gregory N.
Griffin Walter D.
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