Organic compounds -- part of the class 532-570 series – Organic compounds – Heterocyclic carbon compounds containing a hetero ring...
Reexamination Certificate
1995-06-07
2001-03-13
Dentz, Bernard (Department: 1625)
Organic compounds -- part of the class 532-570 series
Organic compounds
Heterocyclic carbon compounds containing a hetero ring...
C549S355000
Reexamination Certificate
active
06201139
ABSTRACT:
This invention pertains to isomerization processes and, more particularly, to processes whereby &ggr;,&dgr;-epoxyalkenes and &ggr;,&dgr;-epoxycycloalkenes are isomerized to obtain the corresponding 2,5-dihydrofuran compounds. This invention also pertains to novel catalyst systems useful in the described isomerization processes and to methods for the preparation of supported catalyst systems.
Dihydrofurans are reactive heterocyclic species which are useful in a variety of applications, e.g., as intermediates in the production of useful polymers and chemicals. However, the use of dihydrofurans for such purposes has heretofore been restricted due to the non-availability of cost-effective preparative procedures therefor.
In addition, dihydrofurans are readily reduced to produce the corresponding tetrahydrofuran species, which are also useful in a variety of applications, e.g., as polar aprotic reaction solvents, co-solvents, reactive intermediates in the production of useful polymers, copolymers, and the like.
U.S. Pat. Nos. 3,932,468 and 3,996,248 disclose the production of 2,5-dihydrofurans by the rearrangement of substituted or unsubstituted epoxyalkenes with a homogeneous catalyst system comprising hydrogen iodide or hydrogen bromide and a transition metal Lewis acid in an organic solvent. This process suffers from a number of disadvantages including the use of corrosive hydrogen halides, the need for expensive, high-boiling tertiary amide solvents, e.g., N-methyl-2-pyrrolidinone, to dissolve the transition metal Lewis acid. We have found that the process of U.S. Pat. Nos. 3,932,468 and 3,996,248 also results in the unwanted production of up to 15% &agr;,&bgr;-unsaturated aldehydes or ketones.
The thermal (i.e., non-catalytic) rearrangement of 3,4-epoxy-1-butene has been studied and shown by Crawford et al in the Canadian Journal of Chemistry, Vol. 54, pages 3364-3376 (1976) to produce a variety of products, including 2,3-dihydrofuran, cis and trans 2-butenal and 3-butenal.
Other reactions of epoxides have been reported. See, for example, U.S. Pat. No. 4,600,800, where epoxides are converted to allylic alcohols by contacting an epoxide in the liquid phase with solid alumina catalysts.
Another example of the rearrangement of epoxides is described in the Journal of Organometallic Chemistry, Vol. 359, pages 255-266 (1989), wherein Sato et al report the formation of &agr;,&bgr;-unsaturated aldehydes and ketones by the rhodium (I) catalyzed isomerization of 1,3-diene monoepoxides.
U.S. Pat. No. 4,897,498 describes an efficient process for the preparation of &ggr;,&dgr;-epoxyalkenes by the selective monoepoxidation of dienes. Thus, a process is needed for the conversion of such epoxyalkenes to dihydrofurans in satisfactory selectivity and/or yields wherein the product may be readily recovered from the catalyst and the catalyst reused and used in continuous operation.
In accordance with the present invention, we have discovered a catalytic process for the isomerization of &ggr;,&dgr;-epoxyalkenes to produce dihydrofurans. The process provides high levels of epoxyalkene conversion with high selectivity to the desired dihydrofuran product. Long catalyst lifetimes are realized and the product may be recovered by relatively simple means since the catalyst and reaction mixture are readily separated by such simple techniques as distillation, decantation, filtration, gas stripping methods, gas/liquid flow separation, and the like.
Our invention also provides novel catalyst systems, both supported and unsupported, which are useful, for example, to promote the isomerization of epoxyalkenes to dihydrofurans. Processes for preparing the supported catalyst systems are also provided herein.
In accordance with the present invention, there is provided a process for the isomerization of &ggr;,&dgr;-epoxyalkenes to the corresponding 2,5-dihydrofuran compounds, which process comprises contacting a &ggr;,&dgr;-epoxyalkene or &ggr;,&dgr;-epoxycycloalkene with a catalytic amount of a quaternary organic onium iodide, e.g., a compound consisting of an ammonium, phosphonium or arsonium cation and an iodide anion, under isomerization conditions of temperature and pressure.
The &ggr;,&dgr;-epoxyalkene and &ggr;,&dgr;-epoxycycloalkene reactants may contain from 4 to about 20 carbon atoms, preferably from 4 to about 8 carbon atoms. Examples of the epoxyalkene and epoxycycloalkene reactants include compounds having the structural formula:
wherein each R
1
is independently selected from hydrogen, alkyl of up to about 8 carbon atoms, a carbocyclic or heterocyclic aryl group of about 5 to 10 carbon atoms or halogen or any two R
1
substituents collectively may represent an alkylene group forming a ring, e.g., alkylene containing in the main chain up to about 8 carbon atoms. The preferred epoxyalkene reactants comprise compounds of formula (I) wherein only two of the R
1
substituents individually may represent lower alkyl, e.g., alkyl of up to about 8 carbon atoms, or collectively represent straight or branched chain alkylene of up to about 8 carbon atoms. Exemplary compounds contemplated for use in the practice of the present invention include 3,4-epoxy-3-methyl-1-butene, 2,3-dimethyl-3,4-epoxy-1-butene, 3,4-epoxycyclooctene, 3,4-epoxy-1-butene, 2,5-dimethyl-2,4-hexadiene monoepoxide, and the like. The epoxyalkene reactant of primary interest is 3,4-epoxy-1-butene.
The 2,5-dihydrofuran compounds obtained in accordance with our novel process have the structural formula:
wherein the R
1
substituents are defined above. Of the compounds which may be obtained in accordance with our invention, the most important is 2,5-dihydrofuran.
The quaternary onium iodide compounds which may be used as the catalyst in our novel process are known compounds and/or may be prepared according to published procedures. See, for example, U.S. Pat. No. 3,992,432 and the references cited therein. Exemplary quaternary organic onium iodide compounds include mono-, di-, tri-, or tetra-substituted quaternary onium iodides, wherein said substituents are selected from hydrogen, alkyl or substituted alkyl groups, cycloalkyl or substituted cycloalkyl groups, carbocyclic aryl or substituted carbocyclic aryl groups, heteroaryl or substituted heteroaryl groups, ferrocenyl, wherein each of said substituents may be bonded to one another to form a cyclic, heterocyclic, polycyclic or poly-heterocyclic structure. When used on a support or as a melt, the onium compounds normally contain at least 6 carbon atoms, preferably at least 12 carbon atoms, and have melting points not greater than about 225° C., preferably not greater than about 200° C.
Examples of the onium iodide catalysts are compounds conforming to the formulas
wherein
each R
2
independently is selected from hydrogen, alkyl or substituted alkyl moieties having up to about 20 carbon atoms, cycloalkyl or substituted cycloalkyl having about 5 to 20 carbon atoms, or aryl or substituted aryl having about 6 to 20 carbon atoms; or when Y is P, each R
2
also may be selected from alkoxy of up to about 20 carbon atoms, cycloalkoxy of about 5 to 20 carbon atoms, aryloxy of 6 to 10 carbon atoms or halogen;
two or three R
2
substituents collectively may represent joined hydrocarbylene groups, e.g. alkylene having 4 to 6 main chain carbon atoms or unsaturated groups such as —CH═CHCH═CHCH═ and lower alkyl substituted alkylene and unsaturated groups, which form a mono- or poly-cyclic ring with the Y atom to which they are bonded;
each R
3
is independently selected from hydrocarbylene moieties or substituted hydrocarbylene moieties;
x is 0 or 1, and
Y is N, P or As; provided that the quaternary onium iodide compound contains at least 6 carbon atoms. The substituted groups and moieties referred to above bear one or more substituents such as groups having the formulas
wherein each R
4
is independently selected from hydrogen or alkyl of up to about 20 carbon atoms and X is halogen. As used herein, the terms “hydrocarbylene moieties” refers to alkylene moieties having up to about 6 carbon at
Falling Stephen Neal
Lopez-Maldonado Patricia
Dentz Bernard
Eastman Chemical Company
Gwinnell Harry J.
Thomsen J. Frederick
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