Organic compounds -- part of the class 532-570 series – Organic compounds – Heterocyclic carbon compounds containing a hetero ring...
Reexamination Certificate
1998-08-28
2002-01-01
Kight, John (Department: 1612)
Organic compounds -- part of the class 532-570 series
Organic compounds
Heterocyclic carbon compounds containing a hetero ring...
C549S469000
Reexamination Certificate
active
06335455
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
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 in the presence of a catalyst system comprising an organotin compound and an alkali metal iodide in the presence or absence of a solvent at a temperature of 50 to 200° C.
2. Description of the Related Art
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.
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 disadvantages of the use of corrosive hydrogen halides, high level of oligomer formation, and complications in product isolation. 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.
U.S. Pat. No. 5,034,545 describes a method for the isomerization of epoxyalkenes to 2,5-dihydrofurans, in the liquid phase, in the presence of a catalyst system containing an alkali or alkaline earth metal halide or an onium halide, a Lewis acid, and an organic solubilizer. The best reported results were attained by using the combination of a zinc halide and an alkali metal halide. We have found that such combinations of catalyst system described in U.S. Pat. No. 5,034,545 gave very poor catalyst lifetime. The catalyst activity and the reaction of the epoxide decrease considerably after a short operation time and result in a high level of oligomer formation. Therefore, this method is uneconomical.
Furthermore, U.S. Pat. No. 5,315,019 discloses the isomerization of epoxybutenes in the liquid phase, wherein organotin and a tetraalkylammonium or phosphonium iodide are used as the catalyst system. European Patent No. 0 691 334 A1 discloses a method for the rearrangement of epoxybutenes to 2,5-dihydrofurans, in the liquid phase, in the presence of a Lewis acid and a phosphazenium halide or a phosphazanium halide in an organic solvent. Catalysts used in these methods are expensive. Some of them are not readily commercially available. Moreover, relatively large quantities of catalysts must be used in order to obtain satisfactory yields and selectivities.
The invention under consideration was thus based on the task of finding a catalyst system for the isomerization of epoxybutenes to 2,5-dihydrofurans, which is free of the aforementioned disadvantages.
SUMMARY OF THE INVENTION
We have discovered a catalytic process with a novel catalyst system 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. Catalysts involved in the process of this invention are readily obtainable by simple synthetic preparations or are commercially available.
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 an organotin compound in combination with an alkali metal iodide to catalyze the isomerization process of our invention under isomerization conditions of temperature and pressure.
DETAILED DESCRIPTION OF THE INVENTION
The &ggr;,&dgr;-epoxyalkene and &ggr;,&dgr;-epoxycycloalkene reactants suitable for use in the process of our invention 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 (I):
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 (II):
wherein the R
1
substituents are defined above. Of the compounds which may be obtained in accordance with our invention, the compound of primary interest is 2,5-dihydrofuran.
The preferred alkali metal iodides for use in the present invention include lithium iodide, sodium iodide, and potassium iodide. Lithium iodide and potassium iodide are particularly preferred.
The alkali metal iodide is used in combination with an organotin compound to catalyze the isomerization process of our invention. The organotin compound may be selected from organotin (IV) compounds such as hydrocarbyltin iodides, dihydrocarbyltin iodides, trihydrocarbyltin iodides, and tetrahydrocarbyltin compounds. Examples of such organometallic compounds include compounds having the formula:
wherein each R
2
independently is selected from alkyl or substituted alkyl moieties having up to about 20 carbon atoms, cycloalkyl or substituted cycloalkyl having about 5 to 20 carbon atoms, carbocyclic aryl or substituted carbocyclic aryl having about 6 to 20 carbon atoms, or heteroaryl or substituted heteroaryl moieties having about 4 up to 20 carbon atoms; and n is 1, 2, 3, or 4.
Specific examples of the organometallic compounds include dibutyltin diiodide, tributyltin iodide, trioctyltin iodide, triphenyltin iodide, trimethyltin iodide, butyltin triiodide, tetrabutyltin, tetraoctyltin, triphenyltin iodide, tribenzyltin iodide, dimethyltin diiodide, diphenyltin diiodide, tricyclohexyltin iodide, and dicyclohexyltin diiodide.
The preferred organometallic compounds comprise tin (IV) iodides having the above general formula and a total of about 2 to 36 carbon atoms wherein each R
2
substituent independently is selected from alkyl of up to about 12 carbon atoms, benzyl, phenyl, or phenyl substituted with up to 3 substituents selected from lower alkyl, lower alkoxy, or halogen; and n is 2 or 3.
Some of the tetra-alkyl or -aryl substituted tin compounds may react with the alkali metal iodide co-catalyst under the conditions of isomerization to form in situ organotin iodide compounds. Such tetrahydrocarbyltin compounds include tetraphenyltin.
The amount of the organotin component of the novel catalyst compositions of this invention can vary substantially depending on the mode in which the isomerization process is operated, the particular organotin compound and alkali metal iodide present, etc.
The catalyst system is preferably employed in our process as an intimate mixture of one or more of the organotin compounds and one or more of the a
Liang Shaowo
Liu Yao-Ching
Blake Michael J.
Covington Raymond
Eastman Chemical Company
Gwinnell Harry J.
Kight John
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