This invention relates to the catalytic isomerization of isolated double bonds to conjugated double bonds in optionally substituted octadienes.
The individual, isomeric forms of unconjugated cyclooctadienes such as, for example, cis,cis-1,4- and cis,cis-1,5-cyclooctadiene, are valuable starting materials for various syntheses. In some cases however, for example, for polymerizations or epoxidations, it is desirable to have the double bonds present in the conjugated form. Furthermore, optionally substituted cyclooctadienes with conjugated double bonds have the advantage that they can be hydrogenated to the corresponding monoenes in a single-step reaction without any appreciable formation of saturated by-products.
All methods heretofore known for the isomerization of isolated to conjugated double bonds in optionally substituted cyclooctadienes, however, are more or less hampered by deficiencies. Thus, in the process according to U.S. Pat. No. 3,398,205 wherein iron pentacarbonyl is primarily used as the catalyst, problems are encountered in the clean separation of the isomerized product on account of the volatility of the catalyst. In the method disclosed in U.S. Pat. No. 3,767,716, wherein the catalyst is alkali metal hydroxide applied together with an alkali metal or aluminum oxide, there is a different drawback. Here, the catalysts are difficult to handle technically since they are very sensitive to air and entail a certain risk. Finally, in the process of U.S. Pat. No. 3,124,621 wherein isomerization is conducted using alkali or alkaline earth metal amides in the presence of ammonia or amines as the solvent, relatively high catalyst concentrations must be employed to attain an industrially interesting degree of isomerization. An additional disadvantage in this process is the necessity of using relatively large quantities of a solvent.
Although the process according to U.S. Pat. No. 4,434,310 has managed to overcome disadvantages of the above-described methods, the isomerization catalyst employed in said process suffers an appreciable loss of activity upon repeated usage.