Cyclic diolefins

The study of the action of alkali metal catalysts has been largely confined to cyclic diolefins because of the hydrogen elimination reaction yielding aromatics that occurs with these compounds. 

The double-bond isomerization of cyclic materials possessing two double bonds takes place readily. When 1,4-cyclooctadiene is contacted with high-surface sodium on alumina at 0° for a short time, over 95% of the 1,3-cyclooctadiene results (IIS). However an even more interesting reaction takes place when the cyclic diolefin possesses a six-membered ring. An example is the reaction (D) of d-limonene which yields p-cymene and hydrogen (6). 

If the reaction (G) is not carried out to completion, some cyclic diolefins will remain. Those from limonene consist mainly of the exocylic diolefins 2,4(8)- and 3,8(9)-p-methadienes,... 

Pines and Kolobielski (18) have shown that phenylcyclohexene, although it is not a cyclic diolefin, will also undergo reactions similar to those that cyclic diolefins undergo when treated with base catalysts. When heated to 200-220 with a sodium-benzyl-sodium catalyst, it underwent a hydrogen transfer reaction resulting in the formation of biphenyl and of phenyl-cyclohexane molecular hydrogen was not produced. The mechanism of this reaction may be pictured as an elimination of sodium hydride from one molecule with the hydride ion being accepted by another molecule (A"-E"). 

The cyclic diolefin formed can then dehydrogenate as was discussed previously for this type of compound, and the hydrogen eliminated may be transferred to -methylstyrene, as was previously discussed for phenyl-cyclohexene, resulting in the formation of cumene. The diaryldiolefin shown in this mechanism was synthesized and successfully cyclized to p-terphenyl in the presence of sodium 55). 

Linear and cyclic diolefins form a variety of clusters with trirutheniumdodeca-carbonyl or the tetraruthenium carbonyl hydrides. These belong to the compound types H2Ru3(CO)9L [56] or HRu3(C0)gl/ [55]. Type [56] complexes are obtained from cyclopentadienes (27 7), cyclooctadienes (74), or bicyclooctadiene (146). 

We note at this point that it is possible for an olefin-ion to cyclize by reacting with its own double bond to form a cyclic, saturated carbenium ion. Such an ion can desorb as a cyclic monoolefm, or, after further eliminations, as a cyclic diolefin or aromatic. Since few cyclic olefins or linear or cyclic diolefins are observed in the products of cracking (10) it seems that unsaturated carbenium ions either continue to eliminate smaller molecules until they deactivate the site completely, or cyclize and eliminate small molecules until the residual fragment desorbs as an monocyclic aromatic or a more complex minor product This is probably the process by which all of the small amounts of aromatics, indenes etc. found in the cracking products of pure paraffms are formed. Notice that the desorption which results in the formation of an aromatic in this way "rejuvenates" a site and returns it to a pristine high activity condition. 

The stereochemistry of addition of nucleophiles to Pd(II) cyclic diolefin adducts was next studied, and in all cases it was found to be trans (Section IV, A). However, strained diolefins such as norbornadiene tend to add nucleophiles exo, whereas the metal involved is held in the endo position. Thus, mercury(II) does not form strong n bonds and hydroxymercuration of norbornene is cis-exo (7, 262). However, the trans addition to unstrained olefins could not be explained in this way. 

In case (3) it cannot be excluded that the intermediate olefin complex would be a chelate with both olefmic bonds of the 1,4-cyclohexadiene coordinated to the palladium, and the oxypalladation product is in fact expected to be trans orientated as rotation of the double bond is blocked as with analogous complexes of cyclic diolefins such as 1,5-cyclooctadiene, dicyclopentadiene, norbomadiene, etc. From these, stable fran -oxymetallation products can be obtained [39 1] others are listed in [12, Table IV]. 

Selective hydrogenation of cyclic diolefins to monoolefins taking advantage of substitution is also catalyzed by a Ni complex" ... 

Cyclic diolefins resins n. Polymerized products obtained from the cracked distillates of petroleum. They are unsaturated products, with excellent solubility, acid, alkali, and water resistance. A special application is in metallic paint media. 

As shown in eqs. (21.3) and (21.4), the reactions of platinum halides with diolefins afford diolefin platinum complexes. In these diolefin platinum complexes, the order of the stability of the four compounds is shown in Figure 21.1 [18]. The figure shows that the complexes of cyclic diolefins, such as cycloocta-1,5-diene and dicyclopentadiene, are more stable than those of linear unsaturated compounds. 

Cyclic diolefins with isolated double bonds give mixtures of mono- and dialdehydes (see table 15). The hydroformylation of these materials has been thoroughly investigated. Bis-(hydroxymethyl)-cycloaliphatics are very useful starting materials for polyester fibers and have been used for this purpose at the rate of several thousand tons per year [252]. 

Another type of epoxy oligomers are the cyclo-aliphatic ones, obtained by oxidation of cyclic diolefins with various peroxidic compounds (organic or inorganic hydroperoxides), hypochlorous acid, halogenhydrines and their derivatives, and oxygen or ozone. At present, the main industrial procedure for their production uses peracetic acid. In keeping with initial cycloolefin structure, diepoxides with different structures are produced, with the peculiarity that peroxidic oxygen is bound to the aliphatic cycle. 

FEAST [Further Exploitation of Advanced Shell Technology] Not a single process, but a range of processes for converting cyclic diolefins into alpha-omega dienes. The catalyst is based on rhenium on alumina. Operated in France since 1986. 

---