Dicyclopentadiene, formation

Less commonly used as third monomer is dicyclopentadiene [77-73-6] or DCPD, for which, due to its symmetrical shape, the tendency of the second double bond to take part in the polymeri2ation process is more pronounced than for ENB. This is one of the reasons for the formation of long-chain branches. The resulting product is poly(ethylene- (9-prop54ene- (9-DCPD) [25034-71-3]. 

As was mentioned, cycloaddition of unactivated hydrocarbons, namely, that of cyclopentadiene, has practical significance. 5-Vinyl-2-norbomene is produced by the cycloaddition of cyclopentadiene and 1,3-butadiene546,547 [Eq. (6.96)] under conditions where side reactions (polymerization, formation of tetrahydroindene) are minimal. The product is then isomerized to 5-ethylidene-2-norbomene, which is a widely used comonomer in the manufacture of an EPDM (ethylene-propylene-diene monomer) copolymer (see Section 13.2.6). The reaction of cyclopentadiene (or dicyclopentadiene, its precursor) with ethylene leads to norbomene548,549 [Eq. (6.97)] 550... 

The polymerization of norbornene, Eq. (19), is stopped by cooling the reaction mixture to room temperature. The active polymer 11 can be stored for long periods of time. Heating 11 to temperatures above 65 °C in the presence of monomer causes renewed chain propagation. The subsequent addition of different cyclic olefins, such as endo- and exo-dicyclopentadiene, benzonorbomadiene and 6-methylbenzonorbornadiene resulted in the formation of well-defined AB- and ABA-type block copolymers, Eq. (21) [38]. Triblock copolymers 13 with narrow molecular weight distributions (polydispersity = 1.14) were prepared. Thus, the living character enables the preparation of new uniform block copolymers of predictable composition, microstructure and molecular weight. 

Table II summarizes the initial results of a further study on the modification of sulfur by dicyclopentadiene at 140°C. The efficiency of dicyclopentadiene in inhibiting the formation of orthorhombic sulfur is...

We can confirm the reports of Sullivan et al. that the reaction between dicyclopentadiene and sulfur is exothermic. If the temperature rises above 150 °C, the extreme viscosity increase causes the mixture to become almost solid and the reaction difficult to control. Diehl (5) and Bordoloi and Pearce (6,7) have reported quantitative studies of these viscosity changes. They show that there are large viscosity increases as the amount of dicyclopentadiene added, reaction temperature, and reaction time are increased. Our results show that these increases in viscosity are caused by the formation of high-molecular-weight polysulfides. 

Reactions were also attempted in the presence of N,NyN, N -tetra-methylethylenediamine. Unlike the dicyclopentadiene examples these reactions gave copious formation of hydrogen sulfide. 

Of great industrial interest are the copolymers of ethene and propene with a molar ratio of 1/0.5, up to 1/2. These EP-polymers show elastic properties and, together with 2-5 wt% of dienes as third monomers, they are used as elastomers (EPDM). Since they have no double bonds in the backbone of the polymer, they are less sensitive to oxidation reactions. As dienes, ethylidenenorbomene, 1,4-hexadiene, and dicyclopentadiene are used. In most technical processes for the production of EP and EPDM rubber in the past, soluble or highly disposed vanadium components are used [69]. Similar elastomers can be obtained with metallocene/MAO catalysts by a much higher activity which are less colored [70-72]. The regiospecificity of the metallocene catalysts toward propene leads exclusively to the formation of head-to-tail enchainments. The ethylidenenor-bornene polymerizes via vinyl polymerization of the cyclic double bond and the tendency to branching is low. The molecular weight distribution of about 2 is narrow [73]. 

The formation of dicyclopentadiene is so rapid that it takes only a few hours at room temperature for cyclopentadiene to completely dimerize. How, then, can cyclopentadiene be used in a Diels-Alder reaction if it really exists as a dimer ... 

The skeletal isomerization of tetrabydrodicyclopentadiene into adamantane is an example of a very complex rearrangement diat is commercially carried out over strong Lewis acids with a hydride transfer initiator. The reaction can be catalyzed by rare earth (La, Ce, Y, Nd, Yb) exchanged faujasites (Scheme 1) in a Hj/HCl atmosphere at 25(yX3. Selectivities to adamantane of up to 50% have been reported, when a metal fimction, such as Pt, capable of catalyzing hydrogenation is added [54]. Initially acid catalyzed endo- to exo- isomerization of tetrahydro-dicyclopentadiene takes place and then a series of 1,2 alkyl shifts involving secondary and tertiary carbonium ions leads eventually to adamantane[55]. The possible mechanistic pathways of adamantane formation from tetrahydro-dicyclopentadiene are discussed in detail in ref [56]. 

Cyclopentadiene is obtained from the light oil from coal tar distillation but exists as the stable dimer, dicyclopentadiene, which is the Diels-Alder adduct from two molecules of the diene. Thus, generation of cyclopentadiene by pyrolysis of the dimer represents a reverse Diels-Alder reaction. See Figs. 1 and 2 for nmr and infrared spectra of dicyclopentadiene. In the Diels-Alder addition of cyclopentadiene and maleic anhydride the two molecules approach each other in the orientation shown in the drawing above, as this orientation provides maximal overlap of ir-bonds of the two reactants and favors formation of an initial ir-complex and then the final e do-product. Dicyclopentadiene also has the endo-configuration. 

More recently published ideas include the formation of solid derivatives of alkyl azides by treatment with acetylene dicarboxylic acid to form 1-alkyl-triazole-4,5-dicarboxylic acids. These frequently form hydrates with poor melting points and generally poor analytical properties. Alternatively, one can obtain bicyclic fused-ring triazolines by treatment with norbornadiene or dicyclopentadiene °. 

With this background of information, Alder and Stein were surprised to find that phenyl azide reacts exothermally at room temperature with dicyclopentadiene to form a monoadduct, m.p. 130-131°, in quantitative yield. Two formulas had been advanced for dicyclopentadiene. Kramer and Spilker, discoverers of cyclopen-tadiene, assigned to the dimer the symmetrical cyclobutane structure (1), resulting from dimerization analogous to the formation of the truxillic acids from cinnamic acid. Wieland suggested the unsyrametrical formula (2), resulting from 1,4-addition of one molecule to the double bond of another. Two lines of evidence favored the... 

Under the catalytic action of palladium(O) complexes, (2-siloxyallyl) acetates and the vinylogous [4-(trimethylsiloxy)penta-2,4-dienyl] acetate (Table 18), (2-oxo-3-silylpropyl) acetates (1-acetoxy-3-silylpropan-2-ones), ° and (2-oxoalkyl) carbonates react with the strained, but otherwise nonactivated double bonds in norbornene, norbornadiene, and dicyclopentadiene to form polycyclic cyclopropyl ketones, see also formation of 1, 2 °and 3. In contrast, the (2-siloxyallyl) acetates failed to react with simple alkenes such as dec-1-ene and cyclohexene. " With the substrates mentioned, the exo anti) diastereomers were obtained exclusively. 

A similar reaction pathway is discussed in other cases of palladium-mediated cyclopropane formation. Thus diastereoselective [2 + 1] cyclopropanation, instead of [3 + 2] cyclopentane formation, is observed if norbornene (3), norbornadiene (6), or dicyclopentadiene (9) is treated... 

Partially reduced vanadium oxide catalysts have been examined in the selective oxidation of pentane and pentene to phthalic and maleic anhydride. The anhydride selectivity has been shown to be a strong function of catalyst pre-reduction and reaction temperatures. Controlled-atmosphere, postreduction and post-reaction surface characterization experiments have shown the most selective catalyst surface to.be comprised of VgO,j, V.,09, and VOg species. In this phase of the research, dicyclopentadiene has been used as a probe molecule to elucidate the reaction network for the formation of phthalic and maleic anhydrides. 

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