Cyclopentadiene from dicyclopentadiene

Nearly all synthetic methods for cyclopentadienyl metal compounds require first the preparation of cyclopentadiene from dicyclopentadiene. This is accomplished by thermal depolymerization of dicyclopentadiene at temperatures above 180° C. Because cyclopentadiene is unstable at room temperature it must be stored at low temperatures to prevent dimerization to dicyclopentadiene. The rate of dimerization is about 0.05% per hour at — 20° C and 1% per hour at 10° C (5). 

In each problem, the synthesis must begin with the preparation of cyclopentadiene from dicyclopentadiene. 

As recently as 1986 almost all addition polymers were excluded from the ranks of engineering plastics. However, progress since then has been made in the development of addition polymeric resins such as polymethylpentene and polycyclopentadiene and its copolymers (see CYCLOPENTADIENE AND dicyclopentadiene). 

Dicyclopentadiene is a feedstock for both the fragrance and polymer industries. It forms spontaneously from cyclopentadiene by a Diels-Alder reaction, and a retro-Diels-Alder reaction can be used to regenerate cyclopentadiene from it. A number of minor fragrance ingredients are produced by Diels-Alder reaction of the monomer with a variety of activated olefins in which the activating group X, is usually an aldehyde, ketone, ester or nitrile. However, the main fragrance uses stem from the dimer. 

To a mixture of 880 mg (2.35 mmol) of methyl L-araWno-4,5,6,7-tetraaceloxyhept-2-enoate (8) and 9 mL of toluene, are added 6 mg (0.045 mmol) of hydroquinone and 0.45 mL. (5.46 mmol) of cyclopentadiene (2) (freshly distilled from dicyclopentadiene). The mixture is refluxed under an atmosphere of argon. An additional... 

A series of low-molecular-weight resins from natural products or industrial side products is known as cumarone-indene-like resins, since these resins have similar physical properties to the actual cumarone-indene resins. For example, cyclopentadiene from the petroleum process dimerizes easily to what is known as dicyclopentadiene (lUPAC 4,7-methylene-4,7,8,9-tetrahydroindene). Dicyclopentadiene cationically polymerizes to polymers with different monomeric units. The commercially available polymers soften at 100-120°C and become insoluble as surface films on further heating. 

When cyclopentadiene is allowed to stand at room temperature, it is completely converted into the dimer in just a few hours. For this reason, cyclopentadiene cannot be stored at room temperature for long periods of time. When cyclopentadiene is to be used as a starting material in a Diels-Alder reaction, it must first be formed from dicyclopentadiene via a retro Diels-Alder reaction and then used immediately or stored at very low temperature. 

Aliphatic C-5—C-6. Aliphatic feedstreams are typically composed of C-5 and C-6 paraffins, olefins, and diolefins, the main reactive components being piperylenes cis-[1574-41 -0] and /n j -l,3-pentadiene [2004-70-8f). Other main compounds iaclude substituted C-5 and C-6 olefins such as cyclopentene [142-29-OJ, 2-methyl-2-butene [513-35-9] and 2-methyl-2-pentene [625-27-4J. Isoprene and cyclopentadiene maybe present ia small to moderate quaatities (2—10%). Most steam cracking operatioas are desigaed to remove and purify isoprene from the C-5—C-6 fraction for applications ia mbbers and thermoplastic elastomers. Cyclopentadiene is typically dimerized to dicyclopentadiene (DCPD) and removed from C-5 olefin—diolefin feedstreams duriag fractionation (19). 

Gyclopentadiene/Dicyclopentadiene-Based Petroleum Resins. 1,3-Cyclopentadiene (CPD) is just one of the numerous compounds produced by the steam cracking of petroleum distillates. Due to the fact that DCPD is polymerized relatively easily under thermal conditions without added catalyst, resins produced from cycloaHphatic dienes have become a significant focus of the hydrocarbon resin industry. 

Sulfur Polymer Cement. SPC has been proven effective in reducing leach rates of reactive heavy metals to the extent that some wastes can be managed solely as low level waste (LLW). When SPC is combined with mercury and lead oxides (both toxic metals), it interacts chemically to form mercury sulfide, HgS, and lead sulfide, PbS, both of which are insoluble in water. A dried sulfur residue from petroleum refining that contained 600-ppm vanadium (a carcinogen) was chemically modified using dicyclopentadiene and oligomer of cyclopentadiene and used to make SC (58). This material was examined by the California Department of Health Services (Cal EPA) and the leachable level of vanadium had been reduced to 8.3 ppm, well below the soluble threshold limit concentration of 24 ppm (59). 

Cyclopentadiene was prepared by cracking dicyclopentadiene of 95% purity purchased from Aldrich Chemical Company, Inc. 

Cyclopentadiene, b.p. 40°, is obtained by heating commercial 85% dicyclopentadiene (e.g., from Matheson, Coleman and Bell Company, Norwood, Ohio) under a short column (M in. diameter X 8-12 in. length) filled with glass helices. The distilled cyclopentadiene is collected in a receiver which is maintained at Dry Ice temperature until the cyclopentadiene is used. Methylcyclopentadiene and other substituted cyclopentadienes such as indene may also be employed for the synthesis of the correspondingly substituted ferrocenes. In these cases, the reaction of the hydrocarbon with sodium is much slower than with cyclopentadiene, and refluxing for several hours is required to complete the reaction. 

The recovery of cyclopentadiene is based on the rapid dimerization rate of this compound to dicyclopentadiene, and the ease of separating heavy dimer from the feedstock. 

Cyclopentadiene was prepared2 by heating dicyclopentadiene (purchased from Eastman Organic Chemicals) and a pinch of hydro-quinone (1,4-benzenediol) under a column of glass helices or a Vigreux column at 175° and collecting the distillate in a receiver cooled with a 2-propanol-dry ice bath. The monomer was dried over Linde 4A Molecular Sieves at —20° and could be stored at this temperature for several weeks without excessive dimerization. 

Cyclopentadiene was obtained by pyrolysis of dicyclopentadiene (pract., 90%) which was purchased from Fluka. Pyrolysis was carried out following the previously described general procedure.2, Dicyclopentadiene (80 mL) was placed in a round-bottomed flask equipped with a magnetic stirbar and a Vigreux column fitted with a distillation head through which cold water was circulated. The contents of the flask were slowly heated with stirring at 160°C in an oil bath, and ca. 60 mL of cyclopentadiene (bp 38-42°C) was collected in a receiver cooled in an ice-salt bath. The cyclopentadiene was used... 

Several different companies have greened various steps of the process. In VNB production by-products come from competing Diels-Alder reactions and polymerization, largely of cyclopentadiene. The reaction is usually carried out in a continuous tube reactor, but this results in fouling, due to polymerization, at the front end, where the dicyclopentadiene is cracked to cyclopentadiene at temperatures over 175 °C. Whilst fouling does not have a very significant effect on yield, over time it builds up. 

The 1 2 adducts in these examples were accounted for by dimerization of cyclopentadiene and subsequent hydrosilation of dicyclopentadiene. The 3-trichlorosilyl isomer is that expected from 1,4 addition of trichlorosilane. Unless isomerization occurred, the 4-isomer could arise only by 1,2 addition... 

As a last example we mention polydicyclopentadiene (DCPD). Dicyclopentadiene is the Diels-Alder adduct of cyclopentadiene, an abundant product from the cracker in the refinery. It contains a strained norbomene ring and a less strained cyclopentene ring. ROMP leads to opening of the norbomene ring, but some reaction of the cyclopentene ring also takes place, which leads to cross-linking (Figure 16.26). 

A. Cyclopentadiene. Two hundred milliliters (195 g.) of technical dicyclopentadiene (Note 1) is placed in a 500-ml. twonecked round-bottomed flask equipped with thermometer and an upright Friedrichs-type condenser (through which water at 50° (Note 2) is circulated). The ground-glass (Note 3) outlet of the Friedrichs condenser is connected to the side arm of a simple distilling head fitted with a thermometer and attached to an efficient water-cooled condenser held in a vertical position. At the lower end of this condenser is a receiver which consists of a carefully weighed 500-ml. two-necked round-bottomed flask immersed in a Dry Ice bath (Note 4) and protected from the air by a calcium chloride drying tube. 

The flask containing dicyclopentadiene is now heated by means of an electric heating mantle or oil bath to approximately 160°, or until cyclopentadiene distils smoothly at 38-46° and a little dicyclopentadiene refluxes from the cold-finger (Friedrichs) condenser. After two-thirds of the dicyclopentadiene has been pyrolyzed (during the course of 4 5 hours), the residue in the Mask may lend to become viscous and a higher temperature for... 

The metathesis polymerisation of dicyclopentadiene, an inexpensive monomer (commercially available cyclopentadiene dimer produced by a Diels-Alder addition reaction containing ca 95 % endo and ca 5 % exo form), leads to a polymer that may be transformed into a technically useful elastomer [144-146, 179] and thermosetting resin [180,181]. The polymerisation has characteristics that make it readily adaptable to the reaction injection moulding ( rim ) process [182], The main feature of this process comes from the fact that the polymerisation is carried out directly in the mould of the desired final product. The active metathesis catalyst is formed when two separate reactants, a precatalyst (tungsten-based) component and an activator (aluminium-based) component, are combined. Monomer streams containing one respective component are mixed directly just before entering the mould, and the polymerisation into a partly crosslinked material takes place directly in this mould (Figure 6.5) [147,168,183-186],... 

---