1.4- Hexadiene manufacture

The major use of this compound is in the production of mordant and acid dyes. 2-Amino-4-nitropheno1 also has found limited use as an antioxidant and light stabilizer in butyl mbbers and as a catalyst in the manufacture of hexadiene. The compound has been shown to be a skin irritant and continuous exposure should be avoided. Toxicological studies indicate that it is nonaccumulative (162). 

One of the butadiene dimeri2ation products, COD, is commercially manufactured and used as an intermediate in a process called FEAST to produce linear a,C0-dienes (153). COD or cyclooctene [931-87-3], obtained from partial hydrogenation, is metathesi2ed with ethylene to produce 1,5-hexadiene [592-42-7] or 1,9-decadiene [1647-16-1], respectively. Many variations to make other diolefins have been demonstrated. Huls AG also metathesi2ed cyclooctene with itself to produce an elastomer useful in mbber blending (154). The cycHc cis,trans,trans-tn.en.e described above can be hydrogenated and oxidi2ed to manufacture dodecanedioic acid [693-23-2]. The product was used in the past for the production of the specialty nylon-6,12, Qiana (155,156). 

Codimerization of ethylene and 1,3-butadiene is also of commercial significance since the product 1,4-hexadiene is used as a comonomer in the manufacture of ethylene-propylene-diene elastomers. Rhodium and nickel catalysts are used since they are the most active and selective, bringing about the formation of the required... 

With larger amount of propylene a random copolymer known as ethylene-propylene-monomer (EPM) copolymer is formed, which is a useful elastomer with easy processability and improved optical properties.208,449 Copolymerization of ethylene and propylene with a nonconjugated diene [EPDM or ethylene-propylene-diene-monomer copolymer] introduces unsaturation into the polymer structure, allowing the further improvement of physical properties by crosslinking (sulfur vulcanization) 443,450 Only three dienes are employed commercially in EPDM manufacture dicyclopentadiene, 1,4-hexadiene, and the most extensively used 5-ethylidene-2-norbomene. 

Butadiene could also be trimerized to give cyclododecatriene. The trimer is again used by Hulls to manufacture nylon 12 and Vestamid . The codimerization of butadiene and ethylene is used by DuPont to manufacture 1,4-hexadiene, one of the monomers of EPDM (ethylene, propylene, diene, monomers) rubber. The role of the diene monomer in EPDM rubber is to provide with two double bonds of different reactivities. The more reactive, terminal double bond takes part in the polymerization with ethylene and propylene. The less reactive internal one is used later on for cross-linking. These important catalytic reactions are shown in Fig. 7.6. 

Hexadiene in its E form is manufactured from butadiene and ethylene (Equation 20). The Z isomer must be kept to a minimum owing to its adverse effect on polymerization. The reaction, first reported in 1961, was commercialized by DuPont. The present world production is estimated around 2.5-3 kt/a. Various metal salts (Ni, Co, Fe) were tested, but the best results were obtained with RhCls.hydrate. 

Ethenolysis of cycloalkenes is a convenient route for production of certain polyunsaturated compounds. Shell have developed a process for the manufacture of a,w-diolefins via ethenolysis of cyclic olefins (the reverse of Eq. 4) [21,22]. Thus, 1,5-hexadiene and 1,9-decadiene were produced via ethenolysis of cyclo-octadiene and cyclooctene, respectively (Eqs. 7a,b). 

It is still unclear how the initiation step in alkene metathesis occurs and how the initial carbene forms. Commercial applications of metathesis include the triolefin process, in which propylene is converted to ethylene and butene, the neohexene process, in which the dimer of isobutylene, Me3CCH=CMe2, is metathesized with ethylene to give Me3CCH=CH2, an intermediate in the manufacture of synthetic musk, and a 1,5-hexadiene synthesis from 1,5-cy-clooctadiene and ethylene. Two other applications, SHOP and ROMP (Shell higher olefins process and ring-opening metathesis polymerization), are discussed in the next section. 

Formerly, one manufacturer of EPDM used a noncyclic diene 1,4-hexadiene [592-45-0], but this was displaced by ENB because of the latter s superior performance both in incorporation during polymerization and in vulcanization. EPDM containing hexadiene is not commercially available anymore. 

Selective codimerization of ethene and 1, 3-butadiene is also possible because the diene first forms an f/ -allyl complex with the metal centre (Fig. 12.4). An industrial process along these lines has been developed in the USA by Du Pont. A rhodium catalyst is employed rhodium trichloride in ethanol itself gives 80% selectivity towards the desired product, irflns-1,4-hexadiene, which is used in the manufacture of an ethene-propene-hexadiene synthetic rubber. The diene introduces some double bonds into the polymer chains which are required for vulcanization. 

Multi-ton quantities of 1,5-hexadiene have been manufactured in alkene metathesis semi-works units and the process has been studied in a small specialty olefin pilot plant by the Phillips Company. Feedstocks for this process are the commerically available butadiene derivatives (1,5-cyclooc-tadiene and 1,5,9-cyclododecatriene). The use of excess ethylene and a... 

FIG. 7 Schematic diagram of the process for manufacturing 1,5-hexadiene (a) dimerization (b) disproportionation (c) separation (d) catalyst recovery. (From Ref. 22.)... 

EPDM is also manufactured with dicyclopentadiene as the third monomer. In the past, 1,4-hexadiene was used as the third monomer as well, see Eigures 3.13 and 3.14. 

Figure 3.13 EPDM manufactured with 1,4 hexadiene as third monomer...

The codimerization of butadiene and ethylene is used to manufacture 1,4-hexadiene, one of the monomers of ethylene, propylene, diene (EPDM) rubber (see Section 6.7). As mentioned earlier, the role of the diene monomer in EPDM rubber is to provide two double bonds of... 

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