Neohexene, manufacture

Further important industrial applications of olefin metathesis include the synthesis of 3,3-dimethyl-l-butene ( neohexene , intermediate for the production of musk perfume) from ethene and 2,4,4-trimethyl-2-pentene, the manufacture of a,co-dienes from ethene and cycloalkenes (reversed RCM), and the ROMP of cyclooctene and norbomene to Vestenamer and Norsorex , respectively. 

Neohexene can be a very important intermediate in the manufacture of a synthetic musk. Hence the market for neohexene grew rapidly. Phillips started the industrial development in 1969 with a small pilot plant producing 20kg of neohexene per year and which worked during three years and produced 3 tons of neohexene which were sold. As the demand increased, a larger unit, with four times the capacity of the smaller pilot, was then constructed. As the demand for neohexene continued to increase ( from 90 tons in 1973 to 270 tons in 1979), a commercial unit was constructed in 1980. It is located at the Phillips petrochemical complex near Houston (Texas, U.S.A.) and has a capacity of 1400 tons per year. 

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. 

Hie neohexene process starts with the acid-catalyzed dimerization of isobutene, followed by metathesis with ediylene, to give neohexene, an intermediate in the manufacture of synthetic musk, and regenerate isobutene. 

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