Myrcene purification

Myrcene Manufacture. An important commercial source for mycene is its manufacture by pyrolysis of p-piaene at 550—600°C (87). The thermal isomerization produces a mixture of about 75—77 wt % myrcene, 9% limonene, a small amount of T -limonene [499-97-8] and some decomposition products and dimers. The cmde mixture is usually used without purification for the production of the important alcohols nerol and geraniol. Myrcene may be purified by distillation but every precaution must be taken to prevent polymerization. The use of inhibitors and distillation at reduced pressures and moderate temperatures is recommended. Storage or shipment of myrcene in any purity should also include the addition of a polymerization inhibitor. 

In a subsequent examination of the cyclases that formed ( 4-)- and ( — )-pinene, cyclase 1,96,000 MW, converted geranyl pyrophosphate to (-1-)-a-pinene (d-a-pimm) (14), but produced smaller amounts of (-b)- or if-camphene (15) and (+)- or /-limonene (11) as side products (Johnson and Croteau, 1987). Cyclase II, 55,000 MW, transformed geranyl pyrophosphate into ( —)-p-pinene (/- -pinene) (16) along with smaller amounts of /-a- or (— )-a-pinene, (-)- or /-camphene, ( —)- or /-limonene, and myrcene (17) as coproducts (Fig. 19.7) (Croteau, 1984 Johnson and Croteau, 1987). Extensive purification of each enzyme and differential inactivation studies ensured that each set of stereochemi-cally related products was synthesized by a single, distinct enzyme. 

Myrcene is not extracted commercially from natural sources. It can be prepared by dimerization of isoprene (1) [73-75], but the major industrial production route is by pyrolysis of P-pinene (31). This is carried out at 550-600°C (18) and gives a mixture containing 75-77 wt% myrcene together with limonene (11) ( 9%), i i-limonene (60) and other products of isomerization and dimerization. The crude material is usually used directly in further conversions. Its tendency to polymerize means that purification by distillation must be carried out carefully under reduced pressure, moderate temperatures, and preferably in the presence of a polymerization inhibitor. Inhibitors are also required if the material is to be stored or shipped. 

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