Synthesis of myrcene by pyrolysis of β-pinene: Analysis of decomposition reactions

Turpentine, an important source of terpenes, is composed mainly of α- and β-pinene. It is possible to pyrolyze β-pinene to form myrcene, which is used as an intermediate for the production of various terpenic alcohols and chemical aromas, as well as vitamins A and E. In the current work we develop a theoretical equilibrium model of the main synthesis reactions that have been described in the literature plus postulated decomposition reactions. The model predicts that 93.5% yields of myrcene from β-pinene would be possible whereas the highest reported yield is 85%. In order to investigate the less than theoretical yields, we investigated the decomposition of myrcene experimentally. The various degradation products that appeared were consistent with a degradation mechanism involving breakage next to conjugated double bonds, producing an alkyl radical. Decomposition of myrcene by this route would form 1,3-butadiene (C4H6) and 4-methyl-1,3-pentadiene (C6H10), which then further decompose into various other products. These results contribute to a better understanding of the production of myrcene by pyrolysis of β-pinene and could form the basis for optimization of product yields.