Gas Chromatographic Analysis of Branched Olefins

Two previous articles in this series were devoted to gas chromatographic analysis of monoalkyl-branched paraffins and polymethyl-branched paraffins. The present paper represents an extension of the principles used for the analysis of alkanes to the analysis of olefins (alpha and internal) with branched alkyl groups. The principal approach was synthesis of a series of olefins with known structures. These olefins were obtained by co-oligomerization of ethylene with higher alpha olefins (propylene, 1-butene, 1-hexene, 1-heptene, 1-octene, and 1-decene), as well as by thermocracking of branched alkanes (e.g., 2-methyltetradecane, 7-methylpentadecane, 9-methylhep-tadecane, 2,6-dimethylundecane), and by catalytic isomerization of the olefins obtained in thermocracking reactions. Analysis of experimental data on retention times of various branched olefins demonstrated validity of the additivity principle earlier developed for multibranched alkanes, for the estimation of retention times of olefins with branched alkyl groups. Applications of the additivity principle are demonstrated in the analysis of olefins formed in thermocracking of three multibranched alkanes: pristane, phytane, and squalane.