Kinetics and mechanism of the thermal elimination of alkenes from secondary stanyl and triterpenyl esters: implications for sedimentary processes

The liquid phase thermal decompositions of a secondary stanyl ester and a secondary triterpenyl ester have been investigated in the temperature range from 275° to 320°C. First-order rate constants have been measured and the activation energies and frequency factors for the processes determined. The reactions of naturally occurring sedimentary esters were also investigated by heating an oil shale at 295°C in the presence of tetralin for various periods of time. Analysis of the reaction products showed that Δ2-sterenes and Δ3-sterenes were produced at a rate consistent with their formation from secondary stanyl esters by a concerted reaction mechanism. The extent of reaction of secondary triterpenyl esters in a sedimentary sequence from the Gippsland Basin, Australia, was also investigated. A correspondence was observed in the depth-calculated-for-reaction obtained using the laboratory-derived kinetic parameters and the measured depletion of triterpenyl esters in the soluble organic matter in samples from the sequence.