Reaction kinetics and pathways for phytol in high-temperature water

We examined the behavior of phytol, an acyclic diterpene C20-alcohol and a model compound for algal biomass, in high-temperature water (HTW) at 513 K, 543 K, 573 K, and 623 K. Under these conditions, the major products include neophytadiene, isophytol, and phytone. The minor products include pristene, phytene, phytane, and dihydrophytol. Neophytadiene likely forms via dehydration of phytol, while isophytol can be obtained via an allylic rearrangement. We have quantified the molar yields of each product at the four temperatures, and the carbon recovery was greater than 90% for most cases. Phytol disappearance follows first order kinetics with an activation energy of 145 ± 20 kJ/mol and pre-exponential factor of 109.94±0.12 s−1. Delplot analysis discriminated between primary and non-primary products and led to a potential set of reaction pathways. A kinetics model based on the proposed pathways was consistent with the experimental data.

► Dehydration to form neophytadiene and allylic rearrangement to form isophytol are the main reactions of phytol in HTW.
► Phytol disappearance in HTW follows first order kinetics.
► Comprehensive reaction pathway obtained for phytol reaction in HTW.
► Kinetics model for proposed reaction network is consistent with experimental data.
► Phytol study in high-temperature water (HTW) has implications for hydrothermal liquefaction of algae.