Abiotic degradation of intact and photooxidized chlorophyll phytyl chain under simulated geological conditions

3,7,11,15-Tetramethyl-2-hexadecen-1-yl propionate (a model for the intact phytyl side chain of chlorophyll), 3-hydroxy-3,7,11,15-tetramethyl-1-hexadecen-1-yl propionate and 2-hydroxy-3-methylidene-7,11,15-trimethylhexadecyl propionate (models for a photo-oxidized chlorophyll phytyl chain) were heated in the presence of montmorillonite in order to simulate their abiotic degradation under geological conditions. Thermo-catalytic breakdown of phytyl propionate yielded most of the degradation products previously generated from phytol by heating in the presence of clays. Some interesting mechanisms involving protonation of the phytol double bond are proposed to explain the formation of phytanal and prist-1-ene observed during these manipulations. The abiotic degradation of 3-hydroxy-3,7,11,15-tetramethyl-1-hexadecen-1-yl propionate led to the production of 6,10,14-trimethylpentadecan-2-one, phytenals and phytenic acids as major products, whereas 2-hydroxy-3-methylidene-7,11,15-trimethylhexadecyl propionate afforded 6,10,14-trimethylpentadecan-2-one, 3,7,11,15-tetramethyl-2-oxohexadecanol-1 and 3,7,11,15-tetramethylhexadecan-1,2,3-triol. A kinetic study allowed comparison of the abiotic stability of intact and photooxidized chlorophyll phytyl chains in sediments and suggested potential markers for monitoring chlorophyll photodegradation.