posted on 2021-09-17, 21:08authored byKristin N. Johnson-Finn, Lynda B. Williams, Ian R. Gould, Hilairy E. Hartnett, Everett L. Shock
Hydrothermal experiments were undertaken
to explore the reaction
pathways of phenyl-containing carboxylic acids in the presence of
iron oxide minerals. At 300 °C and 1 kbar (100 MPa), in addition
to the previously reported decarboxylation and ketonic decarboxylation
pathways, phenylacetic acid undergoes oxidation to form benzoic acid,
which eventually forms 2-phenylacetophenone via ketonic decarboxylation
with phenylacetic acid. The production of benzoic acid in the presence
of magnetite (Fe3O4) or hematite (Fe2O3) parallels the production of benzoic acid in the presence
of Cu(II) salt solutions observed in previous hydrothermal studies,
which was attributed to a sequence of one-electron-transfer processes.
We propose a similar one-electron oxidation reaction pathway in the
presence of minerals. Complexity builds as the reaction options increase.
Hydrothermal experiments with hydrocinnamic acid were performed to
demonstrate the generality of the reaction pathways for carboxylic
acids, although the rate of consumption of hydrocinnamic acid was
slower than that of phenylacetic acid and yielded a complex variety
of detected products. Hydrocarbons are produced at the longest observed
time points of a reaction through either decomposition or C–C
bond formation to larger compounds. These results indicate that minerals
can enhance the complexity of organic product pathways for carboxylic
acids and resulting products during hydrothermal transformations and
may enable the production of hydrocarbons from organic acids and other
precursors.