Title: A Fundamental Approach to Organic Reactions Involving Minerals

Speaker:Kristin Johnson

Abstract: 
Organic compounds and mineral surfaces interact in a variety of geologic locations including hydrothermal systems, sedimentary basins, and meteorite parent-bodies. Organic reaction pathways in the presence of minerals can differ dramatically from reactions without minerals [1]. I will be presenting the results of hydrothermal (300˚C, 1 kbar) experiments involving phenylacetic acid (C6H5CH2CO2H; PAA) with spinel (MgAl2O4) or magnetite (Fe3O4) as examples of a simplified experimental approach to complex organic systems. Spinel and magnetite both have the same crystal structure but differ in their central metal atoms. By holding the crystal structure constant, we can explore the other chemical differences between these minerals and how those differences influence organic reactions. New reaction pathways with minerals lead to the generation of larger organic compounds. Some reaction products are observed in both sets of experiments involving minerals while others are only observed in the presence of one mineral and not the other.

Phenylacetic acid (PAA) is an aromatic carboxylic acid which differs from compounds studied in previous mineral-organic investigations [2,3] by the addition of a phenyl ring. PAA was chosen as a model compound to allow for the investigation of mechanistic pathways for product formation and as an analog for naturally occurring carboxylic acids. In the absence of minerals, PAA reacts primarily through decarboxylation (C6H5CH2CO2H → C6H5CH3 + CO2) [4]. In the presence of minerals, a new reaction pathway yields the formation of a symmetrical ketone. In addition to ketone formation, magnetite-activated product pathways form a shorter chain carboxylic acid, an asymmetrical ketone, diphenyl alkanes and an alkene. These results demonstrate that mineral surfaces can facilitate carbon-carbon bonds and the formation of larger organic structures. By discussing the results of experiments involving phenylacetic acid with spinel-type minerals, I hope to demonstrate that exploring fundamental chemistry questions with simplified experimental systems can inform our understanding of complicated pre-biotic chemical systems.