[MIS17-12] Following the fundamentals of serpentinization: an experimental approach to mineral and organic reaction pathways at serpentinizing conditions
Keywords:hydrothermal, astrobiology, electrochemistry, catalysis, experiments, organic chemistry
By performing simplified experiments using both hydrothermal and electrochemical methods, I can determine the role of minerals in abiotic organic reactions. The experimental mixtures contain only one organic compound as the starting material and one pure mineral phase so that detailed kinetic studies can be investigated. By focusing on a singular functional group, the exact reactions can be pursued as a component of the overall reaction web for many different functional groups. My focus is the reaction pathways of carboxylic acids. Carboxylic acids are prevalent in Earth-based metabolism and abundant in abiotic samples such as the Murchison meteorite . Previous work has demonstrated that at hydrothermal conditions, phenylacetic acid (C6H5CH2COOH; PAA) in the presence of magnetite (Fe3O4) or hematite (Fe2O3) results in the formation of several different organic product pathways at hydrothermal conditions (300°C, 100 MPa) . Dibenzyl ketone ((C6H5CH2)2CO; DBK) and benzoic acid (C6H5COOH; BA) were both observed products in these experiments. It was proposed that the reaction path to form BA from PAA was a stepwise oxidation through the reaction intermediates of benzyl alcohol (C6H5CH2OH) and benzaldehyde (C6H5CHO) by the loss of electrons to redox active metal cations in solution or at the surface of a mineral [2,3]. Magnetite, a promininate mineral product of serpentinizing reactions with iron-containing starting minerals, may serve as an electron conductor during hydrothermal reactions. The exact mechanism is unknown and the extent to which magnetite and hematite differ as potential electron acceptors during organic reactions is unclear.
I performed experiments with propanol (CH3(CH2)2OH) and propionaldehyde (CH3CH2CHO) as analogs to the benzyl alcohol and benzaldehyde intermediates hypothesized in hydrothermal experiments. Propanol and propionaldehyde, unlike aromatic compounds, are soluble in room temperature water and have been used previously in experiments to investigate the formation of acetic acid in oil field brines . I will discuss the results of preliminary experiments to probe the use of magnetite as a catalyst for the electrochemical oxidization of propanol to propanoic acid (C3H5COOH) at the basic pH conditions of serpentinization. I am conducting complimentary hydrothermal experiments starting with butanoic acid (CH3(CH2)2COOH) to see if propanoic acid will still form in hydrothermal conditions. In this way, electrochemistry can be used as a tool to understand the mechanisms of hydrothermal reactions and the role that minerals can play as electron acceptors for carboxylic acid reaction pathways.
 Martins Z. (2011) Elements  Johnson KN (2017) PhD Dissertation, Arizona State University  Yang Z (2015) J. Org. Chem  McCollom TM and Seewald JS (2003) GCA