Reactions among minerals and organic compounds in hydrothermal systems are critical components of the Earth’s deep carbon cycle; they provide energy for the deep biosphere, and may have implications for the origins of life. However, there is limited information as to how specific minerals influence the reactivity of organic compounds. Here we present a range of effects that naturally occurring Earth-abundant minerals can have on hydrothermal organic reactions. Some minerals act as reagents, creating different products suites. Some minerals act as catalysts, not contributing atoms to the reaction, but dramatically increasing reaction rates. Some minerals, notably sphalerite (ZnS), are both selective and catalytic. In particular we focus on mineral catalysis of the most fundamental component of an organic reaction: the breaking and making of a covalent bond. In the absence of any mineral, the hydrothermal reaction of <i>cis</i>- and <i>trans</i>-1,2-dimethylcyclohexane is extremely slow and generates many products. In the presence of sphalerite (ZnS), however, the reaction rate increases dramatically and one major product is formed: the corresponding stereoisomer. The reaction proceeds rapidly toward a metastable equilibrium. Isotope studies show that the sphalerite acts as a highly specific heterogeneous catalyst for activation of a single carbon−hydrogen bond in the dimethylcyclohexanes. Results from these experimental studies provide new insight into the roles minerals play in subsurface organic reactions. Furthermore, they suggest that appropriately optimized minerals may represent a new approach to the development of heterogeneous catalysts for a wide range of organic transformations.

Minerals can be catalysts for organic reactions in hydrothermal environments

249th National Meeting (2015)

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