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Reactions among minerals and organic compounds in hydrothermal systems are critical components of the Earth's deep carbon cycle, 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 demonstrate mineral catalysis of the most fundamental component of an organic reaction: the breaking and making of a covalent bond. In the absence of mineral, hydrothermal reaction of cis-and trans-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. Isotope studies show that the sphalerite acts as a highly specific heterogeneous catalyst for activation of a single carbon−hydrogen bond in the dimethylcyclohexanes.hydrothermal organic geochemistry | organic catalysis O rganic compounds are practically ubiquitous in natural hydrothermal environments, in deep sedimentary systems, in subduction zones, at spreading centers, and at continental hot spots. They are critical constituents in the deep branch of Earth's global carbon cycle (1). Hydrothermal organic reactions affect petroleum formation, degradation, and composition (2, 3), provide energy and carbon sources for deep microbial communities (4, 5), and may be important in the origin of life (6, 7). The essential ingredients that control the chemical reactions of organic material in hydrothermal systems are the organic molecules, hot pressurized water, and associated mineral assemblages. To date, there have been many studies of organic reactions in water at high temperatures and pressures (8-10). Relatively few of these, however, have incorporated the inorganic mineral components present in natural systems (11)(12)(13)(14). Furthermore, studies of the ways in which individual minerals control organic reactions at the mechanistic level are virtually nonexistent. Geochemical organic reactions tend to generate complex product mixtures (15, 16), which can obscure the fundamental mechanistic understanding required to establish guiding principles on which to build predictive models of organic reactivity under relevant conditions. Here, we describe an efficient and highly specific catalytic effect of the sphalerite (ZnS) mineral surface on a fundamental process in organic chemistry: carbon-hydrogen bond breaking and making. Sphalerite is a common precipitate in sedimentary exhalative base metal deposits (i.e., black smokers), along with other common sulfides (CuFeS 2 , PbS, FeS 2 , FeS) (17, 18), and has been the focus of recent origins-of-life investigations (19,20).The idea of mineral-surface promoted organic reactions is not new (refs. 6 and 21−23, but see also reviews in refs. 7 and 12) and has been the subject of several recent studies related to the origin of life and to hydrothermal systems. For example, studies have demonstrated that (Ni, Fe) sulfides are necess...

Earth as Organic Chemist everett shock, christiana bockisch, charlene estrada, kristopher fecteau, ian r. gould, hilairy hartnett, kristin johnson, kirtland robinson, jessie shipp, and lynda williams Introduction: The Disconnect between Earth and the LabEarth is a powerful organic chemist, transforming vast quantities of carbon through complex processes leading to diverse suites of products that include the fossil fuels upon which modern societies depend. When exploring how Earth operates as an organic chemist, it is tempting to turn to how organic reactions are traditionally studied in chemistry labs. While highly informative, especially for insights gained into reaction mechanisms, doing so can also be a source of frustration, as many of the reactants and conditions employed in chemistry labs have few or no parallels to geologic processes. It is difficult, for example, to find natural conditions where laboratory reagents such as concentrated sulfuric acid are available, or where extreme oxidants such as chromate and permanganate or reductants such as lithium aluminum hydride are in abundance. Likewise, organic solvents other than the complex mixtures in petroleum and high-pressure natural gases are impossible to find. Instead, the most Earth-abundant fluid that could serve as a reaction medium is water, which is often excluded from organic chemistry procedures and labs. Nevertheless, Earth uses water at high temperatures and pressures as a reactant, catalyst, and solvent for organic transformations on a massive scale.A common approach to understanding traditional organic reactions is to analyze them in terms of the strengths of the bonds that are broken versus the bonds that are made. When weaker bonds in the reactants are transformed into stronger bonds in the products, the energy of the electrons decreases and the reaction is considered likely to proceed. This is a common approach because it usually works. Those reactions that form stronger bonds are the reactions that are observed to occur, and they are those that are included in traditional organic chemistry textbooks. This is a purely enthalpic view of chemical reactions; the role of entropy is not included. With the exception of some fragmentation reactions that form more product molecules than there were reactant molecules, enthalpic effects tend to dominate the majority of traditional organic chemistry at ambient laboratory conditions. Organic reactions under hydrothermal conditions occur at higher temperatures and pressures than ambient, by definition, and the entropic contribution to the reaction free energy is thus larger than at ambient, to the extent that reactions can start to be controlled by entropic rather than enthalpic effects. Several examples of this contrast in thermodynamic