TY - JOUR
T1 - The central role of ketones in reversible and irreversible hydrothermal organic functional group transformations
AU - Yang, Ziming
AU - Gould, Ian
AU - Williams, Lynda
AU - Hartnett, Hilairy
AU - Shock, Everett
N1 - Funding Information:
The work is supported by National Science Foundation Grant OCE 0826588. We thank all the members of the hydrothermal organic geochemistry (HOG) group at ASU for many stimulating discussions and helpful suggestions. We thank support from Gordon Moore and the Omni-pressure lab facilities, and Natasha Zolotova for assistance with GC–MS in the HR–MS Laboratory at ASU. We also appreciate the comments and suggestions from three anonymous reviewers, and the recommendation from Associate Editor Dimitri Sverjensky.
PY - 2012/12/1
Y1 - 2012/12/1
N2 - Studies of hydrothermal reactions involving organic compounds suggest complex, possibly reversible, reaction pathways that link functional groups from reduced alkanes all the way to oxidized carboxylic acids. Ketones represent a critical functional group because they occupy a central position in the reaction pathway, at the point where CC bond cleavage is required for the formation of the more oxidized carboxylic acids. The mechanisms for the critical bond cleavage reactions in ketones, and how they compete with other reactions are the focus of this experimental study. We studied a model ketone, dibenzylketone (DBK), in H2O at 300°C and 70MPa for up to 528h. Product analysis was performed as a function of time at low DBK conversions to reveal the primary reaction pathways. Reversible interconversion between ketone, alcohol, alkene and alkane functional groups is observed in addition to formation of radical coupling products derived from irreversible CC and CH homolytic bond cleavage. The product distributions are time-dependent but the bond cleavage products dominate. The major products that accumulate at longer reaction times are toluene and larger, dehydrogenated structures that are initially formed by radical coupling. The hydrogen atoms generated by dehydrogenation of the coupling products are predominantly consumed in the formation of toluene. Even though bond cleavage products dominate, no carboxylic acids were observed on the timescale of the reactions under the chosen experimental conditions.
AB - Studies of hydrothermal reactions involving organic compounds suggest complex, possibly reversible, reaction pathways that link functional groups from reduced alkanes all the way to oxidized carboxylic acids. Ketones represent a critical functional group because they occupy a central position in the reaction pathway, at the point where CC bond cleavage is required for the formation of the more oxidized carboxylic acids. The mechanisms for the critical bond cleavage reactions in ketones, and how they compete with other reactions are the focus of this experimental study. We studied a model ketone, dibenzylketone (DBK), in H2O at 300°C and 70MPa for up to 528h. Product analysis was performed as a function of time at low DBK conversions to reveal the primary reaction pathways. Reversible interconversion between ketone, alcohol, alkene and alkane functional groups is observed in addition to formation of radical coupling products derived from irreversible CC and CH homolytic bond cleavage. The product distributions are time-dependent but the bond cleavage products dominate. The major products that accumulate at longer reaction times are toluene and larger, dehydrogenated structures that are initially formed by radical coupling. The hydrogen atoms generated by dehydrogenation of the coupling products are predominantly consumed in the formation of toluene. Even though bond cleavage products dominate, no carboxylic acids were observed on the timescale of the reactions under the chosen experimental conditions.
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U2 - 10.1016/j.gca.2012.08.031
DO - 10.1016/j.gca.2012.08.031
M3 - Article
AN - SCOPUS:84867432565
SN - 0016-7037
VL - 98
SP - 48
EP - 65
JO - Geochimica et Cosmochimica Acta
JF - Geochimica et Cosmochimica Acta
ER -