Alcohol dehydration by elimination
of water is central to a series of functional group interconversions
that have been proposed as a reaction pathway that connects hydrocarbons
and carboxylic acids under geochemically relevant hydrothermal conditions
such as in sedimentary basins. Hydrothermal dehydration of alcohols
is an example of an organic reaction that is quite different from
the corresponding chemistry under ambient laboratory conditions. In
hydrothermal dehydration, water acts as the solvent and provides the
catalyst, and no additional reagents are required. This stands in
contrast to the same reaction at ambient conditions, where concentrated
strong acids are required. Hydrothermal dehydration is thus of potential
interest in the context of green chemistry. We investigated the mechanism
of hydrothermal alcohol dehydration for a series of secondary alcohols
using studies of kinetics and stereoelectronic effects to establish
reaction mechanisms. The E1 elimination mechanism dominates over the
corresponding E2 mechanism, with the E2 mechanism being competitive
with E1 only for the most favorable stereoelectronically restricted
alcohols included in the present study. These results are relevant
to understanding the kinetics and product distributions of alcohol
dehydration reactions in natural geologic systems and can guide the
development of organic chemical reactions that mimic geologic organic
reactions under laboratory green chemistry conditions.
Hydrothermal organic transformations under geochemically relevant conditions can result in complex product mixtures that form via multiple reaction pathways. The hydrothermal decomposition reactions of the model ketone dibenzyl ketone form a mixture of reduction, dehydration, fragmentation, and coupling products that suggest simultaneous and competitive radical and ionic reaction pathways. Here we show how Norrish Type I photocleavage of dibenzyl ketone can be used to independently generate the benzyl radicals previously proposed as the primary intermediates for the pure hydrothermal reaction. Under hydrothermal conditions, the benzyl radicals undergo hydrogen atom abstraction from dibenzyl ketone and para-coupling reactions that are not observed under ambient conditions. The photochemical method allows the primary radical coupling products to be identified, and because these products are generated rapidly, the method also allows the kinetics of the subsequent dehydration and Paal-Knorr cyclization reactions to be measured. In this way, the radical and ionic thermal and hydrothermal reaction pathways can be studied separately.
Reduction of carbon–carbon π-bonds has been demonstrated using iron powder as the reductant and simple powdered nickel as the catalyst in water as the solvent at 250 °C and the saturated water vapor pressure, 40 bars.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.