Retro-Diels-Alder Reaction in Aqueous Solution: Toward a Better Understanding of Organic Reactivity in Water.
The retro-Diels-Alder (RDA) reaction of anthracenedione 1a proceeds considerably faster in aqueous solutions than in organic solvents. Addition of organic solvents to water retards the reaction, whereas glucose induces a modest acceleration. SDS micelles induce a considerable retardation, but even at high concentrations of surfactant (complete micelle-substrate binding), the cycloreversion is not fully inhibited. Correlation with data for solvatochromic indicators strongly suggest that the origin of the water-induced acceleration involves primarily enhanced hydrogen bonding of water to the activated complex for the RDA reaction of 1a. Activation parameters support this view. A comparison of the present results with previous kinetic data for bimolecular and intramolecular Diels-Alder reactions provides insights into the contributions of hydrogen-bond and hydrophobic interactions to the aqueous accelerations of the latter two types of reactions.
Wijnen
Jan W.
JW
Department of Organic and Molecular Inorganic Chemistry, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands.
Engberts
Jan B. F. N.
JB