Reactions of methylene and ether bridges

Abstract

The reactions of model compounds containing methylene and ether bridges were examined, in the temperature range 350–400 °C. Aromatic displacement reactions, in which atomic hydrogen displaced the bridges, and homolysis via a keto-enol intermediate were the dominant modes of bridge decomposition. The aromatic displacement reactions of methylene-bridge compounds occurred with activation energies of ≈10 kcal mol −1 and with A factors of 10 10.5–12 Is −1 m −1. The A factors vary with the size of the rings and the substituents on the rings connected by the methylene bridges. The activation energy is relatively independent of these effects. When phenolic substituents are present, methylene bridges can unimolecularly decompose via a keto-enol tautomerism, and the rate of product formation is solvent-dependent. Reactions for ether bridge decomposition were more complex and the rate parameters encompassed a much larger range of values.