Facile Aryl Ether Hydrolysis: Kinetics and Mechanism of 9-Anthryl Ether Cleavage in Aqueous Solution

Article abstract of DOI:10.1021/jo00377a008

The hydrolysis rates of anthryl ether, 4-(9-anthroxy)butylamine (1), have been determined in aqueous solution from pH 1 to 12 and 25 to 80 deg C, wherein it was found that this ether reacted significantly faster than other aryl ethers.The observed rate constants varied with pH according to eq 1 and values for k_H+, k_O, k_N, and K_a (1) have been evaluated.At low pH, hydrolysis of 1 is characterized by general acid catalysis with carboxylic acid buffers (α = 0.61 +/- 0.06) and a solvent isotope effect of 1.85 +/- 0.09 at 25 deg C.Further, the product deut erium isotope effect for reaction of 1 and H⁺ is ca.3 and, when the reaction is carried out in 18O water, the anthrone reaction product contains exlusively 18O.These observations show unequivocally that acid hydrolysis occurs by rate-determining proton transfer to the 10-position of the anthracene moiety, followed by rapid reaction of water at the 9-position of the oxonium ion intermediate.The acid-catalyzed hydrolysis of 1 was thus found to resemble vinyl ether hydrolysis (i.e., an A-S_E2 mechanism) instead of an A-2 mechanism shown by most other aryl ethers, such as anisole.