Reactions of Allyl Phenyl Ether in High-Temperature Water with Conventional and Microwave Heating

In a systematic study, allyl phenyl ether (1) was heated in water for 1 h at temperatures of 180 degrees C and above. Parallel experiments were conducted with a conventionally heated autoclave and a recently developed microwave batch reactor. Relatively modest temperature differences resulted in diverse product distributions, and these were independent of the method of heating. Maximum conversion of 1 to 2-allylphenol occurred at 200 degrees C (56%) and to 2-methyl-2,3-dihydrobenzofuran at 250 degrees C (72%). Although 2-(2-hydroxyprop-1-yl)phenol comprised less than 1% of the product mixture at both 180 and 260 degrees C, it accounted for 37% at 230 degrees C. The reaction sequence was investigated by heating intermediates individually at selected temperatures up to 290 degrees C. Hydration of 2-allylphenol to 2-(2-hydroxyprop-1-yl)phenol was partially reversible. The work showed that high-temperature water constitutes an environmentally benign alternative to the use of acid catalysts or organic solvents and offers scope for interconversion of alcohols and alkenes.