Carbon-Resource Recovery from Vinyl Polymers of Cyclic\nKetene Acetal Esters Using High-Temperature Water

Vinyl polymer prepared\nfrom 2-methylene-4H-benzo[d][1,3]dioxin-4-one\n(MBDO), a cyclic ketene acetal ester, is a chemically recyclable polymer\nthat is hydrolyzed to salicylic acid (SA) and acetic acid (AA). Despite\nthis potential, the polymer, poly-MBDO, required a strong acid or\nbase in organic solvent for the hydrolysis. In this study, we report\nthe quantitative conversion of poly-MBDO to phenol by treatment in\nhigh-temperature water. Hydrolysis of poly-MBDO afforded SA, which\nunderwent rapid decarboxylation to phenol. For example, poly-MBDO\nquantitatively afforded phenol upon heating in water at 300 °C\nfor 5 min and freeze-drying. Although the hydrolysis of the main chain\nwas incomplete, the products were volatile and removed by drying the\nreaction mixture, leaving the residue of pure phenol. Since SA is\nindustrially synthesized from phenol and CO<sub>2</sub>, the synthesis\nof poly-MBDO from phenol is in principle possible. The quantitative\nconversion of poly-MBDO to phenol can also be considered as carbon-resource\nrecovery, since phenol is a raw material for various fine chemicals.