Ship-in-a-Bottle Synthesis of Methylphenols in HSAPO-34 Cages from Methanol and Air

Abstract

The conversion of methanol to olefins on the silico-aluminophosphate solid acid catalyst HSAPO-34 usually requires methylbenzenes that function as scaffolds (reaction centers) for carbon−carbon bond making and breaking steps. Here, we report the first high-yield synthesis of heteroatom-substituted methylbenzenes in HSAPO-34 cages. When we metered 20% air into the He carrier gas during methanol conversion at 350 °C the methylbenzenes initially formed were partially oxidized in the HSAPO-34 cages to methylphenols with very high selectivity. 100% N2O was less effective than 20% air. Methylphenols proved to be substantially less active than methylbenzenes as reaction centers for methanol to olefin (MTO) catalysis on HSAPO-34. Even pentamethylphenol resisted the loss of methyl groups as olefin products, and phenols showed little carbon label scrambling into the ring during methanol conversion. Whereas 1:10 (mol:mol) toluene in methanol was very reactive on zeolite HZSM-5, 1:10 (mol:mol) p-cresol in methanol was no more reactive than pure methanol. We speculate that the MTO deactivating effect of oxygen substitution on methylbenzene rings is a consequence of the high gas-phase proton affinities of phenolic groups.